Near Record-Breaking Dry Year, Drought Reigns

18 01 2022

Dale C. S. Destin |

It was a near-record-breaking dry year (2021) for Antigua. The year produced a measly island-average rainfall of 600.7 mm (23.65 in), the second lowest on record behind 2015 with 574.5 mm (22.62 in). Officially, 2021 was easily the second most parched year in a series from 1928 and unofficially, since, at least, 1871.

The yellow broken line represents the rainfall anomaly trend, which indicates no significant change to wet (positive) or dry (negative) anomaly.

It was a year reigned by drought from beginning to end, and the reign is likely to go on through the upcoming months. The drought has a firm grip on the weather, being at the most intense category: severe, exceptional by some other standards. The normal annual total is 1156.7 mm (45.54 in), nearly twice the amount measured for 2021.

The rainfall deficit amounts to a whopping 556.0 mm (21.89 in) or 48 percent of the usual total for the year. This is more than the average for the first seven months of a year. Every month accrued a shortfall with the usually wettest month of the year–November, accounting for over 22 percent of the overall rainfall shortage.

This level of waterlessness for a year is extremely rare. There is only a 0.5 percent chance of the island-average being 23.65 inches or lower. This translates to the kind of dryness that has a return period of once in 200 years (1-in-200 years), on average.

Alternatively, there is less than a 10 percent chance of such harsh weather reoccurring in the next 20 years. One is, at least, twice as likely to see a hat-trick in a cricket match than experience the likes of such lacklustre annual rainfall.

268Weather accurately predicted a drier than usual year was likely. As early as May 2021, we indicated a 46 percent chance of below normal rainfall. The chance rose to 58 percent in June and peaked at 61 percent in August. There was also a peak of 19 percent for the year to rank among the top 10 driest.

The usually wettest consecutive pair of months, October-November, almost literally produced a speck in the bucket. The frequently rainiest duo was the record driest with the trivial amount of 63.8 mm (2.51 in) with each month recording less than an inch-and-a-half of rainfall for the first time, on record. Combined, the shortfall for the months accounted for 45 percent of the year’s deficit. The previous lowest for this period was 89.7 mm (3.53 in), in 1983.  

The last quarter (October-December) was also the driest on record, dating back to 1928. The total of 127.3 mm (5.01 in) shattered the previous record of 143.0 mm (5.63 in), for the last three months of the year, set in 1983. Usually, this period precipitates 397.5 mm (15.65 in), over thrice what actually fell.

It was essentially a year without a wet season (July-December). The dry season pretty much went on and on, for the whole year, resulting in a record-breaking dry wet season. The season’s total of 396.0 mm (15.59 in) retired the previous driest wet season of 1983, which accumulated 405.6 mm (15.97 in). Cumulatively, the third and fourth quarter rainfall represented just 53% of the normal amount of 746.8 mm (29.40 in). A typical dry season (January-June) averages more rainfall than occurred for the 2021 wet season.

While the island on a whole had near-record-breaking low rainfall, parts of the country actually had record dryness. Coolidge, in northeast Antigua, had a record low rainfall of 469.6 mm (18.49 in), crushing the previous record of 554.0 mm (21.81 in) set in 2015. This represents only 47 percent of the normal annual total of 1000.8 mm (39.40 in). This kind of rainfall scarcity occurs only once every 333 years, on average, or a less than 10 percent chance of occurring in the next 35 years or the next generation.

It is unclear as to what was responsible for this nearly unprecedented dryness. The usual culprit: El Niño was not only absent but his sister: La Niña, usually the rainmaker, was present, yet to little avail. The dryness may have been mainly the result of a consistent stream of dry and dusty air from the Sahara Desert along with a cooler than usually tropical North Atlantic.

There is the saying: “If rain does not fill a [water] drum, dew is not going to fill it.” Meaning, if the wet season did not end the droughts, particularly the hydrological and socioeconomic ones, how can the dry season, which we are in, do so? It can’t; hence, the sufferation from insufficient rainfall could continue through the next six months.

The last 10 years have been the driest decade for Antigua. Five of the last 10 years have had below normal rainfall with 2015 and 2021 ranking one and two, on record. Only one year (2020) has had above normal rainfall since 2011.

Other Caribbean islands are having similar challenges with rainfall or lack thereof. For example, the Henry Rohlsen Airport in St. Croix was said to be on track, in December, to record its third driest year, on record dating back 58 years. A number of other parts of the Caribbean were also on the way to record rainfall ranking among the top 10 lowest.  

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Third Busiest Hurricane Season Ends

1 12 2021

Dale C. S. Destin |

The third busiest Atlantic hurricane season–2021, ended yesterday. The season produced 21 named storms, the third highest on record, behind 2020 with 30 and 2005 with 28. The season also produced 7 hurricanes, tied for 32nd highest on record dating back to 1851. Further, there were four major hurricanes, Category 3 and over, which tied for the 18th highest on record. Thirty-two other seasons had seven hurricanes and 18 others had 4 major hurricanes.

Although the most eye-catching statistic for a given season is the number of storms, this is not the metric used to determine its overall activity. The Accumulated Cyclone Energy (ACE) index remains the internationally accepted metric used to categorize the activity of a season. The ACE takes into consideration not only the number of named cyclones but also their strength and duration. Hence, based on the ACE, 2021 is the 29th most active hurricane season on record, with an ACE index of 142.

The most active hurricane season on record remains 1933 with an ACE of 259, 44% more than 2020, the record busiest season, w.r.t. the number of named storms, NOT ACE. The 1933 season was also over 80% more active than 2021. Thus, notwithstanding the headline-grabbing 21 named storms for 2021, the season was nowhere close to being the third most active. Activity has to do with the ACE, while busyness has to do with the number of named storms.

Based on NOAA’s classification, the 2021 season was above normal. However, NOAA’s classification of season has its challenges, allowing for one season to simultaneously have two classifications. Also, NOAA uses the 1991-2020 period the define an average season but uses the 1951-2020 period to determine if season is normal or not. A better approach is to classify seasons strictly by the ACE index, as does by 268Weather. This approach categorises the 2021 season as near normal; based on the 1991-2020 climate period, the 2021 ACE of 142 falls in the middle tercile. An average season produces 14 named storms, 7 hurricanes, 3 major hurricanes and ACE of 123.

268Weather’s seasonal hurricane forecasts fairly accurately predicted the number of named storms and major hurricanes. However, we did not do as well with the other parameters, particularly the important ACE index. Based on the number of named storms, the ACE is unusually low. This is largely because of the record high nine shorties–storms lasting two days or less. Notwithstanding, tropical cyclone metric forecast by 268Weather fell within the 70% confidence. Interestingly, as little as 30 years ago, most of these shorties would have gone undetected, resulting in the official numbers being significantly less.

As busy as the season was, thankfully, Antigua and Barbuda along with the rest of the Leeward Islands and the British Virgin Islands were spared. Officially, the record will likely say that we were impacted by Tropical Storm Grace; however, this system bought ZERO storm-force winds to our shores.

The season got off to an early start with Tropical Storm Ana on May 22 and closed early with the dissipation of Tropical Storm Wanda on November 7. After flurry of storms from mid-June to mid-July, ending with Elsa (July 1-14), the season went on a bit of a hiatus until August 11, when Tropical Storm Fred formed. In less than one-and-half month, from August 11 to September 29, 15 storms formed, more than the average for a season. October went virtually stormless except for the eleventh-hour development of Tropical Storm Wanda on October 31, exhausting the 21-name Atlantic list.

The most powerful cyclone for the season was Category 4 Major Hurricane Sam, which had peak sustained winds of 250 km/h (155 mph). Sam did not make landfall; hence, it caused minimal impact.

The most deadly and destructive system was  Category 4 Major Hurricane Ida, which had peak sustained winds of 240 km/h (150 mph). It killed 115 persons and caused over US$65 billion in damage, becoming the sixth costliest Atlantic tropical cyclone on record. It impacted mainly the Cayman Islands, Cuba and the Gulf and East Coasts of the United States.

A couple notable records for the season:

  • Elsa became the earliest 5th Atlantic named storm on record when it was named July 1. The previous record was set by Edouard on July 6, 2020.
  • 2021 tied with 2007 for the most shorties (storms lasting <=2 days), on record.  
  • 2021 marks the first time of back-to-back exhaustion of the list of Atlantic named storms.

The 2022 hurricane season will officially begin June 1 and 268Weather will issue monthly forecasts starting early April.

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Near Normal Rainfall for September, Drought Continues

27 10 2021

Dale C. S. Destin |

September joins June as the only two months of the year, thus far, to register near normal rainfall, all others had below normal figures. The month produced 122.2 mm (4.81 in) of rainfall, the highest total for any month since December 2020; notwithstanding, drought continues through September. The rainfall for the last nine months ranks among the worst on record, and it is still unclear as to when there will be significant respite.

The rainfall for September is the second lowest since 2015. However, the total for the month was a decent 90 percent of the normal value of 136.4 mm (5.37 in), only a deficit of 10 percent.

The period July-September was also drier than usual. The total of 268.7 mm (10.58 in) was the 18th lowest on record starting 1928. The last time this period was drier was 2015 with 168.1 mm (6.62 in).

We continue to witness one of the driest years on record. Thus far, this January to September is the sixth driest on record and the driest since 2015. The first three-quarters of the year has only a meagre 473.5 mm (18.64 in), only a little over 62 percent of the usual rainfall of 759.0 mm (29.88 in). The five drier January to September are 2015, 2003, 2001, 1939 and 1930. The year is on track to be among the top 10 driest or worst, on record.  

Since the 2020 November’s deluge, the last ten months, December-September, is the seventh driest on record and the lowest since 2015. The period has only returned 65 percent of normal rainfall.

The upcoming three months, November to January, has equal chance of below, near or above normal rainfall. Meanwhile, some of the more reliable models are still forecasting the continuation of below usual rainfall being most likely. Looking at the glass half full, near to above normal rainfall is more likely than not.

WMO Lead Centre for Long-Range Forecast Multi-Model Ensemble is forecasting equal chance of below, near or above normal rainfall for Antigua and Barbuda.

As the meteorological drought goes, so go the other droughts: agricultural, hydrological and ecological. There is the continuing concern that this may precipitate a socio-economic drought, if it has not already done so. However, the rainfall of September did stabilise or eased the droughts a bit.

Our conversion of sea water to fresh water has built drought resilience; however, obtaining potable water from this source is several time more expensive than from surface and underground catchments. Also, it has negative climate and environmental consequences, further adding to the overall expense of using the sea as a source for fresh water. Unfortunately, these “evils” are virtually unavoidable, for the foreseeable future.

Potworks Reservoir remains below extraction levels, along with most other surface catchments, according to the Antigua Public Utilities Authority (APUA), the country’s water authority. Water rationing continues and with the rainfall outlook unclear, an end is unforecastable, at this time. Daily water use continues to outstrip production by about one million gallons.

Potworks Reservoir, Bethesda, Antigua, still on the verge of becoming totally dry – Oct 2, 2021. Picture courtesy Karen Corbin of the Humane Society

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Drier than Usual August, Drought Continues

27 09 2021

Dale C. S. Destin |

Like every month of the year, except June, August was drier than usual. The month yielded only 81.0 mm (3.19 in) of rainfall. With continued below normal rainfall, drought continues. The rainfall for the last eight months ranks among the worst on record and there is still not much respite in sight.

The rainfall for August is the second lowest since 2015. The total for the month represents only 71 percent of the normal value of 114.8 mm (4.52 in), a deficit of 29 percent.

The period June-August was also drier than usual. The total of 202.2 mm (7.96 in) was the 18th lowest on record starting 1928. The last time this period was drier was 2015 with 95.0 mm (3.74 in).

We continue to witness one of the driest years on record. The last eight months is the fourth driest on record and the driest since 2015. January to August produced only a meagre 351.3 mm (13.83 in), only a little above half of the usual rainfall of 622.0 mm (24.51 in). Just three years have been drier through August: 2015, 2001 and 1939.  

Since the 2020 November’s deluge, the last nine months, December-August, is the fifth driest on record and the lowest since 2015. The period has only returned 61 percent of normal rainfall.

The upcoming three months, October to December, is likely to see further misery from lower than usual rainfall. Majority of models are forecasting the continuation of drier than normal weather. Hence, more rainfall deficits likely.

WMO Lead Centre for Long-Range Forecast Multi-Model Ensemble is forecasting 50-60% likelihood of below normal rainfall for Antigua and Barbuda. Also, below normal rainfall is likely for much of the rest of the northeast Caribbean.

As the meteorological drought goes, so go the other droughts: agricultural, hydrological and ecological. There is the continuing concern that this may precipitate a socio-economic drought, if it has not already done so. Our utilisation of the ocean for fresh water has made us drought resilient; however, obtaining potable water from this source is several time more expensive than from surface and underground catchments. Also, it has negative climate and environmental consequences, further adding to the overall expense of using the sea as a source for fresh water.  

Potworks Reservoir remains below extraction levels, along with most other surface catchments, according to the Antigua Public Utilities Authority (APUA), the country’s water authority. Water rationing is officially into its second month and with the rainfall outlook being gloomy, it is likely to continue for the foreseeable future.

Potworks Reservoir, Bethesda, Antigua, still on the verge of becoming totally dry – Sep 2, 2021. Picture courtesy Karen Corbin of the Humane Society

APUA water manager, Ian Lewis, told the media on August 31, that the Authority is only able to produce six million of the seven-and-a-half million gallons required to serve the country daily. There is not enough water to go around for everyone each day; hence, the rationing.

Antigua is not alone in experiencing significant rainfall shortages. The countries around us remain  thirsty for rainfall also. Deficit rainfall is occurring across the rest of the Leeward Islands, the northern Windward Islands, Hispaniola, Cuba and the Bahamas. And it is probable that it will worsen, over the upcoming months.

CMORPH 180-Day Total Rainfall Anomaly (mm) for the period 26 Mar to 21 Sep 2021

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Drought is Back

14 03 2021

Dale C. S. Destin |

Drought is back for Antigua. A slight meteorological drought is present as of the end of February. It is most likely to get worse over the next three months, as below normal rainfall is forecast by most models.

The rainfall for winter – December to February (DJF) 2020-2021, was 149.1 mm (5.87 in). This total is deemed below normal and beneath the drought threshold. Usually, DJF yields 225.8 mm (8.89 in) of rainfall, on average; hence, there is over a 75 mm (over 3 in) deficit or a 34 percent shortfall.

Rainfall for Antigua for the period December 2020 to February 2021. Picture in the background is Potworks Dam as of March 3, 2021 courtesy Karen Corbin of the Humane Society.
Rainfall for DJF is well below the slight or worse drought threshold, nearly at moderate drought. Rainfall for this period for Antigua shows no significant trend (black dashed line). Excess rainfall tends to be more extreme than drought rainfall.

The month that is mainly responsible for the scarcity in precipitation is January, which got only 41 percent of the normal amount of 67.3 mm (2.65 in). The rainfall for February was also lower than usual, accounting for 73 percent of the normal amount of 50.0 mm (1.97 in). The rainfall for December was near normal.

The two-month rainfall for January-February (JF) of 63.8 mm (2.51 in) is the lowest since 2001. Thus, the very dry start to the year continues. With this JF ranking the eighth driest on record, only seven other years have had a drier start on record dating back to 1928.

It normally takes a few months for the effects of a meteorological drought to descend to a hydrological drought and cause potable water issues. However, the effects are already manifesting themselves in the lowering of water in catchments. Yesterday, the APUA Business Unit Water Manager – Ian Lewis, said on Observer Radio News that the country has about three to four months of surface water remaining, at current extraction rate.  

We were last in a drought April to October last year. This was a severe drought that was more than meteorological; it resulted in surface catchments transforming into mud patches and then to grass lands. It is unclear, at this stage, whether there will be a repeat of similar rainfall absence this year.

The dry conditions last year, resulted in water rationing and almost a 100 percent reliance on desalinated water. Ian Lewis has already indicated that the absence of notable rainfall over the coming months would usher in return of the water conservation schedule better known as water rationing.

Antigua is not alone in experiencing notable rainfall deficits in the wake of winter. Much of the Caribbean is suffering a similar fate, from a drier than usual dry season, thus far. Short and long-term droughts are evolving across a number of islands and there is the potential of several others joining this drought-list.

Rainfall anomaly (departure form average) in mm for the Caribbean, based on CMORPH data

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Very Dry Start to 2021

16 02 2021

Dale C. S. Destin |

Antiguans have just witnessed the driest start to the year in over a generation. January 2021 was the driest January since 1977 for Antigua, with an island average of 27.4 mm (1.08 in).

Usually January yields 67.3 mm (2.65 in) of rain; however, this time, the total was down by 59%. This puts the rainfall for the month in the well below normal category – the bottom 10 percentile of the most recent climate period – 1991 to 2020.

Such low rainfall is rare for January. How rare? Once in every 27 years, on average, which translates to a 3.7 percent chance of such a low total annually. Usually, there is over a 96 percent chance of the month producing more rainfall.

From a historical standpoint, this is the third driest January on record dating back to 1928. Only January 1977 and 1931 have been drier. January 1931 is the driest on record with 16.3 mm (0.64 in) and January 2006 is the wettest with 2017.7 mm (8.57 in).

Despite the trickle of rainfall for January 2021, the rainfall for the month is usually the most reliable of all months with the lowest variability index of 0.83 or moderate, for the climate period 1991-2020. All other months have a variability index of 1 to 2.37 or moderate to extreme. The variability is obtained by dividing the difference in rainfall of the 90th percentile and the 10th percentile by the median.

Notwithstanding the drier than normal January 2021, the rainfall for January remains without any significant (statistical) trend. The mean rainfall over the past seven climates has not changed significantly, ranging between 65.8 to 79.5 mm (2.59 to 3.13 in), over the period 1928 to 2020.

As we look forward, the rainfall for February is lagging average by about 38 percent, and even if the averaged is reached, there is the high likelihood for rainfall to drop to drought levels by the end of February. About another 35 mm (1.38 in) of rain is needed to stave off drought. This or more rainfall for February 17-28 has only occurred 10 times in the last 55 years – 18 percent of the time.

January is unlikely to be this dry again under the next 27 years. By then, we will be at the middle of the 21st Century – millennials would have reach senior citizen age.

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Post-Hurricane Season – December

19 12 2020

Dale C. S. Destin|

Named tropical cyclones (tropical storms or hurricanes) during December are virtually unheard of for Antigua and Barbuda. However, in 2007, Tropical Storm Olga came close and affected us. Its centre passed around 39 and 78 miles north of Barbuda and Antigua respectively – at least brushing our islands. Its impact was minimal.

Tropical Storm Olga – December 11, 2007. Credit Wikipedia.

Olga went on to become the most destructive and deadly tropical cyclone originating in December. The storm went on to made landfall on Puerto Rico and Hispaniola with peak sustained winds of 95 km/h (60 mph). It killed at least 40 people and caused US$45 million in damage across the Greater Antilles.

In the history of Atlantic named tropical cyclones, which dates back to 1851, only 16 have had their origin in December, according to NOAA. Of the 16, 5 (31 percent) were hurricanes.

All 16 tropical storms and hurricanes originating in December – 1851 to 2019

Of the 16 total December tropical storms and hurricanes, four impacted the Caribbean i.e. passing within 120 miles of the region. The last to do so was Olga. Based on the climate period 1981-2010, the chance of a storm impacting Antigua is about 3 percent, while the chance of the Caribbean being impacted is about 9.5 percent.

The strongest tropical cyclone owing its origin to December is Alice of 1954 – a Category 1 hurricane. Alice formed in late December and crossed over to January 1955 and impacted Antigua and the rest of the Leeward Islands with Category 1 winds. It eventually reached peak sustained winds of 150 km/h (90 mph) about 100-130 miles northeast of Barbuda. Alice is known to be the only post-season hurricane (forming in December, January or February) to impact the Caribbean.

The last Atlantic storm to have its origin in December is an unnamed subtropical storm of 2013. It formed over the northern eastern Atlantic, near the Azores. It had peak sustained winds of 85 km/h (50 mph). Lost of life and damage caused by it were nil.

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Drought Deepens…Relief Uncertain

9 07 2020

Dale Destin|

The paltry rainfall for the last three months for Antigua, has caused the meteorological drought to plunge from moderate to severe levels. The rainfall for April-June (AMJ) amounted to only 82.6 mm (3.25 in). This is the sixth driest AMJ on record, dating back to 1928. Further, the rainfall for AMJ represents only meagre 32 percent of the normal total of 274.6 mm (10.81 in). 

Potworks Dam in the background, going on three months, without a drop of its billion-gallon-water capacity. (“Normal” corrected for units Jul 14, 2020)

Other droughts have also tumbled with the meteotological drought, which is considered the mother of them all. These others are at moderate or worse intensity.

The rainfall for June was below normal for the third month in a row. The rainfall of 45.7 mm (1.80 in) was only 66 percent of the normal total for the month of 69.3 mm (2.73 in).

Although drier than normal, it was wetter than the last two Junes combined and more than the last two months combined. This is an indication of just how dry those months were.

Recall that we had very happy first-quarter rainfall. The first three months of the year was wetter than normal. However, since then, things have gone south. Rainfall for the year, thus far, for the dry season – Jan to June, stands at below normal.

The dry season rainfall of 320 mm (12.6 in) amounts to just 74 percent of the normal total of 434.3 mm (17.1 in). It is the driest three-month period since June-August 2018.

The woefully low rainfall since March looks to be mainly due to higher than normal pressure at the lower levels of the atmosphere. This unusual arrangement of pressure resulted in, more often than usual, sinking air, which inhibited warm rising air needed for cloud formation and rainfall.  A record amount of Saharan Dust during June would have also played a huge role in stifling rainfall.

Low level pessure anomaly across the Caribbean Basin and parts of the North Atlantic – April 1 to June 30, 2020. Higher that usual low level pressure inhibits the water cycle and hence, rainfall.
High-level Omega anomaly across the Caribbean Basin and parts of the North Atlantic – April 1 to June 30, 2020. Positive values indicate sinking motion, which is bad for rainfall.

Relief from the drought weather is becoming uncertain. The forecast for July-September (JAS) is for a 45 percent chance of above normal rainfall. This means that rainfall required to bring us out of drought is unlikely.

Looking beyond JAS, my latest forecast calls for less than 40 percent chance of above normal rainfall for the rest of the year, the wet season – July to December. This means that near or below normal rainfall is more likely than drought busting rainfall.  

Considering the whole year, 2020 will most likely be drier than usual. My latest projection is for a 50 percent chance of below normal rainfall, 30 percent chance of the usual rainfall and 20 percent chance of the year getting more than usual rainfall.

How dry it is projected to be? At this time, Antigua’s most likely rainfall for 2020 is 1026 mm (40.4 mm) with a 70 percent confidence that it will fall in the range of 760 to 1349 mm (30 to 53 in). Normally, the island gets 1207 mm (47.5 in).

Projected rainfall for Antigua in inches. There is a 20% chance of it being above normal (A 20%), 30% chance of it being near normal (N 30%) and 50% chance of it being below normal (B 50%). Background pic courtesy Karen Corbin of the Humane Society.

The parched weather was not restricted to Antigua and Barbuda. Much of the rest of the region have been suffering the same fate. There are a few exceptions, most notably is Cuba.

May was a record dry month for Anguilla and St. Thomas. Parts of the Dominican Republic and Belize saw record low rainfall for April. Severe or worse droughts are being experienced in many islands, including Aruba, Barbados, Martinique and St. Lucia.

Rainfall anomaly across the Caribbean Basin – January 7 to July 4, 2020 based on CPC CMORPH

Large scale atmospheric and ocean conditions continue to trend in the direction that would usually cause relief across the Caribbean Basin, including Antigua and Barbuda. However, models continue to not be very enthusiastic about forecasting significant rainfall for much of the region.

The favourable conditions for rainfall for our area are: warmer than usual tropical North Atlantic and cooling of the central to eastern equatorial Pacific i.e. a developing La Nina. Once these two things happen together, we invariably get good rainfall. However, what we can’t predict beyond a week, could negate the positive conditions – Saharan Dust, the x-factor. If it does not let up, it will suppress rainfall and wipe out any optimism in the forecasts for drought-stopping rain.

From all that have been examined, the drought is unlikely to end for the foreseeable future and if it were to, it would only be temporary. This is not to say that we won’t see more rainfall in the second half of the year than the first. We will; however, it is unlikely to end the drought.

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Hurricane Season History: June

29 06 2019

Dale C. S. Destin|

The first month of the Atlantic hurricane season is coming to a close and the month is yet to see a named storm (tropical storm or hurricane). And as it stands, we are unlikely to see any this June but this is not uncommon.

All 98 Atlantic Named Storms to Have Formed In June – 1851 to 2018

In total, the month has produced 98 named storms on record dating back to 1851; 38 were hurricanes and only 3 were major hurricanes – Category 3 or higher.  

On average, there is a 44% chance of a named Atlantic storm in June, 20% chance of a hurricane and 2% chance of a major hurricane.

In other words, there is a named storm every other June, and hurricane every 5 Junes and a major hurricane every 50 Junes, on average.

From 1851 to present, there have been 75 years with June storms and 93 years without. The June with the most named storms are 2012, 1968, 1936, 1909 and 1886 with three each.

The June with the most hurricanes is 1886. The strongest June hurricane is Alma of 1966 with 205 km/h (127 mph) winds; it did a “number” on Cuba and southeast United States.

The Eastern Caribbean Have Only Had Two Named Storms In June – 1851 to 2018

As the graphic above shows, only three times have we every experienced a named storm across the Eastern Caribbean in June – Tropical Storm Bret in 2017, Tropical Storm Ana in 1979 and an unnamed hurricane in 1933. Bret and the unnamed hurricane impacted Trinidad and Tobago and Ana impacted St. Lucia and Martinique.

Climatological Areas of Origin and Typical Hurricane Tracks for June

Clearly, when storms do form in June, they are likely to develop across the western Caribbean Seas and the Gulf of Mexico – there is very little to no action elsewhere across the basin.

No June Storm has Every Passed Within 120 Miles of Antigua on Record – 1851 to 2018

Quite evident also is that Antigua and Barbuda has never being impacted by a storm or hurricane in June. This may be surprising to many, but it is very much the case and this record is not about to come to an end this year.

This is the second consecutive year no named storm formed in June. The longest streak of no June storm is 7 years – 1947 to 1953. On the other hand, the longest streak of June storms is 8, 2010 to 2017.

Don’t be fouled by a quiet June – it says nothing about the rest of the hurricane season. The probability of an above normal season is similar with or without a named storm in June. Keep your guard up and get or stay prepared. It only takes one storm to ruin your year, if not life.





Tropical Storm in May? Uncommon but not Unheard Of

5 05 2019

Dale C. S. Destin |

The first tropical disturbance for the year has formed and is currently over the Western Atlantic, near the southeast United States. Although this system is unlikely to form, it is not unheard of for tropical storms to develop in May, but it is relatively uncommon.

Looking back at the history, there have been 26 tropical storms in May, 4 of which became hurricanes – all category ones. This means, on average, one tropical storm forms every 6 to 7 years, based on data for the period 1981-2010, upon which the current climate is based.

All Tropical Storms in May on Record, 1851 to 2018

All May Tropical Storms, on Record – 1851 to 2018

The probability of a tropical storm forming in May is 15% (a slight chance), which means storms seldom form in May. The last time this happened was back in 2016 – Tropical Storm Bonnie.

Hurricanes in May are even more uncommon, if not rare. The probability of one forming in May is less than 3%, based on the full history – 1851 to 2018. This means there is a hurricane in May, on average, once every 42 years – once in a generation plus. The last one was Hurricane Alma of 1970.

One may be tempted to think that a tropical storm in May is an omen for an active (above normal) hurricane season. In a (small) poll done by me on twitter, 61% of persons said that a storm in May means an active or hyperactive season; however, this is false. The record shows the following w.r.t. seasons whenever there has been a storm in May:

  • 3 hyperactive;
  • 4 active (above Normal);
  • 11 normal and
  • 5 quiet (below normal).

In other words, whenever there was a storm in May:

  • 4% of the time the seasons were hyperactive;
  • 17% were active;
  • 48% were normal and
  • 22% were quiet.

Hence, a storm in May seems to portend a normal hurricane season, as opposed to an active or hyperactive season. So, we may, perhaps, want to wish for a storm in May.

With all the talk about climate change and tropical cyclones, one may be tempted to think that we are having more storms in May than before. However, the record does not bear that out. In the 38 years from 1981 to 2018, there have been nine tropical storms, no hurricane. By comparison, during the previous 38 years, there were eight tropical storms, two of which became hurricanes.

While tropical storms are not unheard of for the Atlantic Basin, they are unheard of for our neck of the woods – Antigua and Barbuda. We have never been impacted by a tropical cyclone (tropical depression, tropical storm or hurricane) in May.

The fortune of never having a tropical cyclone in May extends to the rest of the Eastern Caribbean. As a matter of fact, none has ever formed east of Hispaniola. Further, no hurricane has ever impacted/affected any Caribbean island in May. Clearly May is not a month to be worried about tropical storms.

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Drought Continues Almost Everywhere

20 04 2019

Dale C. S. Destin |

We continue to see red almost everywhere across the Caribbean region – indicative of drought, severe in some places. The red has spread from the last blog on the subject, suggestive of the drought spreading, one may say, like a wild-fire.

Dec 2018 – Feb 2019 SPI index, characterising rainfall across the Caribbean. More red seen above than below – the last three months drier than the previous three.

Nov – Dec 2018 SPI index, characterising rainfall across the Caribbean

According to data from the latest Caribbean Climate Outlook Newsletter, over the past three months – December to February, rainfall deficits have resulted in the development or continuation of drought across many parts of the Caribbean. The few exceptions include the Bahamas, the Cayman Islands and the western parts of Cuba.

El Nino, warmer than usual sea surface temperature across the eastern tropical Pacific Ocean, is likely to have been the main cause of the deficit in rainfall over the past three months. Regression analysis shows that El Nino normally causes negative rainfall anomalies – below normal rainfall, across much of the region, especially across the Eastern Caribbean during December to February (DJF).

Rainfall and El Nino – The gray areas indicate the places that receive below normal rainfall during an El Nino during the period December-February.

For much of the region, the Newsletter indicates just a low chance of drought-busting rainfall over the period April-June. Beyond June, there is just a slight chance of drought-busting rainfall over the period July-September. Rainfall will most likely be the scarcest across the Eastern Caribbean.

So, unfortunately, we will continue to see mostly red across the area – it is going to be another tough year for rainfall, with eastern area getting the driest end of the atmosphere.

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Relief Unlikely for Drought Stricken Areas of the Eastern Caribbean

1 02 2019

Dale C. S. Destin |

According to the latest Caribbean Climate Outlook Newsletter (CCON), Anguilla south to Trinidad, including Barbados will most likely experience below normal rainfall for the upcoming season – February to April (FMA). This means that any drought occurring in these islands will likely get worse or remain unchanged.

Over the period October-December, severe droughts have developed or are ongoing across parts of a number of islands to include:

  • Hispaniola;
  • Guadeloupe;
  • Martinique and
  • Barbados.

A scarcity of rainfall in 2018 and mostly likely lower than usual rainfall through April 2019 have led to long-term droughts or concern of long-term droughts in many islands, according to the February to April Newsletter. These include:

  • Antigua and Barbuda
  • Cayman;
  • NW Cuba;
  • Northern Dominican Republic;
  •  Grenada;
  • Martinique;
  • Northeast Puerto Rico and
  • Tobago.

CCON blames the likelihood of below normal rainfall for FMA on a weak El Nino, which is forecast to last through the period.

El Nino could last through the wet season, which is bad news, as it normally causes reduced rainfall and or droughts across most of the Caribbean – particularly in the wet season. 

El Nino refers to the unusual warming of the central and eastern tropical parts of the Pacific Ocean, which historically occurs every 2 to 7 years and lasting for 9-12 months, sometimes longer. It generally has the effect of causing drier than usual weather across the Eastern Caribbean.

We are in the dry months of the year. Traditionally, not a lot of rain fall across the Caribbean during FMA. It is a part of the heart of the dry season for the vast majority of the region, with only January-March being drier, as a whole.

The usual rainfall totals: February to April

The dryness of the season is normally especially evident across Aruba, Curacao and Bonaire – the ABC Islands, who have average rainfall for this period of below 75 mm (less than 3 in). It is not unusual for these islands to see zero rainfall during these months, in some years.  

Click here or the graphic above to read the full Newsletter

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Drier Than Normal December; Drought to Reintensify

30 01 2019

Dale C. S. Destin |

DCurrentDroughtIntensityecember was drier than normal for Antigua. The rainfall total of 65.8 mm (2.59 in) was below normal – 65% of the average for the month. This was the driest December since 2015. The month had very little positive impact on the droughts; hence, they will likely reintensify in the upcoming months.

The last three-month period – October to December, upon which the assessment of the current intensity of the drought is based, was slight dry. However, the rainfall total fell in the near normal category. The three-month period had 329.2 mm (12.96 in), while the normal amount of rainfall is 413.5 mm (16.28 in).

Rainfall for the past 24 months

Rainfall for the past 24 months for varying time intervals compared to the normal/average and records

We remain in a severe meteorological drought, the worst category on our drought scale. However, at the moment, the current intensity is slight, for the second month in a row. Recall that the overall description of the drought is based on the worst intensity achieve during its lifetime; however, over time, the intensity will fluctuate.

Potworks Dam, our billion-gallon surface catchment, is again returning to critically low levels. The Authorities will be cutting back on extraction from the Dam and water rationing is imminent, if not already started. This is indicative of the continued drought; notwithstanding the ample rainfall of November.

The fifteen-month period – October 2017 to December 2018, the duration of the drought thus far, is deemed severely dry. The total for the last 15 months of 1043.4 mm (41.08 in) is the second lowest since 1969 and the fourth lowest on record, for such a period, dating back to 1928. This particular interval normally gets 1615.7 mm (63.61 in), which means a rainfall deficit of 35% – more than one-third of the usual rain was absent.

Based on the last set of rainfall forecasts from regional and especially international sources, the news is discouraging with respect to rainfall. Overall, below normal rainfall is likely for the next six months – February to July 2019, with moderate confidence that the period February to April – 2019 having well below normal rainfall. Thus, there is every reason to believe that the droughts will reintensify. The chance of the droughts ending is, at most 20% or slight.

Probabilistic Multi-Model Ensemble Forecast of Rainfall For Jan-Mar 2019, based on 12 global model

Probabilistic Multi-Model Ensemble Forecast of Rainfall For Jan-Mar 2019, based on 12 global models

On average, our severe meteorological droughts last for around 16 months, but not continuously at severe intensity. At current, the drought is in its 16th month; the longest such drought on record lasted 38 months – Jul 2013 to August 2016.

Last year – 2018, was the eighth driest on record, dating back to 1928. It was also the second driest since 1983; only 2015 has been drier since 1983 – 35 years ago.

accumulation_december2018

It is too early to say with any confidence whether the rainfall for 2019 will be below, near or above normal. However, early indicators suggest it could be another tough drought year for Antigua and Barbuda.

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Why Was It So Cold Night Before Last?

19 01 2019

Night before last was the coldest for Antigua and Barbuda for the year and the coldest for some areas in years. Some areas had temperatures as low as 15 °C (59 °F). Why was it so cold, relatively speaking, and is this unusual?

Min Temp for Antigua and Barbuda
Temperatures recorded January 17/18, 2019

The short answer to the question is radiational/radiative cooling. The long answer involves explaining what such cooling is and how it works. Radiational cooling is the process by which the ground and the adjacent air cool by emitting heat (infrared – IR energy).

The relationship between dew point (atmospheric moisture) and min temperature.
On a calm, clear night, the lower the dew-point temperature, the lower the expected minimum temperature. With the same initial evening air temperature (80ºF) and with no change in weather conditions during the night, as the dew point lowers, the expected minimum temperature lowers. This situation occurs because a lower dew point means that there is less water vapor in the air to absorb and radiate (heat) infrared energy back to the surface. More infrared energy from the surface is able to escape into space, producing more rapid radiational cooling at the surface. (Dots in each diagram represent the amount of water vapor in the air. Red wavy arrows represent infrared (IR) radiation.) Graphic courtesy Meteorology Today.

As we all know, as the sun goes down, the heat from it decreases. Consequently, at some point late in any given day, the ground and the air near it lose more heat that it receives.

The ground being denser than air cools more quickly than the air above it. Hence, after the sun goes down, the ground is cooler than the air directly above it.

For any two objects in contact with each other, heat will flow from the warmer to the cooler. Similarly, the warmer air above gives up heat to the ground, which the ground quickly emits away.

As the night progresses, the ground and the air near it continue to cool more rapidly. Air is a poor conductor (transferrer) of heat. As a result, it takes a while for the air to reach it coolest. However, this is normally reached just before dawn, in the Antigua and Caribbean context.

Now, radiational cooling happens 365 nights a year, so what was different last night? The main difference was the fact that the winds were calm, and the skies were clear – the main ingredients.

Additionally, we are in the Northern Hemisphere’s winter – shorter days, as the sun is away over the Southern Hemisphere; consequently, the coldest time of the year. So, we had almost the perfect recipe for radiational cooling to be at its optimum; thus, our colder than normal weather.

If you live at the bottom of a valley, you may have felt colder than most. This is because cold dense air, which originates from the cold hill tops, slowly flows down the hill slopes and settled in the valley – making for colder weather than non-valley areas.

If you live on a hill top you would have been coldest, as the higher you go, the cold it gets generally – 1 °C (1.8 °F) for every 100 metres (330 ft) you go up. Radiational cooling has a greater impact on hill tops that elsewhere.

There is nothing unusual with us having such cold night. No records were broken, which is indicative of the fact that we have had colder temperatures. Actually, as our climate warms like almost every other place on earth, these “extremes” temperature are occurring less frequently.

When I was a child, I recall that it was very common for my siblings and I to see our breaths in the mornings, at this time of the year – due the cold temperatures. We used to make the mirrors frosty with our breaths and then write stuff on them. That has become a rarity, at least for me – anecdotally indicating that our climate is warming and the reduced frequency of such low temperatures.

Radiational cooling operates at it maximum under clear skies, dry air, calm winds and long nights, which are synonymous with the winter months – December to February. So, we are in the period when radiational cooling operates at it best. The winds have the effect of disrupting the cooling; consequently, with the winds not likely to returning to calm over the next several days, a repeat of night before last is unlikely – fortunately or unfortunately.

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Wetter Than Normal November Eases Drought to Slight

31 12 2018

Dale C. S. Destin |

DroughtMeterNovember’s rainfall was higher than usual – 135% of the average for the month. The total of 204 mm (8.03 in) makes this November the 21 wettest on record. The very welcome rainfall has ease the meteorological drought to slight levels and have also eased or eliminated other droughts.

Over 95% of the rainfall for November fell during the first 15 days of the month, making it the second wettest such period on record. The rainfall was caused by a cold front and a series of troughs.

The last three-month period – September to November, upon which the assessment of the current intensity of the drought is based, was slight dry. Notwithstanding a wetter than normal November, the last three months, as a time interval, had below normal rainfall with 370.6 mm (14.59 in) recorded. This is the lowest since 2015 and the second lowest since 2009.

RainfallAccuForPast24Months

Rainfall for the past 24 months for varying time intervals compared to the normal/average and records

We remain in a severe meteorological drought, the worst category on our drought scale. However, at the moment, the current intensity is slight. Recall that the overall description of the drought is based on the worst intensity achieve during its lifetime; however, over time, the intensity will fluctuate. Last month the intensity was at serious levels.

Potworks Dam, with a billion-gallon capacity, has moved from near totally dry to being one-third full, two-third empty – depending on your perspective. The water levels have gone above extraction height and I am advised that the same is true for the other smaller catchments.

Potworks Dams Nov13_2018_KarenCarbin

Potworks Dam – Nov 13, 2018. Complements Karen Corbin of the Humane Society

Potable water has become more readily available and water rationing has apparently cease, for now. This is indicative of huge dent November’s rainfall made on the droughts.

The fourteen-month period – October 2017 to November 2018, the duration of the drought thus far, is deemed severely dry. The total for the last 14 months of 977.6 mm (38.49 in) is the second lowest since 2001 – only the similar period October 2014 to November 2015 was drier. October of one year to November of the next normally gets 1514.6 mm (59.63 in), which means that there is a large rainfall deficit of around 35% – more than one-third of the usual rain did not fall.

Based on the last set of rainfall forecasts from regional and especially international sources, the news is discouraging with respect to rainfall. Overall, below normal rainfall is most likely for the next six months – January to June 2019, with relatively high confidence that the period January to March 2019 will be drier than normal – possibly well below normal. Thus, there is every reason to believe that the droughts will continue and likely reintensify. The chance of the droughts ending is, at most 30% or low.

MultimodelEnsembleRainfall_JFM_2019

Probabilistic Multi-Model Ensemble Forecast of Rainfall For Jan-Mar 2019, based on 12 global model

On average, our severe meteorological droughts last for around 16 months, but not continuously at severe intensity. At current, the drought is in its 15th month; the longest such drought on record lasted 38 months – Jul 2013 to August 2016.

I now expected 2018 to be among the top 10 direst years on record with the island-average total less than 900 mm or less than 35 inches. We normally get 1206.5 mm or 47.5 inches.

AccumulationJan_Dec2018

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All the best for 2019!





Potential Flooding Rainfall to End the Hurricane Season

28 11 2016

Dale C. S. Destin |

Satellite Image - Past 6 hrs Ending 11:45 UTC or 7:45 Local Time

Satellite Image – Past 6 hrs Ending 11:45 UTC or 7:45 Local Time

A surface low pressure system is expected to form near the northeast Caribbean and cause potential flooding rainfall across much of the Eastern Caribbean through Tuesday. Antigua and Barbuda is expected to see peak totals today – Monday.

The system could cause 25 to 100 mm (1-4 in) of rainfall, with locally higher amounts, from the Dominican Republic to Trinidad and Tobago. The epicentre of the rainfall is likely to be just south of Antigua or across the northern Windward Islands where the total could max-out above 100 mm (above 4 in).

North American  Mesoscale Forecast System (Model) Rainfall Accumulations - Nov 27-29, 2016

North American Mesoscale (NAM Model) Forecast System Rainfall Accumulations – Nov 27-29, 2016.

 

Globale Forecast System (GFS) Rainfall Accumulations for the Period Nov 27-29, 2016

Global Forecast System (GFS Model) Rainfall Accumulations for the Period Nov 27-29, 2016

With this type of rainfall, minor flooding is expected and moderate or worse flooding is possible. Hence, flash flood watches and warning may be required for a number of other areas over the next 12 to 36 hours.

This may be a fitting end to a very wet start to November. The month had a near record wet start across the Eastern Caribbean. In Antigua, some areas received upward 200 mm (8 in) during the first 10 days of the month. At the V. C. Bird International Airport, the rainfall stood at 143.5 mm (5.7 in) by November 10 – the third most on record dating back to 1928.

Rainfall Anomalies

Rainfall Anomalies for the Period Nov 1-10, 2016

With this type of rainfall, minor flooding is expected and moderate or worse flooding is possible. Hence, flash flood watches and warning may be required for a number of other areas over the next 12 to 36 hours.

This may be a fitting end to a very wet start to November. The month had a near record wet start across the Eastern Caribbean. In Antigua, some areas received upward 200 mm (8 in) during the first 10 days of the month. At the V. C. Bird International Airport, the rainfall stood at 143.5 mm (5.7 in) by November 10 – the third most on record dating back to 1928.

Recall also, that there were deadly floods and landslides across portions of St. Vincent during the early parts of the month.

The forecast rainfall for Monday is not a foregone conclusion but it is quite possible. If it were to materialized, this November would be one of the wettest on record for much of the Eastern Caribbean. In Antigua, it would be the wettest since Hurricane Lenny’s deluge of 1999 and be among the top 10 wettest Novembers of all time.

After the low, very cool northerly winds are expected to blow across the region. These will likely cause our coolest weather for the season and since February. Night-time temperatures could fall to below 19 °C (66 °F) Monday, Tuesday and Wednesday nights.

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