Early Prediction: Below Normal Rainfall Most Likely for Antigua

21 04 2022

Dale C. S. Destin |

The year will most likely be another drier than usual one for Antigua. My early forecast calls for the rainfall total for 2022 to most likely be 1105 mm (43.50 in) with a 70 percent or high confidence of it being in the range of 811 to 1463 mm (31.93 to 57.60 in).

The main reason for the most likely below normal rainfall forecast is the current cooler than normal sea surface temperatures (SSTs) across the tropical North Atlantic (TNA), which should last, at least, into the second half of the year. Cooler than normal TNA SSTs favour suppressed rainfall conditions while the opposite enhances rainfall.  

The year started out with a severe drought brought forward. This drought started in the winter of 2020/2021 and continues through the present. January 2022 was wetter than January 2021, but it was still only 72 percent of the normal total. The last two months, February and March, have been wetter than normal resulting in the intensity of the meteorological drought easing to slight. This easing is likely to be a brief respite, given the forecast.  

The dry season, January to June, will likely be below normal with a 60 percent chance. The forecast is for 298 mm (11.73 in) with high confidence of it ranging between 182 to 459 mm (7.17 to 18.07 in). This dry season could also be one of the top 10 driest. There is a 33 percent chance of this happening with the possibility of the total falling below 254 mm (10 in). Currently, the total stands at less than 203 mm (8 in) with April running well below normal at less than 25.4 mm (1.0 in) and the forecast indicating a better than 70 percent chance of May-June being drier than normal.

WMO Lead Centre for Long-Range Forecast Multi-Model Ensemble is forecasting 70-80% likelihood of below normal rainfall for Antigua and Barbuda for May to July. Also, below normal rainfall is likely for much of the rest of the Eastern Caribbean.

A typical year, based on the new standard climate period 1991-2020, averages 1156.7 mm (45.54 in). The dry season averages 410 mm (16.14 in) and the wet season, July to December, averages 746.8 mm (29.40 in). The fall/autumn, September-November, accounts for 58 percent of the wet season total and 38 percent of the year’s total.

Rainfall-wise, last year–2021, will be most remembered for being the second driest on record with some parts of the country having record-breaking dry weather. There were likely significant socio-economic impacts but unfortunately, this has not been quantified.

This forecast will be updated monthly around the 21st of each month until August. The first update will be issued around May 21.

Regardless of the forecast, we all need to conserve water and be as efficient with its use as much as possible. Reducing our personal water footprint will literally redound to our individual and collective socio-economic benefit. Minimising your water footprint is also good for the climate and good for our environment.

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Drought Continues

25 05 2021

Dale C. S. Destin |

With continued below normal rainfall through April, the meteorological drought continues for Antigua; however, it has eased to slight intensity as compared to serious at the end of March. Notwithstanding, we remain in a serious drought with significant cumulative rainfall deficits that are likely to have socio-economic impacts. Models continue to portray a dry scene for the upcoming months.

WMO Lead Centre for Long-Range Forecast Multi-Model Ensemble is forecasting 60-70% likelihood of below normal rainfall for Antigua and Barbuda. Also, below normal rainfall is likely for much of the Caribbean Basin.

We continue to witness the driest start to a year since 2015 and the eighth driest quadrimester for Antigua in a series that dates to 1928. The island-average rainfall of 131.8 mm (5.19 in) represents only 55 percent of the normal total for January to April; hence, 45 percent of the regular stream of water from the heaven was missed and is evident by our thirsty brownish landscape. Further, from the flooding rainfall in November to the end of April (December-April), only 64 percent of the normal rainfall has fallen. This is the 10th lowest on record.

The background is a picture of Potworks Dam, Antigua taken May 3, 2021 by Karen Corbin of the Humane Society.

The rainfall for this April of 38.9 mm (1.53 in) is more than twice the amount fell last April; however, it is the second lowest since 2006. The total was only 51 percent of the usual amount for mid-spring; hence, an unmissable deficit of 49 percent.

There is no discernible respite in the near future. The majority of models are forecasting deficit rainfall to be the order of, at least, the next three months. Thus, the drought is likely to continue. Our catchments could again revert to mud patches and or grasslands, which has virtually become an annual phenomenon.

Based on models which correlate our sea surface temperatures, across the tropics, with our rainfall, the medium and long term look brown. There is a 78 percent chance of the dry season, January to June, will suffer below normal rainfall. Further, there is a 52 percent chance of the dry season rainfall being in the bottom 10 percentile i.e. less than 10 inches, when the average is 16.14 inches. For the year, the forecast is for a 46 percent chance of it being drier than usual, with a non-trivial probability of 19 percent of well below usual, possibly with about a 24 percent deficit in the annual total.

Rainfall projection for Antigua in inches. A for chance of above normal; N for near normal and B for below normal. The background is a picture of Potworks Dam taken May 3, 2021 by Karen Corbin of the Humane Society.
Rainfall projection for Antigua in inches. A for chance of above normal; N for near normal and B for below normal. The background is a picture of Potworks Dam taken May 3, 2021 by Karen Corbin of the Humane Society.

Other droughts generally lag meteorological droughts; it is evident from our catchments that agricultural, hydrological and ecological droughts, to some degree, are also occurring or imminent. There is also the concern that this may precipitate a socio-economic drought. Our utilisation of the ocean around us for fresh water has made us resilient; however, there are still likely to be notable impacts, when the other droughts get underway in earnest.

Image from the Landsat satellite showing the contrasting green landscape of December 9, 2020, one month after the deluge of November 9-10, 2020, compared to the brown drought-ridden landscape of May 2, 2021

Potworks Dam is down to around a quarter. With the rainfall outlook bleak, we could virtually be out of surface water soon. Water rationing is imminent, if not already occurring.

Antigua continues not alone in experiencing significant rainfall shortages. Much of the Eastern Caribbean is having a similar thirst for rainfall, especially for December 2020 to April 2021. Short and long-term droughts continue to evolve across many places, and it is probable that the shortfall in precipitation will worsen and or spread to other islands, particularly the eastern ones, over the upcoming months, based on recent forecasts.

Please continue to follow me for more on this evolving drought and all things weather and climate via TwitterFacebook and Instagram. Also, share this blog, if you found it useful. 





Storm-Force Winds and Hurricane-Like Seas to Impact Antigua and Barbuda This Weekend

17 12 2016

Dale C. S. Destin |

Significant tightening of the pressure gradient across the area is expected to cause strong winds with frequent gusts to storm force strength or gale force. The seas will respond to the strong winds and become very rough.

Surface chart

Surface Chart for Sunday 8 am, Showing a Tight Pressure Gradient As Evident by the Closeness of the Isobars (pressure lines)

The winds – they will generally be in excess of 18 mph (16 kt) from late Saturday night to Monday afternoon. The winds will peak as high as 30 mph (26 kt) with frequent gusts between 38 and 46 mph (33 and 38 kt) Sunday morning to Monday morning.

High Sustained Winds

Sustained Winds

Wind Gusts

Wind Gusts

The seas –  they will respond to the winds and become very rough, rising to as high as 3.9 metres (13 ft) on Sunday night. Waves will rise above six feet by Saturday morning and remain above this height through midweek. Waves of 2.7 to 3.9 metres (9 to 13 ft) will prevail from Saturday night to Wednesday. Waves are expected to fall off rapidly after Wednesday.

Seas

Seas

The cause – as indicated above, it is the substantial tightening or steepening of the pressure gradient.  This is in response to a very strong surface high pressure system moving from west to east across the Atlantic from the United States.  This will NOT be due to any tropical cyclone (tropical depression, tropical storms or hurricane).

Fundamentally, wind blow as a result of pressure differential (pressure gradient). The greater the pressure between point A and point B (pressure gradient) the stronger the winds.

Where – the strong winds will mostly take place over open waters, exposed eastern coastal areas and elevated areas of Antigua and Barbuda. The seas will be roughest in the Atlantic coastal waters east of the islands, as the winds will be generally easterly. Similar conditions are expected across most of the rest of the Eastern Caribbean. However, Antigua and Barbuda could get the worst of it.

Precautions – The Antigua and Barbuda Meteorological Services have issued warnings for sea-bather and small craft operators. The former should avoid the beaches, especially those on the Atlantic or eastern side of the islands, and the latter should not venture far from port, at least, until Thursday.

A small craft warning generally means that wind speeds in excess of 16 knots is causing or expected to cause hazardous sea conditions to small craft within 24 hours. Inexperience mariners, especially those operating smaller vessels should avoid navigating these conditions.

According to the Beaufort Scale, gale-force winds run from 39 to 54 mph (34 to 47 kt). Operating a vessel in gale conditions requires special expertise and specially equipped vessels. It is highly recommended that mariners without the proper experience seek safe harbour prior to the onset of gale conditions.

The strong winds, especially if frequently gusting to gale force, could also make some outdoor activities very uncomfortable if not hazardous, please be guided accordingly.

We will be keeping a close eye on this developing situation and keep you informed via our social media platform: twitterfacebookinstagramtumblrflickrgoogle+, and youtube.





May to October 2016 Climate Outlooks for Antigua

3 05 2016

Dale C. S. Destin |

The May to October 2016 climate outlooks are now available for Antigua. In the short-term, the news remains bleak regarding rainfall. However, in the long-term, there is relieving news, as above normal rainfall is likely for the period August-October. Meanwhile, uncomfortably warm temperatures are expected for the upcoming six months.

Drought

Notwithstanding a wetter than normal week in April, droughts (meteorological, agricultural, hydrological and socioeconomic) continue across Antigua. We are now entering the 35th month of mostly moderate or worse rainfall deficits.

Currently, a moderate drought or worse is evolving over the periods – February to July 2016, October 2015 to August 2016 and November 2015 to October 2016. All three periods are likely to have below normal rainfall. Drought warnings remain in place and will likely continue into the third quarter of the year.

Feb-July2016_Rainfall

The current El Nino looks to be on its last gasp. It will transition to a neutral state around the middle of the year and possibly to La Nina during our wet season. La Nina, unlike El Nino, generally encourages rainfall across our area, mainly during the wet season. Although still distant, we appear to be drawing nearer to the light at the end of the tunnel i.e. the end of the droughts.

Precipitation and Temperature

Over the coming three months – May to July, below to near normal rainfall will result in the droughts continuing, at best, slight, and at worse, re-intensifying to serious levels.

Meanwhile, August to October will likely see above normal rainfall. Thus, some droughts may come to an end during the latter half of the upcoming rainy season. However, there remain large uncertainties as to how wet the rainy season will eventually be.

So far, 2016 has been wetter that last year; however, it’s running over 50 mm (2 in) below average. The dry season (January-June) is likely to be drier than usual, and at best, the year will have near normal rainfall.

The heat will likely be on for much of the rest of the year. Warmer than normal temperatures are probable for MayMay-July and August-October.

See the following links for the full outlooks; rainfall: MayMay-July, August-OctoberMay-October 2016 and April Drought Outlook.

The next set of outlooks will be available by June 3, 2016.





The 2016 Atlantic Hurricane Season Early Forecast

15 04 2016

Dale C. S. Destin |

Early forecasts just issued for the upcoming 2016 Atlantic hurricane season (AHS) indicate a near normal season is most likely. However, relative to the past three years, this season could be much more active.

Ensemble forecast

The ensemble (mean) forecast, based on predictions from Klotzbach of Colorado State University, Saunders and Lea of Tropical Storm Risk.com (TSR) and AccuWeather.com, is for 13 named storms, 6 becoming hurricanes and 3 becoming major hurricanes.

2016_Hurricane_Season_Forecast

A better indicator of the activity for the season is the accumulated cyclone energy (ACE) index which is a measurement of the strength and duration of each tropical cyclone. Summing together the ACE of each cyclone, provides a more complete picture of how active the season is likely to be outside of just the number of storms.

This year, the ensemble forecast calls for an ACE index of 85. If this forecast pans out, the 2016 season would be around 136%, 27% and 35% more active than 2013, 2014 and 2015 respectively.

It must be noted though that there is very low skill in forecasting the AHS (June to November) in April. However, this is the best available forecast for the season, at this time, and can be used as a guide for what is possible. A more skillful forecast will be available around June 1.

End of Atlantic active phase?

Around 1995, the AHS went from a quiet to an active phase. The average annual number of named storms increased from 9 to 15. There is now increasing evidence that we have seen the end of that active phase.

If the active phase has in fact ended, it would mean a reduction in the mean number of tropical cyclones (depressions, tropical storms, hurricanes) across the Atlantic over the next 20 to 30 years. This would translate to an annually reduced probability (chance) of us being impacted by a tropical cyclone between now and around the year 2041.

The x factors

There are at least two climate factors that could cause the hurricane season to be quieter than is currently being predicted. El Nino is ongoing and is virtually synonymous with inactive AHSs. The forecast is for a transition from El Nino to neutral conditions around the middle of the year and possible La Nina around October. However, if El Nino were to persist beyond summer, we would see another quiet hurricane season. On the other hand, La Nina could lead to an active season.

The second potential inhibitor of the 2016 AHS is the transport of cooler-than-normal sea-surface-temperatures (SSTs) into the tropical North Atlantic by ocean currents originating south of Greenland. Reduced SSTs hinder tropical cyclone formation and growth.

Probability of Antigua being hit by a hurricane

According to Klotzbach, the likely best similar years to the upcoming 2016 AHS are 1941, 1973, 1983, 1992, 1998 and 2014. Of these years, we were hit by Hurricane Georges and Tropical Storm Bonnie in 1998 and Tropical Storm Christine in 1973. Thus, based ONLY on similar years, the probability of Antigua being hit this year by one or more named storms is around 39%, while the probability of one or more hurricanes is around 15%.

In general, the probability of Antigua being hit by one or more named storms annually appears to vary according to the phase of the Atlantic. During the quiet phase of 1962 to 1994, the probability of one or more named storms was around 26%, while the probability of one or more hurricanes was around 14%. Meanwhile, for the active phase of 1995 to present, the probability of one or more named storms increased to around 55%, while the probability of one or more hurricanes is around 35%.

Based on the climatological period of 1981-2010, the probability of being hit by one or more named storms is around 41%, while the probability of one or more hurricanes is around 28%.

2015 hurricane season and lessons learnt

The 2015 AHS was quiet; it produced 11 named storms, 4 hurricanes and 2 major hurricanes. The ACE index total was 63, the fourth lowest since 1995. Notwithstanding it being a quiet year, Antigua was affected by Tropical Storms Danny and Erika. Damage was minor; however, closure of the country for around 24-hours, due to threat from Erika, caused an unknown loss of revenue.

Erika serves as a perfect reminder of the fact that flooding is a hazard associated with tropical cyclones. The system caused catastrophic flash floods across parts of Dominica, killing dozens of people. I our part of the world, we tend to focus a bit too much on the wind hazard associated with these systems.

Another lesson learnt was that it only takes one named storm to make it an active or miserable hurricane season for us. Thus, quiet season or not, the same hurricane season preparations are required each year.

Follow us and stay updated on the 2016 AHS via our social media platform, which includes twitter, facebook, wordpress, instagram, tumblr, and google+. Follow us also for all things weather and climate.





Our May Newsletter is now Available

19 05 2015

Dale C. S. Destin |

We’d like to present you with our May newsletter. In this newsletter, you’ll find highlights of recent weather and climate news. Additionally, there are outlooks for the upcoming six months. Links are also provided for further information. Please read and feel free to share you feedback.

Newsletter_Pic

 

Follow us also on @anumetservice, facebook and tumblr for the latest on the current drought and other weather & climate news.








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