Saharan Dust to Reduce Air Quality to Unhealthy Levels

20 06 2020

Dale C. S. Destin|

A fresh surge of Saharan Dust is set to reduce the air quality across much of the Caribbean to unhealthy levels on Sunday. The Dust brings with it the potential for wide-reaching health implications from itchy eyes and runny nose to even death.

The presence of particulate matters 2.5 and 10, in the Saharan Dust surge, makes it potentially deadly for sensitive groups people. This includes persons with respiratory or heart disease, the elderly and children.

The unhealthy air quality levels increase the likelihood of respiratory symptoms in sensitive individuals, aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly.

People who are especially sensitive to the Dust should restrict outdoor activity. Also, keep windows and doors closed, as much as possible, and wear a face mask, rated to filter out PM 2.5, when going outside. Already, we are wearing masks to mitigate COVID-19, these masks are also helpful in mitigating against the health impacts of the Dust.

The caution is for mostly sensitive people. However, there is the potential for the air quality to be worse than forecast and impact everyone in the general population, resulting in increased respiratory illnesses.

The health concerns from the dust is not limited to the impacts of particulate matters. This Saharan Dust is also said to contain bacterial and fungal spores, which can also sicken persons.

Of perhaps even graver concern to health professionals is the chemical content of the Dust. It has been tested positive for such pesticides as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and metals, which are known to very harmful to human health.

Research has also shown that the Dust is also harmful to the health of other creatures. It is harmful to coral reefs by way of the pathogens it contains. The dust is also credited for algae blooms or “red time”, resulting in fish kills and the death of other marine life.

The Saharan Dust is ever-present across the Caribbean but not at constant levels. It gets to us via the prevailing easterly winds, which places the Caribbean downwind from the Sahara Desert. The Dust generally peaks in June and is lowest in December.

Sahara Desert - the Source of the Dust
Sahara Desert – the Source of the Dust

This episode of the Saharan Dust will peak on Sunday at unhealthy levels. However, at present, it is moderate and will return to moderate levels on Monday and continue this way through much of the upcoming week.

Air quality index, as measured at various sites across the Eastern Caribbean Sat afternoon, 20 June 2020
Air quality index, as measured at various sites across the Eastern Caribbean Sun morning, 21 June 2020

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The Hurricane Season in June Too Soon

14 06 2020

Dale C. S. Destin|

We, Antigua and Barbuda, have never had a tropical cyclone – tropical depression, tropical storm or hurricane, in June (knock wood). The same is true for much of the Caribbean east of Cuba.

All 107 Named Storms for June 1851-2019, based on data from NOAA

There has only been one hurricane to impact the Eastern Caribbean in June – Unnamed Category 1 Hurricane of 1933, also called the Trinidad Hurricane. It was a deadly hurricane – killing 13 people in Trinidad, 22 in Cuba and killing, at least, 35 people in total across Trinidad, Venezuela, Jamaica and Cuba. It also caused deaths and destruction across Mexico.

The hurricane season in June for the Caribbean – 1851 to 2019

June averages one named storm (tropical storm or hurricane) every other year; one hurricane every 8 years and a major hurricane – Category 3 or higher intensity, every 50 years, on average. It is the least active month of the hurricane season.

Before this year, the last storm in June was Cindy in 2017; the last hurricane was Arthur of 2014 and the last major hurricane was Alma in 1966.

Given the current season, it may be said that Cristobal, of this June, was overdue by a year; the next June hurricane is due around 2022 and the next June major hurricane is overdue by about 3 years. Will this be the year for what would be the fourth major hurricane for the month? Unfortunately, there are no tools available currently to answer this question.

Interestingly, over the relatively reliable data period of 1966-2019, there is no significant difference in the average number of hurricanes in June for above and below normal seasons. A hurricane forms in June around every five above normal seasons and every four below normal seasons. The mentioned period has no hurricanes in June for normal seasons.

There have been three major hurricanes in June based on record dating back to 1851; however, over the period 1966 to 2019, there has only been one major hurricane – Alma of 1966.

Category 3 Hurricane Alma of 1966 – the most powerful Atlantic June Cyclone along with Hurricane Audrey of 1957

So, what is the probability of a hurricane this June, given an above normal season? It’s around 19 percent. What is the probability for a major hurricane? About 5 percent. For all seasons considered for 1966-2019, the probability of a hurricane and major hurricane is 17 and 2 percent respectively. No significant difference between an above and below normal season.

The zones of origin and tracks of storms in June during the hurricane season

Based on record for 1851 to 2019, there have been, in June, 107 named storms of which 37 became hurricanes and 3 reached major hurricane status – Category 3 intensity or higher. For more reliable data, the period 1966 to 2019 have seen, in June, 37 named storms, 7 becoming hurricanes and no major hurricane. For the current standard climate or base period of 1981-2010, there have been 21 named storms, 4 hurricanes and no major hurricanes.

It turns out that like May, storms in June say nothing about the overall activity for the season i.e. whether it will be above, near or below normal.  

Using the current climate period 1981-2010, if storms are going to form in June, they will mostly do so during the first or last 10 days of the month. Over 80 percent of all storms in June, for the current climate period, forms between June 1-10 or June 20-30.

June on 5 occasions had a maximum of three named storms in a given season – 1968, 1959, 1936, 1909 and 1886. On one occasion it had three hurricanes, 3 Category 2s – 1886. Note: these ALL occurred outside the climate change era. This year could make six years since there was a hurricane forming in the month.

Recall that the forecast is for this hurricane season to be above or well above normal. And notwithstanding what happens in June or any other month, it only takes one hurricane to ruin your year or life. Thus, you need to be prepared as best as possible for every hurricane season.

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Updated Hurricane Season Forecast – June Too Soon 2020

10 06 2020

Dale C. S. Destin|

My “June too soon” updated forecast for the 2020 Atlantic Hurricane Season is out, and it continues to call for an above normal season, which is likely to be hyperactive – well above normal.

The forecast predicts an accumulated cyclone energy (ACE) index of 202 (up 13 over the previous forecast), 21 named storms (up 2 to include Arthur and Bertha), 9 hurricanes (unchanged) and 5 major hurricanes (up 1).

To give a clearer picture of the forecast and the uncertianties, there is a 70% confidence of

  • 17 to 26 named storms;
  • 6 to 13 becoming hurricanes;
  • 2 to 7 becoming major hurricanes – Category 3 and higher and
  • 122 to 289 ACE.

If the forecast materialises, the ACE would be top 10 of all times. And if we use the ACE as an indicator of destructive potential, as some do, it means that the season’s destructive potential would also be top 10 of all times.

The main reasons for the above normal forecast are:

  1. the likely continuation of a warmer than usual tropical North Atlantic (TNA) and
  2. the potential for a cooler than normal eastern equatorial Pacific i.e. La Niña.

The greater the likelihood of these two things happening at the same time – August to October , the greater the chances for an above normal season.

TNA Index – very positive since about February 2020, indicative of warmer than usual sea surface temperatures across the region

According to other forecasts surveyed, the consensus is for an ACE of 151 (up 5), 17 named storms (unchanged), 9 hurricanes (up 1) and 4 major hurricanes (unchanged). These numbers represent an above normal season.

Accumulated Cyclone Energy (ACE) based on 15 forecasting entities, including 268Weather.

Compared to my forecast, most other forecasts are also calling for an above normal season. However, compared with most other forecasts, my forecast is calling for a much more active season – 34% more.

Clearly, we have no control over the numbers for the season. But notwithstanding the forecast, you should always prepare the same each season, as it only takes one hurricane to ruin your year and or life.

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Driest April-May for Over 80 Years

6 06 2020

Dale C. S. Destin|

The combined rainfall total for April and May is near record-breaking low levels for Antigua. The total for this Apr-May: 36.8 mm (1.45 in), is the second lowest on record, dating back to 1928. Only Apr-May 1939, 81 years ago, had less rain – 27.9 mm (1.10 in).

Normally, these months would produce a combined rainfall of 189.2 mm (7.45 in). This means that the rainfall for Apr-May is less than 20% of the normal total, a deficit of over 80%.

Such low precipitation for Apr-May only happens once every 67 years, on average. In other words, there is only a 1.5% chance of this happening per year. Most Antiguans alive today have never witnessed such dryness before, for these months, and are very unlikely to witness it again.

Usually, Apr-May would account for 52% of the rainfall for Jan-May but instead it only accounted for less than 14%. Both April and May had similar extreme deficits. There have been only three other occasions when both months registered less than an inch of rain in the same year – 1973, 1939 and 1928.

It was not long ago that we were enjoying ample rainfall. First quarter rainfall, Jan-Mar, was above normal. However, this wonderful start to the year came to a screeching halt.

The horizontal (flat line) from Apr 1 to May 31 is indicative of the rapid downturn in rainfall as compared to the previous three months.

The difference in rainfall between Jan-Mar and Apr-May is the second greatest on record, indicative of the extremely sharp downturn in precipitation. We went from 237.7 mm (9.36 in) for Jan-Mar to 36.8 mm (1.45 in) for Apr-May, a decline of 200.9 mm (7.91 in). Normally, Jan-Mar and Apr-May produce 176.0 mm (6.93 in) and 189.2 mm (7.45 in) respectively.

Few of us alive today have ever seen this kind of change of rainfall, in Antigua. This kind sharp decline in rainfall from Jan-Mar to Apr-May only happens once every 100 years, on average. Only 1967 has had a greater decline, 240 mm (9.45 in), over the similar month periods.

This Apr-May is also the driest two-month period since May-Jun of 2001. It is also the 12th driest combined consecutive two months on record.

This past April and May were clearly extremely dry, and this dryness was magnified by the preceding wetter than normal first quarter.

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4th Driest May on Record for Antigua

5 06 2020

Dale C. S. Destin|

Potworks Dam, Antigua – June 1, 2020. Currently dry but when full, holds a billion gallons. Pic courtesy Karen Corbin – Humane Society

May 2020 was another very dry month for Antigua. The rainfall total of 20.8 mm (0.82 in) was the lowest since 2001 and the fourth lowest on record dating back to 1928. Only May 2001, 1939 and 1928 have been drier, with May 2001 being the driest with 6.4 mm (0.25 in).

Relative to the normal total for the month of 103.6 mm (4.08 in) only 20% fell; hence, the month had a rainfall deficit of 80%, based on the current base period of 1981-2010.

Such a low rainfall total for May is relatively rare. It happens once every 21 years, on average or has only 4-5% probability of occurring each year.

The rainfall for May is almost “bipolar” – you either get a lot or a little. This makes the rainfall for the month the most unpredictable with the highest variability index of all the months.

The dryness for May was not confined to Antigua. Most of the region from Hispaniola to Trinidad saw, at most, only 25% of the normal rainfall for the month.

The reason for the truant rainfall looks to be due mainly to higher than normal surface pressure and lower than normal relative humidity.  

Rainfall for the year has now fallen to below normal after an excellent start in the first quarter. There are some hopes for the return of seasonal or above seasonal rainfall over the upcoming months. The current forecast is for above normal rainfall for the period June to August.

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Pre-hurricane Season Summary – 2020

1 06 2020

Dale C. S. Destin|

It is June too soon – the Atlantic hurricane season officially starts today. However, it seems like no one remembered to remind the “storm gods” of this fact. Already, we have seen two named storms – Arthur and Bertha, resulting in a very active pre-hurricane season 2020. Only twice on record before, dating back to 1842, that May has produced two named storms – 2012 and 1887.

Arthur formed on May 16, just north of the northern Bahamas. It moved north to near the Outer Banks of North Carolina, then out over the Atlantic and lost its tropical characteristics. It caused tropical storm force winds across a small portion of North Carolina and reached peak sustained winds of 97 kph (60 mph).

Tracks of Tropical Storms Arthur (right) and Bertha (left)

Bertha was a bit of a surprise storm. Formation was not expected due to strong upper-level wind shear. On the morning of 12:50 am, May 27, it was given a 30% chance of formation and by 8:30 am, it was declared a tropical storm with sustained winds of 72 kph (45 mph). It eventually reached peak sustained wind speed of 80 kph (50 mph), before dissipating on May 28. The system caused one death.

In terms of pre-season storms – storms forming between March and May, there have been only four occasions when there were two named storms – 2012, 1951, 1908 and 1887. Of course, I am mindful that before the satellite era – pre mid-1960s, a number of short-lived storms went undetected, resulting in gaps in the record.

On average, there is a storm in May once every 7 to 8 years, based on record for the period 1981-2010, whereas, there is a preseason storm once every 5 years. Most pre-season storms form in May – about 85%, 9% in April and 6% in March.

Preseason storms say nothing about the season they precede, in terms of how active or inactive they will be. However, this season is expected to be active and likely to be hyperactive – well above normal.

We all need to be prepared for the hurricane season regardless of the number of storms and hurricanes being forecast, as it only takes one hurricane to ruin our year or life.

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