Drought-Busting, Lenny-Type Rainfall Impacted Antigua

10 11 2020

Dale C. S. Destin|

A newly formed tropical disturbance caused drought-busting, Lenny-type rainfall across parts of Antigua. The system dumped over 373 mm (over 14 inches) across parts of the country, over the last 24 hours.

Of course, with this extreme rainfall, there was massive flooding in some areas. The impact is unfolding with images of almost submerged and abandoned vehicles, flooded businesses and homes and damaged roads.

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Last Night: Flooding at Woods, St. John’s, Antigua
Today: Same area as above (Woods, St. John’s, Antigua) but after the runoff.

This rainfall event was quite extreme, if not in amount, certainly with respect to intensity. In 24 hours, two-and-a-half times the month’s total rainfall fell, yes 250% November’s average in less than 24 hours, in some places. The islands average rainfall for November is 149.4 mm (5.88 inches).

The maximum 6-hour rainfall was higher than the average for most months. We measured up to 156 mm (6.14 inches) in six-hours. This is more rainfall than we would have had from most tropical cyclones that have impacted the island. The max six-hour rainfall on record at the Airport is 175.2 mm (6.90 inches); the max for November for the same location is 158.7 mm (6.25 inches).

In an hour yesterday, we measured peak rainfall total of 97 mm (3.82 inches), at the University of the West Indies – Five Islands Campus. At the Airport, the record of 56.4 mm (2.22 inches) was broken by the 77.9 mm (3.07 inches) measured between 4 and 5 pm, yesterday.

Drilling down even deeper, there were occasions when the ten-minute rainfall total reached close to 25 mm (1 inch). This is almost unimaginable to think that in a space of 10 minutes, some areas would have had nearly an inch of rainfall.

Putting the rainfall total into further perspective, the one-day-total, for some areas, for this event is higher than the one-day-total from Lenny recorded at the Airport. Lenny’s maximum one-day total was 241 mm (9.49 inches), at the Airport, as compared to over 320 mm (over 12.6 inches) from this event, at Five islands.

More rain is in the forecast with another 100 to 200 mm (4 to 8 inches) possible in the next 72 hours. This means more moderate to major flooding is likely.

Potential impacts include:

  • loss of life and injuries;
  • widespread financial losses;
  • disruption to transportation;
  • soil erosion;
  • disruption of schools;
  • damage to dams, embankment, irrigation and drainage facilities;
  • decrease in storage capacity of reservoir due to high sediment rate;
  • contamination of potable water;
  • crop and animal losses;
  • environmental degradation;
  • disruption to communication and
  • damage to infrastructure. 

Stay alert and prepared. If or when a flash flood warning is issued, it means that, at least, moderate or worse flooding is imminent or occurring in the warned area. Thus, residents in these areas should move to higher ground immediately.

Do not drive your vehicle into areas where the water covers the roadway, as the underlying road may have washed away, magnifying the potential for harm. A flash flood watch means to prepare for the possibility of warning conditions.

Flooding across portions of Bolans, Antigua

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Busy Week Ahead for the Caribbean

16 08 2020

Dale C. S. Destin |

Looks like the Caribbean is set for another busy week. There is the potential for two tropical cyclones – tropical depressions, tropical storms or hurricanes, impacting the area.

Tropical Disturbances AL97 (near the Caribbean) and AL96 (near Africa)

It is the start of a new week but the continuation of a record-breaking hurricane season, which could add two more storms to its tally, in days. There are two new disturbances between Africa and the Caribbean, taking aim at the islands.

Satellite picture animation showing the locations of the distrubances

It is uncertain as to whether these disturbances will become tropical cyclones, where they will go and what hazards, they will bring to the area. However, at this time of the year, most disturbances do develop into tropical cyclones, as conditions are generally conducive, like they are currently, bar the dry and dusty Saharan air.

Today, we saw the end of Tropical Storm Josephine, which threatened the area but eventually passed a safe distance north of all the islands.

Tropical Storm Josephine passing by on Saturday afternoon, 15 August, 2020

With Josephine gone, all attention is now on Disturbances AL96 and AL97. They both have a 50 percent chance of formation. And they both have tracks that take them through the Caribbean.

The second of the two systems, AL96, appears to be more of a future threat to the Caribbean, particularly the Leeward Islands. AL97 is perhaps moving too rapidly for much development to take place before reaching the Eastern Caribbean tomorrow; however, it is forecast to slow down in the Caribbean Sea where it will encounter favourable conditions for formation Wednesday.

Most available models have AL97 becoming a tropical storm in 48 hours – Tuesday night/Wednesday
Most available models have AL97 going through the southern Caribbean, at most, as a Tropical Depression

The gold standard of models – the ECMWF IFS or European model is very sweet on AL96. It gives it a relatively high chance of becoming a tropical storm and track towards our “neck of the woods” – the Leeward Islands this upcoming weekend. This week could end similarly to the one just gone – with us under a Tropical Cyclone Alert or worse.

Already for the season, there have been 11 named storms, the most to have ever occurred this early in the year, with the more active half of the hurricane season just getting started. With half of the season to go, only 48 out a total of 169 seasons, dating back to 1851, has seen more storms.

Be prepared! Based on the forecast, the season is likely to produce, at least, nine more named storms, five more hurricanes and three major hurricanes. It is likely to be a very long season.

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Tropical Storms in May Mean Nothing

15 05 2020

Dale C. S. Destin |

The first tropical or subtropical storm for the pre-hurricane season is about to form in the Bahamas. Some think that this is a harbinger (sign) for the upcoming hurricane season – June 1 to November 30, but is it?

Tropical disturbance AL90 across the Bahamas with an 80% chance of becoming Tropical Storm Arthur within 48 hours.

To the “naked eyes”, it is understood why some may take a storm forming in May as a sign of bad news for the upcoming hurricane season; however, the numbers don’t agree.

The numbers say that it usually means nothing in terms of the overall activity of the upcoming season. According to NOAA, there have been 29 named storms in May, spread over 27 seasons from 1842 to 2019. Of the 27 seasons, using NOAA’s definitions, nine were above normal (active or hyperactive), 11 were near normal and 7 were below normal (inactive or quiet).

Overall, most seasons with a storm in May, are near normal – 11 times of 27 – 41%. However, from a statistical standpoint, there are no significant differences between above, near or below normal seasons, when there is a storm in May. Hence, a tropical storm forming in the month has no bearing on the activity of the upcoming hurricane season.

Of the 27 seasons with May storms, 9 or 33% was active or above normal; 11 or 41% was normal and 7 or 26% was quiet or inactive

Notwithstanding the above, this hurricane season is expected to be above normal or likely hyperactive – well above normal, see my latest forecast. Clearly, this has nothing to do with the expected formation of Tropical Storm Arthur over the Bahamas.

Further on the tropical cyclone climatology on May, of the 29 named storms to have formed in the month, 5 became hurricanes with none ever becoming a major hurricane. The strongest tropical cyclone of the month occurred in 1863 – a Category 2 unnamed cyclone.

The only Cat 2 May Hurricane on record – Unnamed Hurricane – 1863

On average, there is one storm forming in May every 7-8 years. However, there have been a storm in May of the last 2 years and 6 in the last 10 years. Twice, two storms formed in May of the same season – 2012 and 1887, the most of any. So much for averages, right!

The Eastern Caribbean has never been impacted by a tropical cyclone in May, “knock wood”, based on available record dating back to 1842.

Storms forming in this part of the region in May are not unusual. Of the 29 May storms, 28% have formed or traverse within 300 miles of Nassau, Bahamas.

Unfortunately for the Bahamas, this year they are still recovering from Super Category 5 Hurricane Dorian of September 2019, which levelled much of Northwest Bahamas. You may say that they can’t “catch a break”, as they are about to deal with potentially strong storm-force winds and flooding rainfall, in addition to dealing with the COVID-19 Pandemic.

Possible tracks of what is expected to become Tropical Storm Arthur in 48 hours

May storms mean nothing in terms of the overall activity of the hurricane season; however, they mean a lot with respect to where they impact. Let us be prepared regardless of omens or forecasts for the season – it only takes one hurricane to ruin your year or life.

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