Antigua and Barbuda Battered by Torrential Rains

16 09 2016

Last week Monday, Antigua and Barbuda was battered by torrential rains from a tropical disturbance. This resulted in major flooding in many parts of the country, especially in low-lying and flood-prone areas. We had not seen such downpours in nearly a decade.

Satellte loop of the tropical disturbance

Satellite loop of the tropical disturbance

Many parts of Antigua got more than the average total rainfall for September in less than 24 hours. On average, Antigua got around 139.7 mm (5.5 in) in less than 24 hours, with many areas getting over 180 mm (over 7 in), which is much more than the island-average of 144.0 mm (5.67 in) for September.

RadarRainfallAccumulation-24hrs ending 2amSep62016

Radar rainfall accumulations for the 24 hrs ending 2 a.m. Sep 6, 2016

With the average rainfall total of 139.7 falling on 108 square miles (the size of Antigua), it means that about 8.6 billion imperial gallons (IG) of water fell on Antigua between 2 am, September 5 and 2 am September 6. As a reference, this amount of water could serve the country for three years. It’s also close to 100 times the 90 million IG collected by Potworks Dam.

Clearly, with all this water, it should come as no surprise the we had areas with major flooding. Notwithstanding the negative impacts of the flooding, it was rainfall to make most Antiguans and Barbudans, particularly water resources managers and farmers, smile from ear to ear. It resulted in significant recharging of catchments, many of which were dry or below extraction levels since early last year.

Potworks Dam: left – Aug 24, 2016, right – Sep 6, 2016

Potworks Dam, which was dry for over a year, was filled to around one-eighth, according to the Antigua Public Utilities Authority – APUA (the water authority) . It collected around 90 million IG of water, enough to augment water supplies for the next three to four months. APUA has since indicated an easing of water rationing, at least, for the short-term.

Monday September 5, 2016 was the wettest day for quite a while for many areas of Antigua. At the Airport it was the wettest day since Hurricane Earl’s unwelcome visit in 2010. It was also one of the wettest days since Hurricane Lenny in 1999. Only three other days have been wetter since Lenny – the “father” of all flooding for Antigua.

Although this type of rainfall has been rare for the past 15 years, it does occur fairly frequently at a rate of around once every four to five years, based on rainfall measured at the V. C. Bird International Airport – the home of the Antigua and Barbuda Meteorological Service. In other words, it has about a 20-25% chance of happening each year.

The rains caused major flooding of low-lying and flood-prone areas. This resulted in an unknown number of cars being stalled in flood waters and a number of homes came very close to being flooded. There were minor rock slides reported but damage, if any, is unknown. In the wake of the event, many roads were damage due to erosion.

Flooded road

Flooded road

Flooded road

Flooded yard

The event proved very challenging to forecast. Several days before the event, most models forecast up to five inches of rainfall to occur. However, as we got closer to September 5, the models shifted the rainfall to the south of Antigua. Up to the morning of the event, none of the models surveyed came remotely close to forecast the rainfall that eventually occurred.  

Can we get a repeat of last week Monday?  It is probable but highly unlikely. The chance of getting two such days in a given year is around seven percent. So whereas getting dowsed by such drenching rainfall is not unusual, especially at this time of the year, it is highly unusual for it to happen twice in a year.

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