#6_Mr Kerr_Hurricane and Wet Season Outlook Final 2021_-25

Kalain Hosein

The Trinidad and Tobago Meteorological Service (TTMS) is forecasting a “very active” hurricane season, with three to six named storms forming east of the country and possibly one to two of them possibly strengthening into hurricanes.

The forecast was made in the National Climate Outlook Forum.

The TTMS has forecast a 59 per cent chance of an above-average Atlantic Hurricane Season within T&T’s area of interest, which spans the area south of 15° North Latitude, from the Eastern Caribbean to West Africa.

It also gives a 28 per cent chance of near-normal activity and a 13 per cent chance of below-normal activity.

With a change in the climatological averages, the Met Office notes that the averages for named storms and hurricanes in the country’s area of interest have increased.

The 1991-2020 average for named storms is now at four, compared to the average three for 1981-2010.

However, the average number of hurricane formations is unchanged.

Although giving a range of outcomes, the Met Office is forecasting that the most likely number of named storms to form in this area is five, with one becoming a hurricane.

Acting Chief Climatologist Kenneth Kerr explained that the main indicators within their analysis show the Atlantic Hurricane Season might trend to above-average activity. These include above sea surface temperatures in the Atlantic and the potential for a weak La Niña in the Pacific.

In addition, higher forecast sea level pressures from June through August can drive tropical cyclones into the Caribbean, increasing the likelihood of impacts in the Lesser Antilles.

Drier start to wetter-than-average wet season

Following a wetter-than-average 2021 Dry Season, the TTMS forecasts a drier than usual start to the 2021 Wet Season. The Met Office has said June is likely to be the driest of the first half of the Wet Season and could become the driest month for the second half of the year.

During the second half of the Wet Season, forecasters call for much wetter than usual conditions from September through November.

October and November, where T&T usually experiences significant flooding events, are expected to be the wettest months.

The Met Office expects a slightly above-average number of wet days, with an average number of heavy rainfall days and extremely heavy rainfall days. However, there may be a slight increase in 7-day wet spells, with one likely being extremely wet. According to the TTMS, these extremely wet or extremely heavy rainfall days typically produce flooding events.

T&T’s new normal – Hotter and…drier?

With all the rainfall and flooding events of the last decade, surprisingly T&T’s 1991-2020 average rainfall has declined compared to 1981-2010. According to the TTMS, annual averages for rainfall have decreased at Piarco slightly. Over the last decade, eight years produced less than average rainfall.

However, intense single-day rainfall events have steadily increased, with six of the top ten years that had single-day highest rainfall events occurring since 1990.

From 1980 to present, there have been increases in single-day extreme rainfall days and an increase in three-day maximum rainfall totals. These latter two rainfall event classifications produce high-impact flood events.

Temperatures have also risen, with the past two decades being the warmest on record at Piarco.

T&T’s maximum surface temperatures have warmed at a rate of 0.24°C per decade since 1946, with 2020 being the eighth warmest year on record.

The Met Office has said days with maximum temperatures above 34.0°C are more common with unusually warm nights.