2021 Wet Season: Dry Start But Wetter Than Usual Conditions Forecast

In Trinidad and Tobago Meteorological Service’s rainfall and temperature outlook for June through August 2021, the Service calls for above-normal temperatures but below-average rainfall. However, by September through November, conditions are forecast to become wetter than average.

What you need to know

  • While a drier than usual start to the 2021 Wet Season is forecast, through the next six months, rainfall totals are forecast to be overall wetter than average.
  • June is forecast to be the driest of the next three months and may be the driest for the Wet Season. Still, flooding is likely during heavy rainfall events.
  • September to November is likely to receive much more rainfall than usual with elevated flooding potential.
  • Above normal heavy and extremely heavy rainfall days and 7-day wet spells are likely.
  • Both day and night temperatures are expected to be much warmer than average during the wet season.
  • A few hot days (maximum temperatures greater than or equal to 34.0°C) and one or two short-duration hot spells (5 or more consecutive hot days) are likely during August to October. with cities and urban areas are likely to get the most intense heat.
  • Rainfall will be suppressed through the first half of the second week of June.

Likely Impacts

  • Even with increased chances for drier than usual conditions, heavy rainfall days are high risk enough to cause severe flooding. Through the next three months, there are elevated risks of heavy rainfall days and prolonged wet periods and heightened concerns for people in occasionally flooded and flood-prone areas.
  • Hotter than average temperatures means there will be heightened concerns for people with heat-sensitive ailments, vulnerable persons exposed to excessive heat, and heat stress in livestock and other animals, as well as in young and transplanted crops.

The 2021 Dry Season Recap

Forecast versus actual rainfall accumulations during the 2021 Dry Season. (Trinidad and Tobago Meteorological Service)
Forecast versus actual rainfall accumulations during the 2021 Dry Season. (Trinidad and Tobago Meteorological Service)

Trinidad and Tobago experienced a wetter-than-average 2021 Dry Season, as forecast. Except for parts of southwestern Tobago, all areas across the country received rainfall that was in excess of the average, according to the Trinidad and Tobago Meteorological Service (TTMS). In fact, some areas received almost double the average rainfall for a typical dry season.

As we shift into the 2021 Wet Season, the TTMS is expecting a drier start, becoming wetter later in the year. However, hot temperatures are forecast to persist through the remainder of 2021.

June 2021 To August 2021 Rainfall Outlook

Category of rainfall likely for June 2021 to August 2021 (Trinidad and Tobago Meteorological Service)
Category of rainfall likely for June 2021 to August 2021 (Trinidad and Tobago Meteorological Service)

From June 2021 to August 2021, most areas of Trinidad and Tobago are likely to experience drier than usual conditions. In their outlook, the odds are tilted in favor of below-average rainfall for both Trinidad and Tobago. The chance of below-average is greater than 40%.

The TTMS is calling for a drier than normal start to the 2021 Wet Season. In fact, the Met Office is calling for the first half of the 2021 Wet Season, from June through August, to have below-normal rainfall. According to the TTMS, June is likely to be the driest of the next three months.

However, below-normal rainfall during the wet season still means substantial rainfall can occur. While it may not be persistent heavy rainfall, rainfall extremes have become increasingly common and can cause localized severe street and flash flooding and other inclement weather impacts. The TTMS advises that periods of prolonged rainfall interspersed by several dry days are likely during June through August.

The percentage of average rainfall likely for June to August ranges between 76 % and 96% of the long term average (LTA) in Trinidad but between 91% and 95% of the LTA in Tobago.

Percentage of average rainfall totals likely for June 2021 to August 2021 (Trinidad and Tobago Meteorological Service)
Percentage of average rainfall totals likely for June 2021 to August 2021 (Trinidad and Tobago Meteorological Service)

However, as we get to the end of the transitionary month of May and head into the 2021 Wet Season in June, heavy rainfall days increase the likelihood for flooding in flood-prone areas. People living in flood risk areas should start their flood planning and preparedness efforts by taking early action by cleaning drains, canals, and guttering. It is not too early to become sand-bag ready.

Chance for extremely dry conditions over the three months, ending July 2021. (Trinidad and Tobago Meteorological Service)

From June through August, there is a low to moderate chance for June through August to be extremely dry, meaning the three-month rainfall totals fall among the lowest 10% of historical June-July-August rainfall totals. The Met Office warns if this materializes, there will be implications for the water sector.

Possible accumulated rainfall totals with the highest chance of occurring during June 2021 through August 2021. (Trinidad and Tobago Meteorological Service)

Based on their outlook, areas in the northeast and eastern half of Trinidad are likely to receive the largest accumulated rainfall totals. This is typical for Trinidad. There is a 41-55% chance that the largest accumulated totals for June through August 2021 are likely to range between 741 mm and 991 mm. Areas in Eastern Trinidad stretching from Mayaro to Valencia are expected to receive the largest rainfall totals.

The least rainfall totals are expected in Tobago and areas near the entire west coast of Trinidad. Possible accumulated totals for these areas range between 719 mm and 789mm.

Increased rainfall raises the potential for surface water ponding, which can promote mosquito breeding. According to the TTMS, this can lead to higher risks for spikes in vector-borne diseases. Increased rainfall, mixed with warm and humid conditions, promotes rapid multiplication of some agricultural pests, diseases, and fungal growth.

September to November 2021 Rainfall Outlook

Category of rainfall likely for September 2021 to November 2021 (Trinidad and Tobago Meteorological Service)
Category of rainfall likely for September 2021 to November 2021 (Trinidad and Tobago Meteorological Service)

During the second half of the 2021 Wet Season, the TTMS calls for much wetter than usual conditions. During September through November, above normal rainfall is favored, with October and November being the wettest months. During these two months, T&T regularly experiences widespread, high-impact flood events.

However, the TTMS is also advising of a possible Petit Careme developing in September.

Looking at the overall 2021 Wet Season, the TTMS calls for above-normal rainfall as the most likely outcome in the coming months. There is an above-normal chance during the wet season, at 61%, for heavy rainfall days, meaning days where T&T records rainfall accumulations at or above 25 millimeters (1 inch). The TTMS is calling for 14 to 20 heavy rainfall days, compared to the normal 15 days.

The TTMS also forecasts a near-normal chance, at 42%, for extremely heavy rainfall days, meaning the country receives rainfall accumulations at or above 50 millimeters (2 inches). Based on the latest forecasts, T&T is likely to receive 3-5 extremely heavy rainfall days, compared to the average of 3 and at least one day likely to produce 75 millimeters (3 inches) or more of rainfall accumulations.

The 2021 Wet Season is expected to produce 106 to 108 wet days, meaning days with at least 1.0 millimeters of rainfall accumulations. The normal is 102 to 106 wet days for a typical wet season. The TTMS is expecting a slight increase in 7-day wet spells, with 1-2 likely to be very wet and 1 to be extremely wet (top 1% of rainfall accumulations).

2021 Wet Season Expected Rainfall (Trinidad and Tobago Meteorological Service)
2021 Wet Season Expected Rainfall (Trinidad and Tobago Meteorological Service)

According to the TTMS, for the 2021 Wet Season, between 850 to 2,000 millimeters of rainfall is forecast in Trinidad, with 1,100 to 1,700 across Tobago, with western coastal areas of both islands receiving the least amount of rainfall, particularly southwestern areas.

2021 Wet Season Temperature Outlook

Color-coded categories (below-normal, above-normal, and near-normal) of maximum and maximum temperatures that are most likely to occur across Trinidad and Tobago for the 2021 Wet Season. (Trinidad and Tobago Meteorological Service)
Color-coded categories (below-normal, above-normal, and near-normal) of maximum and maximum temperatures that are most likely to occur across Trinidad and Tobago for the 2021 Wet Season. (Trinidad and Tobago Meteorological Service)

In the TTMS’s rainfall and temperature outlook, the forecast calls for warmer than normal temperatures across the mean, maximum and minimum through the entire wet season. Cities and urban areas have the highest chances for warmer than average temperatures, with the chance for this to occur between 40% and 60%.

August to October is typically the country’s second peak of the local heat season. Through this period, maximum temperatures are likely to reach and exceed 34.0°C in Trinidad, with a high chance for hot days and one or two hot spells to develop during August through October.

There is an elevated chance for short-duration hot spells, where temperatures reach or exceed 34.0°C (in Trinidad, 33.0°C in Tobago) on 5 or more consecutive days with the peak risk occurring in September and early October. The TTMS is also warning of maximum temperatures reaching and exceeding 35.0°C in cities and urban areas on hot days.

Warmer than usual temperatures on hot and very hot days can lead to warmer than usual water temperatures, which can cause heat stress such as wilting in aquaponic crops. The TTMS urges to take action ahead of time to support crop production and livestock health to prevent agriculture production losses.

Periods of excessive heat can increase heat stress for persons with heat-sensitive ailments, amplify existing health conditions in vulnerable persons and worsen chronic health conditions in others. The TTMS also advises that higher than usual temperatures are likely high enough to impact heat-exposed livestock, other animals, and crops.

Further agricultural impacts are possible as hot days and spells can cause heat stress in livestock and wilting in newly transplanted and younger crops. Warmer than usual temperatures can lead to warmer than usual water temperatures, particularly for aquaponic fishes and plants’ health. Water temperatures much warmer than 30.0°C can affect warm-water fishes such as tilapia.

The TTMS is advising “taking action ahead of time to support crop production and livestock health could prevent agriculture production loses.”

Facebook Comments