TTMS: 2021 Wet Season Start Likely To Be Delayed, Dry Conditions Ahead

In Trinidad and Tobago Meteorological Service’s rainfall and temperature outlook for May through July 2021, the Service calls for above-normal temperatures but below-average rainfall.

What you need to know

  • After a wet March and a transition to a relatively dry April, May is likely to continue the drying trend across most areas.
  • With ongoing drying favored to continue in the short term, the odds are tilted towards drier than usual conditions, with below-average rainfall likely for May to July 2021.
  • Drier than usual does not mean the absence of heavy rainfall days or events. Therefore, concerns remain for flash flooding on high-risk heavy and prolonged rainfall days, especially during June and July. The week of May 10-16 (week 3 ahead) is also likely to be mostly dry. The week of May 17-24 (week 4 ahead) is also likely to be mostly dry, according to the TTMS.
  • The TTMS is also calling mostly hotter than usual conditions are expected for May. The chance for very hot days (temperature of at least 34.0°C) and hot spells has increased for May (high confidence). Warmer than average days and nights are likely for the three months MJJ. The chances of being warmer than average are greater than 80% (high confidence).
  • The Madden Julian Oscillation (MJO) is likely to enhance local rainfall during the 1st week of May and suppress it during the 2nd and 3rd weeks. However, near-average sea surface temperatures (SST’s) in and around Trinidad and Tobago will probably be the main influencer of the local climate in the short term.

Likely Impacts

  • Even with increased chances for drier than usual conditions, heavy rainfall days are high risk enough to cause severe flooding, and there are heightened concerns for persons in flood-prone areas remain, especially for June and July.
  • Hotter than average temperatures during May means there will be heightened concerns for persons 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.

May 2021 To July 2021 Rainfall Outlook

Category of rainfall likely for May 2021 to July 2021 (Trinidad and Tobago Meteorological Service)
Category of rainfall likely for May 2021 to July 2021 (Trinidad and Tobago Meteorological Service)

From May 2021 To July 2021, most areas of Trinidad 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 notes that less than average rains in June and July could still be a large amount of rainfall with periods of prolonged rainfall interspersed by several dry days since both months are usually two of the wettest months for the country. Still, the concern remains for flash flooding during heavy and prolonged rainfall events during the period.

Much of Trinidad and Tobago typically receives a high amount of rainfall (in excess of 600 mm on average in Trinidad and 400 mm in Tobago) during May through July. This means for below-average rainfall to occur, a large shortfall in rainfall amounts (as much as 150 mm on average in Trinidad and 100 mm in Tobago) are needed.

The percentage of average rainfall likely for May 2021 to July 2021 ranges between 78 % and 96% of the long-term average (LTA) in Trinidad but between 88% and 94% of the LTA in Tobago. Importantly, the TTMS has stated, “The start of the wet season is likely to be delayed.”

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

As we progress through one of T&T’s drier months (April 2021) and head into months where less rainfall than average is expected, the TTMS is advising that the population continue water conservation programs and revisit contingency plans to mitigate less than average rainfall. They also advise that rainwater harvesting should also be encouraged to boost residential water availability.

However, as we also near the transitionary month of May and head into the 2021 Wet Season in June, above-normal rainfall totals increase the likelihood for flooding in flood-prone areas on heavy rainfall days, especially during May and June. 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)
Chance for extremely dry conditions over the three months, ending July 2021. (Trinidad and Tobago Meteorological Service)

The TTMS has given the period between May 2021 to July 2021 a moderate chance of the period being extremely dry. An extremely dry period would be where recorded rainfall totals are within the lowest 10% of all totals in the historical record.

The chance for May to July 2021 to be within the lowest 10% of all May through July rainfall totals on record is between 12-29% – still relatively low but very probable. The outlook indicates a 30-40% chance for at least three 7-day dry spells during May to July 2021.

Possible accumulated rainfall totals with the highest chance of occurring during May 2021 through July 2021. (Trinidad and Tobago Meteorological Service)
Possible accumulated rainfall totals with the highest chance of occurring during May 2021 through July 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 May through July 2021 are likely to range between 640 mm and 798 mm, with areas in Eastern Trinidad stretching from Biche 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 384 mm and 554 mm. Fewer wet days (a day with 10.0 mm or more rainfall totals) than usual are possible during May through July.

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.

Possible rainfall totals with the highest chance of occurring during May 2021 (Trinidad and Tobago Meteorological Service)
Possible rainfall totals with the highest chance of occurring during May 2021 (Trinidad and Tobago Meteorological Service)

After a wet March and a transition to a relatively dry April, May is likely to continue the drying trend across most areas. A drier than average pattern is expected to continue for most of May 2021, with rainfall totals likely to be below average.

May is likely to be the driest month within the May through July 2021 period, with rainfall totals likely to range between 47.0 mm and 140.0 mm in Trinidad and between 47.0 mm and 95.0 mm in Tobago. The chance for these totals to occur is greater than 45%, which is larger than the chance for above-average or near-average totals.

May 2021 – July 2021 Temperature Outlook

Category of maximum and maximum temperatures that is most likely to occur across Trinidad and Tobago through July 2021. (Trinidad and Tobago Meteorological Service)
Category of maximum and maximum temperatures that is most likely to occur across Trinidad and Tobago through July 2021. (Trinidad and Tobago Meteorological Service)

Following the trend of the last several years, from May 2021 to July 2021, daytime temperatures are very likely to be warmer than average for most of Trinidad and Tobago according to the TTMS’ outlook.

May is usually the end of the first peak of the local heat season. May 2021 is forecasted to be just as warm as usual, with warmer than average days and nights.

May to July 2021 day and nighttime temperatures are forecast to be warmer than average over all of the country but are expected to be warmer in Trinidad than in Tobago and warmest in the cities and urban areas. The chance for warmer than an average maximum day and minimum night temperatures is 80% for both islands.

There are increased chances for hot days (days with maximum temperatures reaching or exceeding 34.0°C in Trinidad and 33.0°C in Tobago) in May, particularly during the first fortnight.

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.”

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