2021 Dry Season Declared

What you need to know:
— The 2021 Dry Season has officially started according to the Trinidad and Tobago Meteorological Service.
— Compared to average dry-seasons and last year’s record-breaking dry-season, the 2021 Dry Season is likely to produce more rainfall overall over most areas, but a lot of dryness is still likely.
— Localized rainfall events are likely to push the monthly rainfall totals to above average from just a few rainy days during the month.

After considering waning rainfall rates, the absence of typical wet-season weather systems, and the increasing presence of dry season weather and climatic features, the Trinidad and Tobago Meteorological Service declared the 2021 Dry Season has started.

The season is being ushered in by slightly cooler temperatures, lower relative humidity levels, and much stronger lower-level wind speeds. This is due, in part, to an enhanced North Atlantic Sub-Tropical High (NASH) pressure system that has shifted its center further eastward, extended its reaches southward and to a greater depth, compared to two to three weeks ago. The shifting and strengthening of the NASH in recent weeks have also led, at times, to an enhanced trade wind inversion and at other times to the presence of subsidence inversions. Together, these features have acted as suppressors of significant rain-bearing cloud development and are typical region indicators transitioning to its drier state.

What to expect?

Overall, the 2021 Dry Season is likely to be wetter than average for all of Trinidad and Tobago, with accumulated rainfall totals likely to be in the above-normal category. However, the season is still expected to produce many sunny days with typical dry season weather.

Category of rainfall most likely for 2021 Dry Season (JFMAM) with the highest chance of occurrence expressed as probabilities and color-coded on the map. Blues indicate that it is more likely for above-normal rainfall to occur than for below normal or near normal. Browns indicate it is more likely for below normal rainfall, while greens indicate it is more likely for near-normal rainfall. Normal is defined by the rainfall observed in the middle one-third of the JFMAM period rainfall totals during the historical period used to produce the outlook. (Trinidad and Tobago Meteorological Service)
Category of rainfall most likely for 2021 Dry Season (JFMAM) with the highest chance of occurrence expressed as probabilities and color-coded on the map. Blues indicate that it is more likely for above-normal rainfall to occur than for below normal or near normal. Browns indicate it is more likely for below normal rainfall, while greens indicate it is more likely for near-normal rainfall. Normal is defined by the rainfall observed in the middle one-third of the JFMAM period rainfall totals during the historical period used to produce the outlook. (Trinidad and Tobago Meteorological Service)

On average, the country receives 109 dry days (days with less than 1 mm of rainfall) in the dry season. The country is likely to get less than the average number of dry days during the 2021 dry season with a 60% probability for close to 90 dry days according to the TTMS.

Typically, the country receives three to eight 7-day dry spells and one to five 10-day dry spells in the dry season. For 2021 there is a 65% probability for one to four 7-day dry spells and one to three 10-day dry spells.

Possible accumulated rainfall totals with the highest chance of occurring during Dry
Season (January to May) 2021. (Trinidad and Tobago Meteorological Service)
Possible accumulated rainfall totals with the highest chance of occurring during Dry
Season (January to May) 2021. (Trinidad and Tobago Meteorological Service)

Above-average rainfall, according to the Met Office, often does not mean substantial rainfall. The country can expect rainfall to be more localized generally, but some moderate to heavy rainfall events after several days of dryness can push the monthly rainfall totals to above-average totals in just a few rain days.

Category of rainfall most likely for January to March (JFM) 2021 with the highest chance of occurrence expressed as probabilities and color-coded on the map. Blues indicate that it is more likely for above-normal rainfall to occur than for below normal or near normal. Browns indicate it is more likely for below normal rainfall, while greens indicate it is more likely for near-normal rainfall. Normal is defined by the rainfall observed in the middle one-third of the JFM period rainfall totals during the historical period used to produce the outlook. (Trinidad and Tobago Meteorological Service)
Category of rainfall most likely for January to March (JFM) 2021 with the highest chance of occurrence expressed as probabilities and color-coded on the map. Blues indicate that it is more likely for above-normal rainfall to occur than for below normal or near normal. Browns indicate it is more likely for below normal rainfall, while greens indicate it is more likely for near-normal rainfall. Normal is defined by the rainfall observed in the middle one-third of the JFM period rainfall totals during the historical period used to produce the outlook. (Trinidad and Tobago Meteorological Service)

Usually, the country receives 412.0 mm of rainfall during the dry season, with Trinidad receiving on average 434.0 mm and Tobago 344.0 mm. Possible accumulated rainfall totals for the 2021 Dry Season range between 435-920 mm in Trinidad and between 460-660 mm in Tobago. There are strongly enhanced chances for the first half of the dry season (January to March) to be wetter than usual, with greater than 60% in most areas for above normal accumulated rainfall totals to occur.

Category of rainfall most likely for March to May 2021 (MAM) with the highest chance of occurrence expressed as probabilities and colour coded on the map. Blues indicate that it is more likely for above-normal rainfall to occur than for below normal or near normal. Browns indicate it is more likely for below normal rainfall, while greens indicate it is more likely for near-normal rainfall. Normal is defined by the rainfall observed in the middle one-third of the MAM period rainfall totals during the historical period used to produce the outlook. (Trinidad and Tobago Meteorological Service)
Category of rainfall most likely for March to May 2021 (MAM) with the highest chance of occurrence expressed as probabilities and color-coded on the map. Blues indicate that it is more likely for above-normal rainfall to occur than for below normal or near normal. Browns indicate it is more likely for below normal rainfall, while greens indicate it is more likely for near-normal rainfall. Normal is defined by the rainfall observed in the middle one-third of the MAM period rainfall totals during the historical period used to produce the outlook. (Trinidad and Tobago Meteorological Service)

Typically, March is the driest month in the dry season. However, April 2021 is likely to be the driest month in the dry season. Expect an increase in dust-haze days as the season progresses, with March to May likely to produce the largest number of dust-haze days.

The map shows the percent chance of the colour-coded category (below-normal, above-normal, or near normal) of maximum and minimum temperatures that is most likely to occur across Trinidad and Tobago for the 2021 Dry Season. The colour-coded bar-graph with the numbers to the right gives the probability for each forecast category to occur. (Trinidad and Tobago Meteorological Service)
The map shows the percent chance of the colour-coded category (below-normal, above-normal, or near normal) of maximum and minimum temperatures that is most likely to occur across Trinidad and Tobago for the 2021 Dry Season. The colour-coded bar-graph with the numbers to the right gives the probability for each forecast category to occur. (Trinidad and Tobago Meteorological Service)

Meanwhile, the odds are tilted towards the country experiencing a warmer than average dry season. Both day and night-time temperatures are likely to be warmer than average for most of Trinidad and Tobago during the 2021 dry season. The chance for warmer than the average maximum and minimum temperatures is 55% for both islands. March to May which is typically the start of the local heat season is likely to produce one or two short-duration hot spells, but most likely during April and May.

Although warmer than average conditions are forecast, high temperatures are not likely to be very uncomfortable during January and February. In fact, some nights will be chilly in the first two months of the season, as relatively colder air is likely to funnel and encroach into the region due to the sub-tropical high-pressure system’s location and migrating weather systems from colder latitudes. On one or two cloud-free nights, minimum temperatures are likely to cool below 20.0°C during January and February.

What does this mean for you?

It is still important to note that Above normal rainfall totals during the dry season are often not large rainfall totals. Hence, above normal rainfall totals are likely to slow decreases in water levels, river and stream flows.

However, wetter than usual conditions will assist with farmers crop water management but can also promote agricultural pests and diseases growth. In addition, excessively wet days can also elevate flood risk during the dry-season for some flood prone areas, including farm fields.

The good news is that wetter than usual conditions are likely to subdue ideal weather conditions for bush-fires to thrive during the season but will not eliminate the risk of bush, forecast and land-fill fires occurring. Bush, forest, and land-fill fires and dust haze can reduce air quality and negatively affect persons with existing respiratory ailments.

Wetter than usual conditions tend to cause more water to pond, which can promote mosquito breeding and elevate the risk of dengue incidences. Also, elevated daytime and nighttime temperatures from March to May can negatively impact heat-related ailments and livestock. Excessive heat later in the season is likely to increase water evaporation rates.

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