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Forecast: Multiple Tropical Waves To Bring Showers, Thunderstorms

June 1, 2023
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Back-to-back tropical waves are forecast to affect Trinidad and Tobago over the next five days. However, unlike previous multi-day rainfall events, overall rainfall totals through next Tuesday are forecast to be on the lower end of the spectrum. While localized street/flash flooding, gusty winds, and landslides are possible, and while streams/rivers may become elevated, widespread riverine flooding remains unlikely at this time.

What you need to know

— Rainfall: Over the next five days, rainfall accumulations will vary between 15 and 40 millimeters across both islands. Isolated totals exceeding 50 millimeters are possible across eastern and southern areas of Trinidad, eastern Tobago, and western coastal Trinidad. In highly isolated areas, totals could exceed 75 millimeters over the five-day period in the above-mentioned areas. The heaviest rainfall days are expected on Thursday through Saturday due to the passages of successive tropical waves, improving wind shear and deep, tropical moisture.
— Saharan Dust: A surge of Saharan Dust is forecast to begin affecting the area from Thursday evening, with brief improvement Friday evening through Saturday night. Dust levels are set to increase from Saturday night.
— Hazards: The main hazards, particularly from Thursday through Saturday, will be street/flash flooding and gusty winds. Though overall winds are forecast to remain near calm or light, in heavy showers or thunderstorms, wind gusts may exceed 45 KM/H. Daily through the next five days, localized street/flash flooding is possible, with the potential for landslides in elevated areas.
— Marine: Seas are forecast to be slight to moderate in open waters, with waves up to 2.0 meters and below 0.5 in sheltered areas. By Saturday, seas are forecast to become slight, with waves in open waters reaching up to 1.25 meters. Seas may become locally choppy or rough in heavy showers or thunderstorms.

Latest Alerts

2 minute read

Adverse Weather Alert Discontinued For T&T

The Trinidad and Tobago Meteorological Service (TTMS) has discontinued the Adverse Weather Alert for Trinidad and Tobago. — What has happened: Fast-moving showers and thunderstorms affected…
October 25, 2024

Trinidad and Tobago is NOT under any tropical storm or hurricane threat, watch, or warning at this time.

The Forecast

Thursday

Thursday
6 10 0 1
Partly to mostly cloudy skies, with isolated showers affecting mainly Trinidad by the mid-morning. By the late morning, isolated to scattered showers and isolated thunderstorms are forecast to begin across Trinidad, spreading across Tobago by the late afternoon. Conditions to gradually settle by the evening with showers/thunderstorms favoring Tobago and offshore eastern/northeastern T&T. Street/flash flooding, gusty winds possible in heavier showers/thunderstorms.
Partly to mostly cloudy skies, with isolated showers affecting mainly Trinidad by the mid-morning. By the late morning, isolated to scattered showers and isolated thunderstorms are forecast to begin across Trinidad, spreading across Tobago by the late afternoon. Conditions to gradually settle by the evening with showers/thunderstorms favoring Tobago and offshore eastern/northeastern T&T. Street/flash flooding, gusty winds possible in heavier showers/thunderstorms.
6/10
Thunderstorm Chances
Medium – High

Friday

Friday
6 10 0 1
Mostly cloudy to overcast skies with scattered showers and thunderstorms beginning after midnight, favoring offshore areas and primarily affecting eastern and southern areas of Trinidad as well as Tobago. By daybreak, partly to mostly cloudy skies with isolated showers/light rain, turning to scattered pockets of rainfall, with isolated heavy showers and thunderstorms by the late morning through the afternoon. This activity will favor Trinidad initially but spread across Tobago during the early afternoon. Conditions to settle by the evening barring the odd shower favoring Tobago and eastern Trinidad. Street/flash flooding, gusty winds possible in heavier showers/thunderstorms.
Mostly cloudy to overcast skies with scattered showers and thunderstorms beginning after midnight, favoring offshore areas and primarily affecting eastern and southern areas of Trinidad as well as Tobago. By daybreak, partly to mostly cloudy skies with isolated showers/light rain, turning to scattered pockets of rainfall, with isolated heavy showers and thunderstorms by the late morning through the afternoon. This activity will favor Trinidad initially but spread across Tobago during the early afternoon. Conditions to settle by the evening barring the odd shower favoring Tobago and eastern Trinidad. Street/flash flooding, gusty winds possible in heavier showers/thunderstorms.
6/10
Thunderstorm Chances
Medium – High

Saturday

Saturday
6 10 0 1
Variably cloudy conditions after midnight with isolated showers during the early morning. Scattered showers and isolated thunderstorms are forecast to develop during the pre-dawn hours favoring Tobago and offshore eastern Trinidad initially, gradually moving north to northwestward across the country. While rainfall is forecast to decrease across the country as the day progresses, isolated late morning through afternoon thunderstorms and heavy showers are possible across hilly and western areas of Trinidad, settling by the late afternoon. A mostly settled and hazy night. Street/flash flooding, gusty winds possible in heavier showers/thunderstorms.
Variably cloudy conditions after midnight with isolated showers during the early morning. Scattered showers and isolated thunderstorms are forecast to develop during the pre-dawn hours favoring Tobago and offshore eastern Trinidad initially, gradually moving north to northwestward across the country. While rainfall is forecast to decrease across the country as the day progresses, isolated late morning through afternoon thunderstorms and heavy showers are possible across hilly and western areas of Trinidad, settling by the late afternoon. A mostly settled and hazy night. Street/flash flooding, gusty winds possible in heavier showers/thunderstorms.
6/10
Thunderstorm Chances
Medium – High

Sunday

Sunday
3 10 0 1
Mostly sunny, hazy day with isolated late morning showers and isolated afternoon thunderstorms favoring Trinidad. A mostly settled and hazy night.
Mostly sunny, hazy day with isolated late morning showers and isolated afternoon thunderstorms favoring Trinidad. A mostly settled and hazy night.
3/10
Thunderstorm Chances
Low

Monday

Monday
4 10 0 1
Early morning showers and isolated thunderstorms to give way to a partly cloudy and hazy day, additional showers possible across both islands during the late morning into the early afternoon. Increasingly cloudy, but mostly settled conditions are forecast by nightfall.
Early morning showers and isolated thunderstorms to give way to a partly cloudy and hazy day, additional showers possible across both islands during the late morning into the early afternoon. Increasingly cloudy, but mostly settled conditions are forecast by nightfall.
4/10
Thunderstorm Chances
Low – Medium

Marine Forecast

Temperatures

Generally, over the next five days, maximum highs are forecast to be below average due to increased cloud cover, while minimum lows remain near average.

Thursday through Monday

Low: 24-25°C

High: 28-31°C

Maximum high temperatures are forecast to range between 28°C to 31°C, trending cooler across eastern Trinidad and higher across urbanized areas of Trinidad, where in built-up areas, maximum high temperatures could exceed 31°C. Minimum lows are forecast to remain warm, ranging between 24°C and 25°C in Trinidad and Tobago, trending cooler in interior areas. The heat index will generally be near 34°C over the next five days.

Forecast Impacts

Flooding

Flooding
6 10 0 1
Over the next five days, rainfall accumulations will vary between 15 and 40 millimeters across both islands. Isolated totals exceeding 50 millimeters are possible across eastern and southern areas of Trinidad, eastern Tobago and western coastal Trinidad. In highly isolated areas, totals could exceed 75 millimeters over the five-day period in the above-mentioned areas. The heaviest rainfall days are expected on Thursday through Saturday due to the passages of successive tropical waves, improving wind shear and deep, tropical moisture.
Over the next five days, rainfall accumulations will vary between 15 and 40 millimeters across both islands. Isolated totals exceeding 50 millimeters are possible across eastern and southern areas of Trinidad, eastern Tobago and western coastal Trinidad. In highly isolated areas, totals could exceed 75 millimeters over the five-day period in the above-mentioned areas. The heaviest rainfall days are expected on Thursday through Saturday due to the passages of successive tropical waves, improving wind shear and deep, tropical moisture.
6/10
Likelihood
Medium – High

Forecast Rainfall Totals

  • Thursday: Between 5 and 15 millimeters of rainfall across both islands, with totals nearing 25 millimeters across the southern and eastern halves of Trinidad, as well as localized areas of western Trinidad where thunderstorms occur. In isolated areas, totals may exceed 25 millimeters.
  • Friday: Between 0 and 10 millimeters of rainfall across both islands, with totals nearing 20 millimeters across Trinidad, particularly in the east and along western coastal areas. In isolated heavy showers and thunderstorms, totals may exceed 20 millimeters, particularly along western coastal Trinidad, as well as along south-facing slopes of the Northern Range
  • Saturday: Between 0 and 10 millimeters of rainfall across the country, trending higher across eastern and southern Trinidad, eastern Tobago, and western coastal Trinidad in localized areas, with isolated totals near 15 millimeters. In areas where thunderstorms occur, isolated totals could exceed 25 millimeters.
  • Sunday: Between 0 and 5 millimeters across both islands. In areas where thunderstorms occur, isolated totals could exceed 15 millimeters, favoring northwestern, southwestern, and eastern areas of Trinidad.
  • Monday: Between 0 and 5 millimeters across both islands, with totals trending higher across the southern, eastern, and western coastal Trinidad, nearing 10 millimeters.

Putting the rainfall forecast into context, rainfall rates in excess of 50 millimeters per hour or areas that receive in excess of 25 millimeters within an hour tend to trigger street flooding across the country or flash flooding in northern Trinidad. For riverine flooding to occur, a large area of the country (not just in highly localized areas of western coastal Trinidad) would have to record upwards of 75 millimeters within 24 hours, and rainfall would have to fall across major rivers’ catchment areas.

Strong Thunderstorms

Strong Thunderstorms
2 10 0 1
Between Thursday and Saturday, moderate to strong instability is forecast to be present, particularly during the early morning through afternoon hours across T&T, with a very moist atmosphere. As a result, there is a low chance of thunderstorms becoming strong. Shear is forecast to decrease, but generally low-level convergence and upper-level divergence will not be very favorable. The best chances for stronger thunderstorms exist on Friday and Saturday. See forecast discussion for more information.
Between Thursday and Saturday, moderate to strong instability is forecast to be present, particularly during the early morning through afternoon hours across T&T, with a very moist atmosphere. As a result, there is a low chance of thunderstorms becoming strong. Shear is forecast to decrease, but generally low-level convergence and upper-level divergence will not be very favorable. The best chances for stronger thunderstorms exist on Friday and Saturday. See forecast discussion for more information.
2/10
Likelihood
Very Low – Low
What is a strong or severe thunderstorm?

Given how rare these types of thunderstorms are in our region – we classify a severe or strong thunderstorm as one that produces any of the following:

  • Damaging wind gusts exceeding 55 KM/H;
  • Hail (of any size);
  • Rainfall of more than 50 millimeters or more within an hour or exceeding 75 millimeters or more within three hours;
  • The sighting of a funnel cloud or touchdown of a waterspout/tornado associated with the thunderstorm.

Gusty Winds

Gusty Winds
4 10 0 1
Over the next five days, sustained winds are forecast to be light to gentle, generally remaining below 25 KM/H and gusts up to 40 KM/H possible. In heavy showers or thunderstorms, with higher gusts possible exceeding 45 KM/H, particularly from Thursday through Saturday.
Over the next five days, sustained winds are forecast to be light to gentle, generally remaining below 25 KM/H and gusts up to 40 KM/H possible. In heavy showers or thunderstorms, with higher gusts possible exceeding 45 KM/H, particularly from Thursday through Saturday.
4/10
Likelihood
Low – Medium

Possible impacts include localized wind damage to trees, power lines, and small structures.

Other Hazards

Saharan Dust Forecast

Why I May Not/Will Not See Rainfall?

A frequent complaint is the forecast is wrong because I didn’t experience any rainfall. Scattered showers mean that you, individually, may experience some showers intermittently throughout the day, and there is a higher chance for this activity than isolated activity. Widespread showers mean that nearly all persons and areas may experience rainfall.

Through Saturday, isolated to scattered rainfall is forecast, with isolated rainfall forecast on Sunday and Monday.

Forecast Discussion

Tropical Update

The axis of Tropical Wave 06 slowly moved across the southern and central Windward Islands on Wednesday night. Heavy showers and thunderstorms predominantly remained to Trinidad and Tobago’s northeast, where the trailing activity of the tropical wave lingered under favorable upper-level conditions. Some of these heavy showers and thunderstorms affected Tobago on Wednesday evening, producing 61.0mm of rainfall between 2:00 PM and 8:00 PM, pushing Crown Point’s rainfall total for May 2023 to 144.0mm. Overnight, winds remained gentle to near calm across most of Trinidad, with breezier conditions reported across Tobago and northern Trinidad. Precipitation generally remained offshore eastern Trinidad with cloudy skies across most of the country.

For Thursday, on the heels of Tropical Wave 06, Tropical Wave 07 will be approaching the southern Windwards. Note that the National Hurricane Center has dropped this wave from its analysis, but the lingering plume of moisture and instability are forecast to move across Trinidad and Tobago into Friday and Saturday, where Tropical Wave 08 will be moving across Trinidad and Tobago as a weak wave. Both TW07 and TW08 are forecast to pull the Intertropical Convergence Zone (ITCZ) northward, nearing southern Trinidad. Additionally, a mid to upper-level trough is forecast to move across the southern Windwards, including T&T, providing very marginal support for showers and rain into Saturday. At the lower levels of the atmosphere, the Lesser Antilles will be on the periphery of an Atlantic high-pressure system anchored northeast of the Leewards, producing some surface to mid-level confluence, particularly on Saturday, which will support rainfall and cloudiness. For Saturday, winds are also forecast to be southerly to southeasterly, with winds veering at the lower levels of the atmosphere. This wind profile, combined with T&T’s topography and localilzed climatic effects could result in heavier showers/thunderstorms along hilly and western areas of both islands, including the south-facing slopes of the Northern Range.

However, this same high-pressure system has provided a conveyor belt of Saharan Dust to be transported directly from the west coast of Africa to T&T, albeit at slower-than-typical speeds. Dust models show a moderate to high concentration surge of Saharan Dust arriving by late Thursday. In the past, numerical weather prediction models do not accurately take into consideration the role of Saharan Dust in limiting showers and thunderstorms from forming. Hence we could see the forecasted level of showers and thunderstorms not materialize and lead to hazy, humid, and cloudy weather come Friday into Saturday.

Regardless, there will still be fuel for showers and thunderstorms to form and sufficient moisture for cloudiness at all levels of at atmosphere. This is due to very moist conditions persisting, with total precipitable water (TPW – a measure of atmospheric moisture) above 2.0 inches (50mm) through the 5-day forecast period. Wind shear over the next five days will be on the decrease but still be at moderate levels through Sunday. As a result, stronger convection (showers and thunderstorms) are forecast to remain offshore eastern Trinidad and Tobago, with generally eastern and southern areas of both islands receiving the highest rainfall accumulations.

By Sunday, although moderate to high levels of TPW are still forecast to be present, the Atlantic high-pressure system is forecast to regain dominance at all levels of the atmosphere, leading to more stable weather. However, with trade winds remaining light, localized climatic effects (sea-breeze convergence, daytime heating, and orographic convergence) will result in the usual Wet Season late morning through afternoon showers along coastal and hilly areas.

Come late Monday, moisture and instability are set to increase yet again as Tropical Wave 09, currently in the far eastern Atlantic Ocean, is forecast to near the southern Windward islands, including Trinidad and Tobago.

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