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Forecast: Back-To-Back Tropical Waves Bring Wet Weekend For T&T

July 28, 2022
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Dry air ahead of Tropical Wave 23 will bring mostly sunny skies on Friday, but with back-to-back tropical waves over the weekend, there is a high chance for heavy showers and thunderstorms across the country.

What you need to know

— Saharan Dust: Fluctuating Saharan Dust levels are forecast through Sunday, with a high-concentration surge arriving by Sunday afternoon into the evening. Generally, higher dust concentrations are forecast to remain north of T&T.
— Rainfall: Isolated showers and thunderstorms are forecast on Friday, Monday, and Tuesday, while scattered showers and thunderstorms are forecast over the weekend. The wettest day is forecast to be Sunday. Over the next five days, 50 and 100 millimeters of rainfall is forecast across most of the country, with isolated totals up to 200 millimeters favoring southern Trinidad and localized areas of western and northern Trinidad.
— Hazards: The main hazards are localized street/flash flooding favoring the western half of Trinidad, with gusty winds up to and in excess of 45 KM/H accompanying heavy showers or thunderstorms. The chances for riverine flooding remain low at this time. Lightning will accompany thunderstorms.
— Alerts/Watches/Warnings: There are no alerts, watches, or warnings in effect for T&T from the Trinidad and Tobago Meteorological Service at this time.

The Forecast

Friday

Friday
3 10 0 1
Mostly hot, sunny and slightly hazy, becoming increasingly cloudy across the western half of Trinidad by midday. Isolated showers are possible, with the low chance of a thunderstorm, favoring western coastal Trinidad during the afternoon, settling into the evening. A mostly settled and partly cloudy night.
Mostly hot, sunny and slightly hazy, becoming increasingly cloudy across the western half of Trinidad by midday. Isolated showers are possible, with the low chance of a thunderstorm, favoring western coastal Trinidad during the afternoon, settling into the evening. A mostly settled and partly cloudy night.
3/10
Thunderstorm Chances
Low

Saturday

Saturday
7 10 0 1
Variably cloudy with isolated to scattered showers and thunderstorms, generally favoring Trinidad, through the day. Peak activity is forecast during the early morning, and again by the late morning through the mid-afternoon.. By nightfall, mostly cloudy skies with additional showers and isolated thunderstorms favoring Tobago, northern and eastern Trinidad Localized street/flash flooding, gusty winds possible.
Variably cloudy with isolated to scattered showers and thunderstorms, generally favoring Trinidad, through the day. Peak activity is forecast during the early morning, and again by the late morning through the mid-afternoon.. By nightfall, mostly cloudy skies with additional showers and isolated thunderstorms favoring Tobago, northern and eastern Trinidad Localized street/flash flooding, gusty winds possible.
7/10
Thunderstorm Chances
High

Sunday

Sunday
8 10 0 1
Early morning showers and thunderstorms with variably cloudy skies forecast to favor Tobago, northern, and eastern Trinidad initially, spreading across the remainder of the country through the morning. Mostly cloudy to overcast skies are forecast through the day, with intervals of rain, showers and thunderstorms gradually subsiding by the late afternoon. Increasingly hazy skies are forecast after midday, with a mostly settled and hazy night across the northern half of Trinidad and Tobago, while showers and isolated thunderstorms remains possible through the night across the southern half of Trinidad. Street/flash flooding, gusty winds likely!
Early morning showers and thunderstorms with variably cloudy skies forecast to favor Tobago, northern, and eastern Trinidad initially, spreading across the remainder of the country through the morning. Mostly cloudy to overcast skies are forecast through the day, with intervals of rain, showers and thunderstorms gradually subsiding by the late afternoon. Increasingly hazy skies are forecast after midday, with a mostly settled and hazy night across the northern half of Trinidad and Tobago, while showers and isolated thunderstorms remains possible through the night across the southern half of Trinidad. Street/flash flooding, gusty winds likely!
8/10
Thunderstorm Chances
High – Very High

Monday

Monday
4 10 0 1
Variably cloudy and hazy across both islands with isolated showers and thunderstorms favoring Trinidad during the pre-dawn hours, and again during the late morning through the afternoon. A mostly settled and hazy night barring the odd shower.
Variably cloudy and hazy across both islands with isolated showers and thunderstorms favoring Trinidad during the pre-dawn hours, and again during the late morning through the afternoon. A mostly settled and hazy night barring the odd shower.
4/10
Thunderstorm Chances
Low – Medium

Tuesday

Tuesday
3 10 0 1
Partly cloudy, breezy and hazy with brisk isolated showers. There is a low chance of an isolated thunderstorm favoring western coastal Trinidad during the late morning through the afternoon.
Partly cloudy, breezy and hazy with brisk isolated showers. There is a low chance of an isolated thunderstorm favoring western coastal Trinidad during the late morning through the afternoon.
3/10
Thunderstorm Chances
Low

Marine: Through Tuesday, seas are forecast to be slight to moderate, with waves in open waters up between 1.0 and 2.0 meters. In sheltered areas, waves are forecast to be below 1.0 meter and occasionally choppy in the vicinity of heavy showers/thunderstorms.

Temperatures

Through the forecast period, the minimum low in Trinidad and Tobago is forecast to be between 23.0°C and 26.0°C.

Over the next five days, maximum highs across the country are forecast to be up to 33.0°C in Trinidad and 32.0°C in Tobago, with cooler maximum highs up to 31.0°C on Saturday and Sunday across both islands due to increased cloud cover. In urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas, the maximum high temperatures could exceed 34.0°C on Friday, Monday and Tuesday.

Forecast Impacts

Total precipitable water imagery of the Tropical Atlantic as of 7:00 PM Thursday, July 28th, 2022. A trough brought increased moisture to T&T and the Southern Windwards, while an area of very dry air is set to move across the region on Friday, ahead of Tropical Wave 23. Higher moisture levels are set to move across the Leewards on Friday, July 29th, 2022.
Total precipitable water imagery of the Tropical Atlantic as of 7:00 PM Thursday, July 28th, 2022. A trough brought increased moisture to T&T and the Southern Windwards, while an area of very dry air is set to move across the region on Friday, ahead of Tropical Wave 23. Higher moisture levels are set to move across the Leewards on Friday, July 29th, 2022.

Flooding

Flooding
7 10 0 1
Over the next five days, overall rainfall totals between 50 and 100 millimeters of rainfall are forecast across most of the country. However, across southern and western areas of Trinidad, isolated totals of up to 200 millimeters of rainfall are possible.
Over the next five days, overall rainfall totals between 50 and 100 millimeters of rainfall are forecast across most of the country. However, across southern and western areas of Trinidad, isolated totals of up to 200 millimeters of rainfall are possible.
7/10
Likelihood
High

There is a high chance of street and flash flooding, particularly across the western half of Trinidad. Chances for riverine flooding remain low as major rivers across the country are well within their banks.

Forecast Rainfall Totals

  • Friday: Less than 5 millimeters of rainfall across the country, with isolated high totals along western coastal Trinidad in the vicinity of a heavy shower or isolated thunderstorm.
  • Saturday: Between 15 and 25 millimeters of rainfall across both islands, trending higher across eastern and southern areas of Trinidad, as well as along western coastal Trinidad. The GFS model, while the outlier at this time, is showing isolated rainfall totals up to 125 millimeters across southern and southwestern Trinidad due to an active ITCZ.
  • Sunday: Between 15 and 35 millimeters of rainfall across both islands, trending higher across Trinidad with isolated totals between 50 and 75 millimeters.
  • Monday: Less than 15 millimeters of rainfall across the country, trending higher across southern Trinidad, with isolated totals up to 25 millimeters.
  • Tuesday: Less than 10 millimeters across the country, with isolated rainfall totals up to 25 millimeters favoring western coastal Trinidad.

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
5 10 0 1
Conditions appear favorable for the development of deep convection on Saturday and Sunday, though wind shear and dry air intrusions will prevent persisting and widespread activity.
Conditions appear favorable for the development of deep convection on Saturday and Sunday, though wind shear and dry air intrusions will prevent persisting and widespread activity.
5/10
Likelihood
Medium

The chances of strong thunderstorms are medium, but activity will be short-lived. Funnel cloud development is possible through the next five days due to near calm to light and variable winds. The highest chances for funnel cloud/waterspout development exist along western coastal areas of both Trinidad and Tobago, as well as along southern and eastern coastal areas of Trinidad. If a funnel cloud touches down on a body of water, it becomes a waterspout; if it touches down on land, it becomes a tornado.

While abundant frequent cloud-to-ground lightning isn’t likely, lightning is expected in thunderstorm activity.

Gusty Winds

Gusty Winds
5 10 0 1
Low-level winds across Trinidad and Tobago are forecast remain light to moderate but strong gusts could accompany heavier thunderstorms or shower activity, particularly on Sunday. Sustained winds up to 25 KM/H are forecast, with gusts up to 45 KM/H are likely, and gusts up to 55 KM/H are possible, mainly on Sunday. These higher gusts are forecast to accompany heavy shower or thunderstorm activity.
Low-level winds across Trinidad and Tobago are forecast remain light to moderate but strong gusts could accompany heavier thunderstorms or shower activity, particularly on Sunday. Sustained winds up to 25 KM/H are forecast, with gusts up to 45 KM/H are likely, and gusts up to 55 KM/H are possible, mainly on Sunday. These higher gusts are forecast to accompany heavy shower or thunderstorm activity.
5/10
Likelihood
Medium

With wind gusts up to and in excess of 55 KM/H, whole trees are expected to be in motion, and there may be some inconvenience when walking against the wind gusts. Light outdoor objects may topple or become airborne such as garbage cans, potted plants, loose galvanize or construction material, and other outdoor furniture. Tents may jump. Older/weaker trees may fall, bringing down utility poles and lines.

Other Hazards

Saharan Dust will fluctuate over the next five days, occasionally reducing air quality and affecting visibility. Dust levels are forecast to increase by late Sunday.

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.

Isolated to scattered showers and thunderstorms are forecast on Saturday and Sunday, with isolated activity on Friday, Monday, and Tuesday.

Forecast Discussion

8:00 PM Tuesday Tropical Weather Outlook from the National Hurricane Center
8:00 PM Tuesday Tropical Weather Outlook from the National Hurricane Center

Tropical Waves East of T&T: Based on the Tropical Analysis and Forecast Branch’s 18Z surface analysis on July 28th, 2022, as well as the latest satellite and model guidance:

  • The 23rd tropical wave for 2022 (TW23) is a large, elongated wave along 53°W, south of 28°N, moving west at 15-20 knots (28-37 KM/H). No significant showers or thunderstorms are noted near the wave due to abundant Saharan Dust. TW23’s highest moisture levels remain near the northern portion of the wave axis and are forecast to mostly affect the Leewards from Friday, July 29th, 2022, with trailing moisture affecting T&T.
  • The 24th tropical wave for 2022 (TW24) is along 37°W, south of 21°N, moving west at 15-20 knots (28-37 KM/H). Scattered moderate convection is ongoing near the southern portion of the wave. This tropical wave is forecast to move across the region on Sunday, ushering a surge of Saharan Dust across the region.

On Thursday, Trinidad and Tobago was under the influence of a weak Intertropical Convergence Zone, with trailing moisture from a well-defined low-level trough that moved across the region late Wednesday. However, localized climatic features – sea breeze convergence and daytime heating – were the triggers for shower and thunderstorm development across Trinidad and Tobago.

Dry and stable mid- to upper-level conditions are forecast across our area on Friday, combined with a pocket of very dry air ahead of Tropical Wave 23, which is forecast to limit shower or thunderstorm activity across Trinidad and Tobago. However, with near calm to light winds, daytime heating and sea breeze convergence still could trigger and fuel isolated showers across western coastal areas of both islands. While TW23 is forecast to move across the region on Friday, most of the moisture and instability are forecast to remain near the northern portion of the wave axis, affecting the Leewards.

Trailing moisture from TW23 and the Intertropical Convergence Zone are forecast to affect the country on Saturday. A low-level jet and an overall favorable atmosphere are forecast to be present on Saturday, enhancing shower and thunderstorm activity. Still, mid to upper-level moisture will be marginally limited with relative humidities in the 60s.

By Saturday night into Sunday, TW24 is forecast to move across the region but gradually lose its characteristic wind signature and weaken. However, a highly moist atmosphere is forecast through the mid-afternoon will fuel shower and thunderstorm activity, with the Intertropical Convergence Zone remaining near Trinidad through Monday with some mid-level support for convection.

A surge of Saharan Dust and rebuilding of the Atlantic high-pressure system is set to follow the weakening tropical wave by mid-Sunday, drying out the atmosphere across much of the region.

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