Forecast: Multiple Tropical Waves, ITCZ To Bring Rainfall To T&T

Back-to-back tropical waves and the Intertropical Convergence Zone (ITCZ) are forecast to bring cloudy skies, showers, and thunderstorms to Trinidad and Tobago into the weekend. What is not expected to impact Trinidad and Tobago over the next five days – a tropical storm.

What you need to know

Saharan Dust: Through the next five days, mild to moderate levels of Saharan Dust are forecast to remain across Trinidad and Tobago, with increasing levels on Saturday and Tuesday.
Rainfall: Scattered showers and thunderstorms are forecast mainly on Friday, with less impactful rainfall forecast through the weekend into next week. Over the next five days, between 25 and 75 millimeters of rainfall is forecast across most of the country. In highly isolated areas, overall five-day rainfall totals could exceed 125 millimeters.
Hazards: The main hazards, mainly on Friday when most of the impactful weather is forecast for T&T, are gusty winds up to and in excess of 55 KM/H accompanying heavy showers or thunderstorms, as well as localized street/flash flooding favoring eastern and southern halves of Trinidad. The chances for riverine flooding remain low at this time. Lightning will accompany thunderstorms.
Alerts/Watches/Warnings: An Adverse Weather Alert (Yellow Level) is in effect for Trinidad and Tobago from 5:00 AM Friday, July 15th, 2022, through 6:00 PM Friday, July 15th, 2022 from the Trinidad and Tobago Meteorological ServiceThere are no tropical storm or hurricane watches or warnings in effect for T&T at this time.

The Forecast

Thursday Night

Thursday Night
6 10 0 1
Increasingly cloudy conditions with isolated to scattered showers and isolated thunderstorms nearing midnight, favoring southern and eastern Trinidad, as well as Tobago initially.
Increasingly cloudy conditions with isolated to scattered showers and isolated thunderstorms nearing midnight, favoring southern and eastern Trinidad, as well as Tobago initially.
6/10
Thunderstorm Chances
Medium – High

Friday

Friday
8 10 0 1
Mostly cloudy to overcast skies interrupted by periods of light to moderate rain, scattered showers and isolated thunderstorms beginning from the early morning persisting through the mid-afternoon. A variably cloudy evening and night is forecast, with lingering light to moderate rain/showers. A resurgence of heavy showers/thunderstorms is forecast nearing midnight, favoring Tobago and northern Trinidad. Gusty winds, street/flash flooding possible.
Mostly cloudy to overcast skies interrupted by periods of light to moderate rain, scattered showers and isolated thunderstorms beginning from the early morning persisting through the mid-afternoon. A variably cloudy evening and night is forecast, with lingering light to moderate rain/showers. A resurgence of heavy showers/thunderstorms is forecast nearing midnight, favoring Tobago and northern Trinidad. Gusty winds, street/flash flooding possible.
8/10
Thunderstorm Chances
High – Very High

Saturday

Saturday
5 10 0 1
Early morning showers and isolated thunderstorms are forecast to interrupt variably cloudy skies, gradually settling just after sunrise. Isolated showers and thunderstorms are forecast to interrupt increasingly hazy and variably cloudy skies by the late morning through the mid-afternoon. With near calm to light winds from the south/southeast, heavier showers and thunderstorms are forecast to favor southern-facing slopes of the Northern Range, the Main Ridge, Tobago, as well as western coastal Trinidad. Conditions to settle by the night, with partly cloudy and hazy skies.
Early morning showers and isolated thunderstorms are forecast to interrupt variably cloudy skies, gradually settling just after sunrise. Isolated showers and thunderstorms are forecast to interrupt increasingly hazy and variably cloudy skies by the late morning through the mid-afternoon. With near calm to light winds from the south/southeast, heavier showers and thunderstorms are forecast to favor southern-facing slopes of the Northern Range, the Main Ridge, Tobago, as well as western coastal Trinidad. Conditions to settle by the night, with partly cloudy and hazy skies.
5/10
Thunderstorm Chances
Medium

Sunday

Sunday
5 10 0 1
A variably cloudy day, interrupted by isolated early morning showers and thunderstorms favoring offshore northern and eastern Trinidad, and across Tobago, with additional isolated showers and thunderstorms favoring Trinidad by the late morning into the afternoon. A variably cloudy, hazy and breezy night is forecast, with brief isolated showers.
A variably cloudy day, interrupted by isolated early morning showers and thunderstorms favoring offshore northern and eastern Trinidad, and across Tobago, with additional isolated showers and thunderstorms favoring Trinidad by the late morning into the afternoon. A variably cloudy, hazy and breezy night is forecast, with brief isolated showers.
5/10
Thunderstorm Chances
Medium

Monday

Monday
4 10 0 1
A variably cloudy day, interrupted by isolated early morning showers and the odd thunderstorm favoring southern and eastern Trinidad, with additional isolated showers favoring Trinidad by the late morning into the afternoon. A partly cloudy, hazy and breezy night is forecast, barring the odd brisk shower.
A variably cloudy day, interrupted by isolated early morning showers and the odd thunderstorm favoring southern and eastern Trinidad, with additional isolated showers favoring Trinidad by the late morning into the afternoon. A partly cloudy, hazy and breezy night is forecast, barring the odd brisk shower.
4/10
Thunderstorm Chances
Low – Medium

Tuesday

Tuesday
3 10 0 1
Partly cloudy and hazy day barring the odd brisk shower. There is a low chance of an isolated thunderstorm favoring offshore eastern and northern areas after nightfall.
Partly cloudy and hazy day barring the odd brisk shower. There is a low chance of an isolated thunderstorm favoring offshore eastern and northern areas after nightfall.
3/10
Thunderstorm Chances
Low

Marine: Through Monday, seas are forecast to be moderate, with waves in open waters up to 2.0 meters. In sheltered areas, waves are forecast to be below 1.0 meter and choppy.

Temperatures

Through the forecast period, the minimum low in Trinidad and Tobago is forecast to be between 24.0°C and 26.0°C.

From Friday, maximum highs across the country are forecast to be below 30.0°C in Trinidad and Tobago due to increased cloud cover. In urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas, the maximum high temperatures could exceed 30.0°C.

During the weekend, with light winds and variably cloudy skies, maximum highs across the country are forecast to be generally up to 31.0°C in Trinidad and Tobago. In urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas, the maximum high temperatures could exceed 33.0°C.

Forecast Impacts

Flooding

Flooding
8 10 0 1
Over the next five days, between 25 and 75 millimeters of rainfall is forecast across most of the country. Lower rainfall totals are forecast across northwestern areas of Trinidad while higher totals are forecast across the eastern and southern halves of Trinidad, where rainfall totals exceeding 50 millimeters are forecast. In highly isolated areas, overall five-day rainfall totals could exceed 125 millimeters.
Over the next five days, between 25 and 75 millimeters of rainfall is forecast across most of the country. Lower rainfall totals are forecast across northwestern areas of Trinidad while higher totals are forecast across the eastern and southern halves of Trinidad, where rainfall totals exceeding 50 millimeters are forecast. In highly isolated areas, overall five-day rainfall totals could exceed 125 millimeters.
8/10
Likelihood
High – Very High

There is a high to a very chance of street and flash flooding, mainly on Friday, particularly across the southern and eastern halves of Trinidad. Chances for riverine flooding remain low as major rivers across the country are well within their banks.

Forecast Rainfall Totals

  • Friday: Between 15 and 35 millimeters of rainfall across the country. Across eastern, central, and southern Trinidad, rainfall totals up to 50 millimeters are forecast. In these areas, highly isolated rainfall totals exceeding 50 millimeters are possible.
  • Saturday: Between 5 and 15 millimeters across the country, with rainfall totals trending higher across western coastal Trinidad, central and northern areas of Trinidad, as well as across Tobago. Isolated rainfall totals, particularly along western and hilly areas, could exceed 25 millimeters.
  • Sunday: Between 5 and 15 millimeters across the country, with rainfall totals trending higher across central and northern areas of Trinidad, as well as across Tobago. Isolated rainfall totals, particularly across Tobago, could exceed 25 millimeters.
  • Monday: Between 10 and 25 millimeters of rainfall across the southern and eastern halves of Trinidad. Locally higher amounts are possible. Across northern Trinidad and across Tobago, less than 10 millimeters is forecast.
  • Tuesday: Between 5 and 15 millimeters across the country, with rainfall totals trending higher across southeastern Trinidad. Isolated rainfall totals could exceed 15 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
6 10 0 1
There is the medium to high chance of a strong thunderstorm developing, particularly on Friday and Saturday in a high-moisture, low-shear and light wind set up.
There is the medium to high chance of a strong thunderstorm developing, particularly on Friday and Saturday in a high-moisture, low-shear and light wind set up.
6/10
Likelihood
Medium – High

Mainly on Friday into Saturday, funnel cloud development is possible 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
6 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. Sustained winds up to 20 KM/H are forecast, with gusts up to 55 KM/H accompanying heavy shower or thunderstorm activity on Friday through Sunday
Low-level winds across Trinidad and Tobago are forecast remain light to moderate but strong gusts could accompany heavier thunderstorms or shower activity. Sustained winds up to 20 KM/H are forecast, with gusts up to 55 KM/H accompanying heavy shower or thunderstorm activity on Friday through Sunday
6/10
Likelihood
Medium – High

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 remain across the region through the forecast period, with an increase from Saturday, reducing air quality and affecting visibility.

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 rainfall is forecast on Friday, with isolated rainfall thereafter.

Forecast Discussion

8:00 AM Thursday 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 14th, 2022, as well as the latest satellite and model guidance:

  • The 19th tropical wave for 2022 (TW19) is along 54°W, south of 22°N to 09°N, moving west at 10-15 knots (18-28 KM/H). Scattered showers and thunderstorms are ongoing on both sides of the wave axis, across the southern portion of the wave. TW19 is forecast to move across the Lesser Antilles on Friday night, bringing the Intertropical Convergence Zone across T&T from late Thursday into Friday.
  • The 20th tropical wave for 2022 (TW20) is along 43°W, south of 20°N, moving west at 10-15 knots (18-28 KM/H). Scattered showers have been noted near the wave axis. This tropical wave is forecast to move across the region on Saturday night into Sunday.
  • The 21st tropical wave for 2022 (TW21) is along 21°W, south of 20°N, moving west at 10-15 knots (18-27 KM/H). This wave is forecast to move across the Lesser Antilles by next Wednesday into Thursday.

Tropical Wave 19 is approaching the region, bringing the ITCZ near and across Trinidad and Tobago from early Friday morning. Both features are forecast to increase moisture and instability, fuelling scattered showers and thunderstorms through Friday. Activity with the ITCZ has its strongest activity occurring between 12:00 AM and 6:00 AM local time, with another peak during the Northern Hemisphere summer months between 12:00 PM to 3:00 PM. In tandem, T&T will be placed on the favorable side of a developing upper-level trough, extended southwest across the eastern Caribbean Sea. With a low-shear and favorable upper-level environment, showers and thunderstorms may be locally enhanced on Friday and Saturday.

Tropical Wave 19 is forecast to move across the Lesser Antilles by Friday night into Saturday. Forecast models indicate that Trinidad and Tobago will remain across the southern portion of the wave axis, with near calm/variable to light southerly to southeasterly winds on Saturday. Nearly all the active weather associated with this forecasted strong tropical wave is modeled to remain well north of Trinidad and Tobago Friday night into Saturday.

While our Lesser Antilles neighbors, north of Barbados and St. Vincent, are forecast to experience the strongest winds and heavier rainfall, this tropical wave will also maintain elevated moisture and instability across T&T, leading to isolated showers and thunderstorms persisting on both Saturday and Sunday.

However, a moderate to high-concentration surge of Saharan Dust is set to begin affecting Trinidad and Tobago from mid-Saturday. Though models show that isolated to scattered showers and thunderstorms, Saharan Dust and its drying out of the low to mid-levels are habitually understated in weather prediction models, leading to an erroneous abundance of rainfall activity. Still, ample instability and moisture will be present as the ITCZ will remain near/across T&T, leading to a medium chance of heavy showers/thunderstorms on Saturday and Sunday.

On Monday, a deep-layered high-pressure system is forecast to move in, with the ITCZ just south of the country, leading to variably cloudy skies with limited rainfall.

Uncertainty increases into next week, as the ITCZ and surges of Saharan Dust are both forecast to be present across T&T. At least, for now, the prevailing likelihood seems to be a relatively cloudy and wet week on the horizon for those planning ahead.

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