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Forecast: Hurricane Tammy’s Influence To Bring Near-Daily, Isolated Rainfall

October 20, 2023
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While no significant, widespread rainfall is forecast across the country over the next five days, nearby Hurricane Tammy is forecast to influence the atmosphere across T&T, leading to increased cloudiness, isolated showers, and thunderstorms.

What you need to know

— Rainfall: Over the next five days, between 15 and 25 millimeters are forecast across T&T. In isolated areas across Trinidad, up to 50 millimeters is forecast. In highly isolated heavy showers and thunderstorms, 24-hour rainfall totals could exceed 25 millimeters.
— Saharan Dust: Mild Saharan Dust is forecast across T&T over the next five days.
— Hazards: The main hazard over the next five days will originate from isolated thunderstorms, which may produce cloud-to-ground lightning, brief gusty winds, and highly isolated, heavy/violent rainfall, which can trigger short-lived, localized street/flash flooding.
— Marine: Seas are forecast to be moderate initially, with waves in open waters generally reaching as high as 2.0 meters, mainly on Friday and Saturday. In sheltered areas, waves are forecast to be up to 1.0 meter. By Monday, seas become slight in open waters and near calm in sheltered areas.

Latest Alert

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

Friday

Friday
6 10 0 1
Mostly hot, and partly cloudy conditions, becoming increasingly cloudy along hilly areas of both islands by the late morning through the afternoon, with isolated showers and thunderstorms developing, moving from south to north. An initially mostly settled night, with showers developing near Tobago and thunderstorms developing southwest/west of Trinidad, eastern coastal areas and near Tobago, moving northward/eastward after nightfall.
Mostly hot, and partly cloudy conditions, becoming increasingly cloudy along hilly areas of both islands by the late morning through the afternoon, with isolated showers and thunderstorms developing, moving from south to north. An initially mostly settled night, with showers developing near Tobago and thunderstorms developing southwest/west of Trinidad, eastern coastal areas and near Tobago, moving northward/eastward after nightfall.
6/10
Thunderstorm Chances
Medium – High

Saturday

Saturday
7 10 0 1
Partly to mostly cloudy conditions developing from the mid-morning through the afternoon, with the isolated to scattered showers and thunderstorms across both islands through the mid-afternoon. A few showers could become violent, with the possibility of strong thunderstorms. Initially settled night, with offshore thunderstorms from the southwest moving generally north into the Gulf of Paria.
Partly to mostly cloudy conditions developing from the mid-morning through the afternoon, with the isolated to scattered showers and thunderstorms across both islands through the mid-afternoon. A few showers could become violent, with the possibility of strong thunderstorms. Initially settled night, with offshore thunderstorms from the southwest moving generally north into the Gulf of Paria.
7/10
Thunderstorm Chances
High

Sunday

Sunday
6 10 0 1
Variably cloudy day with passing showers and isolated thunderstorms.
Variably cloudy day with passing showers and isolated thunderstorms.
6/10
Thunderstorm Chances
Medium – High

Monday

Monday
3 10 0 1
Partly cloudy day with isolated showers and the odd thunderstorm favoring the first half of the day through the early afternoon across Trinidad, leading to a mostly hot and sunny afternoon and settled night.
Partly cloudy day with isolated showers and the odd thunderstorm favoring the first half of the day through the early afternoon across Trinidad, leading to a mostly hot and sunny afternoon and settled night.
3/10
Thunderstorm Chances
Low

Tuesday

Tuesday
4 10 0 1
Partly cloudy day with isolated showers and thunderstorms favoring the first half of the day through the early afternoon across Trinidad, leading to a mostly hot and sunny afternoon and settled night.
Partly cloudy day with isolated showers and thunderstorms favoring the first half of the day through the early afternoon across Trinidad, leading to a mostly hot and sunny afternoon and settled night.
4/10
Thunderstorm Chances
Low – Medium

Marine Forecast

Temperatures

Friday

Low: 24-26°C

High: 33-35°C

Saturday

Low: 24-27°C

High: 31-33°C

Sunday

Low: 24-27°C

High: 31-33°C

Monday

Low: 24-26°C

High: 32-34°C

Tuesday

Low: 24-26°C

High: 32-34°C

Maximum high temperatures are forecast to return to average levels for October across Trinidad and Tobago over the next five days, with actual temperatures reaching as high as 33°C in Tobago and 34°C in Trinidad. Across the country, over the next five days, the heat index, or feels like temperature, is forecast to range between 34°C and 44°C, reaching as high as 50°C across western and urbanized areas of both islands. Heat indices above 42°C are dangerous. Note that while warm temperatures are still forecast, pop-up showers/thunderstorms could keep the actual temperature lower than forecast while the heat index remains high.

Forecast Impacts

Flooding

Flooding
5 10 0 1
Over the next five days, between 15 and 25 millimeters are forecast across T&T. In isolated areas across western and northern Trinidad, as well as Tobago, up to 50 millimeters is forecast. In highly isolated heavy showers and thunderstorms, 24-hour rainfall totals could exceed 25 millimeters. As a result, the overall risk for street/flash flooding is medium, given these isolated downpours can cause potentially impactful but short-lived floods.
Over the next five days, between 15 and 25 millimeters are forecast across T&T. In isolated areas across western and northern Trinidad, as well as Tobago, up to 50 millimeters is forecast. In highly isolated heavy showers and thunderstorms, 24-hour rainfall totals could exceed 25 millimeters. As a result, the overall risk for street/flash flooding is medium, given these isolated downpours can cause potentially impactful but short-lived floods.
5/10
Likelihood
Medium

Forecast Rainfall Totals

  • Friday: Less than 5 millimeters of rainfall across the country, except areas that experience isolated heavy showers or thunderstorms, where totals could exceed 20 millimeters.
  • Saturday: Less than 5 millimeters of rainfall across the country. Highly isolated totals favoring the northern and eastern halves of Trinidad, southwestern Trinidad, and across Tobago, up to 20 millimeters are forecast.
  • Sunday: Across the western half of Trinidad and Tobago, as well as eastern coastal areas, between 10 and 25 millimeters with isolated higher totals up to 100 millimeters. Elsewhere, less than 5 millimeters are forecast.
  • Monday: Less than 5 millimeters of rainfall across the country, except for the western and northern halves of Trinidad and across Tobago, where totals could exceed 15 millimeters.
  • Tuesday: Between 5 and 10 millimeters across the country, with isolated higher amounts in heavy showers or thunderstorms

Understanding Rainfall Accumulations

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
With veering (clockwise) winds forecast on Friday and Saturday, with some upper-level support, isolated strong thunderstorms are possible on both days. However, these thunderstorms will remain short-lived as strong to very strong southwesterly wind shear is forecast.
With veering (clockwise) winds forecast on Friday and Saturday, with some upper-level support, isolated strong thunderstorms are possible on both days. However, these thunderstorms will remain short-lived as strong to very strong southwesterly wind shear is forecast.
5/10
Likelihood
Medium
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;
  • Frequent lightning (more than 30 cloud-to-ground strikes within a 10-minute period);
  • 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
Through the forecast period, sustained winds are forecast to reach as high as 30 KM/H, with gusts exceeding 45KM/H in showers or thunderstorms, particularly on Friday into Saturday.
Through the forecast period, sustained winds are forecast to reach as high as 30 KM/H, with gusts exceeding 45KM/H in showers or thunderstorms, particularly on Friday into Saturday.
4/10
Likelihood
Low – Medium

Little to no wind impacts are forecast through the next five days. With possible (marginally) stronger gusts Friday into Saturday, some weaker trees may lose some branches, and unsecured outdoor furniture and structures may sustain some damage or move.

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.

Over the next five days, isolated rainfall is forecast.

Forecast Discussion

Tropical Update

Through the next five days, T&T’s forecast will be influenced by Hurricane Tammy. On Friday through Saturday, as Tammy moves slowly west-northwest, winds across T&T will be generally southeasterly to southerly and light due to a southwest-extending surface to low-level trough. Isolated daytime thunderstorms triggered by sea breezes, orographic effects, and daytime heating will be the main weather makers of the day, especially under favorable upper-level conditions. However, given the lopsided nature of Tammy and the uncertain nature of spurious areas of convergence with tropical cyclones, feeder band activity can’t be ruled out, though for T&T, such activity remains low.

On Sunday, Tammy will pull north away from the Leewards but remain just to the north of the region, pulling the Intertropical Convergence Zone northward with a low-level trough in tow into Monday, keeping winds light with another low-level trough moving in, maintaining unstable conditions across the region.

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