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Forecast: Tropical Waves To Bring Isolated Showers, Thunderstorms

July 11, 2024
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Trinidad and Tobago is set to see some welcome rainfall after a fairly dry past few days as a tropical wave moves across the region on Friday into Saturday. Another wave is set to move across the region early next week.

However, outside of Friday through Saturday morning, conditions are forecast to be generally dry over the next five days due to high levels of Saharan Dust, leading to dry low and mid-levels of the atmosphere – which inhibit shower and thunderstorm development.

What you need to know

— Rainfall: Over the next five days, through Monday night, overall rainfall accumulations across the country are forecast to range from 15 to 25 millimeters, with totals up to 50 millimeters favoring eastern and southern halves of Trinidad, as well as localized western coastal areas of Trinidad. In highly isolated areas, overall rainfall totals as high as 75 millimeters are possible. Note that most of the rainfall accumulation is forecast to occur between Friday and Saturday afternoon.
— Saharan Dust: Moderate concentrations of Saharan Dust are forecast across T&T throughout the next five days.
— Hazards: Gusty winds exceeding 45 KM/H are possible in heavy showers/thunderstorms, mainly on Friday and Saturday. Locally intense rainfall during this period may also produce street/flash flooding, with frequent lightning in thunderstorm activity. Over the weekend, between Saturday and Sunday, in isolated heavy showers, gusts may exceed 50 KM/H.
— Marine: Generally moderate seas are forecast over the next five days.

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

Thursday

Thursday
4 10 0 1
Mostly sunny day with a few cloudy periods accompanied by isolated showers from the late morning across southern areas of Trinidad, then across northern areas and Tobago after midday through the mid-afternoon. A mostly settled evening, with isolated showers and the odd thunderstorm favoring eastern Trinidad and Tobago by after nightfall.
Mostly sunny day with a few cloudy periods accompanied by isolated showers from the late morning across southern areas of Trinidad, then across northern areas and Tobago after midday through the mid-afternoon. A mostly settled evening, with isolated showers and the odd thunderstorm favoring eastern Trinidad and Tobago by after nightfall.
4/10
Thunderstorm Chances
Low – Medium

Friday

Friday
7 10 0 1
Mostly cloudy to overcast skies interrupted by showers and thunderstorms favoring eastern and southern areas of Trinidad, as well as Tobago during the early morning, gradually increasing in coverage across both islands through the day with the highest chances for isolated heavy showers/thunderstorms during the mid-morning through afternoon. Conditions become briefly settled by the late afternoon into the early evening with isolated overnight showers and thunderstorms nearing midnight.
Mostly cloudy to overcast skies interrupted by showers and thunderstorms favoring eastern and southern areas of Trinidad, as well as Tobago during the early morning, gradually increasing in coverage across both islands through the day with the highest chances for isolated heavy showers/thunderstorms during the mid-morning through afternoon. Conditions become briefly settled by the late afternoon into the early evening with isolated overnight showers and thunderstorms nearing midnight.
7/10
Thunderstorm Chances
High

Saturday

Saturday
6 10 0 1
Mostly cloudy to overcast start with isolated to scattered showers and thunderstorms through the early afternoon across both islands. Conditions become increasingly hazy and settled by the mid-afternoon. A mostly settled night, barring the odd shower or two favoring eastern areas of both islands.
Mostly cloudy to overcast start with isolated to scattered showers and thunderstorms through the early afternoon across both islands. Conditions become increasingly hazy and settled by the mid-afternoon. A mostly settled night, barring the odd shower or two favoring eastern areas of both islands.
6/10
Thunderstorm Chances
Medium – High

Sunday

Sunday
1 10 0 1
Mostly hot, sunny, breezy, and hazy day across both islands with a very low chance of a stray shower or two.
Mostly hot, sunny, breezy, and hazy day across both islands with a very low chance of a stray shower or two.
1/10
Thunderstorm Chances
Very Low

Monday

Monday
5 10 0 1
Mostly sunny day, becoming increasingly cloudy by the late morning through the afternoon across Trinidad, interrupted by isolated showers and the odd thunderstorm or two favoring western and hilly areas. An initially settled evening, with increasing showers and thunderstorms nearing midnight.
Mostly sunny day, becoming increasingly cloudy by the late morning through the afternoon across Trinidad, interrupted by isolated showers and the odd thunderstorm or two favoring western and hilly areas. An initially settled evening, with increasing showers and thunderstorms nearing midnight.
5/10
Thunderstorm Chances
Medium

Marine Forecast

Temperatures

Thursday

Low: 25-27°C

High: 32-33°C

Friday

Low: 24-26°C

High: 30-31°C

Saturday

Low: 24-26°C

High: 30-32°C

Sunday

Low: 25-27°C

High: 32-34°C

Monday

Low: 25-27°C

High: 32-34°C

Forecast Impacts

Flooding

Flooding
6 10 0 1
Over the next five days, through Monday night, overall rainfall accumulations across the country are forecast to range from 15 to 25 millimeters, with totals up to 50 millimeters favoring eastern and southern halves of Trinidad, as well as localized western coastal areas of Trinidad. In highly isolated areas, overall rainfall totals as high as 75 millimeters are possible. Note that most of the rainfall accumulation is forecast to occur between Friday afternoon and Saturday afternoon. The chances of street/flash flooding are medium across the country, throughout the next five days, but high on Friday into Saturday due to the potential for locally heavy rainfall.
Over the next five days, through Monday night, overall rainfall accumulations across the country are forecast to range from 15 to 25 millimeters, with totals up to 50 millimeters favoring eastern and southern halves of Trinidad, as well as localized western coastal areas of Trinidad. In highly isolated areas, overall rainfall totals as high as 75 millimeters are possible. Note that most of the rainfall accumulation is forecast to occur between Friday afternoon and Saturday afternoon. The chances of street/flash flooding are medium across the country, throughout the next five days, but high on Friday into Saturday due to the potential for locally heavy rainfall.
6/10
Likelihood
Medium – High

Forecast Rainfall Totals

  • Thursday: Less than 5 millimeters of rainfall across the country, with isolated totals along eastern and western coastal Trinidad up to 15 millimeters. Locally higher totals in isolated thunderstorm activity.
  • Friday: Across the country, between 5 and 15 millimeters, with isolated totals exceeding 25 millimeters, mainly in heavy isolated shower and thunderstorm activity, favoring Trinidad.
  • Saturday: Across Tobago, up to 10 millimeters of rainfall. Across Trinidad, between 5 and 15 millimeters, with isolated totals exceeding 25 millimeters, mainly in heavy isolated shower and thunderstorm activity, favoring the southern and western halves of Trinidad.
  • Sunday: No significant rainfall accumulation across the country.
  • Monday: Less than 5 millimeters of rainfall accumulations across both islands, with isolated totals of up to 20 millimeters favoring the western half of Trinidad.

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
3 10 0 1
Throughout the forecast period, the atmosphere is not expected to be conductive for strong thunderstorms outside of Friday afternoon through Saturday afternoon. During this 24-hour period, forecast models show high levels of atmospheric moisture, light wind shear, and a generally favorable mid- to upper-level environment which will lead to locally intense rainfall and isolated strong convection. As a result, there is a low chance of a thunderstorm meeting our strong or severe definition based on rainfall rate.
Throughout the forecast period, the atmosphere is not expected to be conductive for strong thunderstorms outside of Friday afternoon through Saturday afternoon. During this 24-hour period, forecast models show high levels of atmospheric moisture, light wind shear, and a generally favorable mid- to upper-level environment which will lead to locally intense rainfall and isolated strong convection. As a result, there is a low chance of a thunderstorm meeting our strong or severe definition based on rainfall rate.
3/10
Likelihood
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;
  • 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
5 10 0 1
Before Saturday afternoon, sustained winds are forecast to generally remain below 30 KM/H, with gusts likely up to 45 KM/H in isolated heavy showers or thunderstorms. Low-level winds are forecast to increase through the weekend, mainly after Saturday afternoon, which may translate to the surface during showers or thunderstorms. As a result, sustained winds up to 35 KM/H with gusts up to 50 KM/H are likely in isolated showers, and gusts to 55 KM/H are possible.
Before Saturday afternoon, sustained winds are forecast to generally remain below 30 KM/H, with gusts likely up to 45 KM/H in isolated heavy showers or thunderstorms. Low-level winds are forecast to increase through the weekend, mainly after Saturday afternoon, which may translate to the surface during showers or thunderstorms. As a result, sustained winds up to 35 KM/H with gusts up to 50 KM/H are likely in isolated showers, and gusts to 55 KM/H are possible.
5/10
Likelihood
Medium

With winds gusting to 50 KM/H and occasionally above, whole trees can be in motion, with larger trees and weaker branches falling. Light outdoor objects can topple or become airborne, such as garbage cans, loose galvanize, construction material, and outdoor furniture. Tents may also jump.

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.

On Friday, scattered rainfall is forecast, with all other days experiencing isolated to highly isolated rainfall.

Forecast Discussion

A weak tropical wave moved across the region on Wednesday night, with widely scattered showers mainly moving across the Windwards north of Trinidad, with isolated showers likely across Tobago after midnight. This tropical wave is being suppressed by dry air at both the low and mid-levels of the atmosphere. As this wave moves west, trailing instability will lead to a couple of showers and even the odd heavy shower or isolated thunderstorm during the afternoon on Thursday, favoring Trinidad.

In close succession, a well-defined tropical wave with a deep-layered plume of moisture across the southern half of the wave axis is forecast to move across the Windwards on Friday into early Saturday, bringing cloudy skies, scattered showers, and thunderstorms. Forecast models show a generally saturated atmosphere and favorable mid to upper-level conditions with high CAPE, or energy available for shower and thunderstorm development. As a result, locally intense rainfall is possible in isolated to scattered showers and thunderstorms, with generally cloudy skies from Friday through Saturday morning. Model guidance also shows that wind shear will be very light, less than 10 knots, which will allow for some persisting rain and favorable conditions for isolated strong convection.

By Saturday evening, winds at the low levels are forecast to increase as a ridge pattern rebuilds across the region. These stronger low-level winds, up to 56 KM/H, can make it to the surface in showers or thunderstorms, leading to stronger wind gusts through Monday. However, in the wake of Tropical Wave 20, atmospheric conditions are forecast to become increasingly dry, particularly on Sunday and to a lesser extent on Monday.

On Monday, local climatic effects like sea breeze convergence and daytime heating will trigger shower and isolated thunderstorm development across Trinidad, favoring western and hilly areas. Moisture ahead of Tropical Wave 21 will also begin to increase across Trinidad and Tobago from Monday morning, fuelling the isolated afternoon rainfall.

Note that as an extended forecast goes further into the future, it is normal for the certainty to be reduced relative to the extended period.

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