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Forecast: Increased Cloudiness, Rainfall Due To Tropical Waves, ITCZ

July 15, 2024
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Variably cloudy skies with isolated to scattered showers and isolated thunderstorms are forecast daily this week as back-to-back tropical waves interact with the Intertropical Convergence Zone.

What you need to know

— Rainfall: Over the next five days, through Saturday night, overall rainfall accumulations across the country are forecast to range between 25 and 75 millimeters, with five-day totals exceeding 100 millimeters favoring Trinidad. In highly isolated areas, daily rainfall totals exceeding 25 millimeters are likely, favoring the western half of Trinidad.
— Saharan Dust: Mild to low dust levels are forecast over the next five days, increasing by Friday night.
— Hazards: Daily through Friday, locally heavy rainfall is likely in heavy showers/thunderstorms, producing localized street/flash flooding and accompanied by gusty winds up to 45 KM/H. Frequent lightning is possible in thunderstorm activity, and with light southerly winds, funnel cloud activity is possible each late morning through afternoon period from Tuesday through Friday. As the week progresses, with increasing soil saturation, the risk of landslides is likely to increase and particularly in central areas, river levels will need to be closely monitored.
— Marine: Generally slight to occasionally moderate seas are forecast over the next five days.

Latest Alert

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

The Forecast

Tuesday

Tuesday
6 10 0 1
Early morning showers and thunderstorms, favoring eastern and southern areas initially, forecast to spread across the country through mid-morning, with variably cloudy skies. Mostly cloudy day, with showers and thunderstorms developing by the late morning, moving south to north across both islands. Isolated heavy showers/thunderstorms are likely across western coastal Trinidad and along Trinidad’s East-West Corridor during the afternoon. An initially settled evening, with a return of showers and thunderstorms nearing midnight across both islands.
Early morning showers and thunderstorms, favoring eastern and southern areas initially, forecast to spread across the country through mid-morning, with variably cloudy skies. Mostly cloudy day, with showers and thunderstorms developing by the late morning, moving south to north across both islands. Isolated heavy showers/thunderstorms are likely across western coastal Trinidad and along Trinidad’s East-West Corridor during the afternoon. An initially settled evening, with a return of showers and thunderstorms nearing midnight across both islands.
6/10
Thunderstorm Chances
Medium – High

Wednesday

Wednesday
6 10 0 1
Scattered showers and thunderstorms from the early morning through mid-morning across both islands, giving way to a mostly sunny mid-morning across Trinidad, with rainfall continuing across Tobago. A return of rain/showers/thunderstorms by the late morning through the afternoon across both islands, with isolated heavy showers/thunderstorms favoring Trinidad during the early to mid-afternoon. Increasingly settled conditions by the evening with cloudy skies. A return of shower/thunderstorm activity is likely nearing midnight.
Scattered showers and thunderstorms from the early morning through mid-morning across both islands, giving way to a mostly sunny mid-morning across Trinidad, with rainfall continuing across Tobago. A return of rain/showers/thunderstorms by the late morning through the afternoon across both islands, with isolated heavy showers/thunderstorms favoring Trinidad during the early to mid-afternoon. Increasingly settled conditions by the evening with cloudy skies. A return of shower/thunderstorm activity is likely nearing midnight.
6/10
Thunderstorm Chances
Medium – High

Thursday

Thursday
6 10 0 1
Cloudy with scattered showers and thunderstorms across both islands, with isolated heavy showers/thunderstorms favoring Trinidad during the late morning through the afternoon. Conditions to generally settle by nightfall across most of Trinidad and Tobago, with partly to mostly cloudy skies, while along western coastal Trinidad, isolated thunderstorms, mainly in the Gulf of Paria are likely to continue. A return of shower/thunderstorm activity is likely after midnight.
Cloudy with scattered showers and thunderstorms across both islands, with isolated heavy showers/thunderstorms favoring Trinidad during the late morning through the afternoon. Conditions to generally settle by nightfall across most of Trinidad and Tobago, with partly to mostly cloudy skies, while along western coastal Trinidad, isolated thunderstorms, mainly in the Gulf of Paria are likely to continue. A return of shower/thunderstorm activity is likely after midnight.
6/10
Thunderstorm Chances
Medium – High

Friday

Friday
6 10 0 1
Variably cloudy day, interrupted by isolated to scattered showers and thunderstorms during the early morning, and late morning through afternoon, becoming slightly hazy and settled by the late afternoon and evening. A mostly settled night, barring the odd isolated shower.
Variably cloudy day, interrupted by isolated to scattered showers and thunderstorms during the early morning, and late morning through afternoon, becoming slightly hazy and settled by the late afternoon and evening. A mostly settled night, barring the odd isolated shower.
6/10
Thunderstorm Chances
Medium – High

Saturday

Saturday
4 10 0 1
A few early morning showers and isolated thunderstorms to give way to a partly cloudy day. Isolated late morning through afternoon showers and thunderstorms are possible, favoring western and northern areas of Trinidad, and to a lesser extent, Tobago. A mostly hazy and settled night.
A few early morning showers and isolated thunderstorms to give way to a partly cloudy day. Isolated late morning through afternoon showers and thunderstorms are possible, favoring western and northern areas of Trinidad, and to a lesser extent, Tobago. A mostly hazy and settled night.
4/10
Thunderstorm Chances
Low – Medium

Marine Forecast

Temperatures

Tuesday

Low: 23-26°C

High: 29-31°C

Wednesday

Low: 23-25°C

High: 30-33°C

Thursday

Low: 23-25°C

High: 28-30°C

Friday

Low: 23-25°C

High: 29-31°C

Saturday

Low: 23-26°C

High: 30-32°C

Forecast Impacts

Flooding

Flooding
7 10 0 1
Over the next five days, through Saturday night, overall rainfall accumulations across the country are forecast to range between 25 and 75 millimeters, with five-day totals exceeding 100 millimeters favoring Trinidad. In highly isolated areas, daily rainfall totals exceeding 25 millimeters are likely, favoring the western half of Trinidad. Given that most of the overall rainfall accumulations are forecast to come from locally intense rains in showers and thunderstorms, the chances of street/flash flooding are high, and the chance of riverine flooding, particularly for central Trinidad, remain low at this time.
Over the next five days, through Saturday night, overall rainfall accumulations across the country are forecast to range between 25 and 75 millimeters, with five-day totals exceeding 100 millimeters favoring Trinidad. In highly isolated areas, daily rainfall totals exceeding 25 millimeters are likely, favoring the western half of Trinidad. Given that most of the overall rainfall accumulations are forecast to come from locally intense rains in showers and thunderstorms, the chances of street/flash flooding are high, and the chance of riverine flooding, particularly for central Trinidad, remain low at this time.
7/10
Likelihood
High

Forecast Rainfall Totals

  • Tuesday: Between 5 and 15 millimeters of rainfall across Tobago, and up to 25 millimeters of rainfall across Trinidad, with isolated totals across central and northern areas of Trinidad exceeding 25 millimeters.
  • Wednesday: Between 5 and 15 millimeters of rainfall across Tobago, and up to 25 millimeters of rainfall across Trinidad, with isolated totals across central and southern areas of Trinidad exceeding 25 millimeters.
  • Thursday: Between 5 and 15 millimeters of rainfall across Tobago and up to 25 millimeters across Trinidad, with isolated totals across western coastal areas and eastern Trinidad between 25 and 50 millimeters.
  • Friday: Between 5 and 15 millimeters of rainfall across both islands, with isolated totals up to 25 millimeters favoring western coastal areas of Trinidad, as well as Tobago.
  • Saturday: Less than 5 millimeters of rainfall across the country, with isolated higher totals favoring eastern and northern Trinidad, and Tobago.

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
While the threat of damaging wind gusts remains low, the atmosphere remains conducive for locally intense late morning through afternoon rainfall and funnel cloud activity on Tuesday through Friday. Frequent lightning is also possible in isolated strong thunderstorm activity.
While the threat of damaging wind gusts remains low, the atmosphere remains conducive for locally intense late morning through afternoon rainfall and funnel cloud activity on Tuesday through Friday. Frequent lightning is also possible in isolated strong thunderstorm activity.
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
5 10 0 1
Through Saturday, sustained winds are forecast to generally remain below 20 KM/H, with gusts likely up to 45 KM/H in isolated heavy showers or thunderstorms. In isolated strong thunderstorms or intense showers, gusts to 55 KM/H are possible.
Through Saturday, sustained winds are forecast to generally remain below 20 KM/H, with gusts likely up to 45 KM/H in isolated heavy showers or thunderstorms. In isolated strong thunderstorms or intense showers, 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 Tuesday through Friday, isolated to scattered rainfall is likely, with isolated rainfall possible on Saturday.

Forecast Discussion

Two weak tropical waves are analyzed at 57W (Tropical Wave 22) and 35W (Tropical Wave 23), east of Trinidad and Tobago.

Tropical Wave 22 is forecast to move across Trinidad and Tobago tomorrow, Tuesday, July 16th, 2024. However, convergence ahead of the wave axis will increase cloudiness with isolated shower and thunderstorm activity tonight, favoring Trinidad.

The wave axis should clear T&T by tomorrow afternoon, with low-level winds remaining light but now coming from the south to the southeast. As a result of an unstable airmass and southerly winds, isolated late morning through afternoon showers and thunderstorm activity will likely intensify as they move from the south to the north, particularly along south-facing slopes of the Northern Range and along western coastal Trinidad. Low-level instability, light wind shear, and very moist conditions will lead to locally intense rainfall in these afternoon showers/thunderstorms.

This pattern of light southerly winds to near-calm winds is forecast to hold through the week as Tropical Wave 22 brings the Intertropical Convergence Zone (ITCZ) across T&T on Tuesday night into Wednesday. The ITCZ, in addition to trailing convergence from Tropical Wave 22, will produce variably cloudy conditions with isolated to scattered showers and thunderstorms, particularly on Wednesday.

Then, Tropical Wave 23 is forecast to move across T&T on Thursday, interacting with the ITCZ. It will bring more cloudy skies, isolated to scattered showers and thunderstorms, particularly during the early morning and again from the late morning through the afternoon. With generally saturated mid-level conditions and an overall moist atmosphere, locally heavy rainfall is forecast in the isolated late morning through afternoon activity.

This wave is forecast to clear the region by Thursday night, with the ITCZ shifting southward on Friday. However, trailing convergence and moisture from the southeast are still forecast to produce some isolated shower/thunderstorm activity.

By Saturday, the atmosphere is forecast to become increasingly dry as a high-pressure ridge rebuilds and winds at the low levels increase. This ridge is forecast to rebuild while a surge of Saharan Dust moves in.

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