Unusual Heavy Showers, Thunderstorms Forecast During Mid-Dry Season

Thunderstorm over the Gulf of Paria

Trinidad and Tobago has been affected by period showers over the last 48 hours, with brief thunderstorm activity on Saturday afternoon. More rainfall is on the way as different trough systems at varying levels of the atmosphere create favorable conditions for shower and even thunderstorm activity through Tuesday.

Overall, heavier rainfall will favor the eastern areas of Trinidad and Tobago, as well as southern parts of Trinidad. In areas where isolated heavy showers or thunderstorms occur, isolated higher rainfall totals may also occur, particularly along Western Coastal Trinidad.

An Adverse Weather Alert, the first for 2021 and the first to be issued on record during the Dry Season, has been issued for T&T from the Trinidad and Tobago Meteorological Service. It will go into effect at 8:00 AM Sunday 28th March 2021 through 2:00 PM Tuesday 30th March 2021. The alert was updated at 9:22 AM Sunday.

The Forecast

For tonight, mostly cloudy to overcast skies with periods of rain mainly across Trinidad. Rainfall is forecast to increase across T&T after midnight through Sunday

On Sunday, periods of rain and showers, which can get moderate to heavy at times, are forecast to interrupt cloudy to overcast conditions. By the late morning through the afternoon, isolated heavy showers and thunderstorms are possible across Trinidad, in addition to the scattered showers and rain in broad areas. Conditions are forecast to decrease in intensity into the evening gradually, but rainfall is forecast to persist into the night.

Monday is forecast to be another cloudy, windy, and rainy day with mostly cloudy to overcast skies, interrupted by scattered showers and periods of rain in broad areas. Similar to Sunday, by the late morning through the afternoon, showers may become heavy in isolated areas across Trinidad, with isolated thunderstorms developing. Conditions will gradually settle into the evening, with a mostly cloudy and breezy night.

On Tuesday, sunshine will return to T&T, but the partly cloudy and now hazy skies will be interrupted by scattered showers, at times becoming moderate to heavy favoring Trinidad. Rainfall will generally subside by the late afternoon, leading to a partly cloudy and breezy night. Similar conditions are forecast on Wednesday, with hazy skies.

Note that a surge of Saharan Dust is forecast to arrive on Monday and linger through the upcoming week.

Marine: Seas are forecast to be moderate over the next 24 hours, with waves between 1.5 to 2.0 meters in Trinidad’s open waters and between 2.0 to 2.5 meters in Tobago’s open waters. Across sheltered coastlines, waves near 1.0 meter are likely. In heavy showers or thunderstorms, sheltered seas may become choppy. Seas are forecast to become moderate to rough as the week progresses.


Overview: A surface to mid-level trough is now approaching the region, bringing abundant moisture and instability. This layered trough is forecast to move across the region on Sunday and move westward on Monday with moisture and instability trailing.

At the upper levels, an upper level through is favorably positioned through Monday. There will be increasing mid to upper-level instability Sunday into Monday, supporting heavy shower and possible thunderstorm development. The upper-level trough will gradually lift to the north, allowing a subtropical jet to move in late Monday, bringing with it gusty winds.

By Tuesday and into Wednesday, most model guidance show mid and upper-level moisture and instability on the decline but remain at low-levels, allowing for brisk shallow showers to persist with occasionally cloudy skies. The GFS remains the outlier at this time, showing abundant moisture and instability persisting across the region, leading to overall higher precipitation totals. During this Tuesday into Wednesday period, an Atlantic high-pressure system will regain dominance.

Through the forecast period, wind shear will be very strong, up to 80 knots from the southwest to west, bringing upper-level clouds from South America. This will limit the strength of thunderstorms, keeping heavy showers and thunderstorms relatively brief.

Temperatures

Across both islands, overnight lows are forecast to be mild to cool, with daytime highs cool due to cloud cover through Monday. As skies clear somewhat during Tuesday and Wednesday, temperatures may trend warmer during the day.

The minimum low for Trinidad is forecast to be near 22.0°C, and as low as 20.0°C in valleys and forested areas. In Tobago, a minimum low near 23.0°C is forecast.

For Sunday and Monday, the maximum high for Trinidad is forecast to be between 27.0°C and 28.0°C. In Tobago, the maximum high is forecast to be near 28.0°C.

On Tuesday and Wednesday, the maximum high for Trinidad and Tobago is forecast to be near 31.0°C, up to 34.0°C in urban and built-up areas, particularly between 9:00 AM and 3:00 PM.

Temperatures in cities, such as Port of Spain, tend to be much higher than surrounding locations due to a phenomenon called the Urban Heat Island Effect. There are several causes, but the main instigator for this phenomenon tends to be increased dark surfaces such as roads and pavement in cities, which absorb solar radiation more than surrounding areas.

Forecast Impacts

The main hazards over the next 48 hours would be heavy rainfall and gusty winds, particularly in moderate to heavy showers or thunderstorms, bringing the risk of street flooding or flash flooding. There is the potential for landslides across areas of Southern Trinidad by Monday as well as agitated seas.

Winds

Sustained surface winds moderate to fresh (20-38 KM/H). In shower activity, gusts up to and in excess of 55 KM/H are possible.

With wind gusts 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.

Rainfall

Between Saturday and Wednesday, across the eastern and southern halves of Trinidad and Tobago, rainfall accumulations between 20 to 50 millimeters are possible. In isolated areas, 5-day rainfall accumulations could reach up to and in excess of 75 millimeters. Across Northwestern Trinidad and Western Tobago, rainfall accumulations less than 20 millimeters are possible, with higher isolated accumulations in heavy shower or thunderstorm activity. Of the five days, Sunday and Monday will have the overall highest totals.

Saturday: 5-10 millimeters across the entire country, with isolated totals up to 20 millimeters across Eastern and Southern Trinidad as well as in areas of isolated heavy shower or thunderstorm activity.

Sunday: 10-30 millimeters across the entire country but trending higher in eastern areas. Isolated totals up to and in excess of 25-50 millimeters are possible across Eastern and West-Central Trinidad, Eastern Tobago as well as in areas of isolated heavy shower or thunderstorm activity.

Monday: 5-15 millimeters across the entire country but trending higher in eastern and southern areas. Isolated totals up to and in excess of 25 millimeters are possible across Eastern and Southern Trinidad as well as in areas of isolated heavy shower or thunderstorm activity.

Tuesday and Wednesday: Daily, less than five millimeters are possible across the entire country, with isolated totals up to 10 millimeters across Eastern Trinidad and where the odd heavy shower occurs.

Generally, with heavy showers and thunderstorm activity, street flooding, particularly in flood-prone areas or areas with poor drainage, is possible as well as flash flooding in areas where more prolonged heavy rainfall may occur.

Lightning: Lightning is possible in thunderstorm activity. Lightning can cause power outages, voltage dips, damage to life and property, particularly during cloud-to-ground lightning strikes.

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.

Scattered rainfall is forecast on Sunday and Monday, with isolated to scattered activity Tuesday and Wednesday.

Forecast - Isolated, Scattered, Widespread - What do they mean?

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