Trough, Convergence Forecast To Bring Unsettled Weather To T&T

Cloudiness, showers, and thunderstorms are forecast over the next three days as two troughs, a favorable upper-level environment, and convergence affect T&T.

With a favorable atmosphere, isolated heavy showers and thunderstorms are possible particularly Wednesday into Thursday, favoring eastern areas of both islands initially.

Strong low-level winds are forecast to return, agitating seas with long-period swells affecting our northern and eastern coastlines.

There are no alerts, watches, or warnings from the Trinidad and Tobago Meteorological Service at this time.

The Forecast

GOES-16 IR Imagery showing scattered showers, cloudiness and isolated thunderstorms east of the Southern Windward islands (Weathernerds)
GOES-16 IR Imagery showing scattered showers, cloudiness and isolated thunderstorms east of the Southern Windward islands (Weathernerds)

Wednesday: After midnight Tuesday into Wednesday, isolated showers and thunderstorms are forecast to develop across our eastern coastal waters, predominantly affecting Tobago and the eastern half of Trinidad. This activity will gradually spread across the country into the morning, interrupting mostly cloudy to overcast skies. By the late morning through the afternoon, isolated thunderstorms are forecast across Trinidad, with isolated showers across Tobago still interrupting mostly cloudy to overcast skies. Activity will persist into the night, gradually subsiding by the late-night (10 PM).

Thursday: After midnight, heavy showers and isolated thunderstorms are forecast to move across Tobago, Eastern and Southern Trinidad initially, gradually moving westward into the morning. Cloudy skies are forecast to be interrupted by showers, periods of rain, and isolated thunderstorms throughout the day, with heavier showers and thunderstorm activity likely during the afternoon across Southwestern Trinidad. Conditions to settle into the evening with the odd isolated showers.

Friday and Saturday: Showers and isolated thunderstorms are forecast to return after midnight across both islands with mostly cloudy to cloudy skies and persist throughout the day into the night. Heavier showers and isolated thunderstorms are forecast to favor the pre-dawn hours and the afternoon across Trinidad’s eastern and southern halves.

Marine: Seas are forecast to be moderate through Sunday, becoming rough from Monday onwards. Generally, in open waters, waves are forecast to be up to 2.0 meters through mid-Thursday, then up to 2.5 meters through the weekend. From Monday, waves up to 3.0 meters are possible in open waters. In sheltered areas, near 1.0 meter but choppy at times in heavy shower or thunderstorm activity. Along northern and eastern coasts, waves in nearshore areas may exceed 2.0 meters due to long period swells on Thursday through Monday.

Forecast Discussion

A surface to low-level trough is just east of the Eastern Caribbean on Tuesday evening. This trough is forecast to traverse the island chain on Wednesday, with a southeasterly flow of moisture across T&T, bringing an increase in instability. Favorable convergence at low levels of the atmosphere is forecast to remain in place through the weekend.

At the upper levels, conditions will gradually become favorable, particularly Wednesday into Thursday, supporting heavier showers and isolated thunderstorms across T&T. Still, moderate to strong wind shear from the west will limit the duration of stronger activity through the weekend.

On Friday into Saturday, another weak surface to low-level trough will move across the Windwards, including T&T bringing more cloudy skies and periods of showers with possible thunderstorms into the night.

By late Saturday, a deep-layered high-pressure ridge will intensify across the region, increasing wind speeds and agitating seas. Weather-wise, a mostly settled Saturday into Sunday, remaining breezy across the region.

Temperatures

Across both islands, cool conditions are forecast through the remainder of the week.

The minimum low is forecast to be between 21°C to 24°C across Trinidad and 23°C to 25°C across Tobago through the remainder of the week. In interior areas of Trinidad, temperatures may still dip into the upper teens.

The maximum high for Trinidad is forecast to be near or just below 30°C, up to 32.0°C in urban and built-up areas. In Tobago, the maximum high is forecast to be near 30.0°C. On Wednesday and Thursday, maximum highs across both islands are forecast to remain between 27°C to 29°C.

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

Through the remainder of the week, street flooding and flash flooding are possible in thunderstorms and/or heavy showers. Gusty winds up to and in excess of 55 KM/H are possible, which may down trees and cause minor wind damage.

Winds

Sustained surface winds gentle to moderate (10-35 KM/H). In heavy shower or thunderstorm 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

Wednesday: Less than 10 millimeters across T&T, with isolated areas up to 25 millimeters favoring the eastern half of Trinidad and Tobago. In areas where persisting heavy showers or thunderstorms occur, particularly across northern Trinidad and Tobago, isolated rainfall accumulations in excess of 25 millimeters possible.

Thursday: Between 10 to 25 millimeters of rainfall across T&T, with isolated totals in excess of 25 millimeters possible across eastern areas of Tobago, eastern and southern areas of Trinidad.

Friday: Between 10 to 25 millimeters of rainfall across T&T, with isolated totals in excess of 25 millimeters possible across eastern and southern areas of Trinidad.

Saturday: Up to 15 millimeters of rainfall possible across T&T, favoring eastern areas of Trinidad.

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 throughout the remainder of the week.

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