[Updated] Heavy Rainfall Forecast For T&T Through End of Week

Key Messages:
Weather: A deep-layered surface to mid-level trough is forecast to affect T&T beginning Wednesday through Saturday, bringing variably cloudy skies, isolated to scattered showers with thunderstorm activity and periods of rain, with heavier activity favoring late Wednesday through Friday.
Rainfall: Note the highest rainfall totals will remain offshore and model guidance has notably backed off higher rainfall accumulations. Through Sunday, between 2 to 3 inches (50-75 millimeters) of rainfall is forecast across T&T. Higher totals up to and in excess of 4 inches (100 millimeters) are possible in isolated areas across Trinidad. Street flooding and flash flooding are likely, particularly across Central and Southern Trinidad. There is a medium chance of riverine flooding, particularly across Southern, Central, and Eastern Trinidad, by Friday.
Seas & Tides: Seas are forecast to be moderate with waves between 1.5 to 2.0 meters in open waters and below 1.0 meter but choppy in sheltered areas. Seas are forecast to be moderate to slight through the weekend, with waves in open waters up to 1.5 meters and below 1.0 meter in sheltered areas.
Winds: Winds are forecast to be moderate to strong through Friday, with sustained winds up to 35 KM/H and gusts in excess of 45 KM/H possible, particularly in heavy showers or thunderstorm activity. Winds of this strength may produce wind damage including downed trees, utility poles, and roof damage. Localized power outages possible.
Other Impacts: Landslides possible in elevated areas, particularly in Eastern areas of Trinidad and across Tobago.

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

The Forecast

Remainder of Tuesday: Partly to mostly cloudy and hazy skies with brisk shower activity favoring Trinidad.

Wednesday: Higher rainfall accumulations to favor offshore eastern Trinidad initially, then across southern and eastern Trinidad as the day progresses. Partly to mostly cloudy and hazy skies initially across T&T with brisk showers. By the late morning, skies are forecast to gradually become overcast, with these conditions persisting into the night. Isolated to scattered showers, periods of rain, and isolated thunderstorms are forecast by the late morning through the afternoon. Brisk showers may persist through the night, mainly favoring eastern Trinidad and Tobago.

Thursday: Higher rainfall accumulations to favor Trinidad’s eastern and southern halves. Scattered showers, isolated thunderstorms, and periods of rain are forecast to interrupt cloudy skies through Thursday. Conditions may gradually settle by nightfall with isolated showers possible overnight.

Friday: Higher rainfall accumulations to favor southern Trinidad. By the early morning (3:00 AM), scattered showers and periods of rain are forecast to develop across Tobago and eastern Trinidad, gradually moving across the island into the morning, interrupting partly to mostly cloudy skies. Conditions may settle after daybreak, with isolated showers and possible thunderstorms by the late morning through the afternoon, across both islands, with heavier activity favoring western and southern areas. Settled conditions are forecast by the late afternoon into the evening, with few brisk, isolated showers overnight.

Saturday & Sunday: Partly cloudy skies to mostly cloudy skies, with isolated to scattered showers and isolated thunderstorms across central and Western Trinidad by the late morning through the afternoon. Settled conditions are forecast by the evening, with brisk, isolated showers possible overnight.

The Forecast Discussion

From Tuesday night through the first half of Wednesday, surface to low-level confluence (winds slowing down, piling up, and causing convergence) will trigger brisk showers.

A deep-layered trough is northeast of the Lesser Antilles, drifting westward on Wednesday. At the mid-levels, to the surface, this trough is forecast to approach Trinidad and Tobago, advecting equatorial moisture and creating sufficient lift across the country to trigger heavy showers, persisting rains, and isolated thunderstorms through the remainder of the week.

Atmospheric conditions are generally supportive for heavy rainfall Wednesday through Friday, with the sole exception of strong westerly wind shear. Wind shear will remain high into the weekend, from the northwest to southeast, up to 55 knots. Wind shear will keep stronger activity, favoring southern and eastern halves of Trinidad. Any activity that may develop across the western half of Trinidad and in the Gulf of Paria, upper-level clouds may stream across T&T, but the rainfall will remain out at sea for the most part.

The mid- to upper-level atmoshpere will gradually become drier over the weekend, with a supportive convergence lower and mid-levels of the atmosphere diminishing by Saturday evening into Sunday.

Temperatures

With increased cloud cover across both islands, temperatures are forecast to be relatively cool through the next three days, becoming slightly warmer over the weekend

The maximum high for Trinidad is forecast to be near 31.0°C on Wednesday through Friday, and higher in urbanized areas but generally remaining much cooler when persisting cloudiness, showers, and thunderstorms occur, in the upper twenties. From Saturday onwards, up to 32.0°C, and higher in urbanized areas.

In Tobago, the maximum high is forecast to be near 30.0°C on Wednesday through Friday, with highs near 31.0°C Saturday onwards.

Forecast Impacts

Hazards associated with a surface to low-level trough over the next five days.

For Trinidad and Tobago, the main hazards will be heavy and persistent rainfall, mainly across Trinidad producing flooding of all types, as well as gusty winds up to and in excess of 45 KM/H. Street flooding and flash flooding are likely with a medium chance of riverine flooding by Friday.

While thunderstorm activity is forecast to be brief, due to strong low-level winds, frequent lightning will still be possible. Violent rainfall, gusty winds in a downburst-like fashion, up to and in excess of 45 KM/H may accompany heavy showers or thunderstorms. Landslides are also possible in elevated areas, particularly Wednesday through Friday.

Winds

Outside of heavy shower and thunderstorm activity, winds are forecast to be moderate to strong, up to 30 KM/H. Across Trinidad, gusts up to and in excess of 45 KM/H are possible, and across Tobago, gusts up to and in excess of 50 KM/H are possible.

With wind gusts in excess of 45 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.

For unsecured roofs, and weaker structures, wind damage will be possible.

Rainfall

Note the highest rainfall totals will remain offshore and model guidance has notably backed off higher rainfall accumulations.

Through Sunday, between 2 to 3 inches (50-75 millimeters) of rainfall is forecast across T&T. Higher totals up to and in excess of 4 inches (100 millimeters) are possible across eastern and southern halves of Trinidad, and in isolated areas of Western Trinidad and parts of Tobago where thunderstorms occur.

Street flooding and flash flooding are likely, particularly across Central and Southern Trinidad. There is a medium chance of riverine flooding, particularly across Southern, Central, and Eastern Trinidad, by Friday.

There is still some disagreement in top models on where heavy rainfall may occur, as well as timing. The below forecast will be updated as new model runs occur. (Latest update: 12Z 25/11/20)

Wednesday: Up to 25 millimeters (1 inch) of rainfall across much of Trinidad and Tobago. In isolated areas, particularly across the eastern half of Trinidad, between 25 to 37.5 millimeters (1 to 1.5 inches) are possible. Model guidance has backed off widespread heavy rainfall on Wednesday night.

Thursday: Up to 25 millimeters (1 inch) possible across Trinidad and Tobago. In heavier showers and thunderstorms, mainly across Eastern and Southern Trinidad, as well as Eastern Tobago, and where violent rainfall occurs, isolated totals up to 50 millimeters are possible.

Friday: Up to 25 millimeters (1 inch) possible across Trinidad and Tobago. Across the northern half of Trinidad and parts of Tobago, up to 37.5 millimeters (1.5 inches) are possible.

Saturday: Up to 10 millimeters possible across Trinidad and Tobago with isolated totals up to 25 millimeters possible across Eastern Trinidad and Tobago.

Sunday: Up to 10 millimeters possible across Trinidad and Tobago with isolated totals up to 20 millimeters possible across Eastern and Northern Trinidad and Tobago.

Other Impacts

Landslides possible in elevated areas, particularly Wednesday through Friday.

Frequent 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.

Seas are forecast to be moderate with waves between 1.5 to 2.0 meters in open waters and below 1.0 meter but choppy in sheltered areas. Seas are forecast to be moderate to slight through the weekend, with waves in open waters up to 1.5 meters and below 1.0 meter in sheltered areas.

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.

Isolated to scattered rainfall is forecast over the next 3 days, becoming isolated over the weekend.

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