Forecast: Trough To Bring Showers, Thunderstorms, & Gusty Winds To T&T

A low-level trough with a surge of winds following the trough axis is forecast to affect T&T over the next 36-48 hours, bringing periods of rainfall, increased sustained winds, and gusts. Here is what you need to know:

— Through Wednesday, a surface to low-level trough, in the presence of a highly favorable atmospheric environment, is forecast to produce scattered showers and isolated thunderstorms. However, overall heavier rainfall is forecast to remain mainly across southern and eastern areas of T&T due to persisting strong westerly wind shear.
— The main hazards include heavy rainfall, flooding, and gusty winds. Generally, the street and flash flooding threat will be medium to high.
– Additionally, sustained winds up to 30 KM/H and wind gusts in excess of 45 KM/H are likely, mainly from Tuesday afternoon. From the late afternoon Tuesday into Wednesday, gusts in excess of 50 KM/H are possible, particularly across and north of Tobago. Winds of this strength can cause power dips and outages, fallen trees, utility poles, and lines, as well as sporadic areas of wind damage.
Lightning will accompany thunderstorms. Funnel clouds and waterspouts are unlikely through the forecast period due to elevated low-level winds, and landslides are possible across elevated areas.
— At this time, an Adverse Weather Alert (Yellow Level) is in effect for Trinidad and Tobago from the Trinidad and Tobago Meteorological Service from 6 PM Tuesday through 2 PM Wednesday.

The Forecast

Moisture associated with a trough system east of Trinidad and Tobago. (SSEC/CIMSS/UW-Madison)
Moisture associated with a trough system east of Trinidad and Tobago. (SSEC/CIMSS/UW-Madison)

Heavier showers, thunderstorms, and overall higher rainfall accumulations are forecast to remain south and east of the county through the forecast period.

Tuesday: Variably cloudy skies with intervals of showers and isolated thunderstorms beginning from the late morning through the afternoon. Increasingly breezy conditions are forecast from the late afternoon through the night, with periodic showers and thunderstorms. Gusty winds are likely to accompany rainfall.

Wednesday: Scattered showers and thunderstorms are forecast to continue from the overnight hours through the day, with breezy and variably cloudy conditions. Gusty winds are likely to accompany rainfall activity. By the afternoon, rainfall is forecast to begin subsiding, leading to a mostly settled evening, barring the brisk shower.

Thursday: Mostly sunny and breezy conditions through the day, barring the odd, brisk shower.

Scattered showers and thunderstorms east of the Lesser Antilles on Tuesday morning. (Weathernerds.org)
Scattered showers and thunderstorms east of the Lesser Antilles on Tuesday morning. (Weathernerds.org)

Marine: Seas are forecast to be agitated through the forecast period due to increased low-level winds and long-period swells. In open waters, waves are forecast to be between 1.5 meters to 2.5 meters, higher near eastern Tobago. Seas are forecast to be near 1.0 meter and choppy in sheltered areas due to swell periods up to 14 seconds arriving from the north. Small craft operators are advised to exercise caution.

Temperatures

Through the forecast period, the minimum low in Trinidad and Tobago is forecast to be between 24.0°C and 26.0°C.

Maximum highs across the country are forecast to be generally up to 31.0°C in Trinidad and Tobago. However, with increased cloud cover, maximum highs are forecast to be relatively cooler.

In urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas, the maximum high temperatures could exceed 33.0°C.

By Thursday, with the return of sunny skies, temperatures are forecast to trend warmer.

Forecast Impacts

Forecast impacts and confidence for an approaching low-level trough and surge of winds.
Forecast impacts and confidence for an approaching low-level trough and surge of winds.

As mentioned above, the main hazards include heavy rainfall, flooding, and gusty winds, though lightning will accompany thunderstorms.

Rainfall & Flooding

Through the forecast period, wind shear is forecast to remain unfavorable for persisting heavy rainfall. Still, favorable upper-level conditions are forecast to produce pockets of deep convection that may produce heavy to violent rainfall rates and thunderstorm activity through Wednesday.

Over the next 48 hours across Trinidad, isolated totals up to 50 millimeters are forecast across southern and eastern areas of the island, with generally 10-25 millimeters across the country. Higher rainfall accumulations are forecast mainly across southern and eastern regions of Trinidad and offshore eastern Trinidad, and isolated high totals are also possible along the western coastal areas of Trinidad.

  • Tuesday: This is forecast to be the wettest day. Generally between 5-15 millimeters of rainfall across the country, trending wetter across southern and eastern areas in both islands. Isolated rainfall totals up to 25 millimeters are possible, and higher in isolated or persisting heavy showers or thunderstorms.
  • Wednesday: Generally between 0-15 millimeters of rainfall across the country, trending wetter across southern and eastern areas in both islands. Isolated rainfall totals up to 20 millimeters are possible, and higher in isolated or persisting heavy showers or thunderstorms.
  • Thursday: Little to no rainfall across the country, with isolated totals up to 5 millimeters.

It is noteworthy that the American GFS model, which remains the outlier amongst the suite of models used for this forecast, is showing a significantly wetter Tuesday and Wednesday. Based on the GFS 0Z runs on Tuesday, widespread totals above 25 millimeters and isolated totals above 50 millimeters are shown for Tuesday, with widespread totals above 15 millimeters and isolated totals above 25 millimeters for Wednesday. Though unlikely, if these totals materialize, the street/flash flooding threat will be higher than currently forecast.

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.

Street flooding and flash flooding are forecast on Tuesday and Wednesday, with no (very low) chances for riverine flooding due to limited overall rainfall totals forecast.

Gusty Winds

Low-level winds are forecast to increase due to the presence of a low-level jet north of T&T. Peak sustained surface winds are forecast after midday on Tuesday through Wednesday, between 25 to 35 KM/H. In heavy to violent shower and thunderstorm activity, gusts up to and in excess of 45 KM/H are likely.

From the late afternoon Tuesday into Wednesday, gusts in excess of 50 KM/H are possible, particularly across and north of Tobago.

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.

Other Adverse Weather Impacts

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. Dangerous, frequent lightning is expected on Friday and Saturday.

Landslides: Landslides and fallen trees are possible, particularly along the Northern Range, Southern Trinidad, and Tobago. The threat of landslides will remain elevated Tuesday into Wednesday.

Severe Thunderstorms: The potential for severe thunderstorms, funnel clouds, and waterspouts remain low. If funnel clouds touchdown or waterspouts encounter land, weak tornadoes can form.

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 through Wednesday.

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

Forecast Discussion

Scattered showers and cloudiness approaching T&T as a trough east of the Lesser Antilles near (NASA/RAMMB/CIRA)

Tropical Waves: There are no tropical waves in the Atlantic Basin. Today, November 30th, the Atlantic Hurricane Season officially ends.

This (Tuesday) morning, a surface to low-level trough is forecast to move across Trinidad, Tobago, and the Southern Windward Islands this (Tuesday) morning, bringing a surge in deep tropical moisture and instability.

On Tuesday, at all levels of the atmosphere, conditions are forecast to become favorable for the development of heavy to violent showers and thunderstorms, with mostly cloudy skies. Aiding conditions across the region as this trough moves will be confluence ahead of a surge of low-level winds, which will begin moving across the area Tuesday afternoon.

Winds are forecast to peak overnight, as this surge of winds, associated with a low-level jet north of T&T, lingers through Wednesday.

However, strong wind shear from the west is forecast to remain across Trinidad and Tobago. While showers and thunderstorms will move across T&T, as activity moves west, convection may weaken, with cloudiness associated with showers and thunderstorms that develop across western Trinidad or Tobago moving eastward. This wind shear will also keep heavier rainfall south and east of the country.

A surface to mid-level ridge will return by Wednesday afternoon, mainly bringing settled and breezy conditions into Thursday.

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