Forecast: Wind Shear To Keep Heavy Rainfall East of T&T

Key Messages:
Weather: Hazy skies will be interrupted by showers through the weekend due to the passage of Tropical Wave 66, which is weakening, and a shearline across the area. Rainfall will be brisk across T&T, with heavier rainfall favoring eastern and southern areas due to strong westerly wind shear. A high-pressure ridge will remain the dominant feature through the weekend, into next week at the surface to low-levels.
Rainfall: Through Tuesday, less than 1 inch (25 millimeters) of rainfall is forecast across T&T. Higher totals between 1 to 3 inches (25 to 75 millimeters) are possible across eastern and southern areas of Trinidad, across Tobago, and in isolated areas of Western Trinidad where thunderstorms occur. Note the highest rainfall totals will remain east of T&T. Street flooding and flash flooding are possible, mainly on Saturday into Sunday.
Seas & Tides: While no abnormal tides are forecast this weekend, rough seas are possible on Saturday through Sunday due to strong low-level winds agitating seas in open waters. In sheltered areas, choppy and near 1 meter due to strong low-level winds and long period swells.
Winds: Strong winds are forecast over the weekend, with sustained winds up to 30 KM/H and gusts in excess of 55 KM/H possible, particularly in heavy showers or thunderstorm activity. Winds of this strength will 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. Coastal flooding also possible in eastern and northern areas of both islands due to long period swells.

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

The Forecast

Remainder of Friday: Partly cloudy and hazy skies initially, with increasingly cloudy conditions nearing midnight. Brisk, isolated showers are possible through the night, with heavier rainfall favoring eastern Trinidad. There is a low chance of a thunderstorm.

Saturday: Stronger shower and any thunderstorm activity are forecast to remain east of T&T. Partly to mostly cloudy and hazy skies are forecast throughout the day, with brisk, isolated showers likely accompanied by breezy conditions. Isolated heavy showers and brief thunderstorms are possible during the afternoon. Increasing cloudiness is forecast by nightfall with scattered showers possible. Heavy rainfall will still favor Southern and Eastern Trinidad.

Sunday: Stronger shower and any thunderstorm activity are forecast to remain east of T&T. Scattered showers and periods of rainfall are forecast to interrupt cloudy skies through Sunday, which is expected to be the wettest day of the weekend. Overall heavy rainfall will still favor Eastern Trinidad. Heavy showers and isolated thunderstorms are likely during the late morning through the afternoon, mainly across Trinidad, accompanied by gusty winds. A break in activity will come by the late afternoon into the night, with brisk showers and light rain still possible.

Monday: Partly cloudy skies with brisk isolated showers possible during the late morning through the afternoon, with no significant rainfall totals expected. Gusty winds are possible.

The Forecast Discussion

Note that stronger activity associated with tropical waves tend to follow the wave axis, even with a surge is moisture ahead of the wave.
Note that stronger activity associated with tropical waves tend to follow the wave axis, even with a surge is moisture ahead of the wave.

The axis of Tropical Wave 66 is still well east of T&T, though the signature of the wave is fairly weak, as it is a low-amplitude. Moisture on the periphery of a high-pressure system is moving across T&T and the Windwards with a shearline (a line or narrow zone across which there is an abrupt change in the horizontal). The combination of abundant moisture, Tropical Wave 66, the shearline, and surface to low-level confluence (winds slowing down, piling up, and causing convergence) will trigger shallow showers through the weekend.

In addition, a surface to low-level jet will be in place on Saturday, resulting in breezy conditions across Trinidad and Tobago, with higher wind gusts in shower or thunderstorm activity.

Wind shear will remain high through the weekend, from the west, up to 40 knots. Wind shear will keep stronger activity north and east of T&T and limit shower and thunderstorm development across much 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.

Through the weekend, and into next week, a surface to low-level ridge is forecast to remain across T&T and through the week, with fluctuating Saharan Dust concentrations.

Temperatures

With increased cloud cover across both islands, the heat will be on the lower side through the weekend, becoming elevated on Monday through the week.

The maximum high for Trinidad is forecast to be near 31.0°C on Saturday and Sunday, and higher in urbanized areas but generally remaining much cooler when persisting cloudiness, showers, and thunderstorms occur, in the upper twenties. From Monday onwards, up to 33.0°C, and higher in urbanized areas.

In Tobago, the maximum high is forecast to be near 30.0°C on Saturday and Sunday, with highs near 32.0°C Monday onwards.

Forecast Impacts

Hazards associated with Tropical Wave 66 and a shearline over the next five days.
Hazards associated with Tropical Wave 66 and a shearline over the next five days.

For Trinidad and Tobago, the main hazards will be heavy rainfall, mainly across eastern halves of both islands producing flooding, as well as gusty winds up to and in excess of 55 KM/H. Street and flash flooding will be possible on Saturday and Sunday.

While thunderstorm activity is forecast to be brief, due to strong low-level winds, frequent lightning will still be possible. This means violent rainfall, gusty winds in a downburst-like fashion, up to and in excess of 55 KM/H, and frequent lightning. Landslides are also possible in elevated areas, particularly over the weekend.

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 55 KM/H are possible, and across Tobago, gusts up to and in excess of 60 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.

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

Rainfall

Through Tuesday, less than 1 inch (25 millimeters) of rainfall is forecast across T&T. Higher totals between 1 to 3 inches (25 to 75 millimeters) are possible across eastern areas of Trinidad, across Tobago, and in isolated areas of Western Trinidad where thunderstorms occur.

Note the highest rainfall totals will remain east of T&T. Street flooding and flash flooding are possible, mainly on Saturday into Sunday. Riverine flooding is not expected.

Remainder of Friday: Generally, less than 5 millimeters possible across T&T.

Saturday: Between 5 and 25 millimeters across both islands. In heavier showers and thunderstorms, mainly across Eastern Trinidad and Tobago, and where violent rainfall occurs, isolated totals up to and in excess of 25 millimeters are possible.

Sunday Between 5 and 25 millimeters across both islands. In heavier showers and thunderstorms where violent rainfall occurs, isolated totals up to and in excess of 25 millimeters possible, mainly across Southern and Eastern Trinidad and Tobago.

Monday: Generally less than 5 millimeters across both islands, with higher totals across Southern Trinidad, generally less than 15 millimeters.

Other Impacts

Landslides possible in elevated areas, particularly over the weekend across Eastern Trinidad

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 will be rough through the weekend, with waves up to 3.0 meters in open waters and near 1.0 meter in sheltered areas and choppy due to long period swells and strong low-level winds. This may cause coastal flooding.

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 weekend.

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

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