Tropical Storm Grace Feeder Bands To Continue Affecting T&T, Lesser Antilles Through Sunday

What you need to know:
— Over the next 24-36 hours, Tropical Storm Grace‘s influence on the Lesser Antilles is forecast to continue producing northwardly/northwestwardly moving showers and thunderstorms across T&T and the Windward Islands.
— Main impacts include locally heavy rainfall that may trigger localized street/flash flooding, gusty winds in excess of 45 KM/H causing wind damage, frequent lightning that could become dangerous and with light winds, funnel cloud, waterspout, and possible tornado activity. Landslides are also possible along Northern Trinidad through Sunday afternoon.
— An Adverse Weather Alert will be in effect for Trinidad and Tobago from 2:00 AM Sunday through 6:00 PM Sunday from the Trinidad and Tobago Meteorological Service. Trinidad and Tobago is not under a direct threat from Tropical Storm Grace.

The Forecast

Moisture associated with Tropical Waves 31 and 32, as well as Potential Tropical Cyclone Six moving across and approaching T&T (SSEC/CIMSS/UW-Madison)

Saturday Night: Mostly cloudy with periods of rain, scattered showers, and isolated thunderstorms mainly favoring western and southern areas of Trinidad initially, then across eastern offshore areas closer to and after midnight.

Sunday: Scattered showers and thunderstorms interrupting mostly cloudy to overcast skies through the day, gradually settling into the evening with increasingly hazy skies through the night.

Monday: Mostly hot and sunny skies until the late morning, where cloudiness is forecast to build across Trinidad. Isolated thunderstorms and heavy showers are possible across western and hilly areas of the island, diminishing by the evening. Increasing cloudiness is forecast overnight.

Marine: Over the next 72 hours, seas are forecast to be slight to moderate with waves up to 1.5 meters in open waters and near calm in sheltered areas, with choppy seas in the vicinity and during heavy showers or thunderstorms. Seas further northeast near Tobago and eastward may be further agitated.

Temperatures

Through the forecast period, the minimum low for Trinidad and Tobago is forecast to be between 23.0°C and 25.0°C. The maximum high for Trinidad and Tobago is forecast to be between 29.0°C and 33.0°C.

Higher temperatures are possible in urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas. Lower daytime temperatures are possible on days with increased cloud cover.

Forecast Impacts

Forecast impacts due Tropical Storm Grace.

Over the next 24 hours, the main hazards include heavy rainfall, particularly across Trinidad, with street or flash flooding likely, and a very low to a low chance of riverine flooding. Localized gusty winds and lightning may accompany thunderstorms and heavy to violent showers causing power dips/outages, downed trees, and localized wind damage. In elevated areas, there is also the potential for landslides. With light southerly winds and the potential for strong thunderstorms, funnel clouds, and waterspouts are possible. If funnel clouds touchdown or waterspouts encounter land, weak tornadoes are possible.

Winds

Sustained surface winds up to 25 KM/H are forecast. In shower activity, gusts up to and in excess of 45 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.

Rainfall

Through Monday, overall higher rainfall is forecast to favor much of Trinidad, with accumulations between 25 and 75 millimeters. However, localized totals up to and in excess of 100 millimeters are possible in prolonged heavy showers or isolated thunderstorm activity.

  • Saturday: Between 10-25 millimeters of rainfall across the country and isolated areas receiving between 25-40 millimeters, with highly isolated higher totals.
  • Sunday: Between 10-30 millimeters of rainfall across the country and isolated areas receiving near 50 millimeters, with highly isolated higher totals. favoring Trinidad.
  • Monday: Less than 5 millimeters across the country. In isolated heavy showers or thunderstorms across western, southwestern and hilly areas of Trinidad, totals may reach and exceed 25 millimeters.

As mentioned earlier, all types of flooding are on the table through the next five days, with high to very high chances for street flooding and flash flooding, and very low to low chances for riverine flooding, mainly across the North Oropouche River Basin, the Caroni River Basin and the South Oropouche River Basin.

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.

Landslides: Landslides and fallen trees are possible through the forecast period, particularly in areas where heavy thunderstorms or persisting rains occur.

Tornadic Activity: With light southerly winds and the potential for strong thunderstorms, funnel clouds, and waterspouts are possible. If funnel clouds touchdown or waterspouts encounter land, weak tornadoes are possible.

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.

On Sunday, scattered showers and thunderstorms are forecast. On Monday, isolated activity is forecast.

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

Forecast Discussion

Infrared satellite imagery showing scattered showers and thunderstorms near Trinidad and Tobago associated with Tropical Storm Grace. (Weathernerds)
Infrared satellite imagery showing scattered showers and thunderstorms near Trinidad and Tobago associated with Tropical Storm Grace. (Weathernerds)

Tropical Waves: At 18Z Saturday 14th August 2021, the axis of Tropical Wave 34 is along 61W, south of 24N, moving westward at 15 knots (28 KM/H). A second wave, Tropical Wave 32, is along 38W from 20N southward and moving west at 20 knots (37 KM/H), forecast to move across the region on Tuesday. A second wave, Tropical Wave 35, is along 22W from 20N southward. Tropical Wave 33 spawned Tropical Storm Grace which is now moving across the Lesser Antilles.

Over the next 24 hours, Tropical Storm Grace will continue its westward/west-northwestward path across the Leewards. Grace’s influence on our atmosphere continued to draw equatorial moisture northward across Trinidad and Tobago. With light winds and strong daytime heating, heavy showers, thunderstorms, and even a funnel cloud developed across the country.

This northward pull of moisture and instability, feeding into the tropical storm is forecast to continue overnight tonight into Sunday. A highly favorable atmosphere remains in place through Sunday afternoon with the high potential for strong thunderstorms and heavy to violent showers.

Trinidad and Tobago’s saving grace from this rainfall event also turning into a widespread flood event is strong northeasterly to easterly wind shear that is forecast to limit persisting showers and thunderstorms across the island. This strong wind shear is forecast to continue through Sunday.

Atmospheric moisture is forecast to decrease as Tropical Storm Grace moves west, and a high-pressure system re-establishes itself across the region, accompanied by a surge of Saharan Dust Sunday evening into Monday.

Moisture ahead of Tropical Wave 34 is forecast to begin moving across the region on Tuesday, with Tropical Wave 35 following quickly thereafter on Wednesday night into Thursday.

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