Forecast: Tropical Wave 36, ITCZ & Trough Affect Lesser Antilles

What you need to know:
— Through the next 48 hours, the Intertropical Convergence Zone will linger across the Windward Islands, north of Trinidad and Tobago but activity is expected to occasionally affect the country as a surface trough nears the islands.
— Main impacts include locally heavy rainfall that may trigger street or flash flooding. Riverine flooding remains unlikely though soils remain saturated. Localized gusty winds in excess of 45 KM/H 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, mainly along the Northern Range and Tobago. With light easterly to southeasterly winds and the potential for strong thunderstorms, funnel clouds, and waterspouts are possible.
— There are no alerts, watches, or warnings in effect for T&T from the Trinidad and Tobago Meteorological Service at this time. Trinidad and Tobago is not under a tropical storm watch or warning.

The Forecast

Moisture associated with Tropical Wave 36, as well as the Intertropical Convergence Zone moving across and approaching T&T (SSEC/CIMSS/UW-Madison)

Monday: Mostly cloudy with periods of rain, scattered showers, and isolated thunderstorms mainly favoring Tobago, Northern, and Eastern Trinidad initially, then drifting across the country through the day. Isolated heavy showers and thunderstorms are also possible across western areas of Trinidad during the afternoon. Conditions to persist into the evening, with variably cloudy skies.

Tuesday: Through the afternoon, partly to mostly cloudy skies with scattered showers and isolated thunderstorms favoring Eastern and Northern Trinidad, as well as Tobago, moving northwestward. By the late afternoon, partly cloudy skies with mostly settled conditions. A mostly fair night is forecast

Marine: Through Tuesday, seas are forecast to be moderate in open waters with waves up to 2.0 meters and below 1.0 meter to near calm in sheltered areas. Note seas may become locally choppy or rough in the vicinity and during heavy showers or thunderstorms. Mariners should also exercise caution in nearshore areas due to ongoing Spring Tides.

Temperatures

Through the forecast period, the minimum low for Trinidad and Tobago is forecast to be between 23.0°C and 26.0°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 to the Intertropical Convergence Zone, Tropical Wave 36
Forecast impacts due to the Intertropical Convergence Zone, Tropical Wave 36

Through the next 48 hours, the main hazards include locally heavy rainfall that may trigger street or flash flooding. Riverine flooding remains unlikely though soils remain saturated. Localized gusty winds in excess of 45 KM/H 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, mainly along the Northern Range and Tobago. With light easterly to southeasterly 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 35 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 Wednesday, overall higher rainfall is forecast to favor much of Trinidad, with accumulations between 15 and 25 millimeters. However, localized totals up to and in excess of 75 millimeters are possible in prolonged heavy showers or isolated thunderstorm activity, particularly across the eastern halves of Trinidad and Tobago.

  • Monday: Between 10-30 millimeters of rainfall across Trinidad and Tobago, with isolated areas receiving up to 50 millimeters mainly across Northern and Eastern areas of Trinidad and Tobago.
  • Tuesday: Between 10-25 millimeters across the country. In isolated heavy showers or thunderstorms across western and hilly areas of Trinidad, totals may reach and exceed 25 millimeters.

As mentioned earlier, street flooding and flash flooding are likely with medium to high chances and a very low chance of riverine flooding.

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 easterly to southeasterly 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.

The most widespread showers and thunderstorms are forecast to occur on Monday, with isolated to scattered rain on Tuesday.

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

Forecast Discussion

Infrared satellite imagery showing scattered showers and thunderstorms near Trinidad and Tobago associated with the Intertropical Convergence Zone. (Weathernerds)
Infrared satellite imagery showing scattered showers and thunderstorms near Trinidad and Tobago associated with the Intertropical Convergence Zone. (Weathernerds)

Tropical Waves: At 06Z Monday 23rd August 2021, the axis of Tropical Wave 36 is along 62/63W, south of 20N, moving westward at 10-15 knots (18-28 KM/H), a surface trough is located along 57/88W also moving westward towards Trinidad and Tobago.

Over the next 36 hours, the Intertropical Convergence Zone, coupled with the passage of Tropical Wave 36 and the approaching trough is forecast to produce scattered to widespread showers and thunderstorms across Trinidad and Tobago. Highly favorable atmospheric conditions are forecast with high moisture and low wind shear through early Tuesday with shear increasing by late Tuesday.

A high-pressure ridge is forecast to return by Wednesday with the typical wet season pattern of afternoon showers and isolated thunderstorms favoring western and hilly areas of Trinidad is forecast. Atmospheric moisture is forecast to decrease on Thursday with a brief surge of Saharan Dust.

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