Tropical Wave 19 To Bring Isolated Showers, Thunderstorms To T&T on Thursday

Tropical Wave 19 approaching the Windward Islands

What you need to know:
— A tropical wave is forecast to move across Trinidad and Tobago on Thursday. However, moisture and instability are forecast to begin affecting T&T from overnight tonight.
— Isolated rainfall is forecast to begin during the predawn hours of Thursday morning, with increasing cloudiness. Scattered showers and isolated thunderstorms are forecast to begin after daybreak on Thursday morning through the afternoon. Note that the heaviest rainfall is forecast to remain east of Trinidad and Tobago.
— An Adverse Weather Alert has been discontinued by the Trinidad and Tobago Meteorological Service as of 4:22 PM Thursday.

The Forecast

Tropical Wave 19 approaching the Windward Islands (RAMMB/CIRA/NOAA)
Tropical Wave 19 approaching the Windward Islands (RAMMB/CIRA/NOAA)

Wednesday night: Partly cloudy skies across the country, with increasing cloudiness. Brisk showers favoring the southern and eastern halves of Trinidad

Thursday: A mostly cloudy day, interrupted by scattered showers and isolated thunderstorms from the early morning through the afternoon across both islands. Isolated to scattered showers with mostly cloudy skies are forecast to continue into the night. Gusty winds, street/flash flooding possible.

Friday: Early morning showers are forecast to subside by daybreak, with a partly cloudy, breezy, and hot day across Trinidad and Tobago. Few brisk showers are possible through the day across Trinidad, accompanied by gusty winds. Mostly settled conditions overnight, barring the odd, brisk shower.

Saturday: A mostly warm, sunny, breezy, and hazy day across both islands, with brisk isolated showers.

Marine: Seas are forecast to be moderate over the next 72 hours, with waves between 1.5 and 2.0 meters in Trinidad and Tobago’s open waters. Across sheltered coastlines, waves below 1.0 meters are expected, with choppy seas in the vicinity and during heavy showers or thunderstorms.

Forecast Discussion

Infrared satellite imagery showing scattered showers east of Trinidad and Tobago with the approaching Tropical Wave 19. (Weathernerds)
Infrared satellite imagery showing scattered showers east of Trinidad and Tobago with the approaching Tropical Wave 19. (Weathernerds)

As of 2:00 PM, the axis of Tropical Wave 19 is along 56W, south of 15N, moving westward at 10-15 knots (18-27 KM/H). Scattered moderate convection (showers and thunderstorms) is seen on satellite imagery on either side of the wave axis.

Dominating the Atlantic is a deep-layered and broad high-pressure system with a relatively dry and stable low and mid-level atmosphere. Moisture ahead of the tropical wave is forecast to move across Trinidad and Tobago after nightfall tonight, with cloudiness increasing, as well as the chances for isolated showers.

By Thursday morning, a marginally favorable low-level environment and increasing mid- to upper-level instability is forecast to enhance convection, causing localized heavy to violent rainfall rates and isolated stronger thunderstorms mainly after daybreak on Thursday through the afternoon. Gusty winds may accompany showers and thunderstorms.

Moisture will quickly diminish overnight Thursday into Friday as a surface to mid-level ridge pattern, accompanied by a surge in low-level winds and dry air, moves across the Lesser Antilles. Weak surface to low-level instability may allow for brisk showers throughout the day.

By nightfall, Tropical Wave 21, located in the far Eastern Atlantic along 31W, will near the Lesser Antilles and move across the region on Saturday. Notably, most of the moisture and instability is forecast to stay north of Trinidad and Tobago, limiting shower and thunderstorm activity across the country.

Infrared satellite imagery showing Tropical Wave 19 at 56W, Tropical Wave 21 at 31W, and a cluster of convection associated with Tropical Wave 22 moving off the African Coast (Weathernerds)
Infrared satellite imagery showing Tropical Wave 19 at 56W, Tropical Wave 21 at 31W, and a cluster of convection associated with Tropical Wave 22 moving off the African Coast (Weathernerds)

Where did Tropical Wave 20 go?

This tropical wave lost its moisture and wind signature overnight Monday into Tuesday and was dropped from the analysis. We’re entering a period with frequent tropical waves moving off the African coast. Dry air, Saharan Dust, and strong high-pressure systems can diminish tropical waves as it moves across the Atlantic Ocean.

On average, about 60 waves are generated over North Africa each year, but it appears that the number that is formed has no relationship to how much tropical cyclone activity there is over the Atlantic each year. While only 60% of the Atlantic tropical storms and minor hurricanes originate from easterly waves, nearly 85% of the intense (or major) hurricanes have their origins as easterly or tropical waves.

Temperatures

Across both islands, overnight lows are forecast to be mild, with daytime highs warm.

From Thursday through Saturday, the minimum low for Trinidad and Tobago is forecast to be between 24.0°C and 26.0°C. The maximum high for Trinidad and Tobago is forecast to be between 30.0°C and 33.0°C. Higher temperatures are possible in urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas.

Forecast Impacts

Forecast impacts due to Tropical Wave 19

The main hazards include heavy rainfall triggering localized street flooding and flash flooding. Lightning and gusty winds up to and in excess of 45 KM/H may accompany thunderstorms or heavy showers and cause power dips/outages, downed trees, and localized wind damage.

Winds

Sustained surface winds up to 30 KM/H are forecast. In shower activity, gusts up to and in excess of 45 KM/H are likely. 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

Over the next 72 hours, overall higher rainfall is forecast to favor eastern areas of Trinidad and Tobago, with accumulations between 5 and 35 millimeters as Tropical Wave 19 moves across the region. However, localized totals up to and in excess of 50 millimeters are possible in prolonged heavy showers or isolated thunderstorm activity.

  • Thursday: Between 5-30 millimeters of rainfall across the country with isolated areas receiving up to 40 millimeters, favoring eastern, southern and central areas of Trinidad as well as parts of Tobago.
  • Friday: Between 5-10 millimeters of rainfall across the country with isolated areas up to 15 millimeters.
  • Saturday: Little to no rainfall is forecast, with isolated areas reciving up to 5 millimeters accumulation.

As mentioned earlier, mainly on Thursday, heavy rainfall may trigger localized street flooding and flash 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.

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 Thursday, isolated to scattered showers and thunderstorms are forecast. On Friday and Saturday, highly isolated showers are forecast.

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

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