Tropical Wave 23 To Bring Showers, Thunderstorms To T&T Over Next 48 Hours

Cloudy sunrise spotted from Northwestern Trinidad, overlooking the Gulf of Paria as a tropical wave moved across the region on July 11th, 2021. (Ryan Kyle Daniel)

What you need to know:
— A tropical wave is forecast to move across Trinidad and Tobago on Thursday night into Friday. However, moisture and instability are forecast to begin affecting T&T overnight tonight into Thursday.
— 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. Better rain chances come this weekend as another Tropical Wave moves across the region.
— There are no alerts, watches, or warnings from the Trinidad and Tobago Meteorological Service at this time.

The Forecast

Tropical Wave 23 approaching the Windward Islands (RAMMB/CIRA/NOAA)

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

Friday: A partly to a mostly cloudy day, interrupted by scattered showers and isolated thunderstorms from the early morning through the afternoon across both islands. Heavier rainfall and thunderstorms are forecast to favor Trinidad. Hazy and partly cloudy conditions are forecast by the evening into the night, with brisk showers. Gusty winds, street/flash flooding are possible.

Saturday: A partly cloudy and warm day, with showers and isolated thunderstorms developing after daybreak through the afternoon across both islands. Periodic showers and isolated thunderstorms are forecast near and after midnight across both islands.

Sunday: Showers and isolated thunderstorms are forecast to continue after midnight and continue through the day, with heavier rainfall favoring Trinidad. Conditions to settle by the late night. Partly cloudy skies, with occasional cloudy periods expected.

Marine: Seas are forecast to be moderate over the 4 days, with waves between 1.0 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 23. (Weathernerds)
Infrared satellite imagery showing scattered showers east of Trinidad and Tobago with the approaching Tropical Wave 23. (Weathernerds)

Tropical Waves: At 12Z Wednesday 21st July 2021, the National Hurricane Center added a tropical wave to its analysis as it moved across the Lesser Antilles, now moving across the Caribbean Sea. This tropical wave became the 24th analyzed wave for the season, but for continuity of waves moving across T&T, it was the 22nd. Tropical Wave 22 is suppressed by dry, Saharan Dust and is not producing any significant shower or thunderstorm activity. As of 11:00 PM, the axis of Tropical Wave 23 is along 56W, south of 23N, moving westward at 10-15 knots (18-27 KM/H). Scattered moderate convection (showers and thunderstorms) is seen on satellite imagery, mainly east of the wave axis. Another wave, Tropical Wave 24, is along 38W, south of 21N, moving westward at 15-20 knots (27-37 KM/H).

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 midnight tonight (Wednesday into Thursday), with cloudiness increasing, as well as the chances for isolated showers and thunderstorms. Wind shear and low-level winds are forecast to be light through the forecast period, allowing for heavier showers or thunderstorms to develop and persist.

By Thursday morning, a marginally favorable low-level environment and increasing mid- to upper-level instability are 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. More favorable conditions are forecast on Friday, with higher chances of rainfall.

Though conditions will briefly settle by late Friday, by midnight, Tropical Wave 22, located in the Eastern Atlantic will near the Lesser Antilles and move across the region on Saturday into Sunday.

Infrared satellite imagery showing Tropical Wave 23 at 56W and Tropical Wave 24 at 36W (Weathernerds)

Temperatures

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

From Thursday through Sunday, 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 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 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 4 days hours, overall higher rainfall is forecast to favor eastern areas of Trinidad and Tobago, with accumulations between 5 and 35 millimeters as Tropical Wave 23 moves across the region and between 20 to 75 millimeters by Monday as Tropical Wave 24 moves westward. However, localized totals up to and in excess of 75 millimeters are possible in prolonged heavy showers or isolated thunderstorm activity.

  • Thursday: Between 5-15 millimeters of rainfall across the country with isolated areas recieving between 15 to 25 millimeters. Heavier rainfall to favor coastal eastern and western Trinidad, as well as southern areas of Trinidad and Tobago.
  • Friday: Between 10-15 millimeters of rainfall across the country with isolated areas receiving up to 35 millimeters in thunderstorms or heavy showers.
  • Saturday: Between 5-15 millimeters of rainfall across the country with isolated areas recieving between 15 to 35 millimeters. Heavier rainfall to favor Trinidad.
  • Sunday: Between 5-15 millimeters of rainfall across the country with isolated areas recieving up to 20 millimeters.

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.

Landslides: Landslides and fallen trees are possible through the forecast period, particularly in areas where heavy thunderstorms occur or persisting rains over the next 4 days.

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 through the weekend, isolated to scattered rainfall is forecast.

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

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