Forecast: Tropical Wave 48 To Move Across T&T

An isolated thunderstorm affects north-central Trinidad on Thursday 23rd September 2021.

Key Messages:
— A weak tropical wave is forecast to move across T&T, producing isolated showers and thunderstorms through Saturday, mainly north of Trinidad, with localized afternoon activity favoring western and hilly areas of Trinidad as well as across Tobago.
— Highly isolated areas of street or flash flooding are possible through the next three days. Winds are forecast to be light and variable, with localized wind gusts in excess of 45 KM/H possible. Maximum temperatures are forecast to be hot.
Lightning may accompany thunderstorms. Funnel clouds and waterspouts are possible.
— Weatherwise, there are no alerts, watches, or warnings in effect. However, a Hazardous Seas Alert (Yellow Level) is in effect for Trinidad and Tobago from the Trinidad and Tobago Meteorological Service until 11:00 AM Monday.

The Forecast

Moisture ahead of Tropical Wave 48 nearing T&T, with higher moisture totals north and east of the country (SSEC/CIMSS/UW-Madison)
Moisture ahead of Tropical Wave 48 nearing T&T, with higher moisture totals north and east of the country (SSEC/CIMSS/UW-Madison)

Friday: Mostly hot and sunny conditions are forecast across Trinidad, lesser so Tobago with variably cloudy skies. Across Tobago, isolated to scattered showers and the odd thunderstorm are forecast through the day, with most activity remaining north of the island. Across Trinidad, by the late morning through the afternoon, isolated showers and the odd strong thunderstorm are forecast to develop along western and hilly areas, subsiding by the evening. Overnight is forecast to be mostly settled, barring the odd, brief shower across both islands and thunderstorm activity favoring Tobago.

Saturday: Overnight showers and thunderstorms, favoring Tobago, are forecast to give way to a mostly hot and partly cloudy day across the country. Brisk isolated showers, favoring the late morning through the afternoon across western and hilly areas of Trinidad are also expected, with strong thunderstorms during this period across the western and hilly areas of Trinidad. A mostly settled evening and night are expected.

Sunday: Mostly hot and sunny conditions with brisk isolated showers and a low to medium chance of thunderstorms favoring western and hilly Trinidad during the late morning through the afternoon. A mostly settled evening and night are expected.

Marine: Over the next 72 hours, seas are forecast to be slight to moderate in open waters with waves up to 1.5 meters and up to 1.0 meters in sheltered areas. These higher-than-usual waves in sheltered areas are due to long-period swells from ex-Tropical Storm Odette. A Hazardous Seas Alert is in effect.

Temperatures

Over the next 72 hours, the minimum low is forecast to be between 24.0°C and 26.0°C for the country. The maximum high temperature is forecast to be 34.0°C in Trinidad and 32.0°C in Tobago.

In urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas, the maximum high temperatures could exceed 34.0°C. The feels-like temperature, or heat index, is forecast to range between 35.0°C and 48.0°C through Monday, with high temperatures continuing into next week.

This level of heat puts everyone at risk for heat illnesses; however, the risks are greatest for the elderly, young children, people with chronic illnesses such as breathing difficulties, heart conditions or psychiatric illnesses, people who work or who exercise in the heat, and the socially displaced.

Forecast Impacts

Forecast impacts due to Tropical Wave 48

Tropical Wave 48 is not forecast to be a high-impact event. Over the next three days, the main hazards are forecast to be highly isolated heavy showers or thunderstorms triggering very localized street or flash flooding and gusty winds in excess of 45 KM/H. In thunderstorm activity, cloud-to-ground lightning is possible. Funnel clouds and waterspouts are possible, with landslides also possible if heavy rainfall falls over elevated terrain.

Winds

Sustained surface winds less than 25 KM/H are forecast through Monday. In heavy to violent shower and thunderstorm 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

Widespread, heavy rainfall is not expected. Overall, higher rainfall totals are forecast to favor localized western areas of Trinidad and localized areas across Tobago, with up to 25 millimeters in the next three days. However, localized totals up to and in excess of 150 millimeters are possible in prolonged heavy showers or isolated thunderstorm activity across western coastal Trinidad.

  • Friday: Between 0-15 millimeters across the country, with isolated totals up to 50 millimeters favoring western coastal Trinidad and across Tobago.
  • Saturday: Less than 10 millimeters across the country with isolated totals up to 75 millimeters favoring western coastal Trinidad.
  • Sunday: Less than 5 millimeters across the country with isolated totals up to 20 millimeters favoring western coastal Trinidad.

Highly localized street flooding or flash flooding is possible with medium to high chances. Riverine flooding is not expected.

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. Dangerous, frequent lightning is expected on Friday and Saturday.

Landslides: Landslides and fallen trees are possible, particularly along the Northern Range but low rainfall totals are forecast to this is unlikely.

Tornadic Activity: With the potential for thunderstorms, funnel clouds, and waterspouts are possible. If funnel clouds touchdown or waterspouts encounter land, weak tornadoes can form.

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 showers and thunderstorms are forecast to occur through the forecast period.

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

Forecast Discussion

Infrared satellite imagery showing scattered showers and thunderstorms associated with Tropical Wave 48 east of the Lesser Antilles. (Weathernerds)

Tropical Waves: At 00Z Friday 24th September 2021, the axis of Tropical Wave 48 is along 55°W, south of 20°N, moving westward at 10-15 knots (18-27 KM/H) with scattered shower and thunderstorm activity. Tropical Wave 50 is along 24W, south of 20N, moving west at 10 knots (18 KM/H). Tropical Wave 49 formed into Tropical Storm Sam.

Over the next 24 hours, Tropical Wave 48 will be moving across the region, bringing increased instability, an increase in atmospheric moisture, and coupled with a low-shear environment. Isolated, brief showers and thunderstorms are forecast through Saturday.

Presently, a mid- to upper-level trough northeast of the islands is enhancing showers and thunderstorms. Through Friday and into Saturday, moisture will move across the islands from the southeast, supporting isolated heavier showers moving to the northwest. Light winds and high temperatures will allow heavy isolated afternoon showers or thunderstorms to develop along western and hilly areas.

As the tropical wave moves west on Saturday, confluence (winds slowing down, piling up, and causing convergence) on the southern periphery of a high-pressure system anchored in the far Eastern Atlantic will allow for isolated showers and thunderstorms, favoring the early morning and overnight hours, with isolated activity also forecast during the afternoon across western and hilly areas. Similar conditions are forecast on Sunday.

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