Forecast: Hurricane Larry Will Not Directly Impact T&T, The Lesser Antilles

Key Messages:
Hurricane Larry will not directly affect Trinidad, Tobago, and the Lesser Antilles.
— As the hurricane slowly moves to the northeast of the region, its influence on our atmosphere, pulling the ITCZ northward and inducing a trough will allow for light southerly to southeasterly winds through Tuesday, hot temperatures, and potentially slow-moving showers and thunderstorms favoring Trinidad.
— Highly isolated areas of street or flash flooding across both islands, favoring western areas possible. Localized wind gusts in excess of 45 KM/H possible. Frequent lightning may accompany thunderstorms. Landslides are possible across the Northern Range and Tobago. Funnel clouds and waterspouts are possible on Sunday and Monday.
— A Hazardous Seas Alert (Yellow Level) is in effect for T&T from 2:00 AM Saturday 5th September 2021 to 12:00 PM Friday 10th September 2021.

The Forecast

Moisture associated with the ITCZ and Hurricane Larry approaching T&T (SSEC/CIMSS/UW-Madison)

Sunday: A few early morning showers and thunderstorms are forecast to give way to mostly hot and sunny conditions with somewhat hazy skies across Trinidad and Tobago. By the late morning through the afternoon, isolated heavy showers and one or two thunderstorms may develop across western and hilly areas of Trinidad, as well as across western areas of Tobago with variably cloudy skies. Conditions to settle into the evening across both islands with mostly fair skies, barring the odd shower or thunderstorm generally remaining offshore.

Monday: After midnight, isolated showers and thunderstorms are forecast, interrupting partly cloudy skies and subsiding by daybreak. Foggy conditions are possible during the early morning. After a mostly hot and sunny morning, isolated showers and thunderstorms are possible again from the late morning through the afternoon, favoring Trinidad. Conditions to settle into the evening across both islands with mostly fair skies, barring the odd shower or thunderstorm generally remaining offshore.

Tuesday: Mostly hot and sunny conditions, interrupted by brisk isolated showers. Isolated showers and thunderstorms are possible during the afternoon and continue into the overnight hours, favoring Trinidad.

Marine: Over the next 72 hours, seas are forecast to become agitated with waves in open waters up to 2.0 meters and less than 1.5 meters in sheltered areas. These higher-than-usual waves in sheltered areas are due to a combination of ongoing spring tides and long-period swells from Hurricane Larry.

Temperatures

With the influence of Hurricane Larry, light winds and mostly sunny skies are forecast across T&T.

The combination of light winds, heat, and humidity will likely result in the heat index or feels-like temperature threat rising to high levels, with the potential for extensive impacts.

Over the next 72 hours, while the minimum low is forecast to be between 23.0°C and 25.0°C for the country, the maximum high temperatures are forecast to be up to 35.0°C in Trinidad and 33.0°C in Tobago.

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

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 localized climatic effects and three tropical waves over the next 5 days.

Over the next 72 hours, the main hazards include hot temperatures with slow-moving, afternoon showers and thunderstorms that could produce gusty winds, frequent lightning, and periods of heavy rainfall that may trigger street or flash flooding across both islands. Generally, wind gusts in excess of 45 KM/H are possible, which may cause further power dips/outages, downed trees, and localized wind damage. Landslides are possible across the Northern Range and Tobago. With light surface winds and strong daytime heating expected, funnel clouds and waterspouts are possible. Hazardous seas are also forecast.

Winds

Sustained surface winds less than 20 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

Overall, higher rainfall is forecast to favor northern and easter Trinidad and Tobago, with accumulations between 25-75 millimeters. However, localized totals up to and in excess of 75 millimeters are possible in prolonged heavy showers or isolated thunderstorm activity.

  • Sunday: Between 5-15 millimeters across the country, with isolated totals up to 20 millimeters favoring Tobago.
  • Monday: Between 15-25 millimeters across the country. In heavy showers or thunderstorms favoring western and northern Trinidad, totals may reach and exceed 25 millimeters, up to 50 millimeters possible.
  • Tuesday: Between 5-15 millimeters across the country, with isolated totals up to 25 millimeters favoring Trinidad.

As mentioned earlier, street flooding and flash flooding are likely with medium chances in heavy showers or thunderstorms 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 the potential for thunderstorms, funnel clouds, and waterspouts are possible, particularly on Sunday through Monday. 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.

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

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

Forecast Discussion

Hurricane Larry’s probabilities for tropical-storm-force winds as of 11:00 PM Saturday 4th September 2021. (National Hurricane Center)
Hurricane Larry’s probabilities for tropical-storm-force winds as of 11:00 PM Saturday 4th September 2021. (National Hurricane Center)

Tropical Waves: At 00Z Sunday 5th September 2021, the axis of Tropical Wave 43 is along 35W, south of 20N, moving westward at 10-15 knots (18-27 KM/H) with no significant shower and thunderstorm activity. This wave is forecast to move across T&T on Thursday. Tropical Wave 44 is along 17W, south of 19N, moving west at 10-15 knots (18-27 KM/H), forecast to move across the region on Saturday 11th September 2021. Tropical Wave 42 developed into Hurricane Larry and was dropped from the analysis.

The main weather influencer over the next three days will be Hurricane Larry. This powerful hurricane is moving safely northeast of the Lesser Antilles so there is no threat of feeder band activity. In fact, the hurricane has taken on annular characteristics, meaning there is a large, symmetric eye surrounded by a thick and uniform ring of intense convection with no discrete rainbands – i.e. no feeder bands.

Extending southwestward from the low-pressure is an induced, deep-layered trough that is forecast to have several consequences through at least the next three days. Wind speeds across the region are forecast to notably drop off, with near-calm to light winds from the south or southeast Sunday into Monday. In addition, the Intertropical Convergence Zone will drift northward, across T&T, and even move north of the country.

Though widespread rainfall is not forecast, this set-up is supportive of showers and thunderstorms during the late morning through the afternoon, triggered by daytime heatingsea breeze convergence, and orographic effects, that will slowly move from the south/southeast to the north/northwest. In addition, because of these light and variable winds, funnel cloud or waterspout development will be possible across western areas of both islands.

Marginally favorable atmospheric conditions, with relatively high atmospheric moisture and moderate to light wind shear, will allow for deeper convection to develop, potentially producing heavy to violent rainfall rates and gusty winds. It should be noted that wind gusts are not expected to be as strong as what the country experienced last Thursday into Friday.

Swells from Larry will begin to affect T&T’s northern and eastern coasts from Sunday evening, with abnormal waves possibly affecting western coasts.

Infrared satellite imagery showing Hurricane Larry northeast of the Lesser Antilles. (Weathernerds)
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