Forecast: *Very* Hot With Afternoon Showers, Thunderstorms

It is going to be hard to ignore how still (no winds) and hot Thursday will be. Winds are forecast to be near calm, at times up to 10 KM/H from the north. This means, with our light winds and mostly sunny skies, strong daytime heating, isolated showers, and thunderstorms are possible across Trinidad by the late morning, through the afternoon.

Heat-driven showers and thunderstorms can be intense, producing localized street/flash flooding and gusty winds in downburst-like activity. Today’s showers and thunderstorms will be scattered across Trinidad due no prevailing low-level steering pattern. With light winds, funnel clouds are also possible.

There are no alerts, watches, or warnings from the Trinidad and Tobago Meteorological Service at this time.

The Forecast

Sea breeze convergence mechanisms for the Gulf of Paria and the Atlantic Ocean across Trinidad which can produce thunderstorm activity. On Thursday, sea breeze convergence will be possible across all coasts of Trinidad and Tobago due to light to no winds.
Sea breeze convergence mechanisms for the Gulf of Paria and the Atlantic Ocean across Trinidad which can produce thunderstorm activity. On Thursday, sea breeze convergence will be possible across all coasts of Trinidad and Tobago due to light to no winds.

Overview: Increasing low-level moisture is forecast as Hurricane Teddy pulls equatorial moisture northward. Teddy has also induced a surface to a low-level trough which has eroded the pressure gradient across the Lesser Antilles, resulting in near calm conditions, with the weak steering pattern from the south. Increasing easterly wind shear is forecast across T&T, which will weaken isolated activity as rapidly as it forms. Strong daytime heating, orographic lift (along the Northern and Central Range), and sea breeze convergence are forecast to as triggers for late morning afternoon shower and thunderstorm development.


Forecast: A very hot and sunny day is forecast across both islands. By the late morning, partly cloudy skies are forecast to develop Trinidad. By 11 AM, isolated showers are possible, mainly across hilly areas, but by the afternoon, isolated thunderstorms are possible across Central and Southern Trinidad. Conditions are forecast to settle by the evening.


Marine: Seas are forecast to be moderate to rough. Swells from Hurricane Teddy will be affecting the Lesser Antilles, Northern South America, including T&T. In open waters, generally northern and eastern areas, waves up to 3 meters are possible and choppy conditions are forecast in sheltered coasts, with waves generally below 1 meter along these areas.

Large, breaking waves will likely exceed that 1-meter mark along Eastern and Northern coastlines. Spring tides will be at its peak due to New Moon Thursday night, hence minor coastal flooding will be possible. Winds are forecast to be generally calm, with light winds up to 10 knots from the north.

Hazards: The main hazards include localized heavy rainfall, which may reduce visibility and gusty winds in downburst-like fashion, up to and in excess of 50 KM/H. Street or flash flooding will be possible in slow-moving showers and thunderstorms. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage. With light winds, funnel clouds are also possible.

Temperatures

Depending on when showers finally develop, Thursday 17th September 2020 may rival September 14th for the hottest day across Trinidad due to sunny skies, no winds and increasing moisture.

Across both islands, hot and humid conditions are forecast. The maximum high for Trinidad is forecast to be near 35.0°C, up to 38.0°C in urban and built-up areas, particularly between 9:00 AM and 3:00 PM. In Tobago, the maximum high is forecast to be near 33.0°C.

Temperatures in cities, such as Port of Spain, tend to be much higher than surrounding locations due to a phenomenon called the Urban Heat Island Effect. There are several causes, but the main instigator for this phenomenon tends to be increased dark surfaces such as roads and pavement in cities, which absorb solar radiation more than surrounding areas.

The Heat Index

The heat index will be near dangerous levels on Thursday across Trinidad and Tobago. The heat index and is a combination of air temperature and relative humidity, determining what the air feels like to a person, i.e., how hot it actually feels.

Across Trinidad, the maximum heat index is forecast to be between 38°C and 45°C and even higher in urbanized areas. In Tobago, the maximum heat index is forecast to be between 35°C and 41°C

The heat index is important because of sweating. Your body sweats to cool the skin and maintain a constant, healthy body temperature. This cooling process means that the sweat has to evaporate off the skin to remove heat. However, if the sweat is unable to evaporate, the body isn’t able to regulate temperature.

 Heat Index Values Explained
Heat Index Values Explained

Heat index is generally classified into four categories: caution, extreme caution, dangerous, and extremely dangerous. On Thursday, the heat index is forecast to be near dangerous levels! Remain hydrated!

Forecast Impacts

Winds

Sustained surface winds will be light to nonexistent. However, during heavy showers and thunderstorms, sustained winds between 25 KM/H and 35 KM/H with gusts up to and in excess of 50 KM/H are possible.

With wind gusts in excess of 50 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

Across most areas of Trinidad and Tobago, little to no rainfall is anticipated, with maximum accumulation totals near 5 millimeters. However, across parts of Southern and Central Trinidad, up to 25 millimeters are possible, with isolated totals in excess of 25 millimeters, particularly in slow-moving downpours or thunderstorms.

Generally, with heavy showers and thunderstorm activity, street flooding, particularly in flood-prone areas or areas with poor drainage, is possible as well as flash flooding in areas where more prolonged heavy rainfall may occur.

Frequent Lightning: Frequent 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.

Isolated to scattered rainfall is forecast on Thursday. Most will experience very hot and sunny conditions.

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

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