Tropical Storm Paulette’s Influence: Showers, Thunderstorms For T&T

Tropical Storm Paulette remains thousands of kilometers to our northeast, but a surface to low-level trough extending from the tropical cyclone continues to affect our wind regime and moisture levels. Hence, another day of light southerly winds, to at times southwesterly winds, are forecast. Combined with strong daytime heating, isolated showers and thunderstorms are possible, mainly across Northern and Eastern halves of Trinidad by the late morning, through the afternoon.

Heat-driven showers and thunderstorms can be intense, producing localized heavy rainfall, rapid street/flash flooding and gusty winds. This activity will mainly be possible across the northern half of Trinidad. With light winds, funnel clouds are also possible.

By nightfall, showers and thunderstorms are forecast to spread across Trinidad, as activity across Northern Venezuela drifts northward. Activity may be locally intense, particularly across the Southern half of Trinidad and in the Gulf of Paria, producing hazardous seas.

The Trinidad and Tobago Meteorological Service has issued an Adverse Weather Alert Yellow Level for parts of Trinidad from 12:00 PM through 5:00 PM

The Forecast


Overview: A surface to low-level trough extending from Tropical Storm Paulette has degraded the pressure gradient across the Lesser Antilles, causing light winds across the region. Abundant moisture is present as the ITCZ remains over T&T. Strong daytime heating, orographic lift (along the Central and Northern Range), and sea breeze convergence (both Western and Eastern Coasts) forecast to act as triggers for late morning through afternoon shower and thunderstorm development.

Sea breeze convergence mechanisms for the Gulf of Paria and the Atlantic Ocean across Trinidad which can produce thunderstorm activity.. Note that sea breeze convergence is possible across all coasts of both islands. Diagram: Trinidad and Tobago Weather Center

Forecast: A mostly hot and sunny day is forecast across both islands. By the late morning, partly cloudy skies are forecast to develop across the Northern half of Trinidad. After midday, isolated showers and thunderstorms are possible, mainly across the Northern half of Trinidad, gradually becoming scattered through the mid-afternoon across much of the island.

Conditions are forecast to settle by the evening initially. Then, models show an increase in shower and thunderstorm activity after nightfall, as convection develops along the Northern coast of Venezuela and drift northward. Heavier activity will favor Southern and Southwestern Trinidad, with hazardous marine conditions in the Gulf of Paria.


Marine: Slight to Moderate. Across Northern and Southern Coasts of Trinidad, as well as the Western coasts of Tobago, slight seas are anticipated with waves less than 1.5 meters. Across the Atlantic facing coasts of both islands, moderate seas with waves between 1.5 meters to 2.0 meters.

Low-level winds are forecast to be from the south to southeast at 10 knots initially. These winds may become south to southwesterly overnight Friday into Saturday. In sheltered areas, waves are forecast to be near calm to below 1.0 meter and choppy at times. Long period swells (generally between 10-12 seconds) will produce larger than usual waves in nearshore areas of northern and eastern coasts of T&T through Sunday.

Note: Overnight Friday into Saturday, strong winds and agitated seas are possible in the Gulf of Paria. Particularly along the Northwestern coasts, waves near 1 meter are possible. Particularly if strong thunderstorms persist across the Gulf of Paria as it moves north.

Hazards: The main hazards include heavy rainfall, which may reduce visibility and gusty winds 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. Across the Northern Range, landslides are possible.

Temperatures

Across both islands, hot and humid conditions are forecast. The maximum high for Trinidad is forecast to be near 34.0°C, up to 36.0°C in urban and built-up areas, particularly between 10:00 AM and 2:00 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 relatively high on Friday 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 35°C and 38°C and even higher in urbanized areas. In Tobago, the maximum heat index is forecast to be between 33°C and 37°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 Friday, the heat index is forecast to be near levels where extreme caution is needed. 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.

High Wind Event Precautions
High Wind Event Precautions

Rainfall

Across most areas of Tobago, little to no rainfall is anticipated, with maximum accumulation totals near 10 millimeters. However, across Trinidad over the next 24 hours, rainfall totals between 10-20 millimeters are possible, with much of the rainfall occurring overnight tonight into Saturday. Isolated totals during Friday afternoon, particularly along the south-facing slopes of the Northern Range and the northern half of Trinidad, rainfall totals of 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 Friday. Most will experience hot and sunny conditions.

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

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