Trough, ITCZ Forecast To Bring Showers, Thunderstorms to T&T

A surface to low-level trough interacting with the ITCZ is forecast to move across T&T on Sunday, bringing isolated to scattered showers and thunderstorms.

As of 7:00 AM Sunday 11th October 2020, the axis of this trough was analyzed along 60W, moving west very slowly, at 5 to 10 knots.

Higher rainfall accumulations are forecast to favor isolated areas of Trinidad, mainly across eastern areas initially and western areas after midday.

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

Forecast For Sunday

Sunday: A mostly sunny start to the day will give way to increased cloudiness, possible showers, and thunderstorms after 8:00 AM, moving in from the east. These cloudy periods will be interrupted by isolated activity through the afternoon across both islands.

Conditions will gradually settle through the late afternoon, leading to a mostly clear and cool night across T&T. Showers and thunderstorms may return across parts of northern and eastern Trinidad, as well as Tobago during the pre-dawn hours of Monday.

Hazards: The main hazards include heavy rainfall, which may reduce visibility and gusty winds up to and in excess of 55 KM/H. Street or flash flooding will be possible in violent showers and thunderstorms. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage.

Marine: Seas are forecast to be slight, with waves below 1.25 meters in open waters. Swells are forecast to be from the northeast, with a swell period between 6 and 7.5 seconds. In sheltered areas, near calm. However, in areas where thunderstorms occur, seas can become choppy and locally rough.

Winds are forecast to be light to moderate offshore, between 10 and 15 knots prevailing from the southeast.

Forecast Discussion: A surface to low-level trough is interacting with the Intertropical Convergence Zone. Abundant moisture is moving across the Windwards, fuelling shower and thunderstorm activity. In addition, a marginally favorable upper-level environment will allow for enhancement of convection (showers and thunderstorms), with low wind shear allowing strong thunderstorms to develop.

Across Trinidad, by the late morning through the afternoon, light winds, daytime heating, and sea breeze convergence will act as triggers for shower and thunderstorm development across western parts of Trinidad, with orographic lift triggering/enhancing showers along hilly topography of both islands.

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 Monday, lingering surface to mid level moisture combined with surface to low level confluence will generate a few scattered light to moderate showers across the island chain. Meanwhile, a westward propagating tropical wave presently located near 43W (at 0600UTC) will be inching closer to the region.


Across both islands, even with the forecast showers and thunderstorms, warm and humid conditions are anticipated. The maximum high for Trinidad is forecast to be near 30.0°C, up to 33.0°C in urban and built-up areas. In Tobago, the maximum high is forecast to be near 30.0°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 elevated across Trinidad and Tobago. The heat index 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 and Tobago, the maximum heat index is forecast to be between 30°C and 35°C and even higher in urbanized areas.

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

Forecast Impacts


Sustained surface winds will be light, peaking during the afternoon. By the afternoon, sustained winds between 20 KM/H and 35 KM/H with gusts up to and in excess of 55 KM/H are possible.

With wind gusts in excess of 55 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.


Across most areas of Trinidad and Tobago, low rainfall accumulations are anticipated, with maximum accumulation totals between 5-10 millimeters over the next 24 hours.

In isolated areas across Trinidad, rainfall accumulations up to 25 millimeters are possible.

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.

Brief, isolated to scattered rainfall is forecast on Sunday, interrupting partly to mostly cloudy periods.

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

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