Forecast: Showers, Isolated Thunderstorms Possible Over Next 48 Hours

An unstable atmosphere with elevated low-level moisture is forecast to create somewhat favorable conditions over the next 48 hours for isolated to scattered showers and isolated thunderstorms, mainly across Trinidad.

Overall, heavier rainfall will favor the eastern areas of Trinidad. In areas where isolated heavy showers or thunderstorms occur, isolated higher rainfall totals may also occur, particularly across southern and western coastal Trinidad.

At this time, there are no alerts, watches, or warnings issued for T&T from the Trinidad and Tobago Meteorological Service.

The Forecast

On Monday, partly to mostly cloudy skies are forecast to become increasingly overcast as the day progresses, with brisk, isolated shower activity across both islands. Still, heavier showers are possible across Trinidad from the late morning through the afternoon. There is a low chance of a thunderstorm favoring western coastal Trinidad and hilly areas during the afternoon. Conditions will gradually settle into the evening, with isolated showers and the odd thunderstorm possible near and after midnight.

Similar conditions are forecast on Tuesday, with an increase in cloudiness, showers, and the odd thunderstorm from midnight through the early afternoon. Skies are forecast to be mostly cloudy. As the afternoon progresses, increasingly hazy skies are expected as a surge of Saharan Dust moves into the region.

Marine: Seas are forecast to be moderate over the next 48 hours, with waves between 1.5 to 2.0 meters in Trinidad and Tobago’s open waters. Across sheltered coastlines, waves below 1.0 meter are likely. In heavy showers or thunderstorms, sheltered seas may become choppy.


Overview: A surface to low-level trough is east of the Lesser Antilles, forecast to move across the region overnight Monday into Tuesday. Moisture surging ahead of this trough, and instability is forecast to move in from the southeast. This pattern of easterly to southeasterly moisture flow is forecast to hold through the next 36-48 hours. In fact, forecast models show during this period, high amounts of atmospheric moisture will be present mainly across Trinidad, providing fuel for localized showers and possible isolated thunderstorms.

At the mid-levels, a weak trough is positioned across the Leewards, aiding the southeasterly flow across the Windward Islands. Winds across T&T through Tuesday are forecast to remain light, supporting localized heavy shower and possible thunderstorm development due to localized climatic effects such as sea breeze convergence, orographic effects, and daytime heating.

Through the forecast period, wind shear will be moderate to strong, up to 50 knots from the northwest. This will limit the strength of thunderstorms, keeping heavy showers and thunderstorms relatively brief, mainly on Monday and most of the heavy rainfall east of T&T. Still, isolated heavy rainfall is forecast across eastern areas generally and across western coastal Trinidad during the late morning through the afternoons.

Total precipitable water imagery showing high levels of atmospheric moisture approaching Trinidad and Tobago as a low-level trough nears the region. According to the National Hurricane Center, the ITCZ is across Trinidad as of 00Z Monday 17th May 2021 (8:00 PM Sunday 16th May 2021). (CIMSS, Space Science & Engineering Center, University of Wisconsin - Madison)
Total precipitable water imagery showing high levels of atmospheric moisture approaching Trinidad and Tobago as a low-level trough nears the region. According to the National Hurricane Center, the ITCZ is across Trinidad as of 00Z Monday 17th May 2021 (8:00 PM Sunday 16th May 2021). (CIMSS, Space Science & Engineering Center, University of Wisconsin – Madison)

Note: Based on our analysis, this is not a tropical wave. However, according to the National Hurricane Center, the Tropical Analysis and Forecast Branch have analyzed the Intertropical Convergence Zone across Trinidad as of 8:00 PM May 16th, 2021. If the Trinidad and Tobago Meteorological Service agrees with this analysis, it would technically mean the start of the 2021 Wet Season. However, models continue to show mostly dry weather continuing from Wednesday onward through the end of May.

Temperatures

Across both islands, overnight lows are forecast to be mild, with daytime highs cool due to cloud cover through on Thursday. As skies clear somewhat at times on Friday, through the weekend, and into next week, temperatures may trend warmer during the day.

The minimum low for Trinidad is forecast to be near 23.0°C, and as low as 22.0°C in valleys and forested areas. In Tobago, a minimum low near 25.0°C is forecast. For Monday and Tuesday, the maximum high for Trinidad and Tobago is forecast to be between 31.0°C and 33.0°C, higher across Trinidad.

Temperatures may record higher in urban and built-up areas, particularly between 9:00 AM and 3:00 PM. The maximum heat index in Trinidad is forecast to be between 35.0°C and 40.0°C while across Tobago between 33.0°C and 36.0°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.

Forecast Impacts

The main hazards through the next 48 hours would be localized heavy rainfall and gusty winds, particularly in moderate to heavy showers or thunderstorms, bringing the risk of street flooding or flash flooding.

Winds

Sustained surface winds light to fresh (6-38 KM/H). 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

Over the next 48 hours, heavier rainfall is forecast to favor eastern Trinidad, with localized high totals across southern and western coastal Trinidad.

Rainfall accumulations between 10 to 25 millimeters are possible through the next 48 hours. In isolated areas, rainfall accumulations could reach up to and in excess of 50 millimeters.

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.

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.

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.

Brisk, isolated to scattered rainfall is forecast on Monday and Tuesday.

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

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