Low-Level Trough, Dense Saharan Dust Forecast For T&T This Weekend

GOES-East Imagery showing few low-level cloud patches embedded within the strong trade wind flow of the dominating high-pressure system.

This weekend will be a battle of rain and dust for Trinidad and Tobago – ultimately culminating in what may be “muddy rainfall” on Sunday and Monday for both islands. A low-level trough will bring some cloudiness and showers while a large and dense plume of Saharan Dust will bring hazy skies to the region.

Contrary to what most may think, rainfall and Saharan Dust can and do exist simultaneously. A key piece of information into understanding this weekend’s forecast is where each weather feature exists in the atmosphere. Moisture and instability associated with a low-level trough will generally remain below 8,500 feet (2,600 meters) and showers will be isolated.

The Saharan Dust layer is a massive and well-mixed layer of dry air between 5,000 to 15,000 feet (1,500 meters to 4,600 meters). This means that as the Saharan Dust and showers interact, the dust won’t be eliminated by rainfall (though localized air quality improvement is possible). Showers won’t entirely be hindered by oppressive Saharan Dust provided sufficient instability is present.

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

The Forecast

Saturday: A mostly sunny start to the day will gradually increase in cloudiness, particularly after midday with showery intervals. Gusty winds may accompany and precede showers. Saharan Dust concentrations will be on the increase overnight into Sunday.

Sunday: A mostly dull and hazy day is forecast with showers favoring Trinidad. Heavier rainfall to favor southern and eastern areas of Trinidad, accompanied by gusty winds. High concentrations of Saharan Dust will be present, with increasing concentrations overnight into Monday.

Monday: Dull and cloudy conditions across Trinidad and Tobago with periods of showers and rain, favoring Trinidad. Gusty winds may accompany showers. High concentrations of Saharan Dust will be present.

Marine: Seas are forecast to remain moderate over the weekend, with waves in open waters generally between 2.0 meters to 2.5 meters. Along northern, eastern, and sheltered coastlines, waves near 1.0 meters are likely.


Overview: Dominating the overall wind flow, a deep layered high-pressure system will remain in place through the weekend. On Saturday, a surface to low-level trough will move across the region. However, moisture and instability trailing the trough will begin to affect the islands from the late afternoon on Saturday. At the low- to mid-levels of the atmosphere, Saharan Dust concentrations will be increasing across the region.

Moisture and instability will continue to affect T&T and the Windwards on Sunday into Monday, while Saharan Dust also moves across the region.

No significant change is forecast for T&T and the Southern Windward islands through Tuesday as the deep layered high-pressure system regains dominance.

Temperatures

Across both islands, overnight lows are forecast to be mild to cool with daytime highs warm.

The minimum low for Trinidad is forecast to be near 21.0°C, and as low as 19.0°C in valleys and forested areas of Central and Southern Trinidad. In Tobago, a minimum low near 23.0°C is forecast.

The maximum high for Trinidad is forecast to be near 31.0°C, up to 34.0°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 31.0°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 weekend into next week would be gusty winds, particularly in showers on land, reduced air quality and visibility. Rainfall is forecast to remain fairly brisk so the risk of street flooding is low.

Winds

Sustained surface winds moderate to fresh (20-38 KM/H). In shower activity, 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, daily rainfall accumulations are forecast to be less than 5 millimeters of rainfall, with daily maximum accumulation totals up to 10 millimeters favoring eastern areas.

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 rainfall is forecast through the weekend.

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