Forecast: Showers, Cloudy Periods To Persist on Wednesday

Weather Forecast

As of 9:30AM Wednesday 3rd April 2019, scattered showers are occurring mainly across Trinidad. These showers are generally remaining light to moderate, with heavier pockets predominantly across Southern and Eastern areas of the island. Isolated showers are interrupting cloudy to overcast periods across Tobago.

Over the next 12 hours, these conditions are forecast to persist throughout today, with an overall decrease in showery activity by the late evening into nightfall. Showers are forecast to generally remain light to moderate, but isolated heavy pockets and accompanying gusty winds are possible. These heavier showers are forecast to favor the afternoon hours.

Cloudy conditions, with isolated showery activity are forecast overnight, persisting into Thursday. Thursday is forecast to be much drier, as a surface to mid-level Atlantic high pressure system regains dominance over T&T. Breezy conditions are forecast as the pressure gradient tightens.

The present overcast and showery conditions are due to a surface to low-level shearline moving across area. Combined with increased surface to low-level moisture and marginal increase in instability, a wet Wednesday is forecast. However, mid to upper level conditions remain unfavorable for widespread showers or thunderstorm development.

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Some welcome rainfall accumulations are forecast over the next several days, between 0-5 millimeter accumulations, daily, across both Trinidad and Tobago through Thursday. Accumulations up to 10 millimeters, daily, is forecast across parts of Eastern and Northern Trinidad.

Surface to low-level winds are forecast to increase, with winds up to 40 KM/H, and higher gusts possible accompanying showers.

Note: Showers, rainy or wet days and thunderstorms are possible and do occur in the dry season, such as the severe thunderstorm on March 4th 2018, which produced flash floods across Northern and Central Trinidad. Similarly, dry spells also occur during the wet or rainy season. These seasons generally dictate the overall climate, i.e. generally drier or wetter conditions, but day-to-day weather can vary.

What is a shearline?

Shearlines routinely affect the Eastern Caribbean, mainly during the Northern Hemisphere’s late autumn through early spring months (November through April). It is the final stage in the life cycle of a cold front over the subtropics and tropics. Lying equatorward of the subtropical ridge, these boundaries have lost all temperature contrast over the warm ocean, which is usually an indicator of a frontal boundary. Shearlines also have minimal dewpoint (moisture) contrast across them. They delineate an area where wind speed quickly increases on the poleward side (northern or southern sides) at least 10 knots (~20 KM/H) from nearly the same direction (within 45 degrees).

Mid and high level cloudiness previously associated with the cold front has dissipated due to lack of upper level support. Therefore, a shearline is indicated on satellite imagery as the leading edge of a line of low-level clouds with tops near 10,000 feet.

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Temperatures

Minimum low temperatures across Trinidad and Tobago over the next 3 days are forecast to range between 23°C-26°C, with temperatures at the upper end of the minimum low temperature range favoring Tobago. Low temperatures are likely to be lower across inland and mountainous areas. Last nights minimum temperatures were 23.1°C at Piarco, Trinidad. At Tobago, the minimum low temperature was 23°C at Crown Point.

Cloud cover is forecast to reduce maximum high temperatures on Wednesday, with 30°C forecast at Piarco, Trinidad and 29°C forecast at Crown Point, Tobago. Maximum high temperatures across T&T on Thursday and Friday however are forecast to be warm, near 32°C at Piarco, Trinidad. Across Tobago, maximum high temperatures are forecast to near 30°C.

The maximum high heat index, or “feel’s like” temperature is forecast to generally remain near a hot 36°C during the early to mid-afternoons of Trinidad and 34°C in Tobago. Again, cloud cover and increased surface winds may reduce the “feels like” temperature on Wednesday.

Seas

Seas are forecast to remain moderate in open waters through the week. Waves in open waters are forecast to remain up to 2.0 meters particularly East of Trinidad and Tobago. In sheltered areas, seas are forecast to remain smooth, below 1.0 meters. Winds are forecast to be from the northeast to east at 15-20 knots.

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No Saharan Dust In Sight

Dust concentrations remain at negligible levels across the Southern and Eastern Caribbean. In fact, most places across the Eastern Caribbean are presently experiencing good air quality. Air quality is forecast to remain at good levels for the next several days. Areas in the immediate vicinity of bushfires may experience moderate air quality.

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EPA Air Quality Index Risk Levels

At moderate air quality levels, unusually sensitive groups should consider reducing prolonged or heavy exertion.

Thankfully, long range dust models aren’t indicating any major intrusions of Saharan Dust over the next 10 days! However, over the longer range, models are indicating the return of Saharan dust by the middle of April (15th-17th). This is nearly 2 weeks away, so we’ll be monitoring the situation.

12Z April 2nd 2019 NASA GEOS-5 Dust Model, no Saharan dust concentrations across the Eastern Caribbean over the next several days. Credit: Weatherbell

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