Surface Trough Brings Isolated Showers, Low Chance of Thunderstorms Forecast Friday into Saturday

Weather Forecast (Next 24 Hours)

As of 9:15 AM Friday 10th May 2019, mostly hazy and partly cloudy skies are occurring across Trinidad and Tobago. A few isolated showers favoring Eastern Trinidad are occurring, with heavy pockets. Breezy conditions are forecast across both islands. Isolated showers are possible across Trinidad and Tobago throughout the day, with heavier showers and the low chance of a thunderstorm favoring Southern Trinidad. Gusty winds up to 60 KM/H possible.

Note, a surface to low-level trough is responsible for today’s weather, not the passage of a tropical wave that originated from the African Easterly Jet and North African convection.

Throughout Friday, mostly hazy skies with partly cloudy conditions are forecast across Trinidad and Tobago. A considerable increase in low-level to upper-level moisture has moved over and is still present across Trinidad and Tobago. As the day progresses, favorable low-level convergence is forecast, mainly across Southern parts of Trinidad. A surface to low-level trough northeast of Trinidad and Tobago is forecast to progress west-northwestward throughout today, causing some instability.

These features, in combination with local climatic effects such as sea breeze convergence and day time heating, is forecast to trigger some isolated to scattered showers across Trinidad, and to a lesser effect, Tobago. Showers are generally forecast to remain light to moderate, with a few isolated heavy pockets. Upper-level enhancement may allow for a few isolated showers becoming generally heavy and the low chance of a thunderstorm, again, favoring Southern Trinidad and into the Gulf of Paria.

Thunderstorm and Heavy Shower Chances and Impacts Across Trinidad and Tobago For Friday into Saturday May 10th-11th 2019.
Thunderstorm and Heavy Shower Chances and Impacts Across Trinidad and Tobago For Friday into Saturday, May 10th-11th, 2019.

By the late evening into nightfall, mostly settled conditions are forecast. Partly cloudy and hazy skies, with generally breezy conditions. The odd isolated shower can’t be ruled out but will favor Eastern Trinidad and Tobago.

Saharan dust is present in mild concentrations across Trinidad and Tobago and is forecast to remain in place over the next two weeks. Concentrations are forecast to continue increasing this weekend.

Generally moderate to strong breeze is forecast (20-49 KM/H) for Friday mainly from the east. However, wind gusts in the range of strong breeze to high wind are possible (up to 61 KM/H) across Trinidad and Tobago in the vicinity of showers.

Beauford Wind Scale Land Impacts
Beauford Wind Scale Land Impacts

With wind gusts up to 60 KM/H, whole trees can 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, loose galvanize or construction material and other outdoor furniture. Tents may jump. Winds are forecast to lessen as the weekend progresses.

So is it a tropical wave?

Lots of social media posts are calling this surface trough a Tropical Wave. In fact, even the Barbados Meteorological Service has designated this feature as a tropical wave. This is likely due to is origins near Africa.

However, the National Hurricane Center did not determine classical genesis from the African Easterly Jet and convection over North Africa, hence keeping this wave analyzed as a surface trough over the Central Atlantic. In addition, the classical atmospheric dynamics preceding and proceeding the wave axis are not typical of a tropical wave.

Something that will be clearly noticeable today across Trinidad and Tobago is the effects of this surface trough and somewhat favorable atmospheric dynamics are the lack of widespread showers and generally scattered thunderstorms, which is typically associated with a tropical wave.

This whole designation issue may come across to the layman as pedantic, as the impacts of locally heavy rainfall, thunderstorms, and gusty winds are generally the same. However, the designation is significant to Trinidad and Tobago because the passage of the first Tropical Wave (or the first time the ITCZ modulates across T&T) signals the start of the wet season for the islands. Following the passage of the first true tropical wave, as designated by either the National Hurricane Center or by the discretion of the Trinidad and Tobago Meteorological Service, the wet season is declared.

This surface trough is not the start of the wet season, but we are entering the transition period from the dry season to the wet season. Hence, showers are likely to be on the uptick.

Weekend Forecast

The big weather stories this weekend will be the continuing increase of Saharan Dust and gusty winds.

On Saturday, generally a sunny and hazy day is forecast across Trinidad and Tobago. A few isolated showers are possible across mainly Trinidad, likely by late morning through the afternoon. Settled conditions are forecast overnight. Saharan dust concentrations are forecast to be increasing on Saturday, but air quality generally is forecast to remain at moderate levels.

On Sunday, the trade wind surge is forecast to arrive. A trade wind surge is an increase in the surface wind speed which comes from the general direction of the trade winds and is caused by any feature which causes a tightening in the pressure gradient. This could include the strengthening of a nearby high-pressure system or the passage of a low-pressure system. Gusty winds typically accompany this surge of winds at the surface.

This surge is forecast to increase wind convergence and result in increased convection and the development of showers and the possible thunderstorm across Trinidad on Sunday. In fact, Sunday has higher chances (still relatively low to medium) than Friday. These showers are forecast to begin after midnight Saturday into Sunday, and continue throughout Sunday, favoring Trinidad. Gusty winds up to and possibly in excess of 60 KM/H possible. These showers are forecast to interrupt partly cloudy to cloudy skies, becoming more settled by the late evening. Peak Saharan Dust concentrations are also forecast on Sunday into Monday.

Temperatures

Last night’s minimum temperatures were 25.8°C at Piarco, Trinidad, and 25.1°C at Crown Point, Tobago. Tonight’s minimum temperatures are forecast to be near 25°C at Piarco, Trinidad, and 25°C at Crown Point, Tobago.

Today’s maximum high temperatures across T&T is forecast to be near 32°C at Piarco, Trinidad and 31°C at Crown Point, Tobago. Similar temperatures are forecast through the next three days, with maximum high temperatures forecast to be near 33°C at Piarco, Trinidad, and 31°C at Crown Point, Tobago. Heat indices may top at 35-38°C at Piarco, Trinidad and 33-35°C at Crown Point, Tobago. The heat index is an index that combines air temperature and relative humidity, generating a “feel’s like” temperature.

Seas

Seas are forecast to remain slight to moderate in open waters through the week. Waves in open waters are forecast between 1.5 and 2.0 meters, particularly East of Trinidad and Tobago over the next 24 hours. In sheltered areas, seas are forecast to remain smooth, below 1.0 meters. Winds will be from the east through the next several days at 10-20 knots from the east.

Increasing Saharan Dust Concentrations This Weekend

Saharan Dust concentrations are mild across Trinidad and Tobago on Monday. Increasing concentrations are forecast through the weekend, degrading air quality.

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