Forecast: Increased Cloudiness, Brisk Rainfall & Gusty Winds Possible Into Next Week

The interaction of multiple trough systems, an upper-level jet, and deep, tropical moisture is forecast to bring brisk periods of rainfall to Trinidad and Tobago through the next four to five days. Enhancing rainfall will be favorable mid and upper-level conditions, creating conditions for potentially heavy rainfall across the country. Strong wind shear is forecast to keep the heaviest rains east and south, mainly affecting eastern and southern halves of Trinidad initially.

Here is what you need to know:

— Through Tuesday, a multi-layered trough is forecast to affect the region in the presence of a highly favorable upper-level environment, producing variably cloudy skies, scattered showers, and isolated thunderstorms. However, overall heavier rainfall is forecast to remain south and east of T&T due to persisting strong westerly wind shear.
— The main hazards through Thursday will mainly be gusty winds and brief, heavy rainfall. Through the next five days, sustained winds up to 30 KM/H and wind gusts in excess of 45 KM/H are likely, with gusts in excess of 50 KM/H are possible. Winds of this strength can cause power dips and outages, fallen trees, utility poles, and lines, as well as sporadic areas of wind damage.
— In addition, street and flash flooding is possible, but the overall threat will be lower than usual due to brisk-moving rainfall. Riverine flooding is not expected.
Lightning will accompany thunderstorms. Funnel clouds and waterspouts are unlikely through the forecast period due to elevated low-level winds. Landslides are possible across elevated areas.
— An Adverse Weather Alert (Yellow Level) is in effect for Trinidad from 3:30 AM to 4:00 PM Sunday from the Trinidad and Tobago Meteorological Service.

The Forecast

Moisture associated with a trough system east of T&T. (SSEC/CIMSS/UW-Madison)
Moisture associated with a trough system east of T&T. (SSEC/CIMSS/UW-Madison)

Heavier showers, thunderstorms, and overall higher rainfall accumulations are forecast to remain south and east of the county through the forecast period. Gusty winds are likely to accompany heavy showers or thunderstorms.

Saturday: From midnight, scattered showers and thunderstorms are forecast to mainly affect eastern Trinidad and Tobago, weakening as activity moves west across the country through the morning and interrupting variably cloudy skies. Through the day, brisk showers and isolated thunderstorms are forecast to affect the country, mainly southern and eastern areas of Trinidad, interrupting partly cloudy and breezy conditions. Lingering showers are forecast to continue into the overnight hours.

Sunday: After midnight, showers and thunderstorms are forecast to return, initially favoring offshore coastal areas of northern and eastern Trinidad and Tobago. Throughout the day, variably cloudy and breezy conditions are forecast to be interrupted by brisk showers and the odd thunderstorm. Heavier rainfall will favor the afternoon hours across both islands, initially settling into the evening with cloudy skies. Isolated heavy showers and the odd thunderstorm may affect eastern areas of the country nearing midnight.

Monday: Scattered showers and thunderstorms are forecast from midnight through the day, generally favoring eastern halves of both islands until the late morning through the afternoon, where heavier rainfall and isolated thunderstorms move across western Trinidad. These intervals of rain will interrupt primarily cloudy to cloudy skies and breezy conditions. Rainfall is forecast to initially subside into the evening, with lingering showers mainly affecting eastern Trinidad and Tobago.

Tuesday: After early morning showers and isolated thunderstorms favoring eastern Trinidad and across Tobago, a partly cloudy day is forecast. By the late morning through the afternoon, isolated showers are forecast across the country, with heavier rainfall and the isolated thunderstorm or two favoring western Trinidad. A mostly settled evening is forecast, barring the odd brisk shower.

Wednesday: Partly cloudy and breezy conditions forecast through the day, interrupted by isolated showers and thunderstorms across mainly western and southern Trinidad by the late morning, becoming settled by the late afternoon. However, winds are forecast to increase by the afternoon into the night.

 Scattered showers and cloudiness east of the Lesser Antilles on Friday night. (Weathernerds.org)
Scattered showers and cloudiness east of the Lesser Antilles on Friday night. (Weathernerds.org)

Marine: Seas are forecast to return to remain elevated through the next five days. Seas in open waters are forecast between 1.5 and 2.5 meters. In sheltered areas, near 1.0 meters and occasionally choppy, higher along northern and eastern coastlines. By Wednesday into Thursday, seas are forecast to be near and above 2.5 meters and up to and above 3.0 meters by the end of the upcoming week.

Temperatures

Through the forecast period, the minimum low in Trinidad and Tobago is forecast to be between 22.0°C and 25.0°C.

Maximum highs across the country are forecast to be generally up to 31.0°C in Trinidad and Tobago. However, with increased cloud cover, maximum highs are forecast to be relatively cooler.

In urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas, the maximum high temperatures could exceed 33.0°C on days with sunny mornings.

Forecast Impacts

As mentioned earlier, the main hazards through Thursday will mainly be gusty winds and brief, heavy rainfall. Through the next five days, sustained winds up to 30 KM/H and wind gusts in excess of 45 KM/H are likely, with gusts in excess of 50 KM/H are possible. Winds of this strength can cause power dips and outages, fallen trees, utility poles, and lines, as well as sporadic areas of wind damage. Street and flash flooding is possible, but the overall threat will be lower than usual due to brisk-moving rainfall. Riverine flooding is not expected. Lightning will accompany thunderstorms. Funnel clouds and waterspouts are unlikely through the forecast period due to elevated low-level winds. Landslides are possible across elevated areas.

Rainfall & Flooding

Forecast chances of heavy to violent showers and thunderstorms associated with a trough system over the next five days.

Through the forecast period, wind shear is forecast to remain unfavorable for persisting heavy rainfall. Still, favorable upper-level conditions are forecast to produce pockets of deep convection that may produce heavy to violent rainfall rates and thunderstorm activity through Thursday.

Over the next five days across Trinidad, isolated totals up to 150 millimeters are forecast across southern and eastern areas of the island, with generally 30-75 millimeters across the country. Higher rainfall accumulations are forecast mainly across southern and eastern regions of Trinidad and offshore eastern Trinidad, and isolated high totals are also possible along the western coastal areas of Trinidad.

  • Saturday: Between 5 to 15 millimeters of rainfall across the country, with isolated areas up to and in excess of 35 millimeters favoring the eastern halves of both islands, as well as southern Trinidad.
  • Sunday: Between 5 to 15 millimeters of rainfall across the country, with isolated areas up to and in excess of 30 millimeters favoring the eastern halves of both islands, as well as southern Trinidad.
  • Monday: Up to 15 millimeters of rain across the country, with high accumulations up to 25 millimeters favoring eastern and southern areas of both islands.
  • Tuesday: Up to 15 millimeters of rain across the country, with high accumulations up to 25 millimeters favoring eastern and southern areas of both islands.
  • Wednesday: Up to 10 millimeters of rain across the country, with high accumulations up to 25 millimeters favoring eastern and southern areas of both islands.

Putting the rainfall forecast into context, rainfall rates in excess of 50 millimeters per hour or areas that receive in excess of 25 millimeters within an hour tend to trigger street flooding across the country or flash flooding in northern Trinidad. For riverine flooding to occur, a large area of the country (not just in highly localized areas of western coastal Trinidad) would have to record upwards of 75 millimeters within 24 hours, and rainfall would have to fall across major rivers’ catchment areas.

Forecast chances of street or flash flooding resulting from heavy rainfall associated with a trough system over the next five days.
Forecast chances of street or flash flooding resulting from heavy rainfall associated with a trough system over the next five days.

Street flooding or flash flooding is forecast over the next five days, with the highest chances expected on Sunday and into Monday, lowering as we progress through the week. Chances for riverine flooding remain very low through the forecast period.

Forecast chances of riverine flooding resulting from heavy rainfall associated with a trough system over the next five days.

Gusty Winds

Forecast chances for gusty winds associated with a trough system over the next five days.
Forecast chances for gusty winds associated with a trough system over the next five days.

Low-level winds are on the decline over the next 48 hours. Through Sunday, peak sustained surface winds are forecast to be between 25 to 35 KM/H. In heavy to violent shower and thunderstorm activity, gusts up to and in excess of 45 KM/H are likely, with higher gusts possible.

Through the first half of the upcoming week, the chances for gusty winds will gradually decrease as winds at low levels of the atmosphere decrease. By Wednesday, another high-pressure system is forecast to strengthen, with a strong pressure gradient allowing for breezy to windy conditions through the second half of the upcoming week.

With wind gusts up to and 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.

Other Adverse Weather Impacts

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. Dangerous, frequent lightning is expected on Friday and Saturday.

Landslides: Landslides and fallen trees are possible, particularly along the Northern Range, Southern Trinidad, and Tobago.

Severe Thunderstorms: The potential for severe thunderstorms, funnel clouds, and waterspouts remain low to very low. If funnel clouds touchdown or waterspouts encounter land, weak tornadoes can form.

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.

Scattered rainfall is forecast through the next five days, and rainfall activity will be brisk.

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

Forecast Discussion

Annotated satellite update as of 6:30 PM Friday 10th December 2021 (NASA/CIRA/RAMMB)
Annotated satellite update as of 6:30 PM Friday 10th December 2021 (NASA/CIRA/RAMMB)

Tropical Waves: There are no tropical waves in the Atlantic Basin.

As of Friday night, a high-pressure system anchored in the Atlantic Ocean remained the dominant weather feature across the Lesser Antilles, with breezy conditions as winds move in from the northeast. A few low-level cloud patches embedded within this northeasterly flow will trigger brisk showers across the region.

However, deep, tropical moisture is moving across Trinidad and Tobago while approaching the Southern Windward Islands on Friday night, associated with a large area of confluencing (winds slowing down, piling up) east of the Lesser Antilles and a surface to low-level trough. An upper-level jet north of T&T is also producing large-scale upper-level divergence (rising air) east of the Lesser Antilles that will move across the region this weekend.

What is an Upper-Level Jet?
A “jet” in meteorology is a fast-flowing, narrow, meandering current of air that is moving at a high velocity in the atmosphere. These features can be at varying levels of the atmosphere. Typically, they are referred to as low-level jets, mid-level jets, or upper-level jets.

From Saturday through Tuesday, the slow-moring surface to low-level trough and the upper-level jet are forecast to remain generally in the same place north of and across T&T, respectively. With abundant moisture and favorable mid to upper-level conditions, variably cloudy skies with brief showers and thunderstorms are forecast and will persist.

While showers and thunderstorms will move across T&T, as activity moves west, convection may weaken, with cloudiness associated with showers and thunderstorms that develop across western Trinidad or Tobago moving eastward. However, strong wind shear from the west is forecast to remain across Trinidad and Tobago. This wind shear will also keep heavier rainfall south and east of the country.

Through the forecast period, a slight increase in Saharan Dust concentrations is forecast, mainly from Sunday through Tuesday, having a marginal impact on air quality, visibility, and the weather. By Wednesday, another high-pressure system is forecast to strengthen, with a strong pressure gradient allowing for breezy to windy conditions through the second half of the upcoming week.

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