Another tropical wave has moved across Trinidad and Tobago, with the ITCZ set to bring rainfall to T&T today (Tuesday).
What you need to know
— Rainfall: Over the next five days, through Saturday night, overall rainfall accumulations across Trinidad are forecast to range between 25 and 50 millimeters, with isolated totals between 50 and 100 millimeters, favoring southern and eastern Trinidad. Across Tobago, between 25 and 75 millimeters of rainfall is forecast. Across both islands, in highly isolated areas where thunderstorms occur, locally higher totals are possible.
— Saharan Dust: For T&T, a moderate to high concentration surge of Saharan Dust is forecast to move in by early Thursday, with significantly higher concentrations north of the country, moving in across the Lesser Antilles. High dust levels are forecast across the region through Sunday, with mild to moderate dust levels expected on Monday.
— Hazards: Through the week, but particularly on Tuesday, heavy showers or thunderstorms may lead to locally heavy rainfall, isolated street or flash flooding, with gusty winds also possible. From Thursday through Sunday, degraded air quality is likely.
— Marine: Slight to moderate seas are forecast in Trinidad and Tobago’s open waters, while near-calm conditions are forecast in sheltered areas through Wednesday, with waves below one meter from Thursday. All marine interests are advised to exercise caution in the vicinity of heavy showers and thunderstorms. Spring Tides end on Sunday, July 13th.
Latest Alerts
Adverse Weather Alert Discontinued. Showers, Thunderstorms Still In The Forecast
Trinidad and Tobago is NOT under any tropical storm or hurricane threat, watch, or warning at this time.
The Forecast
Tuesday
TuesdayWednesday
WednesdayThursday
ThursdayFriday
FridaySaturday
SaturdayMarine Forecast
Seas Forecast: Tropical Waves Bring Anomalous Winds To T&T
Temperatures
Tuesday
Low: 24-26°C
High: 29-31°C
Feels Like: 32-38°C
Wednesday
Low: 25-27°C
High: 30-32°C
Feels Like: 35-40°C
Thursday
Low: 25-27°C
High: 31-34°C
Feels Like: 35-42°C
Friday
Low: 24-26°C
High: 31-34°C
Feels Like: 35-45°C
Saturday
Low: 24-26°C
High: 30-32°C
Feels Like: 32-38°C
Forecast Impacts
Flooding
Over the next five days, through Saturday night, overall rainfall accumulations across Trinidad are forecast to range between 25 and 50 millimeters, with isolated totals between 50 and 100 millimeters, favoring southern and eastern Trinidad. Across Tobago, between 25 and 75 millimeters of rainfall is forecast. Across both islands, in highly isolated areas where thunderstorms occur, locally higher totals are possible.
Street & Flash Flooding
Street & Flash FloodingRiverine Flooding
Riverine FloodingForecast Rainfall Totals
- Tuesday: Across the western half of Trinidad, between 5 and 15 millimeters with isolated higher totals. Across the eastern and southern halves of Trinidad and across Tobago, between 10 and 25 millimeters of rainfall, with isolated totals of 50 millimeters possible. Higher rainfall totals are likely to favor the eastern coastal areas of both islands.
- Wednesday: Isolated totals between 5 and 15 millimeters of rainfall across both islands, with higher totals favoring eastern and western coastal areas of Trinidad, as well as across Tobago.
- Thursday: Less than 5 millimeters across the country, with isolated totals between 5 and 15 millimeters favoring northern and western coastal Trinidad and eastern Tobago.
- Friday: Across the western half of Trinidad, between 5 and 15 millimeters with isolated higher totals. Across the eastern and southern halves of Trinidad, and across Tobago, between 10 and 25 millimeters of rainfall, with isolated higher totals.
- Saturday: Less than 5 millimeters across Tobago, with isolated totals between 5 and 15 millimeters favoring Trinidad. Higher totals are possible across southern and eastern Trinidad. [Low confidence]
Understanding Rainfall Accumulations
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.
Strong Thunderstorms
Strong ThunderstormsWhat is a strong or severe thunderstorm?
Given how rare these types of thunderstorms are in our region – we classify a severe or strong thunderstorm as one that produces any of the following:
- Damaging wind gusts exceeding 63 KM/H;
- Frequent lightning (more than 30 cloud-to-ground strikes within a 10-minute period);
- Hail (of any size);
- Rainfall of more than 50 millimeters or more within an hour or exceeding 75 millimeters or more within three hours;
- The sighting of a funnel cloud or touchdown of a waterspout/tornado associated with the thunderstorm.
Gusty Winds
Gusty WindsWith wind gusts exceeding 55 km/h, whole trees can be in motion, with larger trees and weaker branches falling. Light outdoor objects can topple or become airborne, such as garbage cans, loose galvanize, construction material, and outdoor furniture. Tents may also jump.
Other Hazards
High to significant concentrations of Saharan Dust are forecast from Thursday. Hot temperatures are also forecast this week, particularly on Thursday and Saturday, with heat indices reaching levels that warrant caution.
Saharan Dust Forecast
Short-lived Saharan Dust Surge Forecast on Thursday
Why I May Not/Will Not See Rainfall?
A frequent complaint is that 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 for isolated activity. Widespread showers mean that nearly all people and areas can expect rainfall.
Scattered rainfall is forecast from Thursday afternoon through Friday morning, with isolated rainfall during all other periods over the next five days.
Forecast Discussion
Tropical Waves (As of 2:00 AM July 8th)
— Tropical Wave 14: Located along 65W from 18N, moving west around 15 knots (28 km/h). The wave axis moved across T&T on Monday evening with little fanfare. While no significant convection (showers/thunderstorms) is associated with the wave, it has brought the ITCZ northward across T&T, which is forecast to affect the country on Tuesday. Scattered moderate convection is observed on Monday night east of T&T.
— Tropical Wave 15: Located along 48W from 18N southward, moving west at around 15 knots (28 km/h), forecast to move across T&T late Thursday into Friday. There is no significant convection associated with this wave, and the northern portion of the wave is enveloped in a substantial surge of Saharan Dust with a surge in trade winds. The southern area of the wave axis is embedded in the ITCZ.
— Tropical Wave 16: Located along 31W from 16N southward, moving west at around 10-15 knots (18-28 km/h). This wave is still one week away from moving across T&T and the Windwards. At present, drier air at the lower levels are infiltrating this wave, disrupting widely scattered moderate convection.
Tropical Wave 14 (as Tropical Wave 13 succumbed to unfavorable atmospheric conditions out in the Atlantic and dissipated on July 3rd) moved across T&T on Monday evening without any significant shower or thunderstorm activity. However, this wave modulated the Intertropical Convergence Zone northward and is forecast to affect Trinidad and Tobago on Tuesday.
Atmospheric conditions on Tuesday are favorable for the development of showers and thunderstorms, given light wind shear, a moist atmosphere, and high levels of atmospheric moisture (precipitable water >50 mm). At the mid-levels, abundant instability exists. There are no alerts, watches, or warnings in effect from the TTMS for Tuesday.
By Tuesday night, conditions become slightly drier at the mid-levels of the atmosphere, which is forecast to inhibit long-lived shower or thunderstorm activity. However, given that the lower half of the atmosphere remains moist, isolated, short-lived showers or thunderstorms are possible. As the ITCZ drifts southward, shower/thunderstorm activity will be possible mainly after midnight through the early morning, favoring eastern and southern areas.
On Wednesday, an Atlantic high-pressure system briefly regains dominance across the area, but lingering low-level and weak instability will lead to some isolated showers. Light winds may also result in sea breeze convergence and daytime heating, triggering showers and isolated thunderstorms along the western coast of Trinidad.
As a significant surge of Saharan Dust moves in on Wednesday night, it will lead to a much drier atmosphere compared to Tuesday. However, Tropical Wave 15 is forecast to move across the region on Thursday evening into Friday. This wave will be moving across the area amidst a dense plume of Saharan Dust. While this means for islands north of T&T, this will be a “dry” wave with no notable precipitation, for T&T, conditions will be slightly wetter.
This wave has stronger surface to mid-level winds across the northern portion of the wave, while still elevated, but slower winds are moving across the southern portion of the wave axis. When this wave moves across the region from Thursday evening, elevated winds are forecast to move across the Lesser Antilles, but a shearline, developed from the difference in wind speeds north of T&T and south of T&T, is forecast to produce showers and thunderstorms across (mainly) Tobago and Grenada, but to a lesser extent, Trinidad on Thursday night through Friday morning.
From this point, global forecast models diverge on what the weekend looks like. On one hand, a dense surge of Saharan Dust returns to Trinidad and Tobago (and at this point, it would have been affecting the remainder of the Lesser Antilles), leading to mostly hazy, breezy to windy, and dry conditions across T&T. On the other hand, for Trinidad specifically, an active ITCZ lingers across the island, characterized by a saturated atmosphere and favorable low-level and upper-level conditions, resulting in heavy rainfall throughout the island, particularly in the southern half of Trinidad.
At this point, it’s difficult to bet against the abundant Saharan Dust that will be across the region, which typically inhibits rainfall. We’re still four days away, so there’ll be increased confidence as we near the weekend.
The good news is that another week has passed without a riverine flood threat, but there is still a possibility of sporadic street and flash flooding, as well as wind gusts, accompanying the forecasted heavy showers and thunderstorms.
