ITCZ Begins to Affect T&T Today, To Continue For Next Several Days. Showers, Thunderstorms Forecast.

There is no alert, watch or warning in effect for Trinidad and Tobago from the Trinidad and Tobago Meteorological Service at this time as the ITCZ affects the islands, with Tropical Wave 32 nearing the Lesser Antilles.

What We Know

The axis of Tropical Wave 32 is east of Trinidad and Tobago, along 48/49W. Showers and thunderstorms are approaching and occurring across T&T as the ITCZ and convergence ahead of the wave moves across the area. Street/Flash flooding, gusty winds possible. Credit: Weathernerds.org
The axis of Tropical Wave 32 is east of Trinidad and Tobago, along 48/49W. Showers and thunderstorms are approaching and occurring across T&T as the ITCZ and convergence ahead of the wave moves across the area. Street/Flash flooding, gusty winds possible. Credit: Weathernerds.org

The axis of Tropical Wave 32, along with Invest 96L, is still east of Trinidad and Tobago, along 48/449W. The approach of this wave has brought the ITCZ across Trinidad and Tobago with highly favorable upper-level divergence and favorable low-level convergence.

High total precipitable moisture and minimal wind shear are present. An update will be posted in the next hour or so concerning the severe weather potential as we receive the data from the 8:00 AM atmospheric sounding. This sounding takes a vertical profile of the atmosphere, giving us a better understanding of moisture and parameters that may trigger severe weather.

What We Expect (For T&T)

Impacts

The Takeaway: Scattered showers and thunderstorms are forecast to move across Trinidad and Tobago on Saturday, with heavier activity forecast across the eastern and northern halves of Trinidad, as well as Tobago.

While activity is forecast to subside by the late evening, with lingering showers, additional showers and thunderstorms are forecsat to develop again after midnight tonight into tomorrow, with a similar pattern in place over the next several days.

Generally, widespread or scattered severe weather is not likely. Localized severe weather reports are possible, with locally heavy rainfall.

GOES-East IR-13 Satellite Imagery showing scattered convection (showers and thunderstorms) Trinidad and Tobago with additional showers and thunderstorms south and east of Trinidad. Tropical Wave 32/Invest 96L and the ITCZ are affecting T&T, forecast to bring showers and thunderstorms through next Tuesday into Wednesday. Street/Flash Flooding, Gusty Winds possible. The heaviest rainfall accumulations and thunderstorms likely across the eastern half Trinidad. and Tobago.
GOES-East IR-13 Satellite Imagery showing scattered convection (showers and thunderstorms) Trinidad and Tobago with additional showers and thunderstorms south and east of Trinidad. Tropical Wave 32/Invest 96L and the ITCZ are affecting T&T, forecast to bring showers and thunderstorms through next Tuesday into Wednesday. Street/Flash Flooding, Gusty Winds possible. The heaviest rainfall accumulations and thunderstorms likely across the eastern half Trinidad. and Tobago.

Presently, winds are from the east to east-southeast at low-levels. This overall wind regime is forecast to remain in place over the next 24-36 hours, before markedly shifting on Sunday into Monday. Winds by the end of the week are forecast to become much lighter, mainly from the southeast to south and Invest 96L moves north of T&T. This overall wind regime dictates the forward speed (or lack thereof) of shower and thunderstorm activity and allows for heavy shower and thunderstorm development.

Street/Flash Flooding and gusty winds possible over the next several days as periods of showers and thunderstorms persist across Trinidad, Tobago, and the Southern Windwards.

Across parts of Trinidad and Tobago, mainly across South Trinidad, this activity may subside by the late evening. After midnight tonight, periods of showers and thunderstorms are forecast yet again, following the same pattern as today.

Note that periods of showers and thunderstorms are forecast to interrupt mostly cloudy to partly cloudy skies over the next 24 hours, but as well through Wednesday of the upcoming week.

7:30 AM Saturday 3rd August 2019 Radar Imagery from the Trinidad and Tobago Meteorological Service showing scattered showers and thunderstorms across Trinidad
7:30 AM Saturday 3rd August 2019 Radar Imagery from the Trinidad and Tobago Meteorological Service showing scattered showers and thunderstorms across Trinidad

Based on the latest model guidance, scattered showers, periods of rain and isolated thunderstorms are forecast to move across both islands, with heavier activity favoring much of Trinidad.

Locally Heavy Rainfall & Flooding: Next 24 hours – Based on the latest model runs on Saturday morning, from Saturday (2:00 AM) through Sunday (2:00 AM), generally, over the 24 hour period, models are in agreement of fewer than 20 millimeters across Western halves of Trinidad and Tobago and between 15-30 millimeters across the Eastern halves of both islands. Isolated rainfall totals up to 40 millimeters are possible across Eastern Trinidad and Southwestern Tobago.

Over the next 5 days – Based on the latest model runs on Saturday morning, from Saturday (2:00 AM) through Thursday (2:00 AM), generally, over the 5 day period, models are in agreement of up to 50 millimeters across both islands and between 50-100 millimeters across the Eastern halves of both islands. Isolated rainfall totals up to 125 millimeters are possible across both islands.

Generally, with heavy showers and thunderstorm activity, street flooding, particularly in flood-prone areas or areas with poor drainage, is possible as well as flash flooding in areas where more prolonged heavy rainfall may occur, based on the above-mentioned forecast rainfall totals associated with the ITCZ and Tropical Wave 32.

Frequent Lightning: In addition, with thunderstorms, frequent lightning is likely. As of midnight, through 12:30 PM, over 3400 lightning strikes have occurred near Trinidad and Tobago, with 1435 being dangerous cloud to ground strikes. Note most of these strikes have occurred offshore T&T.

Gusty Winds: Gusty winds, generally between 40 and 50 KM/H are possible Gusty winds are most likely prior to, in the vicinity of, or occur during heavy showers or thunderstorms. With wind gusts up to 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.

High Wind Event Precautions
High Wind Event Precautions

Landslides: Heavy showers across the Northern Range may trigger landslides in landslide-prone areas. Particularly in areas that receive heavy rainfall, landslides and/or mudflows may occur across both islands. These landslides, in addition to gusty winds, may down trees, utility poles and impede traffic on roadways.

Why I May Not/Will Not See Constant Rainfall?

Tropical waves typically have fair weather ahead of the wave axis, though other features in the area such as surface troughs, increased atmospheric moisture, and local climatic effects, to name a few, may trigger showers and the odd thunderstorm. Following the passage of the wave, much of the active weather typically associated with a tropical wave occurs.
Tropical waves typically have fair weather ahead of the wave axis, though other features in the area such as surface troughs, increased atmospheric moisture, and local climatic effects, to name a few, may trigger showers and the odd thunderstorm. Following the passage of the wave, much of the active weather typically associated with a tropical wave occurs.

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.

Generally, because of winds associated with tropical waves, showers and thunderstorms tend to follow a west-northwest track, generally missing areas across Southwestern Trinidad and even Northwestern Trinidad – though activity due to local climatic effects such as daytime heating may trigger shower and thunderstorm development across these areas. See the below graphic for a simple explanation.

With this tropical wave (Tropical Wave 32) and the ITCZ, mostly scattered showers are forecast. Hence, we are likely to see intermittent showers and thunderstorms, interrupting partly cloudy to overcast skies between Saturday and Wednesday.

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