ITCZ, Hind Leg of Tropical Wave 22 Affects T&T. Showers, Isolated Thunderstorms Likely by Midday.

There is no alert, watch or warning in effect for Trinidad and Tobago at this time as the ITCZ, Tropical Wave 22 Affects the Islands.

What We Know

 The axis of Tropical Wave 22 is now west of Trinidad and Tobago. Showers and thunderstorms are approaching T&T as the ITCZ moves across the area. Most of the "active" weather is forecast across this afternoon across Trinidad and Tobago, with isolated showers across T&T on Thursday. Credit: Weathernerds.org
The axis of Tropical Wave 22 is now west of Trinidad and Tobago. Showers and thunderstorms are approaching T&T as the ITCZ moves across the area. Most of the “active” weather is forecast across this afternoon across Trinidad and Tobago, with isolated showers across T&T on Thursday. Credit: Weathernerds.org

The axis of Tropical Wave 22 is now west of Trinidad and Tobago, along 63-64W. It has brought the ITCZ across Trinidad and Tobago with favorable upper-level divergence and low-level convergence.

This tropical wave developed through non-traditional means, via a mid-latitude trough.

High total precipitable moisture and low wind shear are present. As of the 8:00 AM atmospheric sounding from Piarco International Airport, which takes a look at characteristics of the atmosphere, there is marginal instability with a weak to moderate CAP (a stable region in the atmosphere inhibiting shower and thunderstorm development). However, daytime heating and low-level convergence as the day progresses are forecast to create a more favorable atmosphere for thunderstorm development.

Tropical Wave 23, on the heels of TW22, axis is along 49W from 22N southward, moving west at 10-15 knots. Scattered showers prevail along the wave axis.

What We Expect

Impacts

The Takeaway: While showers and thunderstorms have generally remained offshore Trinidad and Tobago through the last few hours, by midday, locally heavy showers and isolated thunderstorms are forecast to move across T&T based on radar trends.

Models indicate that a mostly settled night is ahead with a few isolated showers. On Thursday, during the late morning through the afternoon, isolated showers and a low to medium chance of thunderstorms are possible.

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

GOES-East IR-13 Satellite Imagery showing scattered convection (showers and thunderstorms) across coastal waters of Trinidad and Tobago. Tropical Wave 22 and the ITCZ are affecting T&T, forecast to bring showers and isolated thunderstorms mainly this afternoon. Street/Flash Flooding, Gusty Winds possible. The heaviest rainfall and thunderstorms likely across Eastern Trinidad.
GOES-East IR-13 Satellite Imagery showing scattered convection (showers and thunderstorms) across coastal waters of Trinidad and Tobago. Tropical Wave 22 and the ITCZ are affecting T&T, forecast to bring showers and isolated thunderstorms mainly this afternoon. Street/Flash Flooding, Gusty Winds possible. The heaviest rainfall and thunderstorms likely across Eastern Trinidad.

By midday, showers and thunderstorms are forecast to move across Trinidad from the southeast moving west-northwest. Street/Flash Flooding and gusty winds possible.

This activity is forecast to subside by late evening, with a few lingering showers interrupting a partly cloudy evening.

Wednesday 17th July 2019 Radar Imagery from the Trinidad and Tobago Meteorological Service showing scattered showers and isolated thunderstorms southeast of Trinidad approaching the islands.
Wednesday 17th July 2019 Radar Imagery from the Trinidad and Tobago Meteorological Service showing scattered showers and isolated thunderstorms southeast of Trinidad approaching the islands.

Based on the latest model guidance, intermittent showers and isolated thunderstorms are forecast to favor Eastern and Southern Trinidad on Wednesday, gradually moving across Northern Trinidad and Tobago by the late afternoon.

Mostly drier conditions are forecast across much of Trinidad on Thursday, while across Tobago, an increase in showers is forecast with the low-medium chance of a thunderstorm.

Locally Heavy Rainfall & Flooding: Based on the latest model runs on Wednesday morning, from Wednesday (2:00 PM) through Friday (2:00 PM), generally, over the 48 hour period, models are in agreement of fewer than 15 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 50 millimeters are possible across Eastern coastal Trinidad and Tobago. Much of the heaviest showers and thunderstorms are forecast to occur just offshore Eastern Trinidad and south of Tobago.

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.

Frequent Lightning: In addition, with thunderstorms, frequent lightning is likely. Thunderstorms are likely to begin on Wednesday through Thursday.

Lightning detected southeast of Trinidad and Tobago as thunderstorms approach the islands.
Lightning detected southeast of Trinidad and Tobago as thunderstorms approach the islands.

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: Though there is a low chance of 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 these tropical waves (Tropical Wave 22 and Tropical Wave 23), mostly scattered showers are forecast. Hence, we are likely to see intermittent showers and thunderstorms, interrupting partly cloudy to overcast skies between Wednesday and Thursday.

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