ITCZ, Tropical Wave 29 Forecast to Affect T&T Over Next 36 Hours. Showers, Thunderstorms Likely, Street/Flash Flooding Possible

There is no alert, watch or warning in effect for Trinidad and Tobago at this time as the ITCZ, Tropical Wave 29 Affects the Islands.

What We Know

The axis of Tropical Wave 29 is east of Trinidad and Tobago. Showers and thunderstorms are approaching and occurring across T&T as the ITCZ and convergence ahead of the wave moves across the area. Most of the “active” weather is forecast across this afternoon into Sunday across Trinidad and Tobago. Street/Flash flooding possible.. Credit: Weathernerds.org

The axis of Tropical Wave 29 is still east of Trinidad and Tobago, along 55W. The approach of this wave has brought the ITCZ across Trinidad and Tobago with favorable upper-level divergence and low-level convergence.

High total precipitable moisture and low to moderate 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 weak CAP (a stable region in the atmosphere inhibiting shower and thunderstorm development).

What We Expect

Impacts

The Takeaway: Scattered showers and thunderstorms are forecast to move across mainly Southern and Central Trinidad on Saturday, gradually spreading across the northern half of Trinidad and Tobago by Saturday evening into Sunday.

There is an elevated threat of street flooding across Southern Trinidad due to heavy showers and thunderstorms moving across the same area for the last 3-4 hours.

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, across T&T and approaching the Southern Windwards. Tropical Wave 29 and the ITCZ are affecting T&T, forecast to bring showers and thunderstorms through Sunday. 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, across T&T and approaching the Southern Windwards. Tropical Wave 29 and the ITCZ are affecting T&T, forecast to bring showers and thunderstorms through Sunday. Street/Flash Flooding, Gusty Winds possible. The heaviest rainfall and thunderstorms likely across Eastern Trinidad.

Presently, winds are from the northeast at low-levels. This is keeping showers and thunderstorms mainly across Southern Trinidad. As the evening progresses, showers and thunderstorms are forecast to move across Central, Northern Trinidad and Tobago. Street/Flash Flooding and gusty winds possible.

Across parts of Trinidad, mainly across South, this activity may subside by the late evening. Across the remainder of Trinidad, showers and thunderstorms are forecast to continue into Sunday.

11:45 PM Saturday 29th July 2019 Radar Imagery from the Trinidad and Tobago Meteorological Service showing scattered showers and thunderstorms across South Trinidad with additional activity nearing Central Trinidad.

Based on the latest model guidance, showers, periods of rain and isolated thunderstorms are forecast to favor Eastern and Southern Trinidad on Saturday, gradually moving across Northern Trinidad and Tobago by the late afternoon into Sunday.

This activity is forecast to persist into Sunday, with slightly more scattered showers across both islands due to favorable atmospheric conditions.

Locally Heavy Rainfall & Flooding: Based on the latest model runs on Saturday morning, from Saturday (2:00 AM) through Monday (2:00 AM), 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 north of Trinidad and Tobago. However, it seems that models are underperforming with regards to rainfall outputs, hence the totals may be below

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. As of midnight, through 12:30 PM, over 2600 lightning strikes have occurred near Trinidad and Tobago, with 1775 being dangerous cloud to ground strikes. Note most of these strikes have occurred offshore T&T.

Lightning occurring across the Gulf of Paria and the East Coast of Trinidad as of 12:30 PM

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 this tropical wave (Tropical Wave 29), mostly scattered showers are forecast. Hence, we are likely to see intermittent showers and thunderstorms, interrupting partly cloudy to overcast skies between Saturday and Sunday.

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