Tropical Wave 29 is Over T&T Along With ITCZ. Showers, Thunderstorms Possible Through This Evening.

An Adverse Weather Alert from the Trinidad and Tobago Meteorological Service is in effect for T&T until 6:00 PM as the ITCZ, Tropical Wave 29 Affect the Islands.

What Has Happened Over The Last 12 Hours

The axis of Tropical Wave 29 is across Trinidad and Tobago at this time. Showers and thunderstorms are approaching and occurring across T&T due to activity in conjunction with the ITCZ. Street/Flash flooding possible. Credit: Weathernerds.org
The axis of Tropical Wave 29 is across Trinidad and Tobago at this time. Showers and thunderstorms are approaching and occurring across T&T due to activity in conjunction with the ITCZ. Street/Flash flooding possible. Credit: Weathernerds.org

The axis of Tropical Wave 29 is moving across T&T overnight into this morning. However, as the heavy showers and thunderstorms across the Southern Windwards subsided, widespread low-level divergence occurred. Low-level divergence is spreading and sinking of air at low levels of at atmosphere. This is unfavorable for any shower or thunderstorm development as low-level convergence, the air coming together at low-levels and moving upwards, is required.

Hence, we had a mostly settled but humid night into this morning. Showers and thunderstorms have begun again to move across parts of Eastern and Southern Trinidad today.

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).

In addition, winds are now from the south across Trinidad. Hence, showers and thunderstorms will be enhanced by the Southern Range, Central Range, and Northern Range due to a feature called orographic lifting. Orographic lifting occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it quickly cools down adiabatically, which can raise the relative humidity to 100% and create clouds and, under the right conditions, precipitation.

What We Expect

Impacts

The Takeaway: Scattered showers and thunderstorms are forecast to move across mainly Trinidad on Sunday, with locally heavy rainfall amounts

There is an elevated threat of street flooding across Trinidad due to the slow movement of showers and thunderstorms today.

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

   GOES-East GEOCOLOR (CIRA), IR-13 & Lightning Energy Density Satellite Imagery showing scattered convection (showers and thunderstorms) the Lesser Antilles with thunderstorms occurring and approaching Trinidad and Tobago. 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 interior Central Trinidad.
GOES-East GEOCOLOR (CIRA), IR-13 & Lightning Energy Density Satellite Imagery showing scattered convection (showers and thunderstorms) the Lesser Antilles with thunderstorms occurring and approaching Trinidad and Tobago. 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 interior Central Trinidad.

Presently, winds are from the south to southeast and are fairly weak. This will result in slow-moving showers and thunderstorms expected later today across mainly Trinidad with some showers and possible thunderstorms across Tobago. Street/Flash Flooding and gusty winds possible.

Between 8:00 AM and 10:00 AM, showers and thunderstorms have benefitted from the weak wind shear, but dry mid-levels have inhibited persisting deep convection (heavy showers and thunderstorms) as activity moves across T&T.

10:00 AM Sunday 28th July 2019 Radar Imagery from the Trinidad and Tobago Meteorological Service showing scattered showers and thunderstorms across Trinidad with additional activity east of Trinidad and south of Tobago, generally moving northward. Tropical Wave 29 is moving across the area.
10:00 AM Sunday 28th July 2019 Radar Imagery from the Trinidad and Tobago Meteorological Service showing scattered showers and thunderstorms across Trinidad with additional activity east of Trinidad and south of Tobago, generally moving northward. Tropical Wave 29 is moving across the area.

Based on the latest model guidance, heavier showers and thunderstorms are forecast to favor interior Central Trinidad, particularly after midday through the late afternoon. Note that showers and thunderstorms are possible elsewhere, some of which may become heavy and produce street/flash flooding.

This activity is forecast to subside by the late evening, and a similar pattern is forecast on Monday.

Initially settled conditions will give way to cloudy to overcast skies by the late morning, with afternoon showers and thunderstorms favoring interior central Trinidad, but possible elsewhere.

Locally Heavy Rainfall & Flooding: Based on the latest model runs on Sunday morning, from Sunday (2:00 AM) through Tuesday (2:00 AM), generally, over the 48 hour period, models are in agreement of fewer than 15 millimeters across Southern half of Trinidad and the Northern half Tobago and between 15-30 millimeters across the Northern half of Trinidad and the Southern half of Tobago. Isolated rainfall totals up to 50 millimeters are possible across interior Central Trinidad due to slow-moving showers and thunderstorms later today and on Monday.

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 10:30 AM, over 1600 lightning strikes have occurred near Trinidad and Tobago, with 1178 being dangerous cloud to ground strikes. Note most of these strikes have occurred offshore T&T, north of the area.

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 Sunday.

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