A Freak Storm? Not So Freaky.

What happened on Thursday?

Princes Town Regional Corporation

This was the first area to be affected by gusty winds and heavy thunderstorms by 12:45 PM on Thursday.

Though there were no reports of roof damage, there were reports of power dips and brief outages across the Moruga area.

In addition, some downed trees occurred in rural areas of Moruga and Penal Rock, but no impacts to roadways or structures.

However, closer to Princes Town, in Cleghorn Village, a large tree fell destroying fencing that separates two properties.

Photos of the fallen tree in Cleghorn Village, Princes Town. Credit: Denyse Khan

Penal/Debe Regional Corporation

Without question, this was the hardest hit municipality. Over 21 reports of roof damage were reported across the region with investigations ongoing.

A roof has blown off another home at Bombay Avenue, Quinam Road. Photos: Shanty Boodram

In addition, there were several reports of downed trees and power lines across the region. A fallen tree rendered the San Francique Road impassable. This was cleared as of late Thursday evening by the Penal/Debe Regional Corporation.

Large tree down along the San Francique Main Road

Surprisingly, due to the fast forward motion of this thunderstorm, there were no reports of flooding across this municipality.

Siparia Regional Corporation

There were reports of roof damage across Fyzabad, downed trees across Forest Reserve and street flooding in isolated areas.

Point Fortin Borough Corporation

There were reports of roof damage across the region, with 5 homes and 25 persons affected.

Point Fortin Mayor Abdon Mason said there are also reports of downed electricity lines and fallen trees in Egypt Village, Warden Road and in the vicinity of Heritage Petrotrin Company Ltd (formerly Petrotrin), according to a Newsday report.

What Caused This Severe, Gusty Winds AKA the “Freak Storm?”

Sometimes across Trinidad and Tobago, we experience severe thunderstorms. These thunderstorms can produce copious amounts of rain, severe winds (like on Thursday), frequent thunder and lightning and in the most severe cases – tornadoes and hail.

At 12:30 PM Thursday 15th August 2019, a strong thunderstorm began affecting Southeastern Trinidad. This thunderstorm reached it’s “mature” stage with cloud tops in excess of 14 kilometers – indicative of a strong thunderstorm.

A concerning signature appeared on radar, typically called a “bow-echo” or a downburst.

At this time, an Adverse Weather Alert was in effect for both Trinidad and Tobago, warning specifically for “street and/or flash flooding and gusts up to 65km/h.”

TTWC put out an update, warning of gusty winds at 12:45 PM, seen below.

12:45 PM – A feature called a "bow-echo" has developed as a thunderstorm moves across Southern and Central Trinidad….

Posted by Trinidad and Tobago Weather Center on Thursday, August 15, 2019

What is a “bow echo?”

Conceptual model of bow echo evolution and favored locations for downbursts, tornadoes, and bookend vortices. (b) Conceptual diagram of bow echo features and an example cross-section showing the rear-inflow notch or weak echo notch which signifies the location of a descending rear inflow jet that leads to damaging straight-line surface winds. (c) Example of a bow-echo cross-section showing radar reflectivity and storm-relative flow including the rear inflow jet (from Grim et al. 2009).

A large thunderstorm can form into a Mesoscale Convective System, known as a bow echo, because of its characteristic bow shape on radar displays. These systems typically have life cycles as above.

On radar, a bow-echo looks like a comma, with a round head on one end and a tail on the other. Because in Trinidad, our weather moves from the east to west (generally), this signature looks like a vertically and horizontally flipped comma.

The leading edge has a sharp reflectivity gradient (oranges, reds and black on the below radar image), and there are notches (of dry air) dug into the weak reflectivity gradient on the trailing edge.

These rapid moving storms can produce hail, lightning, large amounts of rain, high winds, and even tornadoes.

Across Trinidad, these strong straight-line winds are typically attributed to a “freak storm,” when in actuality, it is just a thunderstorm.

Thunderstorms and T&T

Trinidad and Tobago has heavy showers and thunderstorms. It’s part of living in a tropical area. These heavy downpours overwhelm what drainage exists from time to time and produce street flooding. In severe cases, very gusty winds occur.

Today’s heavy showers and winds are usually categorized has “freak” storms, but really, there’s nothing freak about them.

These “freak” storms are really thunderstorms. In addition to the winds and rain, they produce thunder and lightning. They are fairly common to Trinidad, Tobago and the vast majority of the world. In fact, there is, on average, 2000 of these storms occurring simultaneously at any given time around the globe.

In Trinidad, these thunderstorms generally occur during the late morning through the afternoon, particularly during the wet season. Any area in Trinidad can experience, on average, 30 to 40 thunderstorms annually. On rare occasions, as many as two to three a day in a given area.

When particular weather features traverse the region – tropical waves, tropical cyclones, surface troughs, mid- and upper-level troughs, and the Inter-Tropical Convergence Zone, thunderstorms can be abundant.

Thunderstorms bring most of our rainfall and nearly all of our street/flash flooding events. Torrential downpours, such as the one today, can produce upwards of 20-30 millimeters of rainfall within an hour.

In addition, these thunderstorms can produce severe winds up to and in excess of 65 KM/H across localized areas of the country.

Stationary thunderstorms, such as those that caused the Divali 2017 floods, can produce upwards of 100 millimeters in one to two hours. Thunderstorms can last from 30 minutes to as long as two hours, depending on the speed of low to mid-level winds. More prolonged thunderstorms begin to trigger different types of flooding – street, then flash and lastly riverine flooding.

As we progress further into the wet season and the 2019 Atlantic Hurricane Season, tropical waves become stronger, the ITCZ may linger across the region even more frequently and for possible prolonged periods and most importantly showers resulting from daytime heating and sea breeze convergence will become more common. Severe thunderstorms may also occur from time to time, causing severe winds as well.

You will begin to see “street/flash flooding, gusty winds possible in heavy showers/thunderstorms” far more frequently, because activity like on Thursday, is not uncommon for the wet season.

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