TTMS: Adverse Weather Alert In Effect From 4:00 AM Saturday.

The Adverse Weather Alert

The Trinidad and Tobago Meteorological Service has issued the Adverse Weather Alert (Yellow Level) as the ITCZ and Tropical Wave 36 nears Trinidad and Tobago. The alert goes into effect from 4:00 AM Saturday 17th August 2019 through 12:00 PM Saturday 17th August 2019.

Although the alert goes into effect at 4:00 AM tomorrow by the Trinidad and Tobago Meteorological Service, according to our analysis, showers and isolated thunderstorms are likely to begin after nightfall tonight across Eastern and Southern Trinidad

Note that due to favorable atmospheric conditions, locally severe thunderstorms are possible, producing heavy rainfall and gusty winds, mainly across the southern half of Trinidad.

Trinidad and Tobago is NOT under any tropical storm threat, watch or warning.

Based on the latest model guidance and analysis, these showers, with isolated heavy showers and thunderstorms, may produce severe weather across Trinidad. This activity is forecast to begin after nightfall tonight and continue into Sunday, though the Adverse Weather Alert ends at midday Saturday.

Regardless, street floodingflash flooding. Gusty winds are likely in the vicinity and during heavy showers or thunderstorms. These gusty winds and heavy rainfall will be capable of triggering landslides in landslide-prone areas, as well as downing trees and utility poles. See below for more details on what impacts to expect.

Information from the Trinidad and Tobago Meteorological Service concerning the Adverse Weather Alert for August 17th, 2019.

Periods of heavy showers and thunderstorms are likely. Street or flash flooding and landslips may occur in areas that are susceptible and it is also likely for winds to gust in excess of 55km/hr.” according to the Trinidad and Tobago Meteorological Service. This “alert” status takes into account the possibility of the event occurring. This adverse weather event is likely.

The color of the watch indicates the severity of the event and the probability of the event occurring. Currently, the alert level is at Yellow. This means that the hazard is possible to be aware of the impacts of Street/Flash Flooding and Gusty Winds in your area. Areas prone to landslides should also be aware of the hazard and impacts.

Image Credit: Trinidad and Tobago Meteorological Service

The 36th tropical wave of the 2019 Atlantic Hurricane Season is approaching Trinidad and Tobago, forecast to move across the area Saturday into Sunday. As of 4:00 PM, this wave is along 56W, moving westward at 10 knots.

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.
Image Credit: Trinidad and Tobago Meteorological Service

What to Expect Over Next 48 Hours

The Takeaway: After nightfall, isolated to scattered showers are forecast to favor Eastern and Southern Trinidad. Increasing showers and isolated thunderstorms are forecast as the night progresses into Saturday.

On Saturday, periods of showers and thunderstorms are forecast to interrupt mostly cloudy skies across both islands, with heavier activity favoring Trinidad.

Showers and thunderstorms are forecast to persist into Sunday due to the ITCZ across the region.

Locally heavy rainfall associated with showers and thunderstorms, gusty winds up to 55 KM/H and landslides possible.

Generally, widespread severe weather is not likely. Localized to scattered severe weather reports are possible, with landslides across the Northern Range and street/flash flooding across Southern and Eastern Trinidad possible through Sunday.

The ITCZ and Tropical Wave 36 are approaching Trinidad and Tobago. Favorable atmospheric dynamics, triggering locally heavy rainfall with street/flash flooding, gusty winds and inclement weather across Trinidad and Tobago beginning tonight through Sunday. Credit: Weathernerds.org
The ITCZ and Tropical Wave 36 are approaching Trinidad and Tobago. Favorable atmospheric dynamics, triggering locally heavy rainfall with street/flash flooding, gusty winds and inclement weather across Trinidad and Tobago beginning tonight through Sunday. Credit: Weathernerds.org

The axis of Tropical Wave 36 is located a few hundred kilometers east of Trinidad and Tobago, dragging the ITCZ northward.

Favorable atmospheric dynamics will be present across Trinidad and Tobago through the weekend. Favorable upper-level and low-level conditions, increased low-level moisture and lowering wind shear will result in periods of showers and thunderstorms beginning tonight through Sunday, with partly cloudy to overcast periods.

Based on the latest model guidance, isolated showers and thunderstorms are forecast to move across both islands, with heavier activity favoring much of Eastern and Southern Trinidad through the weekend.

Locally Heavy Rainfall & Flooding: Based on the latest model runs on Friday evening, from Friday afternoon (2:00 PM) through Monday morning (2:00 AM), generally, over the 60 hour period, models are in agreement of fewer than 20 millimeters across of Trinidad and Tobago and between 15-30 millimeters across isolated areas of Trinidad and Tobago. Up to 50 millimeters are possible across Eastern and Southern Trinidad through 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.

Frequent Lightning: In addition, with thunderstorms, frequent lightning is likely.

Gusty Winds: Gusty winds, generally between 40 and 55 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 55 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.

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