TTMS Update: Adverse Weather Alert Now In Effect From 12 PM Wednesday Through 2 PM Thursday for both T&T

The Adverse Weather Alert

The Trinidad and Tobago Meteorological Service has updated the Adverse Weather Alert (Yellow Level) as Tropical Wave 35 moves away from Trinidad and Tobago, interacting with the ITCZ which is now across the islands. Occasional heavy showers and thunderstorms are likely, according to the TTMS to after 12:00 PM Wednesday 14th August 2019 through 2:00 PM Thursday 15th August 2019 across both Trinidad and Tobago.

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

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

Based on the latest model guidance, these showers, with isolated heavy showers and thunderstorms may produce severe weather across Trinidad and Tobago. 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 14th-15th, 2019.

Occasional heavy showers and thunderstorms are likely in varying localities from midday today over Trinidad and Tobago. This may lead to landslides/landslips mainly along hilly areas. Street and/or flash flooding and gusts up to 65km/h are likely near heavy downpours.” 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 35th tropical wave of the 2019 Atlantic Hurricane Season moved west of Trinidad and Tobago as of 9:00 AM Wednesday 14th August 2019.

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 24Hours

The Takeaway: Showers and thunderstorms are likely to continue across (mainly) Trinidad, but also Tobago through the evening. A brief settled period is forecast after nightfall, with showers and thunderstorms again forecast to develop after midnight.

Locally heavy rainfall associated with showers and thunderstorms, gusty winds up to 65 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.

As expected, isolated showers interrupted mostly settled skies through the early morning, with showers and thunderstorms occurring the region by the late morning.

An 11th-hour update, the Trinidad and Tobago Meteorological Service updated the Adverse Weather Alert to include Tobago, as showers began to affect the island, at 10:00 AM.

Surprisingly, the start time of the alert also changed from 10:00 AM to 12:00 PM, though heavy showers and thunderstorms began to affect Eastern Trinidad at the initial start time of the Adverse Weather Alert #1. We did mention the possibility of gusty winds and heavy rainfall in our prior Adverse Weather Alert update.

Tropical Wave 35 is along 64W. This wave has brought the ITCZ across the region, with favorable atmospheric dynamics, triggering locally heavy rainfall with street/flash flooding and inclement weather T&T possible later today, Wednesday, into Thursday. Credit: Weathernerds.org

Presently, Tropical Wave 35 is located along 64W, moving westward at 15 knots. The axis of this wave moved across the region between 8:00 AM and 9:00 AM this morning.

As forecast, this wave as dragged the ITCZ across T&T yet again, through the end of the week. Combined with favorable upper-level conditions and increased low-level moisture, periods of showers and thunderstorms are likely to continue through the evening.

Lastly, though mostly easterly winds between 20-25 knots (35-45 KM/H) are forecast, light southeasterly winds are forecast across Trinidad during the latter half of Wednesday across Trinidad. Since winds are forecast to move across Trinidad (and Tobago) from the south to southeast, winds across the Northern Range are forced upwards, creating orographic lift. This phenomenon, simply put, aid in the development of showers, or enhance showers and thunderstorms.

With all these features coming together, showers and thunderstorms are forecast to persist across mainly Trinidad throughout the next 24-48 hours, which may dump copious amounts of rainfall.

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

Locally Heavy Rainfall & Flooding: Based on the latest model runs on Wednesday morning, from Wednesday morning (2:00 AM) through Friday morning (2:00 PM), generally, over the 48 hour period, models are in agreement of fewer than 30 millimeters across of Trinidad and Tobago and between 30-50 millimeters across isolated areas of Trinidad and up to 75 millimeters across Eastern and Southern Trinidad.

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 associated with the ITCZ as it moves across the area.

The GFS Accumulated Total Precipitation between 2:00 AM Wednesday through 2:00 AM Friday
The GFS Accumulated Total Precipitation between 2:00 AM Wednesday through 2:00 AM Friday

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

Gusty Winds: Gusty winds, generally between 40 and 65 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 65 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.

With this tropical wave (Tropical Wave 35), 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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