Riverine Flood Alert Yellow Level Now In Effect

Key Messages:
— A Riverine Flood Alert Yellow Level is in effect from 12:00 PM Wednesday through 2:00 PM Thursday for “surrounding areas of smaller rivers and tributaries, particularly in southern Trinidad.
— Through Thursday, an additional 1 to 1.5 inches (25 to 37.5 millimeters) are possible across Trinidad and Tobago with heavier totals across Eastern and Southern halves of Trinidad, as well as Eastern Tobago. There is an elevated threat of street flooding and flash flooding. Note that already between 1-2 inches (25-50 mm) and isolated totals up to 3.5 inches (88 mm) have fallen across parts Trinidad.
— Seas will remain moderate to occasionally rough, with waves up to 2.5 meters are possible in open waters, occasionally up to and in excess of 3.0 meters and less than 1.0 meter but choppy in sheltered areas.
— Gusty winds in excess of 55 KM/H possible, particularly on Tuesday. Winds of this strength will produce wind damage including downed trees, utility poles and roof damage. Localized power outages possible.
Landslides possible in elevated areas.

The Riverine Flood Alert

As we’ve forecast since Monday, locally heavy rainfall was possible today, Wednesday. Overall rainfall totals were notably heavier than expected, with scattered to widespread showers beginning as early as 2:00 AM Wednesday morning. Between 25-50 millimeters of rainfall has fallen across Trinidad, with isolated totals up to 88 millimeters. This triggered widespread street and flash flooding across parts of Southern Trinidad.

By 10:00 AM, with continuing rainfall, major rivers such as the Moruga River, Cipero River, and South Oropouche River were nearing threshold levels, with rising water across much of Debe, Penal and Barrackpore. With more rainfall on the horizon and minor tributaries breaking its banks, the Trinidad and Tobago Meteorological Service has issued a Riverine Flood Alert (Yellow Level) at 12:16 PM Wednesday.

The alert began at 12:00 PM on Wednesday 11th December 2019 through 12:00 PM Thursday 12th December 2019. Note that although rainfall is continuing, the heaviest showers and thunderstorms have already occurred.

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

Information from the Trinidad and Tobago Meteorological Service concerning the Riverine Flood Alert for 11-12th December 2019.

Light to moderate rainfall is expected to continue intermittently over the next several hours. Landslides/landslips are possible in areas so prone. While the main river courses remain contained at this time, smaller rivers and/or tributaries can reach maximum capacity leading to flooding in surrounding areas. Some areas in south Trinidad are already inundated due to localized ponding and this may be further exacerbated at high tide.” according to the Trinidad and Tobago Meteorological Service. This “alert” status takes into account the possibility of the event occurring. This riverine flood event is likely.

The color of the alert 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 and riverine flooding in your area. Areas prone to landslides should also be aware of the hazard and impacts.

Image Credit: Trinidad and Tobago Meteorological Service
Image Credit: Trinidad and Tobago Meteorological Service

What We Know

A surface to low-level trough, which is an area of lower than usual pressure at the surface to low-levels of the atmosphere, continues to produce unsettled weather across the Lesser Antilles.

An upper-level jet, which is a narrow area, at upper levels of the atmosphere, where a current of fast-moving winds exists, is providing ample support for broad periods of rain of varying intensities across Trinidad.

A surface to low-level trough affecting the Lesser Antilles, with continuing showers triggering the Riverine Flood Alert. Credit: Weathernerds
A surface to low-level trough affecting the Lesser Antilles, with continuing showers triggering the Riverine Flood Alert. Credit: Weathernerds

Activity associated with this trough is supported by favorable upper-level divergence and very favorable low-level convergence.

The Weather Forecast

Wednesday: For the remainder of today, scattered to widespread showers and periods of rain are ongoing across Trinidad and Tobago, with overcast skies. Street or flash flooding is ongoing across parts of Trinidad, with additional flooding likely. Gusty winds may accompany heavy showers or possible thunderstorms. Locally heavy rainfall and gusty winds, in excess of 55 KM/H possible. Seas may become moderate to occasionally rough, Thursday in Eastern Coastal Waters.

Thursday: Brisk, isolated showers are forecast throughout the day affecting both islands, interrupting partly to mostly cloudy and breezy conditions. Heavier showers and isolated thunderstorms are forecast to favor Eastern and Southern Trinidad, as well as eastern coastal waters. As the afternoon into the evening progresses, showers are forecast to be on the decline, interrupting partly to mostly cloudy skies. Gusty winds, up to 50 KM/H possible.

Friday: The unsettled pattern remains mostly unchanged from Thursday, with brisk isolated showers throughout the day bringing the threat of gusty winds. Isolated thunderstorms possible during the afternoon, across Southwestern areas.

Impacts This Upcoming Week

Winds: Sustained surface winds between 20 KM/H and 35 KM/H with gusts up to 50 KM/H are likely in heavy showers or thunderstorms across Trinidad and Tobago throughout the week.

With wind gusts in excess of 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, bringing down utility poles and lines.

High Wind Event Precautions
High Wind Event Precautions

Rainfall: Additional Rainfall accumulations are forecast to be scattered totals of 15-25 millimeters. Overall totals are expected to be up to 50-75 millimeters in isolated thunderstorms or heavy downpours.

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 forecast thunderstorms, frequent lightning is likely. Lightning can cause power outages, voltage dips, damage to life and property, particularly during cloud-to-ground lightning strikes.

Landslides: Particularly across Northwestern Trinidad, soils are very saturated with persistent heavy afternoon thunderstorms at the end of the last week. With additional rainfall in the forecast, landslides are possible through Tuesday in landslide-prone and elevated areas.

Hazardous Seas: An increase in strong low-level winds will keep seas at moderate levels, with waves up to 2.5 meters in open waters and even at occasional rough levels, with waves in excess of 2.5 meters, particularly along the Eastern coasts of both islands.

Why I May Not/Will Not See Constant Rainfall?

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. Widespread showers mean that nearly all persons and areas may experience rainfall.

On Wednesday, widespread rainfall is expected. On Thursday, isolated to scattered activity is possible.

Forecast - Isolated, Scattered, Widespread - What do they mean?

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