Forecast: Hurricane Teddy’s Influence To Bring Showers, Thunderstorms To T&T

Moisture from Hurricane Teddy is moving across T&T on Saturday, fuelling scattered showers and isolated thunderstorms, making a noticeably (but shortlived) cooler start to the weekend.

Winds over the next 12 hours are forecast to be near calm across Trinidad and Tobago, generally from the south to southeast with offshore areas experiencing winds up to 25 KM/H, gusting to 35 KM/H. By the evening, a high-pressure system will move in, with winds increasing across T&T.

Showers and thunderstorms can be intense, producing localized street/flash flooding and gusty winds in downburst-like activity. Today’s showers and thunderstorms will be scattered across Trinidad and Tobago due to no prevailing low-level steering pattern. With light winds, funnel clouds are also possible.

A large band of moisture across the Windward Islands Saturday morning, as shown by the EMCWF model for total precipitable water as of 00Z Saturday 19th September 2020. (weathermodels.com)

On Saturday, as the band of moisture from Hurricane Teddy affects T&T, scattered showers (some heavy) and isolated thunderstorms are forecast to initially develop along the northern coasts of Venezuela and drift northward towards Trinidad, with additional activity developing. The limiting factor over the next 24 hours will be moderate to strong easterly to northeasterly wind shear, weakening into Saturday evening.

There are no alerts, watches, or warnings from the Trinidad and Tobago Meteorological Service at this time.

The Forecast


Overview: Increasing low-level moisture is forecast as Hurricane Teddy pulls equatorial moisture northward and a persistent band of moisture moves across the Windward Islands. Teddy has also induced a surface to a low-level trough, which has eroded the pressure gradient across the Lesser Antilles, resulting in near calm conditions and weak steering patterns from the south. Increasing easterly wind shear is forecast across T&T, which will weaken isolated activity as rapidly as it forms. Strong daytime heating, orographic lift (along the Northern and Central Range), and sea breeze convergence are forecast to as triggers for shower and thunderstorm development/

Sea breeze convergence mechanisms for the Gulf of Paria and the Atlantic Ocean across Trinidad which can produce thunderstorm activity. On Thursday, sea breeze convergence will be possible across all coasts of Trinidad and Tobago due to light to no winds.
Sea breeze convergence mechanisms for the Gulf of Paria and the Atlantic Ocean across Trinidad which can produce thunderstorm activity. On Saturday, sea breeze convergence will be possible across all coasts of Trinidad and Tobago due to light to no winds.

Forecast For Saturday: A variably cloudy day is forecast, with periods of showers and isolated showers from midnight through the midmorning, and again through the afternoon. Activity will be isolated to scattered across both islands, with heavier showers and isolated thunderstorms favoring Trinidad. A surface to low-level ridge will move in during the late afternoon into the evening, leading to a mostly settled night barring the odd isolated shower across Eastern areas.


Marine: Seas are forecast to be moderate in Trinidad and moderate to rough in Tobago. Swells from Hurricane Teddy continue to affect T&T. In open waters of Tobago, generally eastern areas, waves between 2.5 and 3.0 meters are possible. In Trinidad, generally northern and eastern areas, waves between 2.0 and 2.5 meters are possible. In sheltered areas across both islands, choppy conditions are forecast, with waves generally below 1 meter.

Large, breaking waves will likely exceed that 1-meter mark along Eastern and Northern coastlines. Spring tides will continue, hence minor coastal flooding will be possible. Long period swells will begin to propagate into the Gulf of Paria on Friday producing larger than usual waves in nearshore areas.

Winds are forecast to be generally calm, with light winds up to 15 knots from the south to southeast.

Note: Overnight Friday into Saturday, strong winds and agitated seas are possible in the Gulf of Paria. Particularly along the Northwestern coasts, waves near 0.5 to 1 meter are possible, capable of damaging small crafts, marinas, and jetties.

Hazards: The main hazards include heavy rainfall, which may reduce visibility and gusty winds in downburst-like fashion, up to and in excess of 50 KM/H. Street or flash flooding will be possible in slow-moving showers and thunderstorms. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage. With light winds, funnel clouds are also possible.

Temperatures

On Saturday, temperatures are forecast to be cooler than the past week due to increased cloud cover.

Across both islands, warm and humid conditions are forecast. The maximum high for Trinidad is forecast to be near 31.0°C, up to 33.0°C in urban and built-up areas, particularly during the late afternoon. In Tobago, the maximum high is forecast to be near 31.0°C.

Temperatures in cities, such as Port of Spain, tend to be much higher than surrounding locations due to a phenomenon called the Urban Heat Island Effect. There are several causes, but the main instigator for this phenomenon tends to be increased dark surfaces such as roads and pavement in cities, which absorb solar radiation more than surrounding areas.

Forecast Impacts

Winds

Sustained surface winds will be light to nonexistent. However, during heavy showers and thunderstorms, sustained winds between 25 KM/H and 35 KM/H with gusts up to and in excess of 50 KM/H are possible.

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.

Rainfall

Across most areas of Trinidad and Tobago, maximum accumulation totals are forecast to be below 10 millimeters. However, in areas where heavy thunderstorms and showers occur, up to 25 millimeters are possible, with isolated totals up to and in excess of 50 millimeters, particularly in slow-moving downpours or thunderstorms.

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: Frequent lightning is possible in thunderstorm activity, particularly Friday night. Lightning can cause power outages, voltage dips, damage to life and property, particularly during cloud-to-ground lightning strikes.

Why I May Not/Will Not See 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.

Isolated to scattered rainfall is forecast on Friday into Saturday. Most will experience very hot and sunny conditions on Friday.

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

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