ITCZ, Tropical Wave 37 Trigger Thunderstorms Across Trinidad

A combination of the Intertropical Convergence Zone (ITCZ) and a tropical disturbance (Invest 97L or Tropical wave 37) is affecting Trinidad and Tobago presently. Invest 97L has influenced our low-level winds, now from the south, bringing strong to severe thunderstorms from across Venezuela towards and across Trinidad.

As of the 8:00 PM Tropical Weather Outlook from the National Hurricane Center, “A tropical wave near the Windward Islands continues to produce a large area of disorganized showers and thunderstorms. This disturbance is moving westward at about 20 MPH and is expected to continue to move quickly westward over the eastern and central Caribbean Sea during the next couple of days, which is likely to limit significant development. After that time, however, the system is forecast to move more slowly westward across the western Caribbean, where upper-level winds could become more conducive for the development of a tropical depression during the latter part of this week. Regardless of development, locally heavy rainfall and gusty winds are expected over portions of the Windward and southern Leeward Islands through Tuesday morning.”

The National Hurricane Center has given this system a medium (60%) chance of tropical cyclone formation over the next 5 days as it moves into the Caribbean Sea.

Because of the threat of adverse weather impacts, the Trinidad and Tobago Meteorological Service has updated its Adverse Weather Alert (Yellow Level) beginning at 11:00 PM Sunday through 11:00 AM Tuesday. Adverse weather may continue through Tuesday afternoon.

The Forecast

Abundant low-level moisture associated with the ITCZ and Tropical Wave 37 will be moving across T&T. Favorable low-level convergence, and upper-level divergence and low wind shear will allow for isolated strong thunderstorms and heavy showers, in addition to an overall favorable atmosphere.

Through midnight, strong to severe thunderstorms will move across Trinidad. These thunderstorms may produce damaging wind gusts, flooding rainfall, and dangerous lightning.

After midnight, isolated to scattered showers and thunderstorms are forecast continue affecting Trinidad, as well as Tobago, with heavy rainfall forecast through daybreak. Conditions will gradually subside through the morning, with lingering light to moderate rain, but isolated thunderstorms and showers may return near midday through the afternoon across both islands, generally favoring Trinidad

A mostly settled evening into the night is forecast across both islands with the odd lingering shower.

Seas forecast to be moderate, with waves up to 2.5 meters in open waters. In sheltered areas, below 1 meter but choppy in areas of heavy showers or thunderstorms.

The main hazards include heavy rainfall, which may reduce visibility and gusty winds up to and in excess of 55 KM/H. Street or flash flooding will be possible in slow-moving showers and thunderstorms. There is the low chance of riverine flooding across southern Trinidad. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage. Particularly across Tobago, landslides are likely in heavy rainfall.

Note that with weak winds, with sea breeze convergence, heat, and orographic effects may act as triggers for additional shower and thunderstorm development across western and hilly areas of Trinidad, particularly on Tuesday afternoon.

Possible Impacts From ITCZ & Tropical Wave 37


Sustained surface winds will be weak, generally below 25 KM/H during the afternoon at its peak. However, Gusts up to and in excess of 55 KM/H are possible in heavy showers or thunderstorms across Trinidad and Tobago.

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

High Wind Event Precautions
High Wind Event Precautions


Overall, less than 25 millimeters are forecast, with areas across southern and eastern Trinidad recording up to 50 millimeters. Isolated totals up to and in excess of 75 millimeters possible, particularly in slow-moving downpours or thunderstorms and across Tobago.

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. There is a low chance of riverine flooding across southern Trinidad.

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.

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.

Widespread activity is forecast through midnight across Southern Trinidad, gradually becoming scattered to isolated as the day progresses on Tuesday.

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

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