Tropical Update – Next Tropical Wave To Bring Isolated Showers, Thunderstorms This Weekend

Tropical Update Overview:
Tropical Wave 61 – This tropical wave moved across the region on Tuesday 5th November 2019. This wave brought heavy rainfall and gusty winds to parts of Trinidad and Tobago, which caused minor roof damage and street flooding.
Tropical Wave 62 – This tropical wave is forecast to move across the Lesser Antilles on Saturday, bringing elevated moisture that may fuel showers and thunderstorms across Trinidad and Tobago, as well as increased cloudiness.
Tropical Wave 63 – This tropical wave is forecast to move across Trinidad and Tobago later next week but it is too soon to tell definitive impacts to the Lesser Antilles.
Imapcts to T&T – The ITCZ is forecast to drift southward on Thursday, bringing showers to Southern and Western Trinidad. Isolated late morning through afternoon showers and thunderstorms are forecast on Friday, with Tropical Wave 62 approaching, leading to increasing cloudiness overnight. Isolated showers and thunderstorms are forecast on Saturday into Sunday, improving by late Sunday. No direct tropical threats to Trinidad and Tobago are forecast over the next week but locally heavy rainfall is possible, particularly on Saturday. Street flooding, flash flooding, gusty winds in excess of 50 KM/H, landslides and frequent lightning possible.

Before we dive into the Tropical Update, a few notes:

  • Tropical waves are a normal part of the rainy season.
  • Not every tropical wave will form into a tropical cyclone.
  • Weaker tropical waves produce more rainfall across Eastern parts of the islands with mostly cloudy conditions and a few showers across western parts of the islands.
  • Rainfall will be more isolated and intermittent with weaker tropical waves that do not have ITCZ or upper-level support.
  • Saharan Dust may weaken tropical waves.

You can read more about the weather associated with Tropical Waves, as well as what to expect as these waves move through the region below.

Tropical Wave 61

Activity associated with Tropical Wave 61 along 65W moving away from the Lesser Antilles with minimal convective activity along the axis but scattered convection is mainly east of the wave axis across the Lesser Antilles. Credit: Weathernerds
Activity associated with Tropical Wave 61 along 65W moving away from the Lesser Antilles with minimal convective activity along the axis but scattered convection is mainly east of the wave axis across the Lesser Antilles. Credit: Weathernerds

This tropical wave moved across the Lesser Antilles on Tuesday, bringing locally heavy rainfall and gusty winds to islands mainly across the Windwards. Wind gusts up to 65 KM/H were recorded, with locally heavy rainfall bringing street and flash flooding to Trinidad, St. Lucia and Guadeloupe over the last 24-36 hours.

As of the 4:00 PM Tropical Update, the axis of Tropical Wave 61 analyzed with axis along 65W from 16N southward moving west at 10 to 15 knots. This wave is moving through the southern part of an Atlantic Ocean-to-SE Caribbean Sea upper-level trough. Precipitation: Nearby widely scattered moderate to isolated strong, that is from 13N southward from 64W eastward, has been moving westward with time from the Atlantic Ocean, off the coasts of Guyana and Venezuela.

This wave continues to influence our wind regime across Trinidad and Tobago, in addition to dragging the ITCZ northward, which has begun to drift southward.

This has allowed for a plume of Saharan Dust to our north to begin moving across our atmosphere.

Tropical Wave 62

Activity associated with Tropical Wave 62 along 42W nearing the Lesser Antilles. This wave is forecast to traverse the region on Saturday, bringing showers and thunderstorms to the region yet again. Credit: Weathernerds
Activity associated with Tropical Wave 62 along 42W nearing the Lesser Antilles. This wave is forecast to traverse the region on Saturday, bringing showers and thunderstorms to the region yet again. Credit: Weathernerds

As of the 5:00 PM Tropical Update, Tropical Wave 62 is along 42W from 14N
southward, moving west 10 to 15 knots. Widely scattered moderate to isolated strong is within 200 nautical miles to the east of the tropical wave from 08N to 13N. It is possible that other nearby precipitation may be more related to the ITCZ.

The tropical wave is forecast to move across the Lesser Antilles on Saturday, with showers lingering into Sunday, bringing another round of showers and thunderstorms to Trinidad and Tobago.

Generally, less than 1 inch (25 millimeters) is expected, with up to 3 inches possible in isolated areas, mainly across Eastern and Southern Trinidad. No significant impacts are expected beyond isolated street/flash flooding and gusty winds in heavier showers and thunderstorms.

This wave is forecast to drag the ITCZ across the region yet again.

Tropical Wave 63

Activity associated with Tropical Wave 63 along 23W in the East Atlantic. Credit: Weathernerds
Activity associated with Tropical Wave 63 along 23W in the East Atlantic. Credit: Weathernerds

As of the 5:00 PM Tropical Update, Tropical Wave 63 is from 15N southward, moving westward 10 to 15 knots. Widely scattered moderate to isolated strong within 120 nautical miles to the west of the tropical wave from 02N to 05N. Isolated moderate within 300 nautical miles to the east of the tropical wave from 02N to 06N.

What does all of this mean for Trinidad and Tobago?

Thursday: The ITCZ begins to drift southwards, as Tropical Wave 61 moves well west. Heavier showers and thunderstorms forecast to favor Western and Southern Trinidad, mainly during the late morning through the evening. A high-pressure ridge builds, leading to a mostly settled night.

Friday: A mostly settled and sunny day is forecast across Trinidad and Tobago, barring the odd isolated shower and thunderstorms during the late morning through the afternoon, favoring Western, Southern and hilly areas of Trinidad. An approaching tropical wave may bring increased cloudiness overnight, particularly after midnight into Saturday.

Saturday: The axis of Tropical Wave 62 is forecast to move across T&T, with showers and thunderstorms developing after midnight, affecting both islands. Periods of showers and thunderstorms are forecast to interrupt partly cloudy to overcast conditions. Note that activity will be intermittent throughout the day. Lingering showers, remaining isolated and interrupting partly cloudy skies, are forecast by the late evening through the night.

Sunday: Another high pressure is forecast to build across the region but with lingering moisture from the passage of that tropical wave, isolated showers and thunderstorms are forecast, mainly during the first half of the day into the mid-afternoon. A mostly settled night is forecast.

Monday: A hot and mostly sunny day, with the typical wet season afternoon showers and possible thunderstorms across Western Coastal Trinidad.

Impacts This Upcoming Week

Winds: Sustained surface winds between 15 KM/H and 30 KM/H with gusts in excess of 50 KM/H are likely in heavy showers or thunderstorms across Trinidad and Tobago throughout the weekend.

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: Throughout the week, daily rainfall accumulations are forecast to be isolated totals of 5-15 millimeters, with in excess of 20-40 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: Models continue to indicate that heavier showers and thunderstorms will favor Eastern and Southern Trinidad, areas with low landslide hazards. However, in heavier showers and thunderstorms across Northern Trinidad, there is the risk of landslides.

Hazardous Seas: Strong low-level winds will keep seas at moderate levels, with waves up to 2.5 meters in open waters and even at rough levels through the first half of Thursday with waves in excess of 2.5 meters, particularly along the Eastern coasts of Tobago. Throughout the remainder of the 5-day period, seas are forecast to remain moderate with waves in open waters above 1.5 meters, becoming slight to moderate by Saturday.

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.

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

Tropical Cyclone Climatology

Tropical Cyclone Points of Origin during the month of November. Though much of the points of origin are west or north of T&T as we move into the last month of the Hurricane Season, we still need to pay attention to some of these waves and the ITCZ, which have historically brought major flooding events to T&T, hence all low-pressure systems in the Atlantic should be closely monitored, as we do in the Tropical Update.

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