Tropical Update: Sebastian Churns in North Atlantic, Two Tropical Waves to Bring Rainfall to T&T

Tropical Update Overview:
Tropical Storm Sebastien – Tropical Storm Sebastien maintains its strength in the North Atlantic, continuing to move towards the northeast.
Tropical Wave 66 – A very weak tropical wave, with little to no convection associated with it, is forecast to move across the Southern Windwards late Saturday into Sunday. Increased moisture may fuel heavier showers and thunderstorms across T&T on Sunday afternoon. No widespread severe weather forecast.
Tropical Wave 67 – This tropical wave was briefly analyzed by the National Hurricane Center on Friday, but was quickly dropped from their analysis. Much of the moisture associated with this wave has been absorbed by Tropical Wave 68.
Tropical Wave 68 – This tropical wave is forecast to move across the Southern Windwards Tuesday into Wednesday, bringing a surge of low-level winds and locally heavy showers and thunderstorms to Trinidad and Tobago. Isolated severe weather possible, with thunderstorms favoring Trinidad.
Impacts to T&T – Late morning through afternoon showers and thunderstorms are forecast to be the norm Sunday through Wednesday, with two tropical waves bringing elevated shower and thunderstorm chances on Sunday and Tuesday into Wednesday. No direct tropical threats to Trinidad and Tobago are forecast over the next week but locally heavy rainfall is possible, throughout the week, mainly during the intense afternoon showers and thunderstorms. Street flooding, flash flooding, gusty winds generally between 30-50 KM/H and occasionally in excess of 50 KM/H, landslides and frequent lightning possible, particularly on Tuesday into Wednesday. A high-pressure system is forecast to bring settled conditions to the region on Thursday.

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 Storm Sebastien

Tropical Storm Sebastien continues northeastward as of the 2:00 PM Tropical Update. Credit: Weathernerds
Tropical Storm Sebastien continues northeastward as of the 2:00 PM Tropical Update. Credit: Weathernerds

Tropical Storm Sebastien, the 18th named tropical cyclone of the 2019 Hurricane Season, continues into the North Atlantic, maintaining strength.

No threat to the Lesser Antilles, including T&T.

Tropical Wave 66

Minimal activity associated with Tropical Wave 66 along 58/59W in the Atlantic. Credit: Weathernerds
Minimal activity associated with Tropical Wave 66 along 58/59W in the Atlantic. Credit: Weathernerds

As of the 2:00 PM Tropical Update, the axis of Tropical Wave 66 is approximately along is along 58W/59W, from 15N southward, moving westward 10 knots. Isolated moderate is in the coastal waters and the coastal plains of Guyana.

Moderate to strong wind shear and unfavorable upper-level conditions continue to limit showers and thunderstorms associated with this wave.

Abundant low-level moisture is forecast, supporting cloudiness and isolated to scattered showers, with brief thunderstorms on Sunday. See below for details.

Tropical Wave 68

Activity associated with Tropical Wave 68 along 40W in the Central Atlantic. Credit: Weathernerds
Activity associated with Tropical Wave 68 along 40W in the Central Atlantic. Credit: Weathernerds

As of the 2:00 PM Tropical Update, the axis of Tropical Wave 68 is approximately is along 40W, from 11N southward, moving westward 10 to 15 knots. Widely scattered moderate to isolated strong within 150 nautical miles to the east of the tropical wave, and within 300 nautical miles to the west of the tropical wave.

A surge of low-level winds is accompanying this wave, in addition to abundant moisture. This is forecast to traverse Trinidad and Tobago on Tuesday into Wednesday, bringing gusty winds up to 60 KM/H, locally heavy showers and thunderstorms. See below for details.

What does all of this mean for Trinidad and Tobago?

Sunday: A weak tropical wave is forecast to move across Trinidad and Tobago. Shortly after daybreak, increasing cloudiness and showers are likely across both islands. Winds will predominantly be from the southeast to east-southeast, so heavier showers and thunderstorms will focus along Western areas and the south-facing slopes of the Northern Range, particularly during the afternoon. Activity is forecast to subside by nightfall, but lingering isolated showers are possible, favoring Eastern Trinidad.

Monday: Partly cloudy skies are forecast to be interrupted by isolated showers during the early morning. By the late morning through the afternoon, showers and thunderstorms are forecast to return, favoring Western areas of both islands, and heavier activity favoring Southwestern Trinidad. Isolated showers are forecast to linger through the night due to an approaching tropical wave.

Tuesday: The axis of Tropical Wave 68 is forecast to move across T&T, with showers and thunderstorms developing after daybreak, 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 mainly across Eastern Trinidad and Tobago. Locally heavy rainfall and gusty winds, in excess of 55 KM/H possible. Seas may become moderate to occasionally rough, between 12:00 PM Tuesday through 12:00 PM Wednesday in Eastern Coastal Waters.

Wednesday: The axis of Tropical Wave 68 is forecast progress westward. However, trailing moisture and instability will also for overnight through early morning showers and thunderstorms, favoring the Southern and Eastern halves of Trinidad, gradually becoming settled by daybreak. Lingering showers, remaining isolated and interrupting partly cloudy skies, are forecast by the late evening through the night mainly across Eastern and Southern Trinidad and Tobago.

Thursday: Drier conditions are forecast following the entire passage of this tropical wave with a high pressure moving into the region and drier atmospheric conditions. Isolated showers are possible during the afternoon, interrupting a mostly sunny day across both islands.

Impacts This Upcoming Week

Winds: Sustained surface winds between 15 KM/H and 30 KM/H with gusts in excess of 55 KM/H are likely in heavy showers or thunderstorms across Trinidad and Tobago, particularly on Tuesday into Wednesday.

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

Rainfall: Throughout the week, daily rainfall accumulations are forecast to be isolated totals of less than 10-20 millimeters, with in excess of 20-40 millimeters in isolated thunderstorms or heavy downpours. Daily rainfall accumulations may range between 15-35 mm on Tuesday and Wednesday.

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.

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.

This week, isolated to scattered activity is forecast.

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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