Tropical Update: Tropical Waves, Hazardous Seas Continue To Affect T&T This Week

Tropical Update Overview:
Hurricane Pablo – Hurricane Pablo transitioned into a post-tropical cyclone on Monday morning. Advisories were discontinued. No additional updates.
Invest 99L – A non-tropical low pressure area located several hundred miles west-northwest of the Azores is producing a large area of gale to storm-force winds. This area has low chances of tropical cyclone development over the next 48 hours and 5 days respectively.
Tropical Wave 58 – A tropical wave traversed the region Monday night into Tuesday, bringing showers and thunderstorms mainly across Tobago, Grenada, and the northern half of Trinidad. Wind gusts up to 35 KM/H, and rainfall accumulation between 0-15 millimeters was recorded across T&T.
Tropical Wave 59 – This tropical wave is forecast to move across Trinidad, Tobago, and the Lesser Antilles by the end of this week, between late Thursday and early Saturday, bringing another round of showers and thunderstorms. Elevated risk of street/flash flooding due to the forecast wet week ahead.
Tropical Wave 60 – This tropical wave is forecast to move across the Lesser Antilles Sunday into Monday of next week, bringing elevated moisture that may fuel showers and thunderstorms across Trinidad and Tobago, as well as increased cloudiness. This wave is forecast to bring the ITCZ across our region next week, potentially creating a multi-day rainfall event.

Large waves continue at Las Cuevas Bay, Northern Trinidad as a long period swell event affects the Eastern Caribbean.

The ITCZ – Following the passage of Tropical Wave 60, the ITCZ is forecast to linger across Trinidad and Tobago while a Saharan Dust plume moves across the remainder of the Lesser Antilles. It is too soon to tell definitive impacts or whether this multi-day rainfall event is forecast to produce copious amounts of rainfall, though longer-range models are trending towards a very wet week next week.
Impacts to T&T – Following the passage of Tropical Wave 58, localized, afternoon showers and possible thunderstorms are forecast favoring Northern and Western Trinidad as well as Tobago on Wednesday into Thursday. Tropical Wave 59 will bring isolated showers and thunderstorms to both islands beginning late Thursday into early Saturday, with the wettest of days occurring on Friday. Tropical Wave 60 will be the wettest of these three waves, bringing isolated to scattered showers and thunderstorms on Sunday into Monday, with the ITCZ keeping showers and thunderstorms on tap throughout next week. No direct tropical threats to Trinidad and Tobago are forecast over the next week. We may experience street flooding and gusty winds in those heavier showers and thunderstorms. Hazardous Seas are forecast to continue through Sunday, although the Hazardous Seas Alert #2 is slated to expire on Saturday Nov. 2nd.

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.

Invest 99L

Invest 99L, an area of non-tropical low-pressure system churning in the North Atlantic. It has low chances of development as of the 2:00 PM Tropical Update Credit: Weathernerds
Invest 99L, an area of non-tropical low-pressure system churning in the North Atlantic. It has low chances of development as of the 2:00 PM Tropical Update Credit: Weathernerds

A non-tropical low-pressure area located several hundred miles west-northwest of the Azores is producing a large area of gale to storm-force winds. This system could acquire some subtropical characteristics over the next couple of days while it moves slowly southwestward to southward over slightly warmer waters.

2:00 PM Tropical Update from the National Hurricane Center, showing Invest 99L in the North Atlantic Ocean.
2:00 PM Tropical Update from the National Hurricane Center, showing Invest 99L in the North Atlantic Ocean.

Environmental conditions are expected to become unfavorable for any further development by Thursday night when the low is forecast to move back over colder waters. This system has a low, 30%, chance of tropical cyclone formation over the next 48 hours and 5 days respectively.

This system poses no threat to Trinidad, Tobago or the Lesser Antilles. However, this low-pressure system is responsible for the ongoing swell event across the Lesser Antilles.

Tropical Wave 58

Isolated showers and thunderstorms associated with Tropical Wave 58 as it moves through the Eastern Caribbean in this latest tropical update. Credit: Weathernerds
Isolated showers and thunderstorms associated with Tropical Wave 58 as it moves through the Eastern Caribbean in this latest tropical update. Credit: Weathernerds

The axis of Tropical Wave 58 is along 62/63W south of 18N, moving W around 10 knots. This wave is well depicted in satellite imagery with scattered showers and isolated thunderstorms just west of the Southern Windwards, as well as across the French Antilles.

This wave moved through the Lesser Antilles overnight with minimal impacts. Thunderstorms put on quite the lightning show across Tobago overnight but minimal rainfall occurred across both islands.

Tropical Wave 59

Activity associated with Tropical Wave 59 along 52W nearing the Lesser Antilles with scattered showers and thunderstorms. Credit: Weathernerds
Activity associated with Tropical Wave 59 along 52W nearing the Lesser Antilles with scattered showers and thunderstorms. Credit: Weathernerds

This tropical wave broke off from the wave to its east, originally called Tropical Wave 59 (now #60), with much of the showers and thunderstorms associated with this wave remaining south of 10N, i.e. south of Trinidad.

As of the 2:00 PM Tropical Update, the axis of Tropical Wave 59 extends its axis along 49W to 52W from 13N southward, moving west at 10 knots. Scattered moderate convection is seen along the wave from 6N to 11N between 55W and 46W.

No development of this wave is forecast, but welcome rainfall is expected mainly for Trinidad on Friday.

Generally, less than 1 inch (25 millimeters) is expected, with up to 2 inches possible in isolated areas, mainly across Trinidad. No significant impacts are expected beyond isolated street/flash flooding and gusty winds in heavier showers and thunderstorms.

For Trinidad and Tobago, moisture from this wave will linger across the region into the weekend, ahead of Tropical Wave 60, fuelling heavier showers and thunderstorms resulting from daytime heating, sea breeze convergence, and orographic precipitation. See below for details.

Tropical Wave 60

Activity associated with Tropical Wave 60 along 39W to 42W nearing the Lesser Antilles with scattered showers and thunderstorms. This wave is forecast to traverse the region Sunday into Monday of next week. Credit: Weathernerds
Activity associated with Tropical Wave 60 along 39W to 42W nearing the Lesser Antilles with scattered showers and thunderstorms. This wave is forecast to traverse the region Sunday into Monday of next week. Credit: Weathernerds

As of the 2:00 PM Tropical Update, Tropical Wave 60 is along 40W/41W S of 18N, moving west at 10 knots. This wave is in the leading edge of a dry/dusty Saharan air mass and is well depicted in satellite imagery. Widely scattered moderate convection is from 04N-17N between 36W-44W.

The tropical wave is forecast to move across the Lesser Antilles early next week, Sunday into Monday bringing another round of showers and thunderstorms to Trinidad and Tobago.

No development is expected of this wave but a surge of trade winds is forecast to accompany this wave next week. Wind gusts in excess of 65 KM/H may accompany shower and thunderstorm activity, lingering through the first half of next week.

Generally, less than 1 inch (25 millimeters) is expected, with up to 2 inches possible in isolated areas, mainly across 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, lingering through much of next week, potentially triggering a multi-day rainfall event.

The ITCZ

Following the passage of Tropical Wave 60, long-range models are indicating that the Intertropical Convergence Zone is forecast to move across T&T next week.

Intermittent showers and thunderstorms are forecast to continue through next week with locally heavy rainfall, gusty winds and elevated risk of street and flash flooding, as well as landslides in elevated areas, particularly as the week progresses.

It is too soon to tell, definitively, rainfall accumulation for next week, but daily rainfall accumulations between 15-25 millimeters are possible and isolated totals up to 50 millimeters.

We’ll have updates in additional tropical updates as the week progresses.

What does all of this mean for Trinidad and Tobago?

Tuesday: Tropical Wave 58 moves out of our region, winds will predominantly be from the south and southeast. Isolated showers and thunderstorms are possible, favoring Western and Northern Trinidad through the afternoon and then Eastern halves of both islands overnight, interrupting partly cloudy skies.

Wednesday: After a hot and sunny morning, late morning through afternoon showers are possible across Western and Northern Trinidad, as well as parts of Tobago. Light winds, day time heating and sea breeze convergence will allow for slow-moving showers and thunderstorms. Conditions are forecast to become settled by the late evening, with brief isolated showers possible across Eastern coastal areas overnight.

Thursday: A copy and paste forecast from Thursday as the overall conditions remain the same. An approaching tropical wave may cause an increase in cloudiness as the evening progresses, with showers developing mainly after 2:00 AM into Friday.

Friday: Tropical Wave 59 moves across Trinidad and Tobago, with periods of showers and thunderstorms interrupting partly cloudy to cloudy skies. Isolated showers and dismal conditions to linger into nightfall.

Saturday: After a partly cloudy to cloudy morning, with isolated showers and thunderstorms, conditions are forecast to become settled by the late afternoon.

Sunday: After a hot and sunny morning, late morning through afternoon showers are possible across Western and Northern Trinidad, as well as parts of Tobago. Day time heating and sea breeze convergence will allow for slow-moving showers and thunderstorms. Conditions are forecast to become settled by the late evening but increasing cloudiness is forecast overnight as Tropical Wave 60 approaches the region.

Activity will be isolated to scattered, with no widespread severe weather forecast. However, with all thunderstorms and heavy showers, there is the possibility of street flooding and gusty winds.

An unwanted by-product of this increased moisture will be particularly humid conditions across Trinidad and Tobago. This means that while the actual recorded temperature on some days may not top 33/34°C, that feels like temperature may easily top 40°C due to that high humidity, particularly on Wednesday and Thursday. However, those showers will bring some brief heat relief.

The Heat Index

The heat index is a combination of air temperature and relative humidity determining what the air feels like to a person i.e. how hot it actually feels.

The heat index is important because of sweating. Your body sweats in order to cool the skin and maintain a constant, healthy body temperature. This cooling process means that the sweat has to evaporate off the skin to remove heat. However, if the sweat is unable to evaporate, the body isn’t able to regulate temperature.

With high volumes of moisture in the air, also known as high relative humidity, which T&T regularly experience due to its tropical climate, the rate of sweat evaporation decreased. This is because the atmosphere is unable, or has limited potential to hold additional moisture in the atmosphere.

This results in you feeling warmer in humid conditions and cooler in less humid conditions i.e. when relative humidity decreases. As temperature increases, the heat index increases. As relative humidity increases, so does the heat index.

 Heat Index Values Explained
Heat Index Values Explained

The heat index is generally classified into four categories: caution, extreme caution, dangerous and extremely dangerous. Generally across Trinidad and Tobago, we experience heat indices of caution to extreme caution in times of hot days, with isolated areas experiencing dangerous heat indices such as urban areas.

This upcoming week, heat index levels are likely to remain at extreme cautious to dangerous levels. Heat cramps and heat exhaustion are likely with heatstroke probable with continued activity.

Heat Safety

Graphic: Beat the Heat. Heat related deaths are preventable.

Graphic: Beat the Heat. Heat related deaths are preventable.

Source: MEMA
Heat Safety Tips and Resources
Heat Safety Graphic. Source: Heat Safety Tips and Resources

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 possible in heavy showers or thunderstorms across Trinidad and Tobago throughout the week.

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 0-10 millimeters, with up to 25 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.

Hazardous Seas: A long period swell event is underway across Trinidad, Tobago, and the Eastern Caribbean. Coastal flooding may be exacerbated during heavy shower and thunderstorm activity.

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.

Throughout the week, mainly isolated activity is forecast, with the exception of Friday, where 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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