Heavy showers, thunderstorms, and possible gusty winds are forecast to affect the Windward Islands from late Tuesday through Thursday associated with Tropical Wave 41 – a large and disorganized tropical disturbance dubbed Invest 91L.
Periods of heavy and potentially flooding rainfall are possible from Trinidad and Tobago extending northwards to Guadeloupe, accompanied by gusty winds and lightning, while seas may become agitated.
What you need to know
— What is it: A tropical wave (also called a tropical disturbance) is producing widely scattered and disorganized showers and thunderstorms. It is not a tropical depression or tropical storm, but it is being monitored for development by the NHC for tropical cyclone formation.
— Who will be affected: Rainfall associated with this tropical wave is forecast to affect the Windward Islands and the French Antilles through Friday. Namely, islands from Trinidad and Tobago to Guadeloupe, including Barbados, are in the path of this tropical wave’s rainfall, with the strongest winds forecast to affect islands between Barbados and Guadeloupe.
— What can you expect: Street/flash flooding is highly likely. Chances for riverine flooding will increase through the week for T&T. Gusty winds up to and in excess of 60KM/H accompanying heavy showers or thunderstorms are possible mainly north of Barbados, with wind gusts in excess of 45 KM/H likely for all Windward and French Antilles islands, including Trinidad and Tobago. Stronger wind gusts are expected across Tobago and northern Trinidad. Lightning will accompany thunderstorms. Landslides, mudslides, and rockfalls are possible across the Windwards, with lahars possible in St. Vincent from mid-week. Seas are forecast to become agitated.
— Alerts/Watches/Warnings: There are no alerts, watches, or warnings in effect for Trinidad and Tobago from the Trinidad and Tobago Meteorological Service (TTMS) at this time, though they have issued a statement. The Barbados Meteorological Service issued a Weather Information Statement and has Barbados under a yellow-level alert for excessive rainfall from Tuesday evening and agitated seas on Wednesday. St. Vincent and the Grenadines (SVG) Meteorological Services has issued its own Weather Information Statement for their country. There are no tropical storm or hurricane watches or warnings in effect for any country within the Lesser Antilles at this time.
The latest from the NHC
As of their 8:00 PM Tropical Weather Outlook, the NHC says, “Showers and thunderstorms are showing some signs of organization in association with a tropical wave located several hundred miles east of the Windward Islands. Further development of the wave is possible, and a tropical depression could form during the next few days while it generally moves westward at 15 to 20 MPH, reaching the Windward Islands and the eastern Caribbean Sea by midweek. “
Development chances for tropical cyclone formation are low over the next 48 hours and medium over the next five days, at 30% and 40%, respectively.
The National Hurricane Center may begin weather reconnaissance flights on Invest 91L at 2:00 PM Tuesday, October 4th, 2022 (18Z October 4th), while Invest 91L is northeast of Trinidad and Tobago
Invest 98L is located approximately just over 1,300 kilometers east of Trinidad and Tobago. However, scattered showers and thunderstorms are widely scattered between T&T and this tropical wave axis and approximate low-pressure center of 1012 millibars.
Who will be affected?
Forecast models have honed in on the weak area of low pressure moving across Trinidad and Tobago or just north of the country and then moving into the Caribbean Sea. Until Invest 98L, which became Hurricane Ian, this tropical disturbance is being steered westward due to the influence of a strong cold front moving off the United States and a mid-level ridge centered near the Gulf of Mexico.
It should be noted that while the low-pressure center may track across or near T&T, the strongest winds are forecast to remain well north of the country, with light and variable winds across Trinidad and Tobago. For Trinidad and Tobago, the timing of this weak and broad area of low pressure across the country is still not definite – sometime between late Tuesday and Wednesday afternoon.
However, given the fairly slow westward movement and largely disorganized nature of the low-pressure area, rainfall and gusty winds are forecast to affect a broad area of the Windwards. Islands from Trinidad and Tobago to Guadeloupe, including Barbados, are in the path of this tropical wave’s rainfall, with the strongest winds forecast to affect islands between Barbados and Guadeloupe.
Models, while there was an uptick in support this morning, are not currently enthusiastic about the development of this tropical disturbance. Upper-level conditions are quite favorable, particularly as it moves into the Caribbean Sea when an upper-level low is positioned to the system’s northeast. Low to moderate wind shear is forecast to affect this system through the next three to four days, and Invest 91L is forecast to traverse very warm sea-surface temperatures between 29°C and 31°C on its Windward Islands approach.
Mid to upper-level moisture is forecast to be moderate between Wednesday and Thursday, with relative humidity values between 50% and 65%. Precipitable water values are forecast to exceed 2 inches (50 millimeters) through the week. These factors, combined with a favorable upper-level environment, will support scattered to widespread showers and periods of rain, with isolated showers and thunderstorms producing heavy/violent rainfall rates.
Islands between Trinidad and Tobago, extending northwards to Guadeloupe, including Barbados, should all be monitoring this system and closely monitoring the meteorological alerts, watches, and warnings from your local meteorological offices.
Invest 91L’s hazards
Rainfall and Flooding
Invest 91L is primarily a rainfall threat to the eastern Caribbean.
Between 50 and 100 millimeters of rain through Friday night is forecast across the Eastern Caribbean southward of Guadeloupe. Isolated higher totals are possible on islands’ Windward (or Atlantic-facing) slopes. Specifically for Trinidad and Tobago, between 25 and 50 millimeters are forecast across both islands, with generally low totals across northwestern Trinidad, with rainfall totals between 50 and 100 millimeters favoring the southern and eastern halves of Trinidad, as well as across Tobago. In highly isolated areas, rainfall totals over the next five days can exceed 125 millimeters.
Putting the rainfall forecast into context, rainfall rates in excess of 50 millimeters per hour or areas that receive in excess of 25 millimeters within an hour tend to trigger street flooding across the country or flash flooding in northern Trinidad. For riverine flooding to occur, a large area of the country (not just in highly localized areas of western coastal Trinidad) would have to record upwards of 75 millimeters within 24 hours, and rainfall would have to fall across major rivers’ catchment areas.
For all islands, street/flash flooding is like to accompany showers and thunderstorms with heavy to violent rainfall rates. Trinidad’s chances for riverine flooding will increase through Wednesday and Thursday as soils become increasingly saturated and rains continue.
Wind
Elevated winds associated with Invest 91L are forecast to affect islands between Barbados and Guadeloupe mainly. Sustained winds are forecast between 35 KM/H and 45 KM/H, with gusts occasionally exceeding 60 KM/H, generally accompanying showers or thunderstorms.
Possible impacts include localized wind damage to trees, power lines, and small structures. 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.
Seas & Surf
Seas across Trinidad and Tobago are forecast to be agitated but generally remain moderate in open waters with waves up to 2.5 meters. North of T&T, waves in open waters could exceed 2.5 meters. Mainly seas east and north of Barbados, waves are forecast to reach up to 3.0 meters.
These waves can produce hazardous marine conditions for small craft and sea bathers.
Landslides
With the forecast rainfall accumulations, landslides, mudslides, and rockfalls are possible across islands from Guadeloupe to Trinidad and Tobago. Lahars are also possible in St. Vincent’s orange and red zones.
Tornadoes
A few funnel clouds are possible, mainly through Wednesday, due to light and variable winds, particularly across Trinidad and Tobago, as well as Grenada and its dependencies, as well as St. Vincent and the Grenadines. If a funnel cloud touches down on a body of water, it becomes a waterspout; if it touches down on land, it becomes a tornado.
What should you do?
As an individual, there are a couple of things you can do as we head through the peak of the 2022 Atlantic Hurricane Season:
- Stock your emergency kit
- Clean your surroundings and gutterings
- Secure light or loose objects outdoors
- If your roof is unsecured, purchase and install hurricane straps
- Clear larger trees near your home
- Ensure you have batteries and battery packs for your flashlights, radios, and mobile devices
- Ensure you have sufficient gas for gas-powered stoves and vehicles
- Ensure you have adequate dry foods and water to rally through an extended power outage (generally, the rule of thumb is 72 hours).
- Stock up on candles and mosquito repellant.
- Ensure you have alternative means of communication (like a battery-powered radio) if the internet or television goes down.
- Have a trusted source of information for the latest news before, during, and after a storm.
For the next 48 hours, it is important to remain indoors during gusty winds associated with showers and thunderstorms, as light objects outdoors could become airborne. Avoid venturing into flood waters. Plan for your commute and expect traffic disruptions due to fallen trees, landslides, and flooding. Avoid entering the sea if not necessary.
Elsewhere in the Atlantic
Looking further east, the National Hurricane Center has tagged Tropical Wave 42 for development. As of their 8:00 PM Tropical Weather Outlook, the NHC says, “An elongated area of low pressure located several hundred miles south of the Cabo Verde Islands continues to produce disorganized showers and thunderstorms. Environmental conditions are forecast to be favorable for some gradual development, and a tropical depression is likely to form around the middle part of this week. The system is forecast to move westward, then turn northwestward or northward by the end of the week over the eastern tropical Atlantic.”
Development chances are low for tropical cyclone formation over the next 48 hours and high over the next five days, at 30% and 70%, respectively. Julia will be the next named storm for 2022 in the Atlantic basin.
