Tropical Update Overview:
— INVEST – 92L – A broad area of low-pressure southeast of Bermuda has medium chances (50%) of development over the next 48 hours and 5 days respectively, possibly attaining subtropical characteristics on Saturday
— Tropical Wave 02 – This weak tropical wave continues in the Caribbean Sea, with isolated showers near the wave axis. This wave will be absorbed by the CAG this weekend.
— Tropical Wave 04 – This weak tropical wave is forecast to traverse T&T Saturday into Sunday, bringing increased rainfall chances to the islands this weekend. With upper-level support, isolated thunderstorms are possible. This wave has not been analyzed by the National Hurricane Center.
— Tropical Wave 05 – This tropical wave has moved into the Atlantic Ocean, yet to be analyzed by the National Hurricane Center. It is still well over a week away from T&T, it is forecast to bring elevated rain chances to T&T late next week into the weekend.
— Impacts to T&T – No direct tropical threats to Trinidad and Tobago are forecast over the next week but locally heavy rainfall is possible particularly Saturday afternoon and between 12 AM to 2 PM on Sunday due to Tropical Wave 04. Street flooding, gusty winds generally between 30-50 KM/H, and occasionally in excess of 55 KM/H are possible. Flash flooding, landslides, and frequent lightning are less likely but 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.
The National Hurricane Center (NHC) is monitoring a tropical disturbance – Invest 92L – in the North Atlantic Ocean, just southeast of Bermuda, for tropical development.
In their special tropical outlook at 9:00 PM, this disturbance and a nearby upper-level low are combining to produce a wide area of showers and thunderstorms. The organization of the disturbance has not changed substantially during the past several hours, but a subtropical depression could still form tonight or tomorrow while the system moves generally northward. Further development is not expected after that time due to unfavorable environmental conditions.
This tropical disturbance has a medium (50%) chance of tropical cyclone formation over the next 48 hours and two days respectively.
Satellite images show this complex already had a comma-shaped subtropical look to it on Friday evening. Relatively cool sea surface temperatures of around 25°C (77°F) and strong wind shear also suggest that any development would be subtropical rather than tropical.
The next name on the Atlantic list is Cristobal. If 92L manages to become a depression, it will be only the second time in Atlantic tropical records that any year has spawned three tropical or subtropical cyclones prior to the official start of hurricane season (June 1st).
The year 1951 saw Tropical Storm One in January (though this system had subtropical characteristics) and a tropical depression as well as Hurricane Able in mid-May. Note that the January 1951 tropical storm could easily be considered a laggard system from the 1950 season, just as Hurricane Alex in January 2016 was arguably the last tropical cyclone of the 2015 season.
The next Special Tropical Weather Outlook on this system will be issued by 9 AM EDT Saturday, or earlier if necessary.
No threat to the Lesser Antilles, including T&T.
Tropical Wave 02
The second tropical wave for the 2020 Atlantic Hurricane Season is located along 76W, from 19N southward. Isolated showers are ongoing along the wave axis. The wave is moving west at 15 knots (28 KM/H) and is forecast to be absorbed by the Central American Gyre this weekend.
A large, complex area of low pressure—a recurring feature called the Central American Gyre—(CAG) will slog from the Northeast Pacific into the Caribbean and Gulf of Mexico over the next few days, potentially causing a variety of trouble. One or more tropical cyclones may spin off from the gyre, and there is a good chance of torrential rains, flooding, and mudslides in the coming week regardless of any tropical development.
This is the case over the next two weeks, with locally heavy rainfall likely across the Central American Region.
No threat to the Lesser Antilles, including T&T.
Tropical Wave 04
As of the 9:00 PM Tropical Update, the axis of Tropical Wave 04 is approximately along is along 58W, from 10N southward, moving westward 10 knots (18.5 KM/H).
While infrared imagery shows abundant upper level moisture and cloudiness streaming across the region, there are few showers with no thunderstorm activity presently associated with the wave axis.
However, as the wave moves across T&T over the next 24-36 hours, upper-level enhancement is forecast to allow for shallow convection and isolated thunderstorms particularly after midnight Saturday into Sunday.
Wind shear, one of the chief factors into our lack of rainfall, remains neutral to strong across the region through the weekend.
Guidance from the top global models is in agreement with periods of showers and isolated thunderstorms between 12:00 AM to 2:00 PM Sunday, with isolated showers on Saturday, favoring the late morning through the afternoon.
Tropical Wave 05
As of the 9:00 PM Tropical Update, the axis of Tropical Wave 05 is approximately along is along 30W, from 11N southward, moving westward 10 to 15 knots (18-28 KM/H). Scattered moderate convection is ongoing from 05N-10N between 25W to 30W following the wave axis, with convection ahead of the wave associated with the ITCZ.
Based on the 12Z and 18Z runs of global models, moisture associated with this wave is forecast to move across mainly Trinidad and Tobago beginning on Friday 5th June through Sunday 7th June 2020.
This is still 7-9 days away but models are hinting at our first widespread moderate to heavy rainfall event. Note that this wave is not forecast to develop into a tropical cyclone at this time.
What does all of this mean for Trinidad and Tobago?
Saturday: After a few early morning showers, a mostly sunny to somewhat hazy conditions are forecast throughout the day. This means hot conditions are likely throughout the day, particularly in areas with partly cloudy skies. By the late morning (10 AM) through the mid-afternoon (3 PM), isolated showers of varying intensities are forecast across both islands, with the medium chance of an isolated thunderstorm favoring western coastal Trinidad and offshore waters. Conditions are forecast to settle across Trinidad by the evening, with isolated activity favoring Eastern Trinidad and Tobago through the night.
Gusty winds up to 55 KM/H, street flooding is possible in heavy to violent showers and isolated thunderstorms. Seas to remain moderate, with waves up to 2 meters in open waters, but may become choppy during heavy showers and thunderstorms.
This axis of Tropical Wave 04 to move across T&T overnight, with winds shifting between east-southeast to the east-northeast, returning to east-southeast throughout the day on Sunday.
Sunday: After midnight, isolated showers are possible, favoring Eastern Trinidad and Tobago. Upper-level support is forecast to aid in the development of shallow convection (showers) and isolated thunderstorms through the mid to late morning. Conditions are forecast to settle by the late afternoon as a high-pressure system rebuilds across the region, becoming increasingly hazy due to the surge of Saharan Dust that follows.
As abundant low-level moisture is forecast for much of Saturday into Sunday, with southeasterly winds – a likely scenario if showers do not move across Trinidad would be sea-breeze convergence, daytime heating, and orographic effects will trigger showers and isolated thunderstorms during the late morning through the afternoon. There may be the occasional enhancement from gust fronts as wind shear causes activity east of Trinidad and Tobago to dissipate, generating said gust fronts.
Particularly during heavy to violent showers and thunderstorms on Wednesday, with gusty winds up to 55 KM/H. Seas to remain moderate, with waves up to 2 meters in open waters, but may become choppy during heavy showers and thunderstorms. Street/flash flooding and landslides are possible.
Monday: A high-pressure system is forecast to regain dominance across the region. This is forecast to allow for mostly sunny, breezy, and hot conditions throughout the day. Low-level cloud patches and isolated pockets of convection is forecast to traverse T&T, bringing brisk isolated showers, accompanied by gusty winds up to 55 KM/H. Afternoon showers are possible, mainly across hilly, southern, and western areas of Trinidad. Mostly settled conditions are forecast during the evening into the night, with the odd isolated showers. Note that a surge of Saharan Dust is forecast to move across the region.
Impacts This Upcoming Week
Winds: Sustained surface winds between 25 KM/H and 45 KM/H with gusts up to 55 KM/H are likely in heavy showers or thunderstorms across Trinidad and Tobago, particularly Tuesday into Wednesday.
With wind gusts up to 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.
Rainfall: This is not forecast to be a widespread, heavy rainfall event. Much of the heavy rainfall is forecast to remain offshore – south of Tobago & east of Trinidad. Generally, most areas that receive rainfall are forecast to see daily totals less than 10 millimeters, with in excess of 15-20 millimeters in isolated thunderstorms or heavy/violent 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. Thunderstorms are forecast to generally remain offshore, more so in the Gulf of Paria.
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.
Tropical Cyclone Climatology
Tropical Cyclone Points of Origin during the month of May. Though much of the points of origin are west or north of T&T as we move into the first 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.