8:30 AM Tropical Update: Tropical Wave East of Trinidad, Possible Long Range Tropical Threat in the Western Caribbean.

Tropical Weather Update Overview:
— The first “official” tropical wave of the 2019 Atlantic Hurricane Season has moved off the West African Coast. Forecast to move across T&T on Tuesday 28th May 2019.
— Eyes are on the Central American Gyre for possible tropical development later next week into early June.

No tropical development is forecast across the North Atlantic Basin over the next 5 days. The first tropical wave has moved off the Western African Coast into the Eastern Atlantic. Presently, as of 8:30 AM Friday 24th May 2019, the axis of this wave is located at 37 degrees west, between 14 degrees to 0 degrees north, moving west at 5-10 knots (very slowly), approximately 2,500 kilometers to the east of Trinidad and Tobago.

The National Hurricane Center has determined classical genesis from the African Easterly Jet and convection over North Africa for this feature.

North Atlantic Tropical Weather Update Overview, as Saharan Dust dominates the Atlantic Basin, with a tropical wave 2,500 KM east of Trinidad and Tobago.
North Atlantic Tropical Weather Update Overview, as Saharan Dust dominates the Atlantic Basin, with a tropical wave 2,500 KM east of Trinidad and Tobago.

Tropical waves typically take 5-7 days to travel across the Atlantic Ocean and move across Trinidad and Tobago. This wave is no different. As of the latest GFS, FV3, and EMCWF in their 0Z run on Friday, show the concentrated plume of tropical moisture arriving across Trinidad and Tobago mainly through Tuesday 28th May 2019 into Wednesday 29th May 2019. With tropical waves, locally heavy rainfall, thunderstorms, and gusty winds are generally possible. Based on present model guidance, this first tropical wave is not forecast to be a large rainmaker, with rainfall accumulations generally 10-15 millimeters, and isolated totals up to 25 millimeters across Eastern parts of T&T.

The designation is significant to Trinidad and Tobago because the passage of the first Tropical Wave (or the first time the ITCZ modulates across T&T) signals the start of the wet season for the islands. Following the passage of the first true tropical wave, as designated by either the National Hurricane Center or by the discretion of the Trinidad and Tobago Meteorological Service, the wet season is declared. Hence, we’re looking towards early next week for the official start of the 2019 wet season.

Long Range, Possible Central American Development

Recent long-range runs of the GFS model and its ensemble members, as well as the EMCWF (EPS) ensembles, have been predicting that a broad area of low pressure will form over Central America 5 – 10 days from now. Such a “Central American Gyres” (CAGs) can spawn a tropical cyclone, though it usually requires many days for this to occur. Hurricane Michael of October 2018 had its origins in a long-lived CAG.

Although no immediate development is forecast, heavy rainfall is forecast across parts of Central America over the next few days. Credit: NHC
Although no immediate development is forecast, heavy rainfall is forecast across parts of Central America over the next few days. Credit: NHC

Some of the model solutions predict that a tropical storm will spin up from a CAG late next week and potentially move north to threaten the U.S. This process will be made more likely to occur by a phase of the Madden-Julian Oscillation (MJO) that is expected to favor upward moving air and low pressure over the region. However, as described in detail in an excellent series of tweets on Thursday morning by Levi Cowan, we shouldn’t believe the GFS model until the European model, which has a better track record handling such systems, comes on board. The strength of a ridge of high pressure over the Southeast U.S. next week will ultimately determine if the CAG and any potential tropical cyclone it may spawn can move northwards and affect the U.S., and it is too early to judge the odds of that occurring. If this system develops, it would be no threat to the Eastern Caribbean, including Trinidad and Tobago. We’ll be monitoring this in further tropical updates.

Tropical Cyclone Climatology

Tropical Cyclone Points of Origin for May (1851-2015). Credit: NWS/NOAA/NHC

While the official start to the Atlantic Hurricane Season isn’t until June 1st, early season tropical cyclones are not unheard of. 51 of the 89 out of season tropical cyclones in the Atlantic Basin have formed in the month of May, with the most recent being Subtropical Storm Andrea on May 20th, 2019. Thankfully, for Trinidad and Tobago, these early season systems tend to form in the Western Caribbean and Southwestern Atlantic, with no impact to the Eastern Caribbean and T&T.

However, it serves as a reminder that the 2019 Hurricane Season is rapidly approaching and it is important to become prepared for both the hurricane season and the rainy season ahead!

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