8:00 AM Tropical Weather Outlook: Invest 90L Continues to Organize, Subtropical Depression in South Atlantic.

At 8:00 AM Monday 20th May 2019, the US NWS National Hurricane Center issued a Special Tropical Weather Outlook concerning a trough of low-pressure southwest of Bermuda in the far western Atlantic. A surface low-pressure is forecast to develop later today and has medium chances of tropical development near 60%, over the next 48 hours, and medium chances of development over the next 5 days, at 60%. This system is of no threat of Trinidad, Tobago and the remainder of the Eastern Caribbean.

Forecast Discussion

The National Hurricane Center (NHC) is monitoring an area in the Western Atlantic for the expected development of a surface low-pressure southwest of Bermuda on Monday. Presently, showers and thunderstorms have increased in association with a trough of low pressure located about midway between the Bahamas and Bermuda.

Solid yellow contours indicate upper level divergence. Solid light blue contours indicate low-level convergence across Invest 90L. Image: (Cooperative Institute for Meteorological Satellite Studies/Space Science and Engineering Center/University of Wisconsin-Madison)
Solid yellow contours indicate upper level divergence. Solid light blue contours indicate low-level convergence across Invest 90L. Image: (Cooperative Institute for Meteorological Satellite Studies/Space Science and Engineering Center/University of Wisconsin-Madison)

Favorable upper-level divergence and low-level convergence are present across Invest 90L. According to the NHC, A low-pressure system is expected to form within this area of disturbed weather later today, and this system could become a short-lived subtropical or tropical cyclone by tonight or Tuesday while it moves northward or northeastward.

By Wednesday, however, conditions are forecast to become unfavorable for further development, and the system should be absorbed by a cold front.

As of the 0Z and 6Z runs of the top three models for forecasting tropical development, the UKMET, GFS, and EMCWF, Invest 90L now has model support from all three. However, all indicate that a surface low pressure will only briefly form from this surface trough late Monday into early Wednesday.

However, models also show quick degeneration as a stronger non-tropical low-pressure system to the north will steer this weaker, potentially tropical or sub-tropical system northward to northeastward, by Wednesday into Thursday 23rd May. It is presently in an area with marginally favorable sea surface temperatures of 26-27 degrees Celcius, and moderate to strong upper-level wind shear of 25 knots.

Track-wise, models are generally in agreement that the low pressure to the north will steer this weaker, potentially tropical or sub-tropical system northward initially, to northeastward, by Wednesday into Thursday 23rd May.

Regardless of formation, interests in Bermuda should monitor the progress of this system, as there is the potential for a near miss or even a direct hit from a weak tropical cyclone by Wednesday. An Air Force Reserve reconnaissance aircraft is scheduled to investigate the disturbance Monday afternoon, if necessary.

The next Special Tropical Weather Outlook will be issued by 2 PM AST on Monday.

This system poses NO threat to the Eastern Caribbean, including Trinidad and Tobago.

If this system were to develop, the first name on the list of names for the 2019 Atlantic Hurricane Season is Andrea.

2019 Atlantic Hurricane Season List of Names
2019 Atlantic Hurricane Season List of Names

Tropical Weather Outlook Elsewhere Across the Atlantic Basin

No tropical development is forecast elsewhere across the North Atlantic Basin over the next 5 days. According to the National Hurricane Center, there are no tropical waves in the Atlantic Basin currently being monitored in their latest tropical weather outlook or discussion.

Other meteorological offices such as the Barbados Meteorological Service and U.S. NOAA NWS Weather Prediction Center – International Desks may be monitoring features they designate as tropical waves, likely due to the origins near Africa.

However, the National Hurricane Center has not determined classical genesis from the African Easterly Jet and convection over North Africa for these features.

See the surface trough looking relatively impressive on the bottom right of the above image. This trough is embedded within the ITCZ and no development is forecast from this feature.

An interesting area of convection has emerged off the Western Coast of Africa. However, this area is likely another surface trough emerging off the African coast with its associated convection entering a more favorable environment, hence its impressive appearance. However, this surface trough is presently interacting with the ITCZ and anomalously warm waters across the Gulf of Guinea and is forecast to remain near the ITCZ with no development forecast.

This whole designation issue may come across to the layman as pedantic, as the impacts of locally heavy rainfall, thunderstorms, and gusty winds are generally the same. However, 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.

Subtropical Depression East of Brazil

Subtropical depression seen east of Brazil at 9:00AM Monday 20th May 2019 by GOES-East.

At 12:00 AM Monday 20th May 2019, the Brazilian Navy initiated advisories on a subtropical depression system located at 23 degrees south, 40 degrees west, moving south to southwest at 15 knots. Gusty winds, up to 74 KM/H and rough seas with waves up to 6.0 meters possible in the immediate vicinity of heavy convection. This system is forecast to move out to sea with little direct land impacts beyond increased surf and swells.

Note that tropical cyclones in the South Atlantic Ocean are uncommon, but we’ve already had one for the year, Tropical Storm Iba at the end of March 2019.

This system poses NO threat to the Eastern Caribbean, including Trinidad and Tobago.

May 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. 50 of the 89 out of season tropical cyclones in the Atlantic Basin have formed in the month of May, with the most recent being Tropical Storm Alberto on May 25th 2018. 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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