| Above: MODIS view of a tropical wave off the coast of Africa that was being given 5-day development odds of 20%. Image credit: NASA. |
The National Hurricane Center has kept their orange and red crayons sheathed over the past day, but there are three “yellow crayon” areas of concern with 5-day odds of development of 20 - 30% in the Atlantic.
94L headed towards the Lesser Antilles has lost most of its convection
A tropical wave (94L) located at 11am EDT Tuesday near 14N, 47W, about 900 miles east of the Lesser Antilles Islands, was headed west at about 10 mph. This system has lost nearly all of its heavy thunderstorms since Monday, and has very poor model support for development.
Satellite images on Tuesday morning showed that 94L had an elongated but fairly well-defined surface circulation, but almost no heavy thunderstorm activity. The severely limited heavy thunderstorm activity was due to dry air, as seen on the latest Saharan Air Layer Analysis.
The 6Z Tuesday run of the SHIPS model predicted that the atmosphere in front of 94L would have mostly favorable conditions for development over the next two days, with low wind shear and sea surface temperatures of 28 – 29°C (82 – 84°F). However, mid-level relative humidity was predicted to remain near 55%, which is on the dry side for tropical cyclone development. Dry air will inhibit development unless 94L can generate enough heavy thunderstorm activity to moisten the atmosphere. By Friday, when 94L will be nearing the Lesser Antilles Islands, some models (though not all) were predicting moderate wind shear that would make development more difficult.
The 0Z and 6Z Tuesday runs of our three top models for predicting tropical cyclone genesis—the GFS, European and UKMET—all showed no support for development, and none of the 70 members of the 0Z ensemble runs of the GFS and European models showed 94L reaching the Lesser Antilles Islands as a tropical depression.
The tropical wave is predicted to take a track mostly to the west over the coming week, and 94L could arrive in the Lesser Antilles Islands as early as Saturday. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave this system 2-day and 5-day odds of development of 20%. The next name on the Atlantic list of storms is Humberto.
Update on the strong convectively coupled Kelvin wave passing the Pacific... This wave is projected to pass the Atlantic basin between September 19-25th. Still keying in on a late September, early October burst in Atlantic tropical cyclone activity. pic.twitter.com/OOpSeBAfJh
— Michael Ventrice (@MJVentrice) September 9, 2019
Next wave to watch is off the coast of Africa
A tropical wave that emerged from the coast of Africa on Monday had less support for development from the Tuesday morning model runs than on Monday, but it is still one we need to keep a close eye on. This wave, which had not yet been given an “Invest” assignment by NHC, had a good deal of spin but limited heavy thunderstorm activity on Tuesday morning, as seen on satellite imagery.
The tropical wave will benefit from the moister atmosphere that 94L has created in its wake, but none of the 0Z and 6Z Tuesday runs of our three top models for predicting tropical cyclone genesis—the GFS, European and UKMET—predicted that the wave would develop in the coming five days. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 0% and 20%, respectively.
Disturbance in the southeast Bahamas
An area of disturbed weather associated with a low pressure system was bringing disorganized heavy thunderstorms to the waters of the southeast Bahamas and Turks and Caicos Islands on Tuesday morning. The system was showing increasing organization on satellite imagery compared to on Monday, but was battling high wind shear near 20 knots.
We can expect the disturbance to bring a few areas of 2 – 4” of rain to portions of Cuba and southern portions of The Bahamas Tuesday through Thursday, and to South Florida Friday through Sunday. This system had support for development from about 10 – 20% of the 70 ensemble members of the 0Z Tuesday GFS and European models, with development most likely to occur on Saturday or Sunday, after the system crosses Florida and enters the Gulf of Mexico. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave this system 2-day and 5-day odds of development of 0% and 30%, respectively.
Gabrielle is gone
Tropical Storm Gabrielle was declared post-tropical in NHC's final advisory at 11 am EDT Tuesday. Far from any land areas, Gabrielle was heading northeast into the cold waters of the North Atlantic graveyard for tropical cyclones. Moisture from Gabrielle's remnants will reach the northern United Kingdom on Thursday.
