*******Note that forecast and outlooks in this post are NOT the official forecast from the National Hurricane Center (NHC). They are my own detailed views on the Atlantic tropics based on current observations and latest computer model runs. As such do not make decisions based on my posts...consult news media...watches and warnings from your local weather office...and any evacuation orders issued by local governments to make the most informed and best decisions. Visit the NHC website hurricanes.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********
...SUNDAY AUGUST 13 2023 12:30 PM EDT...
A surface trough of low pressure has entered the southeastern Gulf of Mexico after it previously passed over the western Bahamas and Florida Straits. Over the next 48 hours this feature is likely to curve northward toward the eastern US Gulf coast (Florida panhandle… Alabama… and/or Mississippi coast) while curving around the west side of the Atlantic surface ridge and moving into a ridge weakness associated with a frontal low over the Great Lakes that will develop with the support of an upper trough that will dive in from western Canada. Although upper winds are generally conducive for the development as an upper ridge with low shear and upper outflow has overspread the region from the southern US… the surface trough has been lacking thunderstorm activity over the last several hours and is not forecast to develop before its landfall with the eastern US Gulf coast.
Elsewhere... the current mid-latitude upper ridge over the Atlantic is forecast to push upper vorticity trapped in the Atlantic tropics westward toward the Caribbean. Within the next few days this will allow tropical upper ridging with low shear and upper outflow to recover in the eastern and central tropical Atlantic. Therefore will keep an eye on surface tropical waves of low pressure currently in the eastern Atlantic and Africa which may later take advantage of the recovering tropical upper ridging:
(1) The first such wave is currently in the eastern Atlantic near 30W longitude and is currently large in size which has allowed it to inhale suppressing dry Saharan air from the north. The east side of the wave appears to have a gyre of showers and thunderstorms currently south-southeast of the Republic of Cabo Verde Islands which yesterday’s 1200Z CMC and yesterday’s 1800Z NAVGEM runs developed. Should this gyre become better organized in future updates… will consider upgrading it to an area of interest in future updates.
(2) Animation of METEOSAT satellite imagery
(https://tropic.ssec.wisc.edu/real-time/europe/movies/m7irn/m7irn_loop.html) suggests another tropical wave of low pressure over western that has moved from 4W to 9W over the last day or so… now featuring a sprawling but disorganized area of thunderstorms. This wave had some long range model support in the CMC through 1200Z yesterday… and continues to have some support in the GFS and also the recent 0600Z NAVGEM run. Should it later become better organized will consider upgrading it to an area of interest in future updates.
(3) Animation of METEOSAT satellite imagery
(https://tropic.ssec.wisc.edu/real-time/europe/movies/m7irn/m7irn_loop.html) suggests another tropical wave over central Africa now crossing 7.5E longitude which shows thunderstorm activity somewhat organized with cyclonic curvature. If it continues to remain organized… will have to monitor its progress as it later enters the tropical Atlantic from the west coast of Africa in a few days.
METEOSAT satellite image showing the position of eastern Atlantic and Africa surface tropical waves of low pressure as of 1200Z August 13. The position of each wave axis is marked with a yellow dashed line:
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Aug 13) CMC Model Run...
**East side of large wave currently at 30W longitude organizes into a tropical low near 14.5N-34W through 78 hours… tropical low opens back to a wave while crossing 47.5W longitude at 120 hours
0000Z (Aug 13) ECMWF Model Run...
**Tropical wave currently over central Africa emerges from west coast of Africa at 96 hours and develops a tropical low just northeast of the Republic of Cabo Verde Islands at 120 hours…. becomes a weak tropical compact cyclone northwest of the islands and near 19.8N-26W at 150 hours… weakens to a remnant low located at 20N-30W by 168 hours
0600Z (Aug 13) GFS Model Run...
**Tropical wave currently over western Africa enters the eastern tropical Atlantic from the west coast of Africa at 66 hours... smaller tropical low develops within the southeast side of the large tropical wave and near 14N-20W at 93 hours... the small tropical low cyclonically orbits northwestward within the eastern outer circulation of the large tropical wave and passes just northeast of the Republic of Cabo Verde Islands through 126 hours… tropical low located just northwest of the islands by 168 hours
0600Z (Aug 13) NAVGEM Model Run...
** Tropical wave currently over western Africa enters the eastern tropical Atlantic from the west coast of Africa at 54 hours... tropical low develops within the southeast side of the wave and near 13N-20W at 72 hours... tropical low develops into a tropical cyclone that moves over the northern Republic of Cabo Verde Islands through 144 hours… tropical cyclone located at 18.5N-27.5W at 168 hours
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