*******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.**********
...TUESDAY MAY 23 2023 7:40 PM EDT...
Usually-reliable GFS and ECMWF model suites continue to forecast a subtropical low pressure area with cyclone development potential for the western Atlantic waters offshore of the southeastern United States... to pivot into the Carolinas... by Friday and the weekend. Therefore daily birdseye view posts on the Atlantic tropics will continue on this site over the next few days. See area of interest #4 section below for more information on the forecast subtropical low pressure system.
As done on this site starting last year... I will be sequentially numbering up areas of interest for possible Atlantic tropical development throughout the year... resetting back to #1 at the start of each year. This scheme is so that each area of interest retains a numeric identity from update to update... which reduces confusion when simultaneous areas of interest begin and end when tropical activity increases during the Atlantic Hurricane Season. The current area of interest is tagged #4 as the first three were assigned in earlier birdseye view posts on this site.
AREA OF INTEREST #4... The usually-reliable GFS and ECMWF models are converging on an upper air pattern conducive for the development of a subtropical low pressure area near the southeastern United States coast within the next few days while a cold-core upper vortex consolidates over the inland southeastern US and a warm deep-layer ridge consolidates over the Great Lakes region. At present the northwestern convergence zone of a sprawling longwave upper trough over eastern North America is ushering in a southeastward-diving and strong central Canada surface ridge. Through day 5... the flow on the west side of the anticyclonic surface ridge will promote northward warm air transport and amplification of a warm core upper ridge over central Canada...with the surface and upper ridges eventually aligning over the Great Lakes region. The formation of the adjacent deep-layer ridge will in turn cut-off the south part of the current eastern North America longwave upper trough into a cut-off upper vortex over the interior southeastern US. The upper vortex is however expected to be positioned near enough to the Atlantic coast to allow for a regime of upper divergence and low shear over offshore warm Gulf stream waters... allowing the formation of a surface low pressure area with enough thunderstorm activity to be considered subtropical. The latest sea-surface temp analysis from the NHC (https://www.nhc.noaa.gov/sst/) shows the Gulf stream has recently warmed to the tropical development threshold of 26 deg C... therefore subtropical cyclone formation appears increasingly possible by Friday and this weekend. Should the core of the subtropical surface low pressure system develop enough thunderstorm activity to develop latent heat release driven outflow for additional strengthening... it could evolve into a fully-tropical storm. Given the persistence of the GFS and ECMWF in showing potential development... I have already assigned peak 20% odds of subtropical cyclone formation for this new area of interest. Should the consensus in the GFS and ECMWF persist... a further increase in odds maybe warranted in future updates.
This system is expected to pinwheel north and then westward in the flow around the east and north sides of the forecast southeastern US upper vortex... and around the south side of the anticyclonic forecast Great Lakes deep-layer ridge. This well-defined steering pattern should allow the subtropical surface low to arc northwestard into the Carolinas... followed by arrival into the core of the inland upper vortex as typically seen with a post-mature subtropical or non-tropical surface low pressure system. Heavy rainfall along coastal and inland areas of the Carolinas appear increasingly likely by the latter part of this upcoming weekend... and depending on the peak strength of the system's core at landfall time some wind and surf impacts cannot be ruled out for coastal areas of the Carolinas.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z May 24)... 0% chance of subtropical cyclone formation (central Florida peninsula near 28N-81.5W)
IOH 48 Hr Outlook (1800Z May 25)... 0% chance of subtropical cyclone formation (just offshore of the east Florida coast near 28.5N-80W)
IOH 72 Hr Outlook (1800Z May 26)... 10% chance of subtropical cyclone formation (offshore of the southeastern US near 31N-79W)
IOH 96 Hr Outlook (1800Z May 27)... 20% chance of subtropical cyclone formation (vicinity of Georgetown South Carolina near 32.5N-79.5W)
IOH 120 Hr Outlook (1800Z May 28)... 0% chance of subtropical cyclone formation (northwestern Georgia near 33N-84W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT*****************************
Area of Interest not in official outlook
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (May 23) CMC Model Run...
**For area of interest #4... frontal low forms offshore of southeastern North Carolina at 132 hours with center passing north-northeastward over Cape Hatteras by 144 hours.
1200Z (May 23) ECMWF Model Run...
**For area of interest #4... broad frontal low forms east of Florida near 28.5N-79W at 84 hours... subtropical cyclone formation suggested offshore of South Carolina near 31.5N-79W at 114 hours... makes landfall near Georgetown South Carolina between 120 and 126 hours.
1200Z (May 23) GFS Model Run...
**For area of interest #4... broad frontal low forms east of Florida near 29N-78.5W at 63 hours... subtropical cyclone formation suggested near 30.5N-78W by 84 hours... makes landfall near Georgetown South Carolina at 99 hours... while quickly arcing westward the inland remnant low weakens to a trough reaching eastern Tennessee by 120 hours.
1200Z (May 23) NAVGEM Model Run...
**For area of interest #4... lengthy surface trough becomes established by 102 hours spanning from the southeastern Gulf of Mexico to waters offshore of the Carolinas... non-tropical frontal low develops at north end of trough and offshore of Virginia and southeastern Maryland by 120 hours.