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BIRDSEYE VIEW POSTS

Since 2012 on the now retired Weather Underground blogs, I have been posting annotated "birdseye view" charts of the Atlantic basin, with a detailed explanation and forecasting that references the chart. From there you may know me as "NCHurricane2009." While I now do these "birdseye view" posts here, I will continue to do comments at Yale Climate Connections via Disqus where the former Weather Underground community has moved to. Feel free to reply to me there, at my Disqus feed at this link, or via e-mail at IOHurricanes@outlook.com 

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MY 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #17

*******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 MAY 28 2023 12:30 AM EDT...

The broad surface low pressure area parked just offshore of the southeastern United States has evolved into a non-tropical frontal cyclone. Although this feature has ran out of time to acquire tropical characteristics... this feature will bring additional impacts as it makes landfall on the South Carolina coast within the next 24 hours. See area of interest #4 section below for more information on this system.


Elsewhere... upper vorticity is expected to spread across the Gulf of Mexico and western Atlantic waters offshore of the Bahamas and southeastern United States within the next five days as current upper trough energy from the western US merges with what will remain of the current southeastern US upper vortex... with the merger shifting eastward with time. At present there is some uncertainty as to whether or not the upper vorticity becomes amplified enough to produce a subtropical or tropical disturbance over Gulf of Mexico or western Atlantic waters (a higher amplitude upper-level feature on its east side produces lower shear and increased upper divergence needed for tropical activity). Should models later converge on a solution favoring a tropical or subtropical disturbance in the region... will initiate an area of interest for potential development in future updates as needed.


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... While remaining parked beneath the supportive eastern divergence zone of the upper vortex in the region... the surface low pressure area near the southeastern United States coast has strengthened into a frontal cyclone over the last 24 hours. Throughout the morning hours of Saturday thunderstorm activity was persisting near the core of the cyclone. However the transition to subtropical status did not occur as the core activity subsided by the afternoon and evening hours as water vapor satelilte imagery suggested invasion of drier cool air from the west associated with the core and western convergence zone of the upper vortex... note this will be my final update on this system on this blog as subtropical cyclone formation odds are now 0%.


The surface cyclone center has been stationary at a location just offshore of the southern South Carolina coast... instead of making landfall by now as previously anticipated... due the strength of the Great Lakes deep-layer ridge to the north. Over the next 24 hours the ridge will be weakened by the southeastward diving upper trough now over central Canada which should allow northward motion of the cyclone to commence. Models are split as to the angle of the north track... with some leaning toward the northeast toward the ridge weakness associated with the trough diving in from central Canada and some leaning toward the northwest under the influence of the ridge and upper vortex. The track in my updated outlook below is nudged eastward to remain aligned in the middle of the latest model spread. It should be noted the surface cyclone will take longer to weaken the further east it stays as it will be more aligned with the eastern divergence zone of the upper vortex. The upper vortex will be kicked east toward the surface cyclone within the next couple of days as upper westerly flow increases with the encroachment of upper trough energy to the west from the western US and central Canadian upper trough from the northeast. Therefore the surface cyclone will ultimately be weakening while becoming trapped beneath the core of the upper vortex... where upper divergence is lacking... sooner or later.


Over the next 24 hours coastal surf and additional wind gusts are possible for the coastal Carolinas... as well as inland areas of southeastern North Carolina and northeastern South Carolina. Rainfall that was over the Carolinas has shifted north and westward into southern Virginia... eastern Kentucky... and eastern Tennessee. Renewed rainfall squalls are developing closer to the center of circulation and are pivoting into the eastern Carolinas. Heavy downpours will remain possible in this region over the next 24 hours.


Here are some National Weather Service station reports of wind (in mph) from the last several hours... available at weather.gov:

**Brunswick GA... sustained 9... gust 22 (Saturday 9:53 PM EDT)

**Savannah GA... sustained 22... gust 30 (Saturday 11:55 AM EDT)

**Charleston SC... sustained 22... gust 36 (Saturday 11:15 AM EDT)

**Florence SC... sustained 18... gust 35 (Saturday 1:53 PM EDT)

**Wilmington NC... sustained 24... gust 41 (Saturday 1:53 PM EDT)

**Lumberton NC... sustained 21... gust 31 (Saturday 1:56 PM EDT)

**Kenansville NC... sustained 17... gust 26 (Saturday 8:25 PM EDT)

**Hatteras NC... sustained 10... gust 26 (Saturday 12:51 PM EDT)

**Nags Head NC... sustained 17... gust 25 (Saturday 9:30 PM EDT)

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (0000Z May 29)... 0% chance of subtropical cyclone formation (northeastern corner of South Carolina near 34N-79.8W)

******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************

Formation chance through 48 hours...0%

Formation chance through 7 days (168 hours)...0%


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)


1200Z (May 27) CMC Model Run...

**For area of interest #4... frontal cyclone makes landfall on central South Carolina coast near Georgetown at 24 hours... inland weakening remnant low drifts northeastward and dissipates over eastern North Carolina at 66 hours.


1200Z (May 27) ECMWF Model Run...

**For area of interest #4... frontal cyclone makes landfall on the North Carolina/South Carolina border at 30 hours... through 48 hours the weakening remnant low arcs northwestward into western North Carolina where it dissipates.


1800Z (May 27) GFS Model Run...

**For area of interest #4... frontal cyclone makes landfall on central South Carolina coast near Georgetown at 18 hours... inland weakening remnant low drifts north-northeastward and dissipates over eastern North Carolina at 42 hours.


1800Z (May 27) NAVGEM Model Run...

**For area of interest #4... frontal cyclone makes landfall on central South Carolina coast near Georgetown at 18 hours... while drifting north-northwest the inland weakening remnant low dissipates over the central North Carolina/South Carolina border at 54 hours

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