*******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 APRIL 23 2024 11:25 PM EDT...
Even though the 2024 Atlantic Hurricane Season does not officially start until June 1... temporarily resuming daily birdseye view posts on the Atlantic tropics while currently monitoring a low pressure swirl in the eastern Atlantic for signs of acquiring tropical characteristics. See area of interest #1 section below for more information.
AREA OF INTEREST #1... Satellite image of eastern Atlantic as of 0020Z April 24... red arrow points to low pressure swirl currently being monitored for signs of tropical characteristics:
Origins of current eastern Atlantic deep-layered low pressure system... from April 15 to 18 the south part of an upper trough that ejected from eastern North America innocuously passed north of the Caribbean islands while its eastern divergence zone produced a band of showers and thunderstorms along with a surface trough. By April 18 a large-scale upper vortex became quasi-stationary over North America... and a piece of this energy ejected from the upper vortex and merged with the pre-existing system that had been north of the Caribbean islands from the 15th to 18th. The merged upper trough then proceeded to shift eastward into the open eastern Atlantic... amplifying into an upper vortex through today in response to amplifying warm core deep-layer ridging to the west associated with the warm sector (northward warm air transport) of what is currently the western Atlantic frontal cyclone. The eastern divergence zone of the amplifying upper trough/materializing upper vortex quickly kicked off a surface cyclone on April 22 that has since become stacked with the upper vortex... resulting in a deep-layer cyclone that has since retrograded south-southwestward in response to the steering flow of the neighboring deep-layer ridge to the northwest. Despite this system traversing waters below 26 deg C (initially starting around 31N latitude where water temps were 20 deg C)... the opportunity for instability and central shower and thunderstorm activity associated with tropical characteristics has arisen from cold upper air temps of the upper vortex where 200 mb heights were as low as 1196 dekameters as of 0600Z early today. The potential for instability has recently increased further with the south-southwestward retrogression of this system which has allowed it reach warmer waters of 22 deg C... and indeed the partial ring of showers and thunderstorms near the surface center has shown some strength in recent hours... particularly north of center. As a result I have upgraded this system to a tropical area of interest.
Various model runs since mid-April hinted at the possibility of an eastern Atlantic surface cyclone with possible tropical characteristics... however my hesitancy to declare this area of interest ahead of time was associated with inconsistencies in model solutions with some showing a weak surface system with multiple centers and others showing a surface cyclone with well-defined center. It was not until April 21 that models agreed on a stronger western Atlantic frontal system whose warm sector would trigger amplification of central Atlantic deep-layer ridging and resultant downstream amplification of the upper trough in the eastern Atlantic. The more amplified eastern Atlantic upper trough was key for this event as its stronger divergence zone triggered a more bonafide initial surface cyclone... which has allowed the surface cyclone to last longer as it now begins a post-mature decay phase underneath the core of the parent eastern Atlantic upper trough/vortex where upper divergence is lacking. Since April 21 was waiting to see how the now-predicted longer lasting surface layer of the cyclone would respond when reaching warmer 22 deg C waters... and with the positive response tonight noted in the prior paragraph I promptly have upgraded it to a tropical area of interest.
As of 0000Z earlier this evening the surface layer of the cyclone was centered near 27N-34.5W while moving south-southwest faster than the parent upper vortex... indicating the surface layer of the steering is stronger than the upper-levels. This will allow the surface cyclone to decouple from the upper vortex... where it will reach a more stable environment away from the colder core of the upper vortex in addition to suppressing upper convergence on the southwest side of the vortex. Indeed since 0000Z the partial ring of showers and thunderstorms around the surface center has begun to wane... therefore I have assigned low 20% odds of subtropical cyclone formation for the next 12 hours and decreased the odds to 0% by 24 hours.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 12 Hr Outlook (1200Z Apr 24)... 20% chance of subtropical cyclone formation (eastern Atlantic near 25N-35.2W)
IOH 24 Hr Outlook (0000Z Apr 25)... 0% chance of subtropical cyclone formation (eastern Atlantic near 23N-36W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Not in the official outlook
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).
1200Z (Apr 23) CMC Model Run...
**For area of interest #1... surface low continues south-southwest while gradually weakening and dissipates near 20N-39W at 60 hours
1200Z (Apr 23) ECMWF Model Run...
**For area of interest #1... surface low continues south-southwest while gradually weakening and dissipates near 20N-40W at 84 hours
1800Z (Apr 23) GFS Model Run...
**For area of interest #1... surface low continues south-southwest while gradually weakening and dissipates near 20.5N-39.5W at 57 hours
0600Z (Apr 23) NAVGEM Model Run...
**For area of interest #1... surface low continues south-southwest while gradually weakening and dissipates near 20.5N-37.5W at 78 hours