MY 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #28
*******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.**********
...WEDNESDAY JULY 12 2023 1:50 PM EDT...
While now back from vacation... we are tracking an Atlantic tropical area of interest in the open central Atlantic. This marks the thirteenth such area of interest tracked on this site this year... see the area of interest section below for more informaiton.
AREA OF INTEREST #13... Over the last few days... an amplified jet stream pattern has been in progress across the mid-latitudes of North America and the North Atlantic... with amplified upper troughs over eastern North America and northeast Atlantic and an amplified upper ridge in between and over the northwestern Atlantic. The warm core amplified upper ridge is persisting due to surface southerly flow (northward warm air transport) ahead of surface frontal systems being generated by the eastern North America trough. As a result the amplified ridge is in the process of pulling some vorticity associated with the northeast Atlantic trough southwestward into the central Atlantic. Over the last several days computer models have insisted that a surface low pressure would initially form in split flow upper divergence between the southwest side of the incoming central Atlantic upper vorticity and southeast side of the northwest Atlantic upper ridge... with the surface low then arcing eastward and the northward around the south and east sides of the central Atlantic upper vorticity while becoming supported by the eastern divergence region of the upper vorticity and potentially gaining tropical characteristics (persisting thunderstorm activity near its center) in the process. The National Hurricane Center has been mentioning this system since July 9 in their tropical weather outlook due to the model support... and indeed over the last 24 hours the surface low pressure has materialized and was centered near 35N-52.5W as of 1200Z earlier today.
The shower and thunderstorm activity of the new surface low pressure was displaced south of its swirl center due to northerly shear induced by the west side of the incoming central Atlantic upper vorticity and southeast side of the northwest Atlantic upper ridge. As the surface low continues east and then north into the east side of the upper vorticity... it will also get closer to the core of the vorticity where the shear is lighter and indeed thunderstorm activity is already beginning to wrap closer to the center from the southeast. However I set my peak odds of subtropical cyclone formation slightly below the NHC... at 40%... as the forecast track keeps the surface low near the 26 deg C isotherm for only 24 more hours before it lifts northward into cooler waters. The upper vorticity is also not particularly cold enough to generate instability and thunderstorms over water temps below 26 deg C. Some recent runs of the GFS model also indicate the upper vorticity may be elongated for much of the forecast period... resutling in an elongated eastern divergence zone and hence elongated broad surface low without a well-defined center needed for subtropical cyclone formation. By 72 hours I taper subtropical cyclone formation odds down to 0% as the surface low continues north toward cooler waters. Note that in the 96+ hour window some model runs indicate the surface low could linger on while curving eastward in track... likely as a less tropical feature due to the mild water temps... as some upper vorticity from the eastern North America upper trough finally arrives and teams up with the central Atlantic upper vorticity to create an eastward-moving supporting upper trough in the environment of the surface low.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jul 13)... 40% chance of subtropical cyclone formation (central Atlantic near 32.5N-46W)
IOH 48 Hr Outlook (1200Z Jul 14)... 20% chance of subtropical cyclone formation (central Atlantic near 34N-45W)
IOH 72 Hr Outlook (1200Z Jul 15)... 0% chance of subtropical cyclone formation (central Atlantic near 37.5N-46W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Formation chance through 48 hours...40%
Formation chance through 7 days (168 hours)...50%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z (Jul 12) CMC Model Run...
**For area of interest #13... subtropical cyclone suggested near 32.5N-47.5W at 36 hours... curves north and weakens to a remnant low near 39N-46.5W through 120 hours
0000Z (Jul 12) ECMWF Model Run...
**Not available at above-mentioned source
0600Z (Jul 12) GFS Model Run...
**For area of interest #13... strengthens as a broad subtropical low without a well-defined center near 32N-46W through 36 hours... northeast end of the broad subtropical low strengthens into a subtropical cyclone near 33.5N-45W through 48 hours... curves north to 39N-45W through 102 hours where it maintains strength as a potentially as a less tropical system over cooler waters... the persisting surface low then curves east to 39N-43W through 120 hours.
0600Z (Jul 12) NAVGEM Model Run...
**For area of interest #13... subtropical cyclone suggested near 32.5N-45.5W at 48 hours... curves north to 39.5N-43W through 96 hours where it maintains strength as a potentially as a less tropical system over cooler waters... the persisting surface low then curves east to 39.5N-39.5W through 120 hours.