*******Note that forecasts 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.**********
...FRIDAY MAY 6 2022 9:45 PM EDT...
Although Atlantic Hurricane Season does not officially start till June 1st... continuing daily birdseye view posts due to potential subtropical cyclone formation in the western Atlantic in the days ahead. Regardless of whether the forecast cyclone acquires tropical characteristics... it is poised to produce sea swells and rip currents for the mid-Atlantic and northeastern United States coast this weekend. See area of interest #1 section below for more details.
AREA OF INTEREST #1... An amplified upper trough and associated surface low pressure pivoting eastward across the southeastern US is producing severe weather tonight... as of this writing severe thunderstorm and tornado advisories span northeastern North Carolinas and Virginia... check your local and national news media for more info on what remains of this severe weather event. Sliding east in tandem with this severe weather system is a current upper trough over eastern Canada.
A frontal cyclone over western Canada is pumping up warm core deep-layered ridging over central and eastern Canada via warm southerly flow on its east side. This ridge will in turn cut-off the aforementioned severe weather system and also a portion of the current eastern Canada upper trough into a western Atlantic upper vortex just after 24 hours. The eastern divergence zone of the upper vortex will trigger the formation of a broad surface cyclone... with the models also agreeing on the upper vortex and surface cyclone drifting west-southwest toward the southeast US coast (after 48 hours) under the influence of the Canadian deep-layer ridge. My odds of subtropical development are initially lower at days 3 and 4 due to lukewarm low-20 deg C water and an upper vortex not very cold (1200 dekameter height at 200 mb... would like to see heights below 1200 dekameters for more confidence in instability for thunderstorms). I raise odds to 30% by 120 hours as the west-southwest forecast track brings this system into warmer Gulf steam waters. It should be noted the GFS and NAVGEM have trended with a better defined core to the surface low pressure field... suggesting the eventual formation of a tropical core (12Z NAVGEM around 84 hours and 12Z GFS by 5+ days). If these model trends remain or if more models join in... will consider raising subtropical development odds in future updates.
I have done the following adjustments to the updated outlook below (relative to my previous blog post):
(1) The 72 and 96 hour subtropical development odds have been raised from 10% to 15% as the latest water temp data shows slightly warmer temps in the western Atlantic (https://www.nhc.noaa.gov/sst/)
(2) The 96 hour forecast point is nudged east as the latest model guidance suggests a southwestern lobe of the Canadian deep-layered ridge may temporarily stunt the west-southwest progress of this system. Energy to eject from the current west Canada/northeast Pacific upper trough is expected to weaken this lobe of the ridge to allow the west-southwest track to resume by day 5
Regarding potential impacts to land areas:
(1) A tight surface pressure gradient is expected to setup between the north side of the forecast surface cyclone and south side of the Canadian deep-layer ridge. This will drive a strong toward-shore wind and ocean flow for the northeastern and mid-Atlantic US east coast this weekend and into early next week... expect coastal sea swells and rip currents here regardless of whether or not the surface cyclone gets tropical characteristics.
(2) This tight pressure gradient will likely produce gusty winds across the mid-Atlantic US coast early next week
(3) Coastal sea swells are possible for the southeast US coast by the middle of next week should the surface cyclone maintain strength through acquisition of tropical characteristics.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z May 7)...0% chance of subtropical cyclone formation (North Carolina/Virginia border near 36N-76.5W)
IOH 48 Hr Outlook (1800Z May 8)...0% chance of subtropical cyclone formation (western Atlantic near 35N-71W)
IOH 72 Hr Outlook (1800Z May 9)...15% chance of subtropical cyclone formation (western Atlantic near 33N-72.5W)
IOH 96 Hr Outlook (1800Z May 10)...15% chance of subtropical cyclone formation (western Atlantic near 33N-72.5W)
IOH 120 Hr Outlook (1800Z May 11)...30% chance of subtropical cyclone formation (offshore of the Carolinas near 32.5N-75W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z CMC Model Run...
**For area of interest #1...broad surface low pressure forecast near 32.5N-72.5W by 120 hours
1200Z ECMWF Model Run...
**For area of interest #1...broad surface low pressure forecast near 33N-71.5W by 120 hours
1200Z GFS Model Run...
**For area of interest #1...broad surface low pressure forecast near 33N-72.5W by 120 hours
1200Z NAVGEM Model Run...
**For area of interest #1...possible subtropical cyclone centered near 34.5N-71W at 84 hours... while accelerating southwest weakens to a remnant low located near 30N-75W at 120 hours