*******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.**********
...SUNDAY MAY 8 2022 12:10 AM EDT...
Although Atlantic Hurricane Season does not officially start till June 1st... continuing daily birdseye view posts due to potential subtropical cyclone formation offshore of the southeastern United States in the days ahead. Regardless of whether or not the surface low pressure of interest acquires tropical characteristics... it is already bringing impact to the mid-Atlantic and northeastern United States coast. See area of interest #1 section below for more details.
AREA OF INTEREST #1... A deep-layer ridge over eastern Canada is in the process of cutting off an amplified eastern US upper trough as well as a portion of another upper trough that has recently entered the northwest Atlantic from eastern Canada. This will result in the formation of a large cut-off upper vortex in the western Atlantic as we progress through Sunday and Monday. To be entangled with and supported by the upper vortex is a large surface frontal low currently exiting the southeastern US... the same system that produced severe thunderstorms across a large swath of the south-central and southeastern US last week. As we progress through next week...the upper vortex and surface low are expected to retrograde southwest under the influence of the Canadian deep-layer ridge... into the waters offshore of the Carolinas... Georgia... and northeast Florida. It is during this time we will be watching this system’s potential to gain tropical characteristics.
My odds that the surface low gains tropical characteristics are initially at a low 15% at days 2 and 3 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 20% by days 4 and 5 as the southwest forecast track brings this system into warmer Gulf steam waters.
I have done the following adjustments to the updated outlook below (relative to my previous blog post):
(1) The 24 hour forecast point is nudged west as the eastern US upper trough... currently supporting the surface low pressure of interest... is currently a little west of previous forecasts. Longer-range forecast points (days 4 and 5) are adjusted based on the position of the parent upper vortex in the recent 18Z GFS model run.
(2) Long range odds of subtropical development are adjusted down to 20% (from the previous 30%). The latest model data suggests an elongation of the upper vortex which will cause the surface low to be elongated (because the supportive divergence zone of the upper vortex will be elongated). Elongated surface lows have a harder time establishing a well-defined center needed for subtropical cyclone status. Also in the latest model runs the surface low is shown to weaken before it gets a chance to reach the aid of warmer Gulf Stream waters... as the surface low is shown to spend some time whirled underneath the core of the upper vortex where there is a lack of upper divergence.
Regarding potential impacts to land areas:
(1) A tight surface pressure gradient has set up between the north side of the surface low and south side of the Canadian deep-layer ridge. This is driving a strong toward-shore wind and ocean flow for the northeastern and mid-Atlantic US east coast. Sea swells... rip currents... and gusty winds will continue here Sunday and into early next week.
(2) 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. However the odds of this occurring appear low at present based on the above-mentioned latest model data
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z May 8)...0% chance of subtropical cyclone formation (western Atlantic near 35N-72W)
IOH 48 Hr Outlook (1800Z May 9)...15% chance of subtropical cyclone formation (western Atlantic near 33N-72.5W)
IOH 72 Hr Outlook (1800Z May 10)...15% chance of subtropical cyclone formation (western Atlantic near 33N-72.5W)
IOH 96 Hr Outlook (1800Z May 11)...20% chance of subtropical cyclone formation (offshore of the Carolinas near 32.5N-74.5W)
IOH 120 Hr Outlook (1800Z May 11)...20% chance of subtropical cyclone formation (offshore of Georgia and northeast Florida near 30.5N-77.5W)
...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 becomes elongated SW-NE at a location offshore of the US east coast by 84 hours... elongated low subsequently weakens to a surface trough while turning southwest and reaches 30N-75W by 120 hours
1200Z ECMWF Model Run...
**For area of interest #1...broad surface low becomes elongated SW-NE at a location offshore of the US east coast by 72 hours... elongated low subsequently weakens to a surface trough while turning southwest and reaches 30N-75W by 120 hours
1800Z GFS Model Run...
**For area of interest #1...broad surface low pressure located near 31N-73W at 96 hours... subsequently weakens to a surface trough located near 30N-79W by 120 hours
1200Z NAVGEM Model Run...
**For area of interest #1...broad surface low pressure located near 30N-72.5W at 90 hours... subsequently weakens to a surface trough located near 29N-75.5W by 120 hours