MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #145
*******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.**********
…TUESDAY OCTOBER 26 2021 1:00 AM EDT...
Satellite image as of 0220Z. Areas of interest circled in yellow are not mentioned in the NHC tropical weather outlook. Areas circled in a green dashed line are in the NHC 5-day tropical weather outlook. Areas circled in a solid green line are in the NHC 2-day tropical weather outlook:
NHC TAFB Surface Analysis 1800Z (Monday Oct 25):
GFS Model Upper-Level Winds 1800Z (Monday Oct 25):
See area of interest #1 section below for more details on the rapidly intensifying surface cyclone located just offshore of the United States east coast being monitored for acquisition of tropical characteristics.
Elsewhere… some model runs suggest a strong tropical wave of low pressure will emerge from Africa and enter the eastern tropical Atlantic in about two days. However upper vorticity in the eastern Atlantic is expected to persist while re-enforced a pocket of upper vorticity to soon be deposited by the current fracturing western Atlantic upper trough. This upper vorticity is likely to make conditions for this wave’s development hostile while inducing westerly wind shear.
And finally… the current highly amplified cold core upper trough moving into western North America is expect to later cross eastern North America and drive a surface cold front as far south as the southern Caribbean Sea in a few days. The tail end of this front is likely to evolve into a tropical disturbance supported by the outflow of the ongoing upper ridge in the Caribbean. Will likely be adding an an additional area of interest for the southern Caribbean in my next update as the possibility of tropical development will be within a five day window by that time.
AREA OF INTEREST #1...The surface trough of low pressure that recently crossed the Florida peninsula from the Gulf of Mexico has accelerated northeast and is a rapidly intensifying surface frontal cyclone located just offshore of the United States east coast. As of 0000Z the swirl center of the cyclone passed offshore of North Carolina near 35N-74W… and has featured an increasingly large and impressive comma-shaped thunderstorm mass on its northeast and east sides. The surface cyclone is being supported by the tremendous upper divergence zone on the east side of a fast-approaching and amplified eastern US cold core upper trough. The upper trough is expected to amplify further into a cold core upper vortex as the west side of the intensifying surface cyclone pulls cold air southward… and as the adjacent warm core Canadian upper ridge amplifies in the warm sector of the current western North America upper frontal system/upper trough.
I have notably raised odds of the surface cyclone becoming a subtropical cyclone for a myriad of reasons including the already impressive thunderstorm comma generated with the aid of the upper divergence which will continue for another 24 hours. Once the upper trough becomes a rather cold upper vortex after that time… the upper divergence directly over the surface cyclone will subside. However the cold temps of the upper vortex are likely to aid in thunderstorm generation despite the surface cyclone being over water temps in the low 20s of deg C. The upper vortex and surface cyclone are expected to shift east toward the north wall of warm Gulf Stream waters by 48 and 72 hours which will only add to the instability needed for thunderstorms… and this is when I forecast a high 70% chance of subtropical cyclone formation.
After 72 hours… the current northwest Atlantic upper trough will be in the northeast Atlantic and amplifying due to the amplified Canadian upper ridge to shift east into the northwest Atlantic. The amplifying northeast Atlantic upper trough is likely to grab and stretch the overhead upper vortex of the surface cyclone… with the upper vortex and surface cyclone diving southeast into the open central Atlantic while pivoting around the southwest side of the upper trough. The stretched vortex may produce a belt of shearing winds over the surface cyclone. In addition… the upper vortex is likely to warm/weaken while remaining cut-off from high latitude cold air courtesy of the warm core upper ridge to eject from Canada. The potential for shear and loss of instability as the upper vortex warms suggest less favorable conditions for subtropical development… and I lower development odds accordingly in the 96 and 120 hour timeframes.
Regardless of subtropical cyclone development or not… the presence of the rapidly intensifying surface cyclone will produce the following impacts:
**Increasing rough surf for the US mid-Atlantic… US northeast… and Atlantic Canada coasts through late tomorrow and into early Wednesday.
**Increasing gusty winds for the US mid-Atlantic and US northeast coast through late tomorrow and into early Wednesday. High wind warnings are currently in effect for eastern Massachusetts and Rhode Island in particular as the intensifying surface cyclone center could pass very close to the region… resulting in wind damage and power outages.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Oct 27)…50% chance of subtropical cyclone formation (southeast of Cape Cod Massachusetts near 40N-70W)
IOH 48 Hr Outlook (0000Z Oct 28)… 70% chance of subtropical cyclone formation (northwest Atlantic near 40N-65W)
IOH 72 Hr Outlook (0000Z Oct 29)…70% chance of subtropical cyclone formation (northwest Atlantic near 40N-60W)
IOH 96 Hr Outlook (0000Z Oct 30)…50% chance of subtropical cyclone formation (north Atlantic near 40N-54W)
IOH 120 Hr Outlook (0000Z Oct 31)…10% chance of subtropical cyclone formation (central Atlantic near 35N-45W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Oct 25) CMC Model Run…
**For area of interest #1… frontal low rapidly intensifies into a frontal cyclone that makes a cyclonic loop just offshore of Massachusetts from 30 to 48 hours after which time it accelerates east… located at 38N-52.5W at 120 hours as a frontal low.
**Tail end of cold front evolves into a southern Caribbean tropical low pressure near 12.5N-79.5W at 144 hours
1200Z (Oct 25) ECMWF Model Run...
**For area of interest #1… frontal low rapidly intensifies into a frontal cyclone that makes a cyclonic loop offshore of the northeast US from 24 to 48 hours after which time it accelerates east… located at 40N-59W at 96 hours as a possible subtropical cyclone… located at 36N-49W at 120 hours as a weakened less tropical remnant low
**Tropical wave forecast to emerge from Western Africa at 48 hours… located at 10.5N-27.5W at 120 hours as a broad tropical low
**Tail end of cold front evolves into a southern Caribbean tropical low pressure near 12N-80W at 168 hours
1800Z (Oct 25) GFS Model Run...
**For area of interest #1… frontal low rapidly intensifies into a frontal cyclone that makes a cyclonic loop just offshore of Massachusetts from 24 to 48 hours after which time it accelerates east…located at 40N-55W at 93 hours as a possible subtropical cyclone…located at 35N-36.5W at 120 hours as a weakened less tropical remnant low
**Tropical wave forecast to emerge from Western Africa in next 48 hours… located at 9N-26.5W at 72 hours as a broad tropical low… tropical low located at 10N-32W at 120 hours
**Tail end of cold front evolves into a southern Caribbean tropical low pressure near 12N-81.5W at 165 hours
1800Z (Oct 25) NAVGEM Model Run...
**For area of interest #1… frontal low rapidly intensifies into a frontal cyclone just offshore of Massachusetts from 18 to 24 hours… while arcing on a cyclonic loop the cyclone makes landfall across eastern Massachusetts and Rhode Island through 30 hours after which time it accelerates east… located at 38.8N-47.5W at 120 hours as a possibly intense subtropical cyclone
**Tail end of cold front evolves into a southern Caribbean tropical low pressure near 13N-80W at 138 hours