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Since 2012 on the now retired Weather Underground blogs, I have been posting annotated "birdseye view" charts of the Atlantic basin, with a detailed explanation and forecasting that references the chart. From there you may know me as "NCHurricane2009." While I now do these "birdseye view" posts here, I will continue to do comments at Yale Climate Connections via Disqus where the former Weather Underground community has moved to. Feel free to reply to me there, at my Disqus feed at this link, or via e-mail at 

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*******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 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 dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.********** ...WEDNESDAY MAY 13 2020 10:50 AM EDT...

Vigorous frontal cyclone with potential to acquire tropical characteristics expected to form in the western Atlantic between the Bahamas...Bermuda...and United States east coast in 3 to 4 days. Therefore temporarily resuming birdseye view posts before the official start of the Atlantic Hurricane Season on June 1st. See area of interest #1 below for details. Elsewhere...longer-range model runs suggest that southward cold air transport on the west side of area of interest #1 could amplify a cold upper trough over the Great Lakes region southward...which could produce high instability over the warm Gulf stream waters just offshore of the eastern United States for yet another potential subtropical cyclone to form here in the wake of area of interest #1. However it is too early to call this a definite second area of interest as it is unclear at this time if this second feature would be elongated without a well-defined center while entagled with area of interest #1. AREA OF INTEREST #1...A shortwave upper trough currently producing showers and thunderstorms over the south-central United States is expected to shift eastward into the western Atlantic over the next few days. As this occurs...a pair of frontal low pressure systems will slide across the Great Lakes region of North America...the first to be supported by an upper trough trailing from the current unseasonably cold upper trough over eastern Canada...the second to be supported by energy currently just offshore of the northwestern US. It appears warm air advection (northward transport of warm air) ahead of both frontal low pressure systems will induce enough upper ridging over the northeastern US and northwestern Atlantic to cause the shortwave upper trough to amplify as it moves into the western Atlantic to the east of Florida. There has been a notable westward shift in the modeling as the trough is shown to amplify sooner...bringing the eastern upper divergence zone of the trough and resulting formation of the surface cyclone further west much closer to warmer Gulf stream waters in the mid-20s of deg C. This provides a much more favorable thermodynamic setup for the forecast surface cyclone to acquire tropical characteristics as the amplifying upper trough is of southern origin and not that cold to provide a boost in instability if the water temperatures were in the lower 20s. As a result...I have notably increased my odds of subtropical development...and now am in agreement with the National Hurricane Center's 70% odds by day 5...due to the strong computer model agreement shown in the GFS...NAVGEM...and CMC. The lastest Euro (ECMWF) is less aggressive...perhaps because it shows the surface cyclone forming further east away from the warm Gulf stream waters. I have also begun raising odds above 0% starting on May the more soon amplification of the upper trough will allow for a faster formation of a surface cyclone. And my odds of development are kept below 70% through 96 hours as the supporting upper trough may induce wind shear over the surface cyclone. However by 120 hours the shear should relax as the second frontal low over the Great Lakes produces enough warm air advection to amplify adjacent upper ridging to the north to allow the upper trough to amplify further. The interaction between the upper vorticity over the Great Lakes and supporting upper trough after 120 hours could be interesting...with the two potentially merging and producing plenty of upper divergence to cause the surface cyclone to become a powerhouse western Atlantic storm...with stronger winds on the west side of the storm sending the cold air associated with the merged upper trough southward and making the merged upper trough more amplified...which would in turn re-enforce the storm as the more amplified upper trough supports the surface storm with additional divergence. Whether or not the storm has or retains tropical characteristics as it moves northeast toward cooler waters during this appears we are in for a storm that will kick up sea swells for the United States east coast...Bermuda...and northwestern Bahamas. ****** outlook. Visit (hurricanes dot gov) for official outlook*********** IOH 24 Hr Outlook (1200Z May 14)...0% chance of subtropical cyclone formation (eastern Texas near 32N-95W) IOH 48 Hr Outlook (1200Z May 15)...0% chance of subtropical cyclone formation (Florida...western Bahamas...and adjacent waters near 29N-82W) IOH 72 Hr Outlook (1200Z May 16)...20% chance of subtropical cyclone formation (just north of the northwest Bahamas near 27.5N-78.5W) IOH 96 Hr Outlook (1200Z May 17)...50% chance of subtropical cyclone formation (western Atlantic offshore of the southeastern United States near 30N-75W) IOH 120 Hr Outlook (1200Z May 18)...70% chance of subtropical cyclone formation (western Atlantic offshore of the eastern United States near 33N-72.5W)

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