Since 2012 on the 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 via Disqus on Weather Underground at You can see my Disqus feed at this link for my latest comments. Feel free to reply to me with your disqus account or e-mail at 

  • NCHurricane2009


*******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.**********

...MONDAY MAY 25 2020 12:26 AM EDT...

Even though the Atlantic hurricane season does not start until June 1...continuing daily birdseye view posts on the Atlantic tropics as I am monitoring two areas for potential tropical development...see pair of area of interest sections below for additional details. Elsewhere...a surface low pressure swirl that formed offshore of the eastern United States coast yesterday has weakened and lost thunderstorm activity while encountering unfavorable upper northwesterly winds in the wake of the upper vortex/trough that generated it that are now shearing this feature...and also weakening this feature as the upper flow converges overhead. Thus tropical development is not expected here.

AREA OF INTEREST #1...The thunderstorm activity in the northwestern Caribbean supported by the eastern upper divergence zone of an upper trough that spans the Gulf of Mexico and western Caribbean has expanded northward across western Cuba and Florida peninsula as the upper trough is drifting northward in the large scale stuck jet stream pattern...specifically in between a persistent upper trough regime over western North America and upper ridge over eastern North America and western edge of the Atlantic. A surface trough of low pressure is likely to form in this disturbance...and continue to track north as the supporting upper trough continues its northward drift. The disturbance would also track northward from the surface flow between western Atlantic surface ridging expected to persist beneath the convergence on the east side of the upper ridge axis and a broad area of surface low pressure over the central United States to be supported by divergence on the east side of of the western North America upper trough. Because such a surface trough disturbance will be largely also tucked beneath the highly amplified upper ridge axis which would favor low shear and upper ouflow for additional support of thunderstorm activity...will be on the lookout for possible tropical cyclone development from this northward shifting disturbance. In my updated outlook below however...I have lowered the odds of development as the curvature of the thunderstorm bands suggest the lowest surface pressure of the disturbance is farther west in the eastern Gulf of Mexico...thus my updated forecast track is shifted westward which increases land interaction with the Florida peninsula and southeastern United States coast. Also I have adjusted the forecast track northward as the disturbance apepars to be located a bit further north compared to my previous forecast.

****** outlook. Visit (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1800Z May 25)...0% chance of tropical cyclone formation (southwest Florida coast near 26.5N-82W)

IOH 48 Hr Outlook (1800Z May 26)...5% chance of tropical cyclone formation (southeast United States coast at the Florida/Georgia border near 30.5N-81.5W)

IOH 72 Hr Outlook (1800Z May 27)...0% chance of tropical cyclone formation (Inland over the Carolinas near 33.5N-79.5W)

AREA OF INTEREST #2...A shortwave upper trough producing showers and thunderstorms is ejecting eastward across the Great Lakes region of the United States and southeastern Canada. Over the next few days computer models still insist that this shortwave upper trough will shift southeastward across the western Atlantic while diving on the east side of the longwave upper ridge over eastern North America. On its southeastward dive the shortwave upper trough has long been forecast by models to amplify into a cut-off upper vortex...producing a frontal low pressure system southeast of Bermuda where water temperatures are currently running at 24 to 26 deg or just below the threshold for tropical development. However the forecast cut-off upper vortex is expected to be cold enough where it can help boost thunderstorm activity...therefore the forecast frontal low pressure system could acquire tropical characteristics and become a subtropical cyclone. I have kept odds of subtropical development at 0% through 72 hours and begin rising odds above 0% at 96+ hours as this is when models generally agree that the surface frontal low pressure will develop. By 120 hours...the longwave upper ridge over eastern North America is finally expected to shift eastward into the northwestern Atlantic...causing the cut-off upper vortex and surface frontal low pressure to drift northwestward around the southwest side of the upper ridge. I am keeping odds of subtropical development on the low side as models have trended weaker with the surface frontal low pressure...perhaps because the robust longwave upper ridge with its east convergence will maintain a strong surface ridge in the western Atlantic...perhaps strong enough to make it more difficult for a surface low pressure to take hold.

****** outlook. Visit (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1800Z May 25)...0% chance of subtropical cyclone formation (east of Cape Cod Massachusetts near 41N-68W)

IOH 48 Hr Outlook (1800Z May 26)...0% chance of subtropical cyclone formation (northeast of Bermuda near 33N-65W)

IOH 72 Hr Outlook (1800Z May 27)...0% chance of subtropical cyclone formation (western Atlantic near 28N-60W)

IOH 96 Hr Outlook (1800Z May 28)...5% chance of subtropical cyclone formation (western Atlantic near 28N-62W)

IOH 120 Hr Outlook (1800Z May 29)...10% chance of subtropical cyclone formation (southeast of Bermuda near 30N-64W)


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