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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.**********

...TUESDAY MAY 19 2020 10:34 AM EDT...

See Tropical Storm Arthur section below for details on the only active tropical cyclone in the Atlantic basin. Elsewhere it is quiet in the Atlantic tropics.

TROPICAL STORM ARTHUR...The upper divergence zone of an upper trough that has arrived to the southeastern Canadian coast has produced a surface ridge weakness to the east of Tropical Storm Arthur manifesting itself as a frontal boundary which separates cold air from an eastern Canada surface ridge from warmer air from a western Atlantic surface ridge. Arthur has continued sliding eastward away from the United States east coast while drawn to this ridge weakness...becoming increasingly entangled with the frontal boundary. Arthur despite being sheared by upper westerly winds out ahead of the southeastern Canadian upper trough is producing boosted thunderstorm activity near the center and has strengthened further to 60 mph maximum sustained winds overnight. This appears to be due to non-tropical processes...specifically from supportive upper divergence out ahead of both the southeastern Canada upper trough and the vigorous upper trough over the eastern United States. Thus it is possible later today the National Hurricane Center declares that Arthur has transitioned into a non-tropical low pressure along the frontal boundary. However in my updated forecast below I opt for now to keep Arthur as a tropical cyclone as models agree the southeatern Canadian upper trough and surface frontal boundary will shift eastward and away and leave Arthur behind. This should mean Arthur would begin to weaken as shear persists and the supportive divergence zone of the upper trough moves away from although my forecast intensity is raised due to the current intensity of the tropical does show weakening going forward. The eastward shift of the surface frontal zone will allow the eastern Canada and western Atlantic surface ridges to bridge...sending Arthur back on a southwestward drift by 48 hours. This is also the time I show dissipation to a remnant low as the southwestward drift would move Arthur out of the Gulf stream and into cooler waters. The CMC...Euro...and NAVGEM models have increasingly converged on the forecast track I have been predicting...which loops Arthur back southwestward at a location just north and west of Bermuda...thus my updated track forecast is essentially the same as my previous. The latest GFS is the eastern outlier while showing the circulation passing directly over Bermuda by 48 hours. With most models now agreeing that Arthur stays just north and west of is likely Bermuda should not see any direct impacts (rain/breezy winds) from the weakening circulation of Arthur. But because the tropical storm has been maintaining is more likely now that Bermuda will see some coastal sea swells from Arthur.

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

0 Hr Position (1200Z May 19)...60 mph maximum sustained wind sheared tropical storm centered at 37.5N-69.5W

IOH 24 Hr Forecast (1200Z May 20)...50 mph maximum sustained wind sheared tropical storm centered north of Bermuda at 36N-65W

IOH 48 Hr Forecast (1200Z May 21)...Remnant low pressure centered northwest of Bermuda at 34N-67W

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