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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 forecast 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.**********

...FRIDAY DECEMBER 9 2022 7:03 AM EDT...

The following is a special update on the central Atlantic subtropical low pressure area which has recently lost tropical characteristics. Therefore this will also be my last regularly-scheduled post on the Atlantic tropics for the time being... will resume regularly-scheduled posts on the Atlantic tropics at the start of the next hurricane season on June 1 2023... or unless the potential for subtropical or tropical development returns to the Atlantic basin before then.

Satellite image of the central Atlantic subtropical low pressure area taken at 0810Z as it loses tropical characteristics:

As discussed in the previous full birdseye post #167 ( a mid-ocean upper trough has developed but with a slightly lower amplitude for reasons covered in the previous post. The lower-amplitude upper trough features a less focused and more elongated divergence zone on its east side... which has resulted in the subtropical surface low pressure area becoming elongated. The elongating structure prevented a focal point of surface convergence needed for the development of a tropical core of thunderstorms... this was illustrated best when the subtropical low was beginning to develop a core area of thunderstorms around 0200Z on Thursday but then lost the core area when the subtropical low subsequently became elongated. The lower amplitude nature of the upper trough has also produced more linear shearing upper flow which has displaced the thunderstorm area well to the northeast of the subtropical low... as opposed to more cyclonic lower-shear flow that would have otherwised occurred if the upper trough had been more amplified. With the lack of core thunderstorms to the subtropical low and whatever remaining being sheared off to the northeast... there is a lack of latent heat release at the core of the subtropical low and hence cold air associated with the upper trough has infiltrated. This means the elongated subtropical low is now a non-tropical frontal cyclone... frontal meaning that there is airmass contrasts on either side of it (cold air associated with the upper trough wrapped up in its core and west side... warm air to the east)... therefore subtropical or tropical cyclone formation is not anticipated.

Even though this system has lost tropical characteristics and is now a frontal cyclone... the cyclone remains large and strong while remaining supported by the large mid-ocean upper trough. Therefore it continues to produce a large area of sea swells which will be transferring into the north and northeastern Atlantic as the cyclone continues northeast... with swells also reaching the shores of the Azores islands today and through the weekend.

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