BIRDSEYE VIEW POSTS

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 IOHurricanes@outlook.com 

 
 
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MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #59 (Weekend Edition)

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


...SATURDAY JULY 24 2021 10:00 PM EDT...

Satellite image as of 2000Z. 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 0600Z:

GFS Model Upper-Level Winds 0600Z:


A tropical wave of low pressure earlier today in the eastern Caribbean Sea produced an area of strong thunderstorms north of the Caribbean islands with the assistance of the eastern divergence zone of an upper vortex to the north. However as the north end of the wave has left the divergence zone and moved into the center of the upper vortex where divergence is lacking…thunderstorm activity has reduced as of this evening and tropical development is not expected here.


See area of interest sections below for multiple areas being monitored for tropical development along a cold front currently in the western Atlantic...which include:

(1) Area of interest #1...surface low pressure area offshore of Florida and Georgia

(2) Area of interest #2...surfacce low pressure area north of Bermuda.


AREA OF INTEREST #1...The strong upper ridge over eastern Canada is in the process of cutting off a large portion of the upper trough spanning the Canadian and eastern US coasts into a string of upper vorticity that will become pushed southeast into the western Atlantic shortly. A surface low pressure swirl offshore of the Florida east coast persists under the support of divergence on the south side of the upper trough which will soon become the upper vorticity string as discussed above. The surface low pressure has drifted southeast since its formation yesterday as the supporting upper trough is shifting southeast. The upper trough has also been disruptive to the surface low pressure’s organization while shearing the thunderstorms to the southeast of the swirl center…and as of this evening lacks strong thunderstorm activity.


Because the upper vorticity string is cold core in nature...it is forecast to generally weaken due to widespread warm southerly flow occurring ahead of the large frontal low pressure system currently moving across Canada. The atmospheric warming will also result in a large warm upper anticyclonic ridge across much of the United States. And as the surface low pressure swirl begins to move west toward the Florida northeast coast over the next 24 hours while steered by the south side of the current eastern US surface ridge…the surface low will be under the southeast side of the anticyclonic upper ridge and northwest side of the decaying upper vorticity string. This upper atmospheric setup could result in upper convergence over the surface low as typically seen in the mid-latitudes where surface ridges tend to occur on the west side of upper troughs and east side of upper ridges. Or alternatively the surface low might fire new thunderstorm activity over its center and create enough focused latent heat release to make upper outflow that combats the upper convergence regime. With either scenario possible…I hold 50% odds of tropical development at this time (note the NHC at one point today had 60% odds in their outlook…but have recently come down to 50% as of this writing). My updated forecast track is nudged north due to the current position of the surface low…which reduces the potential for the surface low to reach the Florida panhandle coast as it curves north in track on the southwest corner of the eastern US surface ridge. Thus my odds of development for Monday July 26 have been dropped to 0%.


Regarding impacts…any short-term tropical development tomorrow could result in sea swells and rip currents along the southeast US and northwestern Bahamas coastline. The potential for similar ocean effects along the northeast US Gulf coast on Monday is reducing with the updated more north & inland track discussed at the end of the previous paragraph. Any short-term tropical development tomorrow could also result in heavy rains and possible breezy or gusty winds across the northern Florida peninsula by tomorrow night. Short-term tropical development could also mean heavy rains for southern Georgia and southeastern Alabama late tomorrow and through Monday.

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

IOH 24 Hr Outlook (1800Z Jul 25)...50% chance of tropical cyclone formation (just offshore of northeast Florida near 29.5N-80.5W)

IOH 48 Hr Outlook (1800Z Jul 26)...0% chance of tropical cyclone formation (inland over Florida/Georgia border near 30.5N-83.5W)


AREA OF INTEREST #2...As noted in the above area of interest #1 section...a large portion of the upper trough spanning the Canadian and eastern US coasts is in the process of becoming cut-off into an upper vorticity string that will become pushed southeast into the western Atlantic in the next 24 hours. The north portion of this upper vorticity string is behaving like an upper trough…resulting in a new surface frontal low pressure north of Bermuda (near 35.5N-65W as of 1800Z) and supported by the eastern divergence zone of the upper trough feature. Because the cold core upper trough feature is forecast to weaken under the warm sector of the current approaching Canadian frontal low pressure system...this could result in reduced southwesterly shear on the east side of the upper trough in the next 24 hours...with the fast northeast track of the surface low pressure also helping to reduce the shearing effect of the southwesterly upper flow. Moreover the latest GFS and ECMWF model runs…usually the more reliable of the global models...are more adamant in showing a compact circular circulation forming at some point within the surface low pressure in the next 24 hours...which could be an indication of a tropical thunderstorm core. Therefore I have raised odds of development further to 20% despite the current lack of strong thunderstorms and no mention in the NHC tropical weather outlook as of this writing. My forecast positions in the updated outlook below are based on the GFS and ECMWF solutions. By 48 hours...I drop odds of development to 0% as the surface low pressure moves northeast into cooler water.

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

IOH 24 Hr Outlook (1800Z Jul 25)...20% chance of tropical cyclone formation (northwest Atlantic near 40N-56W)

IOH 48 Hr Outlook (1800Z Jul 26)...0% chance of tropical cyclone formation (northwest Atlantic near 48.5N-44W)

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