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 #162

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


...SUNDAY NOVEMBER 14 2021 1:29 AM EDT...

Satellite image as of 0550Z. 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 are in the NHC 2-day tropical weather outlook:

NHC TAFB Surface Analysis 1800Z (Nov 13):

GFS Model Upper-Level Winds 1800Z (Nov 13):

See area of interest #1 section below for an update on the potential for subtropical development to the south of the Azores in the days ahead. It remains quiet elsewhere in the Atlantic tropics.


AREA OF INTEREST #1...The current North Atlantic upper trough is continuing to amplify in response to a developing and amplifying warm deep-layer ridge in the western Atlantic (this deep-layer ridge is supported by the warm sector of the current eastern Canada frontal cyclone). The eastern divergence zone of the upper trough continues to support a strong North Atlantic frontal cyclone… with the cold front of the cyclone currently running through the Azores. The upper trough is expected to continue to amplify...with the developing deep-layered western Atlantic ridge beginning to cut-off the south part of the upper trough into a cold core upper vortex near the Azores. The eastern divergence zone of the developing upper vortex is beginning to produce a surface low pressure along the current cold front running through the Azores.


In the 24 to 48 hour window... the surface frontal low and upper vortex may become a more tropical feature of interest as they shift south away from the Azores and toward milder water temps in the mid-20s of deg C while pushed by the deep-layered ridge. The upper vortex is expected to be sufficiently cold (200 mb heights below 1200 dekameters) for instability at these water temps...which could result in thunderstorm activity and potential acquisition of tropical characteristics. After 48 hours...the deep-layered ridge is forecast to have its upper layer to the northwest... and surface layer (supported by the eastern convergence zone of the upper layer) passing to the north. This will result in the surface layer pushing the surface low on a more westward angle in track while the upper layer keeps the upper vortex more toward the east... and the surface low is expected to migrate beneath the west side of the upper vortex as a result. Conditions beneath the west side of the upper vortex will tend to be hostile for subtropical development with northerly wind shear and upper convergence. By 96 hours the current upper trough over western Canada will have made its way to the north Atlantic and generate its own suface frontal cyclone...with this cyclone creating a weakness in the surface layer of the ridge and slowing down the southwest track of the surface low. However this slow down will be too late..with the surface low remaining beneath the west side of the upper vortex. As a result I trim down subtropical development odds to 0% by 96 hours from prolonged exposure to upper convergence on the west side of the upper vortex which will have weakened the surface low by that timeframe...and all models remain in agreement with this idea. However I have peak subtropical development odds of 40% for the 48 hour timeframe as models have maintained forecasting a sufficiently cold upper vortex being stacked over the surface frontal low...which is a classic recipe for possible subtropical development. The 40% odds are on the medium-side...a compromise between the favorable thermodynamic profile caused by the upper vortex and the short window of time this feature will have for subtropical development given that it will migrate beneath the hostile west side of the upper vortex soon after 48 hours.


The current front running through the Azores has generated rainfall across the islands. As the surface low pressure continues to develop along the front… breezy winds will be possible within the next 24 hours as some of the latest model runs have hinted at… by showing a tightening pressure gradient between the surface low pressure and deep-layered ridge encroaching from the west.

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

IOH 24 Hr Outlook (0000Z Nov 15)… 0% chance of subtropical cyclone formation (eastern Atlantic near 34N-27W)

IOH 48 Hr Outlook (0000Z Nov 16)… 40% chance of subtropical cyclone formation (eastern Atlantic near 32N-31W)

IOH 72 Hr Outlook (0000Z Nov 17)… 20% chance of subtropical cyclone formation (eastern Atlantic near 29N-36W)

IOH 96 Hr Outlook (0000Z Nov 18)… 0% chance of subtropical cyclone formation (eastern Atlantic near 27N-38W)


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)


1200Z CMC Model Run...

**For Area of Interest #1... south part of current north Atlantic upper trough becomes cut-off by deep-layered ridge to the west as a vortex... surface frontal low forms with support from the divergence zone of the vortex at a location just east of the Azores at 24 hours...frontal low shifts southwest to 30N-32.5W through 60 hours while potentially acquiring tropical characteristics… frontal low shifts south to 23N-32.5W through 120 hours while weakening


1200Z ECMWF Model Run...

**For Area of Interest #1... south part of current north Atlantic upper trough becomes cut-off by deep-layered ridge to the west as a vortex... surface frontal low forms with support from the divergence zone of the vortex at a location just east of the Azores at 24 hours... frontal low shifts southwest to 29N-33W through 72 hours while potentially acquiring tropical characteristics…frontal low shifts south to 22.5N-35W through 120 hours while weakening

**Current cold front over northern US reaches waters just west of the Azores by 144 hours… possible subtropical development just southwest of the Azores by 168 hours


1800Z GFS Model Run...

**For Area of Interest #1... south part of current north Atlantic upper trough becomes cut-off by deep-layered ridge to the west as a vortex... surface frontal low forms with support from the divergence zone of the vortex at a location over the eastern Azores at 18 hours... frontal low shifts southwest to 32.5N-37.5W through 48 hours while featuring multiple centers which may limit potential for tropical development… frontal low shifts south to 22.5N-37.5W by 120 hours where it weakens to a remnant trough


1200Z NAVGEM Model Run...

**For Area of Interest #1... south part of current north Atlantic upper trough becomes cut-off by deep-layered ridge to the west as a vortex... surface frontal low forms with support from the divergence zone of the vortex at a location just southeast of the Azores at 18 hours... frontal low shifts southwest to 30N-33.8W through 66 hours… frontal low shifts south to 23N-39W by 120 hours where it weakens to a remnant trough

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