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 #135

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


…WEDNESDAY OCTOBER 13 2021 1:06 AM EDT...

Satellite image as of 0230Z. 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 1800Z (Tuesday Oct 12):

GFS Model Upper-Level Winds 1800Z (Tuesday Oct 12):

See area of interest sections below for areas being watched for development in the Atlantic tropics.


AREA OF INTEREST #1… The latest central Atlantic tropical wave of low pressure to cross the Lesser Antilles islands has encountered increased northwesterly shear. This is due to the amplification of warm core upper ridging to the northwest caused by the thunderstorm latent heat release of area of interest #2… which in turn caused the previously weakening upper vorticity near 20N-58W to also amplify. The northwesterly upper-level shearing flow was produced between the upper vorticity and the upper ridging to the northwest… and was enhanced by the outflow of the thunderstorms of area of interest #2. For much of Tuesday the shear kept the thunderstorm squalls of the wave to the east of the wave axis and Lesser Antilles… and the surface low pressure swirl located on the wave axis dissipated while no longer in touch with the supportive upper level outflow of the squalls. As of tonight some thunderstorm activity was able to develop over the islands and eastern edge of the Caribbean while the tropical wave axis encounters an area of upper divergence between the upper vorticity and upper ridging. However conditions for development of this wave remain hostile with northerly wind shear and also due to the dominating surface inflow of area of interest #2… and tropical cyclone formation of this wave is no longer possible. This is my final statement on this wave on this blog.


AREA OF INTEREST #2… As expected… the north apex of the tropical wave of low pressure crossing the central Caribbean Sea has evolved into a surface trough of low pressure over the southeast Bahamas…. supported by the eastern divergence zone of upper vorticity that has settled over the western Bahamas. The forecast position in my outlook below for the next 24 hours is based on the location of the upper divergence maximum as shown in the GFS model. I have 0% development odds during this time as the surface trough lost its organizing thunderstorm activity that it had on Tuesday and will need time to re-organize. By 48+ hours an eastward turn away from the southeast Bahamas is anticipated due to an eastward-shifting surface ridge weakness to be driven by the eastern divergence zone of the upper trough to arrive from its current position over the northeast US. I only assign 10% development odds during this timeframe due to likely westerly shear to be generated by the south side of the upper trough. By 72 hours I assign 0% development odds as this disturbance gets caught in suppressing upper convergence on the southwest side of the upper trough.


This disturbance was able to produce thunderstorms over Haiti and the Dominican Republic (Hispaniola) on Tuesday while activity has been and will continue to be suppressed over the southeast Bahamas by the shear induced by the upper vorticity over western Bahamas. Although there are currently no thunderstorms over Hispaniola… redevelopment of thunderstorms and heavy rain is possible here later today.

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

IOH 24 Hr Outlook (0000Z Oct 14)… 0% chance of tropical cyclone formation (southeastern Bahamas near 22N-71W)

IOH 48 Hr Outlook (0000Z Oct 15)… 10% chance of tropical cyclone formation (north of the Dominican Republic near 22N-70W)

IOH 72 Hr Outlook (0000Z Oct 16)… 0% chance of tropical cyclone formation (north of Puerto Rico near 22N-66W)

...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… no development shown

**For area of interest #2… develops into a broad surface low near 25.5N-66W by 48 hours… located at 30N-46W as an elongated non-tropical frontal low at 96 hours

1200Z ECMWF Model Run...

**For area of interest #1… no development shown

**For area of interest #2… develops into a broad surface low near 23N-70W by 48 hours… becomes a more consolidated circular low pressure near 25.5N-57.5W at 72 hours… located at 35N-35W as an elongated non-tropical frontal low at 120 hours


1800Z GFS Model Run...

**For area of interest #1… no development shown

**For area of interest #2… develops into a surface low near 24N-69W at 30 hours… becomes elongated east-west by 54 hours with the east end becoming a non-tropical frontal low in the long range


1800Z NAVGEM Model Run...

**For area of interest #1…no development shown

**For area of interest #2… develops into a surface low near 25N-70W at 24 hours… becomes elongated east-west by 60 hours with the east end becoming a non-tropical frontal low in the long range.

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