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 #134

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


...TUESDAY OCTOBER 12 2021 12:15 AM EDT...

Satellite image as of 2310Z. 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 1200Z:

GFS Model Upper-Level Winds 1200Z:

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


AREA OF INTEREST #1… The surface low pressure swirl offshore of North Carolina has lost all thunderstorm activity as the north part of the nearby upper vorticity is accelerating east as a shortwave upper trough which has sheared away all the thunderstorm activity. The surface low is not able to accelerate east with the shortwave upper trough while being pinned down by the northwest Atlantic surface ridge. The surface low is also beginning to weaken under the western convergence zone of the shortwave upper trough… and impacts to the US east coast in association with this surface low have diminished. Subtropical cyclone formation chances have dropped to 0% for this surface low… and this is my final statement on this feature on this blog.


AREA OF INTEREST #2…The vigorous central Atlantic tropical wave of low pressure is fast-approaching the Lesser Antilles islands tonight with a low pressure swirl crossing 14N-58.5W as of 0000Z. The wave has been moving faster to the west than I previously anticipated… which has caused the lowest pressure of the wave to be located on the west edge of the thunderstorm activity despite being under a low shear environment beneath the central Atlantic upper ridge… because the fast westward motion of the wave is causing it to outrun its thunderstorm activity. Another negative factor this wave will be dealing with is competition for surface inflow with the increasingly defined disturbance developing near the Dominican Republic and southeastern Bahamas… area of interest #3. Despite this… I have only slightly lowered short-term tropical cyclone development odds to 30% as the wave still has a healthy structure as evidenced by the swirl it has in satellite pictures. The forecast track is adjusted westward to account for the higher westward forward speed the wave has been having… and now brings this wave west-northwest toward the ridge weakness associated with area of interest #3 until that area of interest absorbs it in 48 hours. At that point I drop development odds for this wave to 0%.


With these forecast updates:

**Expect the potential for heavy rains and gusty winds in the Lesser Antilles in the next 24 hours… even if tropical cyclone formation does not occur

**Weather associated with this wave could affect the Virgin Islands and Puerto Rico between 24 and 48 hours

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

IOH 24 Hr Outlook (0000Z Oct 13)… 30% chance of tropical cyclone formation (northeastern Caribbean Sea near 16N-64W)

IOH 48 Hr Outlook (0000Z Oct 14)… 0% chance of tropical cyclone formation (Puerto Rico near 18N-66.5W)


AREA OF INTEREST #3… A surface trough of low presume that formed east of the Lesser Antilles on Friday has since been upgraded to a tropical wave of low pressure that moved across the islands and eastern Caribbean with squalls of showers and thunderstorms. This tropical wave briefly lost activity on Monday… but is redeveloping thunderstorm squalls in the vicinity of the Dominican Republic as it encounters the supportive eastern divergence zone of upper vorticity that has settled over the western Bahamas. This wave has been introduced into the NHC tropical weather outlook while being monitored for signs of development in the days ahead.


The north apex of this wave is likely to evolve into a surface trough of low pressure in the vicinity of the southeast Bahamas… to be supported by the divergence zone of the aforementioned western Bahamas upper vorticity. The forecast positions in my outlook below for the next 48 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 this disturbance will likely struggle to consolidate as it absorbs area of interest #2 incoming from the east-southeast. By 72+ 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 central North America. I only assign 10% development odds during this timeframe due to possible westerly shear to be generated by the south side of the upper trough. By 96 hours I assign 0% development odds as the disturbance gets caught in suppressing upper convergence on the southwest side of the upper trough.

Expect possible heavy rains for the Dominican Republic and southeast Bahamas in the next 48 hours due to this disturbance.

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

IOH 24 Hr Outlook (0000Z Oct 13)… 0% chance of tropical cyclone formation (southeastern Bahamas near 22N-72.5W)

IOH 48 Hr Outlook (0000Z Oct 14)… 0% chance of tropical cyclone formation (southeastern Bahamas near 22N-71W)

IOH 72 Hr Outlook (0000Z Oct 15)… 10% chance of tropical cyclone formation (north of the Dominican Republic near 22N-70W)

IOH 96 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… remnant low shifts east and reaches Bermuda at 84 hours… remnant low weakens to a trough near 30N-60W by 120 hours

**For area of interest #2… no development shown

**For area of interest #3… no development shown


1200Z ECMWF Model Run...

**For area of interest #1…remnant low shifts east and reaches Bermuda at 96 hours… dissipates southeast of Bermuda between 96 and 120 hours

**For area of interest #2… tropical wave crosses Puerto Rico at 48 hours… turns northeast ahead of areas of interest #1 and #3 and becomes a better-defined surface low near 30N-48.5W by 144 hours

**For area of interest #3… organizes into a surface low just north of the eastern Bahamas at 48 hours… weakens to a surface trough northeast of the eastern Bahamas by 72 hours which loses its identity just after


1800Z GFS Model Run...

**For area of interest #1… remnant low dissipates northwest of Bermuda just after 78 hours

**For area of interest #2… no development shown

**For area of interest #3… organizes into a tropical low near 25N-69W at 66 hours… drifts east to 25N-63W by 120 hours

1200Z NAVGEM Model Run...

**For Area of Interest #1…remnant low dissipates over Bermuda at 78 hours

**For area of interest #2… organizes into a surface low north of Puerto Rico at 84 hours… turns northeast and dissipates near 23N-63W just after 102 hours

**For area of interest #3… no development shown

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