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 #105

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


...THURSDAY SEPTEMBER 9 2021 1:30

AM EDT...

Satellite image as of 2350Z. 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:

GFS Model Upper-Level Winds 1800Z:

See Larry and Mindy sections below for more info on the currently active tropical cyclones in the Atlantic basin. See area of interest section below for an update on the west Africa tropical wave being monitored for future tropical development once it enters the Atlantic.


Elsewhere… model support for a tropical low pressure forming in the Bay of Campeche in the timeframe that is now about four days away has decreased. This low pressure was forecast to form with the support of outflow from upper ridging to expand in the wake of the western Gulf cold core upper vorticity as the vorticity weakens while remaining cut-off from high-latitude cold air. However the models that do not develop a compact Bay of Campeche tropical low now show a broad lowering of surface pressure across the Gulf of Mexico in the long range beneath the outflow of the expanding upper ridge. Therefore will still watch for the potential development of a disturbance in the Gulf of Mexico in the days ahead.


HURRICANE LARRY… The tremendous heat engine of large Hurricane Larry has been demonstrated as the latent heat release of the thunderstorms has managed to expand the warm central Atlantic upper ridge enough to push away lingering western Atlantic upper vorticity. Despite this however… the thunderstorm bands in Larry on colorized infrared satellite have continued to be ragged with breaks. This could be a sign of the hurricane ingesting dry air produced by the western convergence zone of the upper vorticity. Whatever is negatively affecting Larry has also affected the eye… as the hurricane has lost its solid eye wall and has weakened gradually to a category 2 as a result. Most recently the max sustained winds have climbed down from 105 mph at 8 PM EDT to 100 mph at 11 PM EDT. My updated intensity forecast is lowered… and assumes that Larry may keep its minimal category 2 status for 24 more hours as the hurricane remains embedded in a low shear and upper outflow environment beneath the central Atlantic upper ridge. However it wouldn’t surprise me at this point if Larry weakens to a category 1 in the next 24 hours.


Regarding track… because the hurricane still has a decent west angle in track due to the current presence of the northwest Atlantic surface ridge… I have nudged my updated forecast track 1 degree longitude to the west for the next 24 hours. However my long term forecast track remains the same with strong model agreement. By day 2… Larry is expected to accelerate north-northeast in the flow ahead of the approaching eastern Canada frontal low. The acceleration will give little time for Larry to weaken over cooler waters before it aligns with the supportive eastern divergence zone of the upper trough tied to the frontal low… with the divergence zone then helping to make the weakening rate of Larry slow after it loses tropical character. This is why by day 2 I have Larry at category 1 hurricane force even after transitioning to a non-tropical frontal cyclone supported by the upper trough. This could result in a significant frontal cyclone that could affect Newfoundland… more on that in the bulletins below:


**Coastal sea swells will continue and remain vigorous for Bermuda through 24 hours… and relax afterwards once the hurricane accelerates to the north-northeast and away. The chances for the west side of the hurricane to pass over the island and bring tropical storm force winds remains low as the forecast track has remained essentially unchanged… however a tropical storm warning is in effect in case the hurricane wobbles more west.

** Coastal sea swells will reach the northeastern US and Atlantic Canada coasts from now through 48 hours. As mentioned above… dynamics could converge in a way that helps Larry maintain strength after losing tropical characteristics while heading toward Newfoundland just after day 2… which could is expected to result in coastal storm surge and gusty winds with damage potential. The greatest risk for wind impact is in southeastern Newfoundland based on the latest model projections of Larry’s remnant cyclone.

** Southeastern Greenland and Iceland will likely see coastal sea swells from the remnant cyclone of Larry by 3 to 5 days…

with the possibility of strong winds for southeastern Greenland.

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

0 Hr Position (0000Z Sep 9)… 105 mph maximum sustained wind hurricane centered east-southeast of Bermuda at 28.9N-59.8W

IOH 24 Hr Forecast (0000Z Sep 10)… 100 mph maximum sustained wind hurricane centered northeast of Bermuda at 34.5N-61.5W

IOH 48 Hr Forecast (0000Z Sep 11)… 85 mph maximum sustained wind non-tropical frontal cyclone centered south of Newfoundland at 44N-57.5W


TROPICAL STORM MINDY… Special update #104A… available on the home page of this site… chronicles the quick formation of Tropical Storm Mindy from the surface trough of low pressure in the Gulf of Mexico. Max sustained winds in a tiny area near the center increased a little further to 45 mph before center made landfall on Apalachicola Florida… and as the center continues to scrape the eastern Florida panhandle Mindy is estimated to have maintained this strength through 11 PM EDT. Doppler radar and satellite imagery shows the center has finally angled its way further inland in its east-northeast track while passing just south of Tallahassee Florida and making its way toward southern Georgia… and Mindy is therefore likely to weaken to an inland tropical Depression soon. Surface wind observations show some breezy winds passing through Tallahassee… so some breezy winds may reach far southern Georgia over the next few hours before Mindy weakens further. Heavy rains with flash flooding potential may occur across northeast Florida… southern Georgia… and southern South Carolina over over the next several hours.


Mindy is being swept east-northeast by the eastern Canada frontal low and its upper trough. The upper trough is not particularly friendly to Mindy while expected to increase southwesterly shear… and also the upper divergence zone in the southern part of the upper trough is linear without a maximum… which could result in Mindy elongating into a remnant low similar to a typical surface frontal zone supported by a mid-latitude upper trough. Thus I forecast Mindy to become an elongated and sheared remnant low in 24 hours as it moves back over water at a location offshore of the southeast US. None of the models predict Mindy making a comeback offshore except the GFS. The updated forecast track is adjusted north and east due to Mindy’s current position…. but the models still have Mindy miss this the surface ridge weakness to be caused by the eastern Canadian frontal low and Hurricane Larry… which will still result in Mindy becoming stalled by days 3 to 4 while trapped between the Atlantic surface ridge to the east and an eastern US surface ridge to the north to be supported by the northwestern convergence zone of the eastern Canadian frontal low’s upper trough. The stalled track below the southwesterly upper flow would make the shear worse… with even the GFS dissipating a stalled Mindy by day 4. With the negative shear Outlook and potential elongation of Mindy which would prevent it from having a defined center… I assume Mindy won’t make a comeback offshore of the southeast US after 24 hours.

Here are observations of peak wind (mph) from Mindy captured by National Weather Service stations:

**Apalachicola FL… sustained 23… gust 33 (8:53 PM EDT)

**Perry FL… sustained 12 (11:15 PM EDT)

**Tallahassee FL… sustained 18… gust 26 (now)

**Valdosta GA… sustained 6 (now)

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

0 Hr Position (0000Z Sep 9)… 45 mph maximum sustained wind tropical storm making landfall at Apalachicola Florida at 29.6N-85.4W

IOH 24 Hr Forecast (0000Z Sep 10)… Remnant low centered just offshore of the South Carolina/Georgia border at 32.5N-80.2W

AREA OF INTEREST #1… Based on Satellite imagery… a tropical wave of low pressure over Western Africa is located near 12N-2W while featuring ongoing thunderstorm squalls on its west side. Model support showing this system developing after entering the Atlantic… after day 2… remains. The upper trough associated with the current northwest Atlantic frontal low is Forecast to amplify in the east Atlantic as the warm Central Atlantic upper ridge amplifies in what will be the warm sector of Larry’s remnant cyclone. This will result in the frontal cyclone associated with the upper trough staying toward the south… which will weaken the east side of the Atlantic surface ridge enough to bend the track of this tropical wave more west-northwest toward the Republic of Cabo Verde Islands. Once the tropical wave moves past the weaker part of the surface ridge… I forecast a more west track by 120 hours.


With model support remaining from the CMC and ECMWF… and increasing from the NAVGEM… and also with ongoing thunderstorm squalls associated with the wave… it does make sense to raise development odds. However I do not raise odds as high as the NHC Outlook… only bringing them to a 30% peak… as the initial north angle in track may cause the wave to ingest the dry Saharan air layer lurking to the north. I trim odds of development to 25% by days 4 and 5 as the forecast track would bring this system closer to upper vorticity to be deposited by the upper trough… resulting in some westerly shear imparted by the upper vorticity. Albeit the latest GFS has trended a little more north with this upper vorticity… so the shear may not be quiet as high as previously thought. Therefore it may make sense in future updates to raise longer term development odds as well.


With models agreeing on this wave potentially developing while aiming for the Republic of Cabo Verde Islands in 3 to 4 days… interests here should be aware of this system.

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

IOH 24 Hr Outlook (0000Z Sep 10)… 0% chance of tropical cyclone formation (Western Africa near 12N-9W)

IOH 48 Hr Outlook (0000Z Sep 11)… 0% chance of tropical cyclone formation (inland near west coast of Africa in vicinity of 13.5N-15W)

IOH 72 Hr Outlook (0000Z Sep 12)… 30% chance of tropical cyclone formation (just east-southeast of the Republic of Cabo Verde Islands near 15N-21W)

IOH 96 Hr Outlook (0000Z Sep 13)… 25% chance of tropical cyclone formation (west of the Republic of Cabo Verde Islands near 16.5N-27W)

IOH 120 Hr Outlook (0000Z Sep 14)… 25% chance of tropical cyclone formation (eastern tropical Atlantic near 17N-32W)


...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 Hurricane Larry… remnant frontal cyclone quickly passes over southeast Newfoundland between 60 and 66 hours…approaching Canadian frontal cyclone to the west of Larry’s remnant becomes the dominant and absorbs Larry by 84 hours.

**For Tropical Storm Mindy…no redevelopment shown offshore of the southeast US

**For area of interest #1… forecast to emerge from Africa at 54 hours… tropical cyclone formation suggested over the Republic of Cabo Verde Islands at 90 hours… located at 18N-27.5W at 120 hours


1200Z ECMWF Model Run…

**For Hurricane Larry… remnant frontal cyclone quickly passes over southeast Newfoundland between 48 and 72 hours… centered between Greenland and Iceland by 120 hours.

**For Tropical Storm Mindy…no redevelopment shown offshore of the southeast US

**For area of interest #1… forecast to emerge from Africa at 48 hours…tropical cyclone formation suggested over the northern Republic of Cabo Verde Islands at 96 hours… located at 19N-26.5W at 120 hours


1800Z GFS Model Run...

**For Hurricane Larry…remnant frontal cyclone quickly passes over southeast Newfoundland at 60 hours…centered between Greenland and Iceland by 120 hours.

**For Tropical Storm Mindy… re-development offshore of the southeast US suggested near 32.5N-74.5W at 42 hours… weakens to a remnant low midway between Bermuda and North Carolina at 57 hours… after stalling west of Bermuda the remnant low dissipates at 108 hours.

** For area of interest #1… forecast to emerge from Africa at 48 hours… passes over the Republic of Cabo Verde Islands at 60 hours as a broad low pressure spin… broad low pressure reaches 14N-32.5W at 120 hours


1800Z NAVGEM Model Run...

**For Hurricane Larry…remnant frontal cyclone quickly passes over southeast Newfoundland at 60 hours… located southeast of Greenland by 120 hours.

**For Tropical Storm Mindy…no redevelopment shown offshore of the southeast US

** For area of interest #1… forecast to emerge from Africa at 54 hours… tropical cyclone formation shown just northeast of the Republic of Cabo Verde Islands at 84 hours… located just north of the islands at 120 hours.

**Tropical low becomes defined in eastern Bay of Campeche at 78 hours… makes landfall south of the Texas/Mexico border at 120 hours

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