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 #104

*******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 SEPTEMBER 8 2021 3:20 AM EDT...

Satellite image as of 0300Z. 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 section below for more info on the only currently active tropical cyclone in the Atlantic basin. See area of interest sections below for an update on areas being monitored for tropical development in the Atlantic.


Elsewhere… some model runs still agree on a tropical low pressure forming in the Bay of Campeche in about five days 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. A new area of interest may emerge here in the coming days.


MAJOR HURRICANE LARRY… Larry has spent the last 24 hours battling with upper vorticity to the west… with the latent heat release of the hurricane helping to weaken the cool core upper vorticity. Despite this… colorized infrared satellite has shown multiple occurrences of thunderstorm bands breaking up on the west side of the hurricane. This could be a sign of the hurricane ingesting dry air produced by the western convergence zone of the upper vorticity… and also some outflow blockage on the southwest quadrant of the hurricane also caused by the upper vorticity. The hurricane has also weakened to a minimal but still formidable category 3 with 115 mph max sustained winds. Because Larry has intermittently shown improved organization over the last several hours… and with upper winds for Larry potentially improving as the upper vorticity continues to weaken… my updated intensity forecast below allows for the possibility of a little re-strengthening over the next 48 hours.


Regarding track… the previous one has performed well and so my updated one is unchanged. Larry is making a full turn to the north due a large surface ridge weakness being induced by the current pair of Canadian frontal lows. It should be noted the western convergence zone of the upper trough tied to the leading eastern frontal low will produce a passing surface ridge in the northwest Atlantic which will keep Larry’s track on a slight west lean thru 24 hours and prevent an immediate east turn at day 2. On day 3… Larry is expected to accelerate north-northeast in the flow ahead of the western of the two frontal lows. 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 western 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 3 I have Larry at strong category 1 hurricane force 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:


**Larry will bring coastal sea swells to the northern Lesser Antilles over the next day… which will gradually fade as the hurricane turns north and away.

**Coastal sea swells will continue for Bermuda through 48 hours… and become vigorous as the hurricane passes just to the east. 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 watch is in effect in case the hurricane wobbles more west.

** Coastal sea swells will reach the northeastern US and Atlantic Canada coasts in 24 to 72 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 3… which could 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 4 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 8)… 115 mph maximum sustained wind major hurricane centered at 25.4N-56.5W

IOH 24 Hr Forecast (0000Z Sep 9)… 120 mph maximum sustained wind major hurricane centered east-southeast of Bermuda at 29.5N-59.5W

IOH 48 Hr Forecast (0000Z Sep 10)… 120 mph maximum sustained wind major hurricane centered east-northeast of Bermuda at 34.5N-60.5W

IOH 72 Hr Forecast (0000Z Sep 11)… 95 mph maximum sustained wind non-tropical frontal cyclone centered south of Newfoundland at 44N-57.5W


AREA OF INTEREST #1… Despite fluctuations up and down in the intensity of thunderstorms in association with the Gulf of Mexico surface trough of low pressure… which is now being supported by the divergence on the east side of upper vorticity in the western Gulf… the overall trend has been a gradual increase in the amount and organization of the activity. The surface trough has finally made a northward migration while transitioning into a feature supposed by the upper vorticity… however this system is still disorganized while the lowest surface pressure of the trough is analyzed to west of the thunderstorms. The CIMSS 850 mb vorticity product (http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=vor&zoom=&time=) suggests two mid-level rotations… one in the Bay of Campeche… the other in the Central Gulf… instead of one single rotation… with both being south and east of the lowest surface pressure. This system is expected to shift east-northeast toward the Florida panhandle in the flow ahead of the current Central Canada frontal low. Due to the current disorganized structure and also the forecast track bringing this system over land not long after 24 hours… unlike the NHC I have opted to keep my odds of development in the Gulf of Mexico at a low 15%. Odds are dropped to 0% by day 2 due to the inland location of the forecast track during that timeframe.


Models have also dropped developing this system except for the GFS… which shows this system re-emerging into water at a location offshore of the southeast US by days 3 and 4. Any development would be facilitated by the eastern divergence zone of the upper trough associated with the central Canadian frontal low. The GFS still shows an upper trough that is not very amplified… resulting in southwesterly wind shear. In addition the current forecast track will allow this system to miss the surface ridge weakness to be caused by the Canadian frontal low and Hurricane Larry… which will result in this system becoming stalled by days 3 to 5 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 Canadian frontal low’s upper trough. The stalled track below the southwesterly upper flow would make the shear worse… with the GFS dissipating the stalled system by day 5 and so I follow suit by showing 0% development odds by then. And with the negative shear forecast… I have low 10% odds at days 3 and 4.


**This system is not expected to impact the Hurricane Ida recovery zone in southeast Louisiana

**Odds are low that tropical storm conditions (gusty winds… some coastal sea swells… and heavy rains with flash flooding potential) will occur for the Alabama and Florida panhandle coastal regions. However as a tropical Depression or tropical low pressure… this system could still produce flash flooding heavy rainfall in this area and also for southern Georgia… northeast Florida… and southern South Carolina on Thursday.

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

IOH 24 Hr Outlook (0000Z Sep 9)… 15% chance of tropical cyclone formation (northeastern Gulf of Mexico near 28N-87.5W)

IOH 48 Hr Outlook (0000Z Sep 10)… 0% chance of tropical cyclone formation (southeast Georgia near 31N-81.5W)

IOH 72 Hr Outlook (0000Z Sep 11)… 10% chance of tropical cyclone formation (offshore of the southeastern US near 32.5N-72.5W)

IOH 96 Hr Outlook (0000Z Sep 12)… 10% chance of tropical cyclone formation (offshore of the southeastern US near 33N-72W)

IOH 120 Hr Outlook (0000Z Sep 13)… 0% chance of tropical cyclone formation (offshore of the southeastern US near 33N-72W)


AREA OF INTEREST #2… Based on Satellite imagery… a tropical wave of low pressure over Western Africa as of 0000Z was located near 12N-4E while featuring a low cloud deck with curvature suggestive of rotation… and strong large western thunderstorm squalls. Model support showing this system developing after entering the Atlantic… after day 3… has increased. The upper trough associated with the current eastern Canada 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. As a result… I have opted for low 20% odds of development as the 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 15% by day 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.


With models agreeing on this wave potentially developing while aiming for the Republic of Cabo Verde Islands in 4 to 5 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 9)… 0% chance of tropical cyclone formation (Western Africa near 12N-2W)

IOH 48 Hr Outlook (0000Z Sep 10)… 0% chance of tropical cyclone formation (Western Africa near 12N-9W)

IOH 72 Hr Outlook (0000Z Sep 11)… 0% chance of tropical cyclone formation (inland near west coast of Africa in vicinity of 13.5N-15W)

IOH 96 Hr Outlook (0000Z Sep 12)… 20% chance of tropical cyclone formation (just east-southeast of the Republic of Cabo Verde Islands at 15N-21W)

IOH 120 Hr Outlook (0000Z Sep 13)… 15% chance of tropical cyclone formation (west of the Republic of Cabo Verde Islands at 16.5N-27W)


...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 90 and 96 hours… located southeast of Greenland by 120 hours.

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

**For area of interest #2… forecast to emerge from Africa at 78 hours… tropical cyclone formation suggested near 12.5N-19.5W at 96 hours… passes through the Republic of Cabo Verde Islands at 108 to 114 hours… located just west-northwest of the islands at 120 hours

**Tropical low becomes defined in Veracruz Bay of Campeche coast of Mexico at 120 hrs


1200Z ECMWF Model Run…

**For Hurricane Larry… remnant frontal cyclone quickly passes over southeast Newfoundland between 72 and 96 hours… centered on the southeast coast of Greenland by 120 hours.

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

**For area of interest #2… forecast to emerge from Africa at 72 hours… tropical cyclone formation suggested just offshore of Africa near 15N-18W at 96 hours… passes over the northeastern Republic of Cabo Verde Islands at 120 hours.


1800Z GFS Model Run...

**For Hurricane Larry…remnant frontal cyclone quickly passes over southeast Newfoundland at 84 hours… approaching Canadian frontal cyclone to the west of Larry’s remnant becomes the dominant and absorbs Larry by 102 hours.

**For area of interest #1… makes landfall as a compact tropical depression on the Florida panhandle coast at 30 hours…. remnant trough reaches South Carolina/Georgia border at 51 hours… remnant trough regains closed low pressure spin soon after… stalls midway between Bermuda and US southeast coast and slowly dissipates through 120 hours

** For area of interest #2… forecast to emerge from Africa at 72 hours… passes over the Republic of Cabo Verde Islands at 84 hours as a broad low pressure spin… broad low pressure reaches 14N-30W at 120 hours


1800Z NAVGEM Model Run...

**For Hurricane Larry…remnant frontal cyclone quickly passes just offshore of southeast Newfoundland at 90 hours… located southeast of Greenland by 120 hours.

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

** For area of interest #2… forecast to emerge from Africa at 72 hours… passes over the Republic of Cabo Verde Islands by 120 hours as a broad low pressure spin

**Tropical low becomes defined in Bay of Campeche coast of Mexico for a short time around 114 hours

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