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 #107

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


...FRIDAY SEPTEMBER 10 2021 7:11 PM EDT...

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 areas being monitored for future tropical development in the Atlantic.


Elsewhere… the remnants of Mindy offshore of the eastern US saw some increased organization in the afternoon as its fast east-northeast track outpaced the the belt of shearing upper southwesterly winds to the west. However as the upper trough over eastern Canada accelerates east… the shearing upper winds have caught up to Mindy and have recently made the remnants less organized. Tropical redevelopment of Mindy is not anticipated.


HURRICANE LARRY... Larry is making the north-northeastward acceleration toward Newfoundland and the surrounding cooler northwestern Atlantic waters...and is making a gradual transition to a powerful non-tropical frontal cyclone. The stage has been set for Larry to maintain strength even as it loses tropical characteristic as follows: (1) The approaching cold core upper trough associated with the surface frontal low from eastern Canada is already amplified due to the vigrous nature of the frontal low which has been pulling cold air southward... (2) Larry has already played a role in making the upper trough amplified as its thunderstorm latent heat release has kept the adjacent central Atlantic warm upper ridge more amplified... with the amplified upper trough having more eastern upper divergence to help the eastern Canadian frontal low be vigorous in the first place... (3) Larry will soon align with the strong eastern divergence zone of the amplified upper trough which will help it retain strength after transition to non-tropical... (4) After aligning with the eastern divergence zone of the upper trough... Larry's strong remnant non-tropical cyclone will help pull more cold air southward on its west side and warm air northward on its east side...which will only aid to make the cold core upper trough more amplified which will further increase the supportive divergence over Larry's remnant cyclone. There is some debate in the modeling as to whether or not Larry will supercede the eastern Canadian frontal low as the dominant feature... or if the eastern Canadian frontal low which will also rapidly intensify (due to the forecast increase in upper divergence) will become the dominant. Regardless of which scenario becomes true... the impacts to Newfoundland...southeastern Greenland... and Iceland in the coming days will be the same. The forecast 24 hour position below is based on the location of the upper divergence maximum associated with the incoming amplified upper trough in today's 1200Z GFS model run.


**Coastal sea swells will continue to reach the northeastern US coast in the next 12 hours. The Atlantic Canada...southeastern Greenland...and Iceland coastlines will experience sea swells over the next few days.

**Southeastern Newfoundland will see gusty winds with damage potential tonight...along with a coastal storm surge. Strong winds are also possible for southeastern Greenland on Sunday.

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

0 Hr Position (1800Z Sep 10)... 80 mph maximum sustained wind hurricane centered offshore of Nova Scotia at 41.8N-59.5W

IOH 24 Hr Forecast (0000Z Sep 11)... 70 mph maximum sustained wind non-tropical frontal cyclone centered midway between Greenland and Newfoundland at 55N-49W


AREA OF INTEREST #1... A tropical wave of low pressure over Western Africa is nearing the eastern tropical Atlantic while maintaining a broad area of cyclonic turning... however the thunderstorm activity has weakened due to ingestion of dry saharan air. The upper trough associated with the current northeast 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 in the short-term. Once the tropical wave moves past the weaker part of the surface ridge... I forecast a more west track by 72 to 96 hours. The upper trough is forecast to deposit upper vorticity to the north of the tropical wave...which will weaken to an upper vortex off to the northwest by 120 hours as the vorticity remains cut-off from high-latitude cold air. The increased north angle in track by 120 hours is to account for the possiblity of this system developing a strong/tall enough structure that can be pulled by the forecast upper vortex.


Due to the aforementioned ingestion of dry saharan air... I have notably lowered short-term odds of development to 30%. This also makes sense as the models showing the wave developing has waned. Odds are plateued to 40% from 48 to 72 hours as this system nears the aforementioned upper vorticity which will increase the wind shear overhead. By 96+ hours...once the upper vorticity is forecast to weaken...the shear could relax enough to faciliate development... and this is when I raise development odds to 60%. This system still has a good structure with cyclonic rotation despite the current loss of thunderstorms...and my medium odds in the longer range are a reflection of that. However depending on how this system negotiates the dry saharan air and wind shear in the short and medium term...longer term odds may be raised or lowered in future updates.


For the Republic of Cabo Verde Islands...the chances of this wave developing over or before reaching the islands this weekend has reduced due to the dry saharan air in the region. However the tropical wave may still generate thunderstorm squalls with gusty winds and heavy rains.

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

IOH 24 Hr Outlook (1800Z Sep 11)... 30% chance of tropical cyclone formation (just east-southeast of the Republic of Cabo Verde Islands near 15N-21W)

IOH 48 Hr Outlook (1800Z Sep 12)... 40% chance of tropical cyclone formation (west of the Republic of Cabo Verde Islands near 16.5N-27W)

IOH 72 Hr Outlook (1800Z Sep 13)... 40% chance of tropical cyclone formation (eastern tropical Atlantic near 17N-32W)

IOH 96 Hr Outlook (1800Z Sep 14)... 60% chance of tropical cyclone formation (eastern tropical Atlantic near 17.5N-37W)

IOH 120 Hr Outlook (1800Z Sep 15)...60% chance of tropical cyclone formation (central tropical Atlantic near 19.5N-41W)


AREA OF INTEREST #2... Gradually organizing and widespread thunderstorm squalls have increased across the Gulf of Mexico and northwestern Caribbean Sea with the support of widespread upper divergence on the east side of western Gulf upper vorticity. Surface convergence has increased as a tropical wave of low pressure has formed with the aid of the upper divergence...and is also aided by a pre-existing surface trough of low pressure that has been in the Gulf of Mexico...which believe it or not is the same surface trough that helped generate Mindy a couple of days ago. Surface convergence has also increased from the north with the aid of the cold front being driven by the northeastern Canadian frontal low. As the cool core vorticity weakens while remaining cut-off from high-latitude cold air... the upper vorticity is forecast to become replaced by expanding upper ridging to the south that will provide a lower shear and upper outflow environment more conducive to tropical cyclone formation. The south and west side of the eastern US surface ridge is forecast to push whatever tropical low pressure area develops to the west and north in the western Gulf of Mexico... with the approach of a frontal system from western North America helping to aid the north turn by days 4 and 5.


I increase odds of development above 0% during the timeframe the shearing western Gulf upper vorticity is dissipated. I agree with raising odds of development due to the notable increase in thunderstorms in the past 24 hours... however I am not quiet as high as the NHC outlook's 70% as this system appears quiet large while composed of a few surface features and large area of upper divergence. This could result in a large broad system that struggles to coalesce a defined center of rotation needed for focused surface convergence and tropical cyclone developemnt. The odds of development are lowered at day 4 due to landfall and also possible westerly shear as this system arrives to the north side of the forecast upper ridging. The positions in the outlook below is north of the increasing model consensus of a more compact tropical low pressure forming in the Bay of Campeche... as I do not see evidence at this time that a more southern compact circulation is developing.


Because it is hard to know exactly where a tropical low pressure might consolidate... interests across Veracruz and Tamaulipas provinces in Mexico as well as the south Texas coast should continue to be aware of this forecast situation... and check back in for updates in the coming days. Tropical storm conditions (gusty winds... heavy rains... coastal sea swells) are possible somewhere in this region after this weekend. Even if tropcial cyclone formation does not occur...widespread heavy rains with flash flooding potential will be possible in this region. Heavy rains will also be possible across Belize and the Yucatan peninsula in the short-term.

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

IOH 24 Hr Outlook (1800Z Sep 11)... 0% chance of tropical cyclone formation (northwestern Yucatan peninsula near Yucatan peninsula near 20N-89W)

IOH 48 Hr Outlook (1800Z Sep 12)... 30% chance of tropical cyclone formation (southwestern Gulf of Mexico near 22.5N-92.5W)

IOH 72 Hr Outlook (1800Z Sep 13)... 60% chance of tropical cyclone formation (offshore of the Texas/Mexico border near 26N-95W)

IOH 96 Hr Outlook (1800Z Sep 14)... 30% chance of tropical cyclone formation (coastal Texas near 28.2N-96.5W)

IOH 120 Hr Outlook (1800Z Sep 15)...0% chance of tropical cyclone formation (northeastern Texas near 32N-96.5W)

AREA OF INTEREST #3...One of the tropical waves of low pressure that emerged from Africa a few days ago… sometime between Larry and area of interest #1… is now in the central tropical Atlantic with an increasingly defined low pressure swirl located near 12.5N-49W as of 1800Z earlier this afternoon. This wave has so far been suppressed by dry Saharan air. Over the last couple of days the CMC model hinted at this tropical wave developing offshore of the southeastern US in the longer range… and now other models are joining suit. Based on analyzing the GFS model upper wind field… this development appears to be aided by the upper divergence zone of the upper vorticity currently just northwest of this tropical wave. This upper vorticity… while remaining cut-off from high-latitude cold air… is forecast to weaken to an upper vortex while being pushed westward by the central Atlantic upper ridge. Towards the end of the 5-day forecast period the upper vortex is slated to be near the Bahamas while pushed further west by upper ridging to be associated with the warm sector of the frontal system that pulls area of interest #2 northbound. In short… the upper vortex will be moving westward in tandem with the tropical wave over the next five days.


The forecast positions in the outlook below are based on the location of the eastern divergence zone of the upper vortex. I have development odds above 0% as soon as day 3 as the forecast upper vortex would have low shear and a defined eastern upper divergence maximum by then. However my odds are kept at a low 10% in the five-day forecast period as the models wait till after day 5 to show any development. It is possible this wave brings heavy rains to the northern Lesser Antilles… Virgin Islands… and Puerto Rico in about 3 days if it sees an increase in thunderstorms with the aid of the upper vorticity as described above.

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

IOH 24 Hr Outlook (1800Z Sep 11)... 0% chance of tropical cyclone formation (east of the Lesser Antilles near near 13N-54W)

IOH 48 Hr Outlook (1800Z Sep 12)… 0% chance of tropical cyclone formation (just east of the Lesser Antilles near near 15N-59W)

IOH 72 Hr Outlook (1800Z Sep 13)… 10% chance of tropical cyclone formation (just southeast of Virgin Islands near 17.5N-64W)

IOH 96 Hr Outlook (1800Z Sep 14)… 10% chance of tropical cyclone formation (just offshore of the northern Dominican Republic coast near 20N-69W)

IOH 120 Hr Outlook (1800Z Sep 15)… 10% chance of tropical cyclone formation (just northeast of the eastern Bahamas near 22N-71W)

...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 at 18 hours... approaching Canadian frontal cyclone to the west of Larry’s remnant becomes the dominant and absorbs Larry by 36 hours.

**For area of interest #1... passes over the Republic of Cabo Verde Islands as a tropical low at 42 hours... tropical cyclone formation suggested at 17.5N-28W at 78 hours... soon after weakens to a norhtwestward moving remnant low which reaches 23.5N-34W at 120 hours.

**For area of interest #2... tropical cyclone formation suggested on the coast of northern Veracruz at 66 hours...weakens to a remnant tropical low after angling north-northwest further inland in track...remnant tropical low located over inland south Texas at 120 hours.

**For area of interest #3... surface trough becomes slightly better defined as it makes landfall on the Georgia coast at 168 hours.

**Strong tropical wave forecast to emerge from Africa at 162 hours.

1200Z ECMWF Model Run...

**For Hurricane Larry... remnant frontal cyclone quickly passes over southeast Newfoundland in the next 24 hours... centered just offshore of northwestern Iceland at 120 hours.

**For area of interest #1... passes over the Republic of Cabo Verde Islands as a broad tropical low pressure at 24 hours...the broad tropical low opens to a tropical wave while passing 36W longitude by 120 hours.

**For area of interest #2... tropical cyclone formation shown on the coast at the Texas/Mexico border at 72 hours... gradually strengthening tropical storm makes landfall between Galveston and Corpus Christi Texas at 96 hours...remnant tropical low located over southeast Texas near 31.2N-95W at 120 hours.

**For area of interest #3... surface trough becomes slightly better defined as it makes landfall on the southeastern United States coast at 168 hours.

**Strong tropical wave forecast to emerge from Africa at 96 hours...tropical cyclone formation shown near 10N-24W at 120 hours... located at 12.5N-39W at 168 hours at hurricane force.

1800Z GFS Model Run...

**For Hurricane Larry... remnant frontal cyclone quickly passes over southeast Newfoundland at 18 hours... approaching Canadian frontal cyclone to the west of Larry’s remnant becomes the dominant and absorbs Larry by 33 hours.

** For area of interest #1... passes over the Republic of Cabo Verde Islands at 33 hours as a broad low pressure spin... broad low pressure reaches 15N-37W at 120 hours

**For area of interest #2... compact tropical cyclone formation shown in the western Bay of Campeche near 21N-96W at 60 hours... makes landfall near the Tamaulipas/Veracruz border at 75 hours after which time the compact system quickly dissipates due to the landfall.

**For area of interest #3...north end of the tropical wave becomes a surface low near 31N-71.5W at 150 hours.

**Strong tropical wave forecast to emerge from Africa at 147 hours.

1200Z NAVGEM Model Run...

**For Hurricane Larry... remnant frontal cyclone quickly passes over southeast Newfoundland at 18 hours... approaching Canadian frontal cyclone to the west of Larry’s remnant becomes the dominant and absorbs Larry 42 hours..

** For area of interest #1... passes over the Republic of Cabo Verde Islands as a broad tropical low pressure at 30 hours... tropical low opens to a wave while passing 33W longitude by 120 hours.

**For area of interest #2... tropical cyclone formation suggested just offshore of Veracruz near 23N-97W at 66 hours...makes landfall just south of the Texas/Mexico border at 84 hours...remnant low dissiptes inland over the Texas/Mexico border at 108 hours.

**For area of interest #3...tropical cyclone formation suggested offshore of the southeastern US near 31N-79W at 168 hours.

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