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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 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #82

*******Note that forecast 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 22 2023 7:45 PM EDT...

Nigel has transitioned to a remnant frontal cyclone in the northeast Atlantic... see remnants of Nigel section below for more details. See area of interest #36 and #38 sections below for an update on a pair of tropical waves of low pressure currently heading for the central tropical Atlantic. See Ophelia section below for the quickly strengthening tropical storm that will be bringing notable impacts from eastern North Carolina to Delaware through this weekend.


Elsewhere... a tropical wave of low pressure with some signs of organization is nearing the west coast of Africa and as such will be entering the eastern tropical Atlantic by tomorrow (Saturday). Some model runs suggest this wave may develop... however development may also be challenged by the current suppressing eastern Atlantic upper vorticity which may be pushed southward toward this tropical wave by the outflow of area of interest #36. Therefore not adding this tropical wave as an area of interest at this time.


REMNANTS OF NIGEL... Hurricane Nigel has zoomed northeastward across the north Atlantic in strong southwesterly flow ahead of a surface frontal cyclone that has emerged from Atlantic Canada and its supporting upper trough. The eastern divergence zone of this upper trough is also supporting Nigel such that at 5 AM EDT early today when it lost its tropical characteristics over the cooler waters well north-northwest of the Azores north it was still rated at 70 mph maximum sustained winds. This means Nigel is now a strong non-tropical remnant frontal cyclone moving northeastward in tandem with the aforementioned adjacent frontal cyclone. The two cyclones will cyclonically orbit each other in the northeast Atlantic while generating a large area of surf. Any surf on the shores of Newfoundland should relax as the two cyclones pull away... while surf increases through this weekend and into Monday for the shores of southeast Greenland... Iceland... the Azores... and the British Isles. Gusty winds are also expected for the British Isles during this timeframe as well. This is my final statement on Nigel on this blog as it is no longer a tropical cyclone... statements regarding impacts to land areas from ex-Nigel will be carried on the home page bulletins of this site.


AREA OF INTEREST #36... The tropical wave of low pressure that spent the last few days departing the west coast of Africa and passing just south of the Republic of Cabo Verde Islands on Thursday initially survived the environmental negative factors of dry Saharan air and nearby suppressing upper vorticity while developing a more concentrated area of thunderstorms and rotation. However as of today the circulation of the tropical wave has become broader and less organized while it absorbs the tropical low pressure tagged as area of interest #38 to the southwest. The estimated center of the broad rotation was near 14N-32.5W as of 1200Z today... or a little northwest of my previous forecast and my updated one below is adjusted accordingly. The track forecast calls for an increase in the north angle of this system's westward track after 48 hours under the influence of the current central Atlantic upper vortex... followed by the development of a surface ridge weakness in the open central Atlantic triggered by the eastern divergence zone of a lengthy western Atlantic upper trough that will materialize from the merger between the upper trough assoicated with the subtropical disturbance currently near the southeastern United States coast (area of interest #37) and current central Canada upper trough. Regarding odds of tropical cyclone formation... the global models still want to consolidate and develop the currently broad circulation into a tropical cyclone... with the ECMWF and CMC showing more gradual development and GFS and NAVGEM showing more rapid development. By 72+ hours... shear imparted by the current central Atlantic upper vortex could become an issue for this system as the upper vortex is squashed southward toward this system by the expansion of the current northwest Atlantic upper ridge (the northwest Atlantic upper ridge inflates due to northward warm air transport ahead of area of interest #37 and the back western side of the surface ridge currently over the northeastern US). For rapid development... the GFS and NAVEGEM rely on thunderstorm latent heat release from this system to accelerate the decay of the cold core central Atlantic upper vortex. However since this system is currently broad... it may need time to develop a consolidated center with strong thunderstorms and I am not certain if that will happen before it runs into the upper vortex. Therefore in this update I have not opted to go with a tropical cylcone formation forecast... but instead raise peak odds of development for the next five days to just above the 50% mark since the models for now eventually develop this system even with the prospect of shear from the upper vortex.


This system may produce coastal surf for the northern Lesser Antilles around day 5 or just after... which is the middle of this upcoming week.

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

IOH 24 Hr Outlook (1200Z Sep 23)... 30% chance of tropical cyclone formation (eastern tropical Atlantic near 14.5N-37.5W)

IOH 48 Hr Outlook (1200Z Sep 24)... 50% chance of tropical cyclone formation (central tropical Atlantic near 15N-42.5W)

IOH 72 Hr Outlook (1200Z Sep 25)... 60% chance of tropical cyclone formation (central tropical Atlantic near 16.5N-47W)

IOH 96 Hr Outlook (1200Z Sep 26)... 60% chance of tropical cyclone formation (central tropical Atlantic near 17.5N-51W)

IOH 120 Hr Outlook (1200Z Sep 27)... 60% chance of tropical cyclone formation (east of the northern Lesser Antilles near 19N-55W)

******National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT***************************

Formation chance through 48 hours... 70%

Formation chance through 7 days... 90%


AREA OF INTEREST #37 (RECENTLY UPGRADED TO TROPICAL STORM OPHELIA)... Satellite image of quickly strengthening Tropical Storm Ophelia as of 2131Z:

Over the last 48 hours a lot has happened with the surface subtropical low pressure area offshore of the southeastern United States. It was only yesterday (Thursday) that upper vorticity over the south-central US merged with the southern fragment of an eastern North America upper trough to produce a more amplified upper trough over the southeastern US... with increased divergence and lower shear on the east side of the trough allowing for the formation of a strengthening and gradually organizing offshore subtropical low pressure. By subtropical... the system was a hybrid where strengthening is aided by both the eastern divergence zone of the upper trough and warm core upper ridging and outflow generated by the latent heat release of thunderstorms. The system was upgraded to potential tropical cyclone sixteen yesterday by the NHC in order to issue early tropical storm advisories along portions of the United States east coast in anticipation that this system had a high chance of becoming a tropical cyclone. Indeed as of 2 PM EDT today the NHC had assessed this system had enough concentrated thunderstorm activity just north of its surface center to be upgraded to Tropical Storm Ophelia and had already strengthened to 60 mph maximum sustained winds. Since then the thunderstorm activity has wrapped into the center from the west and Ophelia is already almost a hurricane with 70 mph maximum sustained winds.


Regarding forecast track... initially (around 1200Z today) Ophelia was slightly northeast of my previous forecast... however through 5 PM EDT Ophelia is located further to the west. It is likely the thunderstorm latent heat release of Ophelia is cutting off the south end of the cold core southeastern US upper trough into something that resembles a cut-off upper vortex... with the vortex attempting to arc Ophelia's northbound track westward. Therefore for the next 24 hours my forecast track remains similar to my previous and continues to call for a landfall between Cape Fear and Cape Hatteras on the North Carolina coast with Ophelia moving northwestward in the flow between the upper vortex feature and southwest side of the current northeastern US surface ridge. After 24 hours... Ophelia and the upper vortex become captured by the amplified upper trough currently approaching from central Canada. The upper vortex and trough are expected to merge into a lengthy upper trough shifting east toward the western Atlantic... with Ophelia moving north-notheastward within the lengthy upper trough. Ophelia will be transitioning into a remnant non-tropical frontal low after losing thunderstorms while pulling away from the heat source of the warm Gulf stream waters and interacting with land and/or offshore cooler waters further north. The decay rate of Ophelia's remnant frontal low is more likely to be quick as the storm is NOT on a further east track in the short-term... which then causes Ophelia's center to more quickly align with the axis of the lengthy upper trough where upper divergence is lacking. Regarding intensity for the next 24 hours... I project Ophelia to become a short-lived category 1 hurricane with max sustained winds as high as 85 mph before landfall. Ophelia should be centered over eastern North Carolina by 24 hours which is why my forecast intensity during that time is a top-end tropical storm with 70 mph maximum sustained winds... as Ophelia will have begun weakening from any hurricane strength it does achieve due to landfall.


Regarding impact to land areas:

(1) Gusty winds with damage potential and coastal surf will be a concern this weekend across eastern North Carolina... southeastern Virgnia... eastern Maryland... and Delaware. The worst of the winds will be near the landfall area in the next 12 hours... between Cape Fear and Cape Lookout North Carolina and areas just inland from this part of the coast... as Ophelia potentially strengthens into a hurricane... it will be crucial to be sheltered indoors here in the short-term. Not expecting wind and surf much further north of Delaware this weekend as Ophelia will tend to have a faster post-landfall decay rate as discussed above.

(2) Based on the latest radar imagery and forecast... heavy rainfall with flash flooding potential this weekend will be a concern across eastern North Carolina... southeastern Virginia... central and eastern Maryland... Delaware... New Jersey... and southeastern Pennsylvania.

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

0 Hr Position (1800Z Sep 22)... 70 mph maximum sustained wind tropical storm centered offshore of North Carolina at 32.9N-76.3W

IOH 24 Hr Forecast (1800Z Sep 23)... 70 mph maximum sustained wind tropical storm centered over eastern North Carolina at 35.2N-77.5W

IOH 48 Hr Forecast (1800Z Sep 24)... Weakening frontal low centered over northern New Jersey at 40.8N-74.5W

******National Hurricane Center (hurricanes.gov) official forecast as of 5 PM EDT***************************

Landfall (0600Z Sep 23)... 70 mph maximum sustained wind tropical storm centered on the North Carolina coast and just west of Cape Lookout at 34.4N-76.8W

Loss of Tropical Cyclone Status (0600Z Sep 24)... 35 mph maximum sustained wind frontal low centered over eastern Virginia at 37.6N-77.2W


AREA OF INTEREST #38... The tropical low pressure in the open central Atlantic failed to escape the grip of the incoming tropical wave to the east tagged as area of interest (AOI) #36 above. While located near 10N-40W... this system is becoming absorbed by the southwest side of AOI #36 and thus it can no longer try and develop as a seperate feature... as such this is my final statement on this system on this blog.

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

IOH 24 Hr Outlook (1200Z Sep 23)... 0% chance of tropical cyclone formation (central tropical Atlantic near 10N-41W)

******National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT***************************

Not in the official outlook


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).


0000Z (Sep 22) CMC Model Run...

**For Area of Interest #36... gradually develops into a tropical cyclone that reaches the waters east of the northern Lesser Antilles by 120 hours

**For Area of Interest #37... subtropical cyclone formation suggested near 30.5N-77W at 18 hours... center of subtropical cyclone makes landfall near Cape Hatteras North Carolina at 36 hours... transitions into a weakening remnant frontal low that dissipates just southeast of Massachusetts at 90 hours.

**For Area of Interest #38... no development shown

**Tropical wave emerges from west coast of Africa at 30 hours... tropical cyclone formation suggested near 15.5N-43W at 144 hours


0000Z (Sep 22) ECMWF Model Run...

**For Area of Interest #36... through 126 hours stays a broad tropical low whose center reaches 16.5N-54W

**For Area of Interest #37... subtropical cyclone formation suggested in next 6 hours near 30.5N-75W... subtropical cyclone makes landfall between Cape Fear and Cape Lookout on the North Carolina coast at 36 hours... transitions into a weakening remnant frontal low that dissipates over southeastern Pennsylvania at 72 hours.

**For Area of Interest #38... no development shown


0600Z (Sep 22) GFS Model Run...

**For Area of Interest #36... tropical cyclone formation suggested near 14.8N-44W at 51 hours... while intensifying into a hurricane reaches 20N-52.5W by 120 hours.

**For Area of Interest #37... elongated subtropical low consolidates into a subtropical cyclone near 32N-77.5W at 15 hours... makes landfall at Cape Lookout North Caorlina at 30 hours... transitions into a weakening remnant frontal low that dissipates over the inland part of the Virignia/Maryland border at 75 hours.

**For Area of Interest #38... no development shown

**Current central Canada upper trough evolves into a cut-off upper vortex to the southeast of Newfoundland by 168 hours... eastern divergence zone of the upper vortex results in surface subtropical cyclone formation near 41.5N-52.5W


0600Z (Sep 22) NAVGEM Model Run...

**For Area of Interest #36... tropical cyclone formation suggested near 17N-43W at 60 hours... while intensifying into a hurricane reaches 20N-53W by 120 hours

**For Area of Interest #37... elongated subtropical low consolidates into a subtropical cyclone near 32.5N-75.2W at 18 hours... subtropical cyclone makes landfall between Cape Hatteras and Cape Fear North Carolina at 30 hours... transitions into a weakening remnant frontal low that dissipates just offshore of southeastern New Jersey at 90 hours

**For Area of Interest #38... no development shown

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