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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 #72

*******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 8 2023 1:30 PM EDT...

See Hurricane Lee and Tropical Storm Margot sections below for the two currently active tropical cyclones in the Atlantic basin. The largest concern in the Atlantic basin for land areas is Hurricane Lee which is expected to remain intense while curving northward between Bermuda and the Caribbean Islands over the course of the next five days... it is not fully clear yet how close Lee will get toward Bermuda... the northeastern United States shoreline... and Atlantic Canada beyond day 5.


In addition... some model runs insist that a strong troipcal wave of low pressure may emerge from western Africa and behind Margot in a couple of days with some development potential:

(1) Current satellite imagery shows a tropical wave of low pressure has recently emerged from western Africa overnight but has also lost a lot of its thunderstorm activity and hence I have not added this tropical wave as an area of interest in this update. Atlhough none of the global models currently develop this wave... the most recent satellite frames as of this writing show a small area of rotation offshore of Senegal with a curved band of increasing thunderstorms on the southwest side of the rotation. Should these current trends continue... will consider adding this tropical wave as an area of interest in a special update later today or by my next full update during the weekend.

(2) Current METEOSAT satellite imagery (https://www.goes.noaa.gov/f_meteo.html) shows a tropical wave of low pressure over western Africa along 2W longitude becoming increasingly defined... this is likely the tropical wave that some global models are currently developing in the long range after having it emerge from the west coast of Africa in a couple of days. This wave may also need to be added as an area of interest in future updates.


MAJOR HURRICANE LEE... Satellite image of Hurricane Lee as of 0400Z earlier today achieving category 5 peak strength:

While crossing an enlarging patch of 30 deg C waters (https://www.nhc.noaa.gov/sst/) and remaining under tropical upper ridging with low shear and upper outflow... Lee was able to continue its rapid intensification and reach a peak of 165 mph maximum sustained winds with 926 mb central surface pressure as measured by aircraft reconaissance overnight. More recently the eye has become more obscured in satellite pictures and the thunderstorm canopy of the hurricane has tilted to a bias east of the eye... indications that the hurricane is encountering increasing westerly shear from the lingering Caribbean upper vorticity and western Atlantic upper trough. The more obscure apperance of the eye may also be a sign Lee is on the verge of beginning an eye wall replacement cycle. Indeed as of the more recent 11 AM EDT NHC advisory Lee has weakened to a top-end category 4 with 155 mph maximum sustained winds and 942 mb central surface pressure while citing the latest aircraft recon data. Over the next 24 hours the Caribbean upper vorticity is forecast to weaken while remaining cut-off from high-latitude cold air... and the western Atlantic upper trough is slated to break into a northern and southern fragment that lift northeastward and out of the way. My updated forecast for this timeframe accounts for the fact these features may have taken longer to weaken/get out of the way while lowering the intensity due to some shear from these features... and by lifting the forecast track a little more northward and showing a slower westward speed (in fact Lee is already a little northeast of my previous forecast track due to the drag of the upper winds from said upper features). Once the shear drops between 24 and 48 hours... I forecast Lee to become a category 5 hurricane again... espeically with the hurricane still being over waters at least 29 deg C. With the drag of the shearing upper winds gone and Atlantic surface ridge remaining intact... I show a faster westward heading during this timeframe as well. For the 72+ hour window the long-range model guidance has trended more westward while delaying Lee's northward turn. In general the northward turn is expected as what are currently upper troughs over the eastern US and western Canada are forecast to push the current eastern US frontal system into the western Atlantic... with the surface front helping to create a surface ridge weakness that helps the northward turn. Also the upper southerly flow ahead of the upper troughs will help the turn. The reason the model guidance has trended more west is the guidance no longer merges the two troughs into one southwest-northeast tilted trough... but instead keeps the two troughs seperate entities that are more amplified... and amplified upper troughs tend to move slower and hence reach Lee a little later. Therefore I have moved my northward turn to 67W longitude from 66W longitude in this update. For my 72+ hour intensity projection... I still show a gradually weakening category 4 hurricane due to potential for shear from the incoming upper troughs... but have trended upward with my intensity forecast for this window as the more amplified nature of the troughs allows for the shear vector to be more southerly instead of southwesterly and more aligned with the forecast track... and hence less severe. In fact for the 48 to 72 hour window I assume that Lee will not be weakening from shear but instead a likely eye wall replacement cycle after acheiving a second category 5 peak at 48 hours.


Regarding impact to land areas... expect wide-reaching surf from this powerful hurricane to reach the northern Lesser Antilles... Virgin Islands... Puerto Rico... the north shores of Haiti and the Dominican Republic... the Bahamas... and Bermuda over the next five days. With the lastest forecast track being nudged north in the short-term... the potential for notable rainfall or breezy winds in the northern Lesser Antilles has ended. Interests in Bermuda... the northeastern United States... and Atlantic Canada should monitor the progress of Lee in the days ahead as the steering pattern shown in the models favors a northward acceleration in the generally direction of this region beyond day 5.

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

0 Hr Position (1200Z Sep 8)... 165 mph maximum sustained wind major hurricane centered in the central tropical Atlantic at 17.8N-53.5W

IOH 24 Hr Forecast (1200Z Sep 9)... 145 mph maximum sustained wind major hurricane centered northeast of the northern Lesser Antilles at 20.2N-57.5W

IOH 48 Hr Forecast (1200Z Sep 10)... 170 mph maximum sustained wind major hurricane centered north of the northern Lesser Antilles at 22N-62W

IOH 72 Hr Forecast (1200Z Sep 11)... 155 mph maximum sustained wind major hurricane centered in the western Atlantic at 23N-66W

IOH 96 Hr Forecast (1200Z Sep 12)... 150 mph maximum sustained wind major hurricane centered in the western Atlantic at 25.5N-67W

IOH 120 Hr Forecast (1200Z Sep 13)... 145 mph maximum sustained wind major hurricane centered southwest of Bermuda at 28N-67W

******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************

5-day Position (1200Z Sep 13)... 130 mph maximum sustained wind major hurricane centered in the western Atlantic at 24.8N-67.5W


TROPICAL STORM MARGOT... After quickly acheiving tropical storm status west of the Republic of Cabo Verde Islands... Margot has spent much of the last 24 hours not strengthening and becoming less organized while the thunderstorm activity has become blobbed rather than banded and lopsided to the north of center. A look at upper winds shows the eastern tropical Atlantic upper ridge has degenerated into two warm core anticyclones... the western one bolstered by the latent heat release of Hurricane Lee's thunderstorms and the eastern one probably bolstered by the latent heat release of Margo'ts thunderstorms... with an inverted upper trough in between the two anticyclones. Margot is positioned close to the inverted upper trough which is probably inducing the southerly shear... with the upper southerly flow on the east side of this trough also helping to bend the westward track of Margot more northward as Margot is currently north of my previous forecast track. With Margot being weaker than my previous forecast and hence closer intensity-wise to neighboring ex-Katia's strength... ex-Katia is probably having more weight in the fujiwhara interaction between the two which is also helping to pull Margot more northward. My updated forecast track below accounts for the storm being further to the north initially. From 48 to 96 hours... I continue to forecast a northward turn along 40W longitude as Margot will likely be strong/tall enough to be steered by the upper southerlies on the east side of the current central Atlantic upper vortex. Even though the models continue showing Margot's latent heat release weakening the cool core upper vortex... I keep the forecast track straight north along 40W longitude as a surface trough/front passing to the north... associated with what will be the eastern divergence zone of the southern fragment of the current western Atlantic upper trough... will likely attract Margot. By 96 to 120 hours it appears for now Margot will be left behind by the passing upper trough fragment and associated surface trough/front... allowing the northeast side of the central Atlantic upper vortex and south side of the Atlantic surface ridge to bend the track back westward... and a westward hook is shown in my forecast below for that window of time.


Intensity-wise... I have nudged the forecast downward overall as Margot has not strengthened yet from the current short-term southerly shear. For the next 24 hours Margot is likely to see a drop in the shear as it lifts northwest past the northern apex of the inverted upper trough and so I forecast some strengthening in the short-term. I then slow the intensification rate between 24 and 48 hours as this system gets disrupted by the central Atlantic upper vortex... but return to a higher rate of development by 48 to 96 hours as the latent heat release of this system weakens the upper vortex as noted above. The intensity situtation beween 96 and 120 hours has two possibilities... (1) the passing upper trough fragment to the north links with the central Atlantic upper vortex such that a wall of westerly shear from both upper features overspreads Margot and weakens it... or (2) there is enough of a gap between the central Atlantic upper vortex and upper trough fragment such that Margot ends up in a high divergence environment between southwesterlies streaming into the east side of the upper trough fragment and the easterly flow on the north side of the upper vortex.. with the divergence resulting in additional intensification. Since I see either scenario as equally likely... I simply keep my intensity forecast flat between 96 and 120 hours.

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

0 Hr Position (1200Z Sep 8)... 40 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 18N-32.5W

IOH 24 Hr Forecast (1200Z Sep 9)... 60 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 20N-37.5W

IOH 48 Hr Forecast (1200Z Sep 10)... 65 mph maximum sustained wind tropical storm centered in the central Atlantic at 23N-40W

IOH 72 Hr Forecast (1200Z Sep 11)... 85 mph maximum sustained wind hurricane centered in the central Atlantic at 27N-40W

IOH 96 Hr Forecast (1200Z Sep 12)... 100 mph maximum sustained wind hurricane centered in the central Atlantic at 30.5N-40W

IOH 120 Hr Forecast (1200Z Sep 13)... 100 mph maximum sustained wind hurricane centered in the central Atlantic at 33N-42W

******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************

5-day Position (1200Z Sep 13)... 85 mph maximum sustained wind hurricane centered in the central Atlantic at 31.8N-43.7W


...COMPUTER MODEL SUMMARY...

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


0000Z (Sep 8) CMC Model Run...

**For Major Hurricane Lee... reaches 24N-69W at 120 hours as an intense hurricane.

**For Tropical Storm Margot... reaches 20.8N-43W at 66 hours... afterwards turns north and intensifies and by 120 hours reaches 28.8N-46W as a strong hurricane.

**Tropical wave emerges from west coast of Africa at 54 hours... develops into a tropical low that passes over the southern Republic of Cabo Verde Islands through 108 hours with the tropical low reaching 16N-39.5W by 168 hours


0000Z (Sep 8) ECMWF Model Run...

**For Major Hurricane Lee... reaches 23.5N-66W at 120 hours as an intense hurricane.

**For Tropical Storm Margot... reaches 20.8N-40.2W at 54 hours as a strengthening compact tropical storm... afterwards turns north and reaches 28N-44.5W as a strong hurricane


0600Z (Sep 8) GFS Model Run...

**For Major Hurricane Lee... reaches 25N-66.5W at 120 hours as an intense hurricane.

**For Tropical Storm Margot... reaches 21.2N-38.8W at 39 hours after which time it turns north... reaches 31N-42.5W at 120 hours as an intense hurricane.

**Tropical wave emerges from west coast of Africa at 54 hours... organizes into a broad tropical low south of the Republic of Cabo Verde Islands at 99 hours... tropical cyclone formation suggested near 13.5N-37W at 165 hours


0600Z (Sep 8) NAVGEM Model Run...

**For Major Hurricane Lee... reaches 24N-64.8W at 120 hours as an intense hurricane.

**For Tropical Storm Margot... reaches 20.2N-38.5W at 48 hours as a strengthening tropical storm after which time it turns north... reaches 31.2N-38.8W at 120 hours as an intense hurricane

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