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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 #73

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


...SATURDAY SEPTEMBER 9 2023 11:30 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... a pair of tropical waves of low pressure behind Tropical Storm Margot are now areas of interest for further development… these are the thirty-fourth and thirty-fifth tropical Atlantic areas of interest tracked on this site this year. See Area of Interest #34 and #35 sections below for more information.


MAJOR HURRICANE LEE... Over the last 24 hours the core of hurricane Lee… located northeast of the northern Lesser Antilles… lost its eye and became disorganized while the hurricane remained disrupted by westerly shear imparted by Caribbean upper vorticity. Despite this… aircraft recon found Lee had not weakened below major category 3 hurricane status with 115 mph maximum sustained winds. Recently the Caribbean upper vorticity has weakened while remaining cut-off from high-latitude cold air… and Lee has spent recent hours re-organizing into a hurricane with symmetric thunderstorm distribution poised to re-intensify once it re-develops an organized inner core and eye.  Over the next 48 hours the Atlantic surface ridge should push Lee more west… but I have also nudged the forecast track a tad north of my previous as the details of Lee’s recent track suggest the hurricane is tracking a little more sharply north under the influence of the lingering Caribbean upper vorticity. I also forecast re-intensification into a strong category 4 thru 48 hours as the shear remains low due to the ongoing weakening of the Caribbean upper vorticity. Beyond 48 hours the long-range model guidance has once again 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 central 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 leading eastern US upper trough is now shown to be more captured by an amplified version of the trailing trough from central Canada… delaying the arrival of the leading trough toward Lee. Therefore I have nudged my northward turn further west to 67.5W longitude in this update. There is also notable north-south spread in the 5-day position of Lee as the CMC… NAVGEM… and ECMWF have a slower north turn and the GFS is faster. My updated forecast track is therefore slower with the north turn and a little slower than what the 1200Z GFS showed. For my 48+ hour intensity projection... the shear starts lower than previously thought due to the delayed arrival of the leading upper trough. However for 48 to 72 hours I assume Lee is likely to weaken from an eye wall replacement cycle after vaulting back to a strong category 4 by 48 hours. From 72 to 120 hours I then show gradual weakening to category 3 due to increased shear from the approaching leading upper trough.


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... Bermuda… and the mid-Atlantic United States coast over the next five days. 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 general direction of this region beyond day 5.


Update as of 11 PM EDT… Lee has weakened further to a category 2 with 105 mph maximum sustained winds as the latest aircraft recon data indicates an eye wall replacement cycle is underway. Therefore Lee is not a major category 3+ hurricane at this time. Re-intensification is still likely in the next 48 hours after the current eye wall replacement cycle finishes due to low wind shear as discussed above… however it is increasingly likely Lee won’t get quiet as strong as what I show at 48 hours as the re-intensification has been delayed by the current eye wall replacement cycle.

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

0 Hr Position (1800Z Sep 9)... 115 mph maximum sustained wind major hurricane centered northeast of the northern Lesser Antilles at 20.3N-58.2W

IOH 24 Hr Forecast (1800Z Sep 10)... 135 mph maximum sustained wind major hurricane centered north of the northern Lesser Antilles at 22.5N-62.5W

IOH 48 Hr Forecast (1800Z Sep 11)... 155 mph maximum sustained wind major hurricane centered in the western Atlantic at 23.5N-66.2W

IOH 72 Hr Forecast (1800Z Sep 12)... 145 mph maximum sustained wind major hurricane centered in the western Atlantic at 25.5N-67.5W

IOH 96 Hr Forecast (1800Z Sep 13)... 140 mph maximum sustained wind major hurricane centered southwest of Bermuda at 27N-67.5W

IOH 120 Hr Forecast (1800Z Sep 14)… 125 mph maximum sustained wind major hurricane centered west-southwest of Bermuda at 29N-67.5W

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

Peak Strength (1800Z Sep 11)… 140 mph maximum sustained wind major hurricane centered in the western Atlantic at 23.3N-64.1W

5-day Position (1800Z Sep 14)… 115 mph maximum sustained wind major hurricane centered west-southwest of Bermuda at 27.9N-68.2W


TROPICAL STORM MARGOT... Margot in the eastern tropical Atlantic has not caught a break from wind shear… after passing north of an inverted upper trough that was shearing it yesterday most of its thunderstorms have been pulled north of the center by the current central Atlantic upper vortex instead of Margot finding a low shear spot between the inverted trough and vortex. The result is that Margot has not strengthened much in the last 24 hours. Models now show the upper trough fragment currently near 42.5N-59W becoming more entangled with the central Atlantic upper vortex to make a central Atlantic upper trough that curves Margot northward with the southerly flow on its east side. The upper trough fragment will also bring a surface front supported by its eastern divergence zone… with the surface ridge weakness associated with the front also helping Margot’s north turn. My early forecast track points are nudged north and west to account for Margot’s current position relative to the prior forecast. A westward hook in Margot’s track remains likely by 96 and 120 hours as a northeast fragment of the current central Canada upper trough moves the cold front northeast and away from Margot… with the western convergence zone of this fragment re-building the Atlantic surface ridge due north of Margot. However there will now be some initial resistance to Margot’s westward hook as we will be dealing with an elongated central Atlantic upper trough instead of a vortex as noted above whose north side will be making resistive upper westerly flow in Margot’s environment… thus my updated forecast track below has a more gradual (less sharp) west hook.


My intensity forecast for the next 24 hours still shows only gradual strengthening due to the current shear from the central Atlantic upper vortex. The strengthening rate is then increased between 24 and 72 hours as the shear reduces while Margot’s thunderstorm latent heat release weakens the materializing central Atlantic upper trough… and as the straight north track during this window is more in alignment with the shearing southerly upper winds. No additional strengthening is shown at 96 hours and weakening is shown by 120 hours as the westward hook in Margot’s track puts it in more opposition to the flow imparted by the central Atlantic upper trough… resulting in more shear. By 120 hours Margot could end up in shearing upper northwesterly flow under the northwest side of the central Atlantic upper trough… with convergence on this side of the trough potentially contributing to the weakening at 120 hours.


Update as of 11 PM EDT… Margot has strengthened a little more to 50 mph maximum sustained winds.

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

0 Hr Position (1800Z Sep 9)… 45 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 21N-38.7W

IOH 24 Hr Forecast (1800Z Sep 10)... 50 mph maximum sustained wind tropical storm centered in the central Atlantic at 24N-40.2W

IOH 48 Hr Forecast (1800Z Sep 11)... 65 mph maximum sustained wind tropical storm centered in the central Atlantic at 28N-40.2W

IOH 72 Hr Forecast (1800Z Sep 12)... 80 mph maximum sustained wind hurricane centered in the central Atlantic at 31N-40.2W

IOH 96 Hr Forecast (1800Z Sep 13)... 80 mph maximum sustained wind hurricane centered in the central Atlantic at 34N-41W

IOH 120 Hr Forecast (1800Z Sep 14)… 60 mph maximum sustained wind tropical storm centered in the central Atlantic at 36N-43W

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

5-day Position (1800Z Sep 14)… 85 mph maximum sustained wind hurricane centered in the central Atlantic at 34.8N-41.8W


AREA OF INTEREST #34... The tropical wave of low pressure that recently emerged from Western Africa with a small low pressure rotation has seen the rotation pass just south of the Republic of Cabo Verde Islands… and as of 1800Z earlier this evening the rotation was southwest of the islands near 12.5N-25.5W with enough persistent thunderstorm activity to be considered an area of interest by the NHC in their tropical weather outlook. Forecast track is a slowing west-northwest trajectory into the surface ridge weakness caused by Margot. I assign a peak 50% odds of tropical cyclone formation in the short-term… a balance between the global models not developing this system while at the same time this system has signs of organization. For the long range I lower development odds to 30% as this system moves into southerly shearing winds on the southeast side of the central Atlantic upper trough to interact with Margot. The shear is not expected to be high enough to  drop development odds to 0% at day 5 as the south part of the upper trough tries to retrograde westward and out of the way under the influence of an amplified mid-latitude western Atlantic warm core upper ridge (the upper ridge will be bolstered by the latent heat release of Lee’s thunderstorms and warm southerly flow ahead of the current eastern US surface front).

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

IOH 24 Hr Outlook (1800Z Sep 10)… 50% chance of tropical cyclone formation (eastern tropical Atlantic near 14N-30.5W)

IOH 48 Hr Outlook (1800Z Sep 11)… 50% chance of tropical cyclone formation (eastern tropical Atlantic near 16.5N-35.5W)

IOH 72 Hr Outlook (1800Z Sep 12)… 40% chance of tropical cyclone formation (eastern tropical Atlantic near 18.5N-39W)

IOH 96 Hr Outlook (1800Z Sep 13)… 30% chance of tropical cyclone formation (central Atlantic near 20.5N-41W)

IOH 120 Hr Outlook (1800Z Sep 14)… 30% chance of tropical cyclone formation (central Atlantic near 22N-44W)

******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************

Formation chance through 48 hours… 30%

Formation chance through 7 days… 30%


AREA OF INTEREST #35… METEOSAT satellite imagery (https://www.goes.noaa.gov/f_meteo.html) as of 1800Z suggested a broad Western Africa tropical wave of low pressure with thunderstorms across its western… northern… and northeastern periphery was located near 11.5N-12W. Because various global model runs suggest its development when it later moves across the tropical belt of the Atlantic… the NHC has added it as an area of interest for development in their tropical weather outlook. Forecast track is a west-northwest trajectory toward the surface ridge weakness caused by Margot and Area of Interest #34. Although this wave thru day 5 will be under favorable low shear and outflow beneath tropical upper ridging… I agree with the NHC on a low peak 30% odds of tropical cyclone formation as the wave is not well-organized at this time and the global models at present are trending toward the evolution of this wave into a broad tropical low rather than outright tropical cyclone formation. Note this wave may produce heavy rain and gusty winds across the Republic of Cabo Verde Islands by Monday and Tuesday.

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

IOH 24 Hr Outlook (1800Z Sep 10)… 0% chance of tropical cyclone formation (west coast of Africa near 12N-17W)

IOH 48 Hr Outlook (1800Z Sep 11)… 0% chance of tropical cyclone formation (southeast of the Republic of Cabo Verde Islands near 13N-21W)

IOH 72 Hr Outlook (1800Z Sep 12)… 10% chance of tropical cyclone formation (southwest of the Republic of Cabo Verde Islands near 13.5N-26W)

IOH 96 Hr Outlook (1800Z Sep 13)… 20% chance of tropical cyclone formation (eastern tropical Atlantic near 14.5N-31W)

IOH 120 Hr Outlook (1800Z Sep 14)… 30% chance of tropical cyclone formation (eastern tropical Atlantic near 15N-36W)

******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************

Formation chance through 48 hours… 0%

Formation chance through 7 days… 30%


...COMPUTER MODEL SUMMARY...

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


0000Z (Sep 9) CMC Model Run...

**For Major Hurricane Lee... reaches waters northeast of the Bahamas by 120 hours while centered near 24.5N-70.5W

**For Tropical Storm Margot... reaches 33N-46W as a hurricane by 120 hours

**For Area of Interest #34… no development shown

**For Area of Interest #35… Tropical wave emerges from west coast of Africa at 36 hours...  develops into a broad tropical low southwest of the Republic of Cabo Verde Islands thru 84 hours… tropical low reaches 14N-47W through 168 hours


0000Z (Sep 9) ECMWF Model Run...

**For Major Hurricane Lee... reaches 23.5N-66W at 120 hours.

**For Tropical Storm Margot... reaches 32N-43W as a hurricane by 120 hours

**For Area of Interest #34… no development shown

**For Area of Interest #35… no development shown


1200Z (Sep 9) GFS Model Run...

**For Major Hurricane Lee... reaches 29.9N-69W at 120 hours.

**For Tropical Storm Margot... reaches 35N-38.8W at 120 hours as an intense hurricane

**For Area of Interest #34… no development shown

**For Area of Interest #35… Tropical wave emerges from west coast of Africa at 45 hours... organizes into a broad tropical low near 12N-30W at 96 hours… tropical cyclone formation suggested near 13N-42W at 150 hours


0600Z (Sep 9) NAVGEM Model Run...

**For Major Hurricane Lee... reaches 27.5N-66W at 120 hours

**For Tropical Storm Margot... reaches 33N-40.5W at 120 hours as an intense hurricane

**For Area of Interest #34… no development shown

**For Area of Interest #35… Tropical wave emerges from west coast of Africa at 78 hours and organizes into a tropical low south of the Republic of Cabo Verde Islands thru 108 hours… tropical low reaches 14.5N-37W by 168 hours

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