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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 #76

Updated: Sep 14, 2023

*******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...nd 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 13 2023 3:00 PM EDT...

See Hurricane Lee and 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 strong while curving northward between Bermuda and the United States east coast over the next few days. After passing near Bermuda over the next 48 hours... Lee is expected to strike the eastern part of the northeastern United States and Atlantic Canada this weekend and into early next week as an enlarging and still strong cyclone. See Lee section below for more information on expected impacts to land areas.


In addition... a broad tropical low pressure far southeast of Margot is expected to develop into the next Atlantic tropical cyclone while moving into the central tropical Atlantic. See area of interest #34 section below for more information.


Elsewhere... satellite imagery shows a well-defined tropical wave of low pressure with strong thunderstorms continuing westward across western Africa. This tropical wave will emerge from the west coast of Africa and into the eastern tropical Atlantic over the next day or so. It is not yet clear if upper winds in the eastern tropical Atlantic will be favorable or not for development as the high-latitude upper trough currently just east of Greenland will be diving southeastward toward the eastern tropical Altantic under the influence of a warm core upper ridge to be bolstered by the warm sector of Lee... if the vorticity of this upper trough digs far south enough it may suppress the outflow of tropical upper ridging in the eastern tropical Atlantic and prevent the development of this wave. Most global models do not develop this wave... and currently not adding this wave as an area of interest for further development.


MAJOR HURRICANE LEE... Lee... now located between the Bahamas and Bermuda... has not strengthened over the last 24 hours while remaining a major category 3 hurricane with 115 mph maximum sustained winds. The NHC advisory at 5 AM EDT early today cited some light westerly shear being imparted by the upper trough fragment now just west of the hurricane. In addition on colorized infrared satellite pictures... the core of the hurricane at times appears to be isolated from the outer bands perhaps as dry air has become ingested by the hurricane... perhaps the source of the dry air is the sinking motion caused by the western convergence zone of the nearby upper trough fragment. Lee has finally made its northward turn along 67.5W longitude in alignment with the previous forecast due to the surface ridge weakness caused by the frontal low now over eastern Canada in conjunction with upper southerly flow ahead of the nearby upper trough fragment and also ahead of the larger scale amplified upper trough now approaching from eastern North America. The other global models have finally aligned with the faster to the north GFS model... therefore my updated forecast track is similar to the previous but faster to the north. Between 24 and 48 hours there is some east lean in my forecast track as Lee gets kicked by the southeast side of the approaching eastern North America upper trough. Then between 48 and 72 hours there is a lean back toward the west as the northwest side of the hurricane pulls down cold air associated with the amplified upper trough from eastern North America... creating a cold core upper vortex just west of Lee whose northeast side bends the track of the hurricane. And finally between 72 and 96 hours there is a lean back toward the east as Lee and the upper vortex become stacked... but the upper vortex and Lee get pushed in unison by the next North America amplified upper trough that approaches in the mid-latitude westerlies.


For intensity... due to the degraded structure of Lee caused by dry air noted in the prior pargraph and expected increase in shear as the approaching eastern North America upper trough digs into Lee... I forecast a steeper weakening rate for the next 24 hours than I previously showed. Beyond 24 hours I slow the weakening rate as the tremendous eastern divergence zone of the forming upper vortex to the west aids Lee. The size of the upper divergence zone will also help grow the size of the weakening hurricane. Transition into a non-tropical frontal cyclone is anticipated around 72 hours once Lee reaches the cool northwest Atlantic waters well below 26 deg C... with the weakening rate of the frontal cyclone increasing between 72 and 96 hours as ex-Lee and the upper vortex become vertically stacked as traditionally seen with a post-mature frontal cyclone... with a lack of divergence beneath the core of the upper vortex causing the increased weakening rate. From 96 to 120 hours models show ex-Lee maintaining strength while moving northeastward near southeastern Quebec... the northern Gulf of St. Lawrence... and into northwestern Newfoundland as the overhead upper vortex opens into a trough due to the approach of the next amplified upper trough in the mid-latitudes... with ex-Lee aided by the eastern divergence zone of this next trough. Due to the faster northward updated track forecast which gives less time for ex-Lee to weaken before interacting favorably with the next upper trough... there is an increased chance of a stronger version of ex-Lee which would impact the Gulf of St Lawrence... southeastern Quebec... Newfoundland... and Labrador by day 5.


Regarding impact to land areas:

(1) Expect wide-reaching surf from this powerful hurricane to reach the 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 day or so. Coastal surf will then increase across the coastal northeastern United States and Atlantic Canada (Nova Scotia... New Brunswick... and Newfoundland) by tomorrow and Friday.

(2) The latest forecast track places Bermuda under the eastern periphery of Lee by late Thursday where tropical storm force winds are possible... and a tropical storm warning is in effect as of this writing. I recommend to finish preparations for tropical storm conditions (wind and coastal surf) by tonight.

(3) Interests across Nova Scotia... New Brunswick... Prince Edward Island... Maine... New Hampshire... central and eastern Massachusetts... eastern Connectictut... Rhode Island... and eastern Long Island New York are expected to see more direct impacts such as life-threatening coastal surf and damaging winds this weekend... I recommend to begin preparing now and finish preparations by Friday evening. Even though Lee will be gradually weakening during its approach... damaging winds could affect a large area and life-threatening coastal surf will become a concern due to the expected growing size of the storm. Flash flooding heavy rainfall will be another hazard to contend with.

(4) Per the above notes... the latest forecasts now show an increased wind... coastal surf... and heavy rainfall impact from what will be the remnant frontal cyclone of Lee for southeastern Quebec... Newfoundland... and Labrador by Monday. Interests in this region should monitor the latest forecasts for Lee in the days ahead.


Update as of 1800Z (2 PM EDT)... Lee is no longer a major category 3 hurricane while weakening to 110 mph maximum sustained winds. No changes to the above discussion and below forecast as the forecast and discussion take into account Lee weakening going forward.

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

0 Hr Position (1200Z Sep 13)... 115 mph maximum sustained wind major hurricane centered southwest of Bermuda at 26N-67.2W

IOH 24 Hr Forecast (1200Z Sep 14)... 95 mph maximum sustained wind hurricane centered southwest of Bermuda at 30N-67.5W

IOH 48 Hr Forecast (1200Z Sep 15)... 85 mph maximum sustained wind hurricane centered northwest of Bermuda at 35.5N-66.5W

IOH 72 Hr Forecast (1200Z Sep 16)... 70 mph maximum sustained wind tropical storm transitioning into a frontal cyclone while centered midway between Cape Cod Massachusetts and the southwest coast of Nova Scotia at 42N-67.5W

IOH 96 Hr Forecast (1200Z Sep 17)... 50 mph maximum sustained wind frontal cyclone centered over central New Brunswick at 46.5N-66.5W

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

5-day Position (1200Z Sep 18)... 40 mph maximum sustained wind frontal cyclone centered over the south tip of Labrador at 52.1N-56.4W


HURRICANE MARGOT... Margot has continued northward in the open central Atlantic near 40W longitude while remaining under the influence of upper southerly flow on the east side of the current central Atlantic upper vortex... and also while gravitated toward the surface ridge weakness associated with a surface cold front to the northeast. The track has begun to have a westward lean as the Atlantic surface ridge to Margot's north is recovering under the western convergence zone of a passing high-latitude upper trough. Despite the thunderstorm canopy of Margot continuing to be disrupted by dry air intrustion... the 11 AM EDT NHC advisory cites satellite scans of Margot that support an additional intensity increase to 90 mph maximum sustained winds. Noting that Margot is northeast of my previous forecast track and so my stall position at 24 and 48 hours is adjusted accordingly. Margot is expected to stall as northwesterly flow on the southwest side of the high-latitude upper trough tries to drag Margot eastward while the recovering Atlantic surface ridge tries to do the opposite. The conflicting steering then continues through 48 hours as a warm core upper ridge to the northwest to be bolstered by the warm southerly flow on Lee's east side conflicts with warm core tropical upper ridging to the south. Beyond 48 hours... a north and then northeast track is likely to develop as (1) the Atlantic surface ridge shifts east with the position of the high-latitude upper trough’s convergence zone... allowing Margot to round the northwest side of the surface ridge center... (2) as upper southwesterly flow increases over Margot while what remains of the central Atlantic upper vortex gets pushed into Margot by what will be an upper vortex over Lee. In this update cycle I have trended with a slower north and northeast turn for the 48 to 120 hour window as models have trended with a stronger blocking surface ridge built by the southwestern convergence zone of an upper vortex that moves into Greenland from its current far northeast Canada position.


For intensity... Margot should weaken over the next 24 hours from shearing upper northwesterly flow on the southwest side of the passing high-latitude upper trough overspreading Margot... albeit the shear is expected to be weakened by the formation of a cold core local upper trough as Margot's northwest side pulls in some cooler air and so I only show slow weakening. By 48 and 72 hours the local upper trough becomes a detriment while becoming parked directly over Margot while sandwiched between the aforementioned northwest Atlantic and tropical latitude upper ridges... with suppressing convergence directly below the troughing negatively affecting Margot and hence I show a faster weakening rate. By 96 hours the updated forecast track below places Margot underneath the favorable low shear upper outflow environment directly underneath the northwest Atlantic upper ridge... however I show no re-strengthening as Margot will be right at the 26 deg C sea surface temperaure isotherm barely conducive to tropical development. By 120 hours Margot is likely to transition into a remnant frontal low or cyclone while lifting north into cooler waters and while becoming supported by the eastern divergence zone of what remains of the central Atlantic upper vortex as those remains pivot around ex-Lee’s upper vortex and toward Margot as noted at the end of the prior paragraph.

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

0 Hr Position (1200Z Sep 13)... 90 mph maximum sustained wind hurricane centered in the central Atlantic at 34.1N-40.4W

IOH 24 Hr Forecast (1200Z Sep 14)... 80 mph maximum sustained wind hurricane centered in the central Atlantic at 36N-41W

IOH 48 Hr Forecast (1200Z Sep 15)... 65 mph maximum sustained wind tropical storm centered in the central Atlantic at 36N-41W

IOH 72 Hr Forecast (1200Z Sep 16)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 37N-41W

IOH 96 Hr Forecast (1200Z Sep 17)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 39N-41W

IOH 120 Hr Forecast (1200Z Sep 18)... Frontal cyclone centered in the north-central Atlantic at 42.5N-37W

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

5-day Position (1200Z Sep 18)... 50 mph maximum sustained wind tropical storm centered in the central Atlantic at 40N-43W


AREA OF INTEREST #34... The western of the pair of closely spaced tropical waves of low pressure has evolved further into a tropical low pressure near 11N-32.5W through 1200Z today. The tropical low has been stationary near 32.5W longitude while dragged by the adjacent tropical wave to the east that it is in the process of absorbing... and because it is absorbing an adjacent system the tropical low has become a larger/broader feature. Noting that through 1800Z it appears the broad center of rotation has finally begun to advance westward while nearing 34W longitude. Because this system is gradually seeing an increase in the intensity and organization of its thunderstorms... and because the models continue to forecast development... I am continuing a tropical cyclone formation forecast with a specific track and intensity projection as outlined below. The forecast track remains similar to my previous which has this system bending on a slower and more northwest track through 96 hours as this system reaches the weakened western part of the Atlantic surface ridge (the weakness being caused by the simultaneous presence of tropical cyclones Lee and Margot). Noting that by day 5 the surface ridge is likely to re-build after Lee and Margot lift northward and away... resulting in a more west and less north track with faster forward speed which is reflected by my 120 hour forecast position below. Conditions for development thru day 5 are expected to be favorable with this system remaining parked below tropical upper ridging with low shear and upper outflow. Also the unfavorable central Atlantic upper vortex first pivots west and away from this system under the influence of a northwest Atlantic warm core upper ridge that builds in the warm sector of what will be the remnant frontal cyclone of Lee... and then in 4+ days pivots northeastward and away toward Margot and further away from this system while pulled around the upper vortex that will be on top of ex-Lee. Despite this favorable upper wind outlook... I only show gradaul strengthening into a minimal hurricane through day 4 as this system is currently broad in nature... and broad systems often lack a well-defined center of surface converence with focused thunderstorms needed for rapid development. Also broad systems tend to have a lax surface pressure gradient between the center and outside... requiring more of a central pressure drop to achieve an increase in wind speed. I assume by day 5 this system will have developed a well-defined center and so I begin to show a faster intensification rate during that timeframe.


Note the forecast track below may need to be shifted in future updates as is often the case with broad systems... as there is a degree of uncertanity as to where in the broad circulation that the better defined center will form.

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

0 Hr Position (1200Z Sep 13)... Tropical low centered in the eastern tropical Atlantic at 11N-32.5W

IOH 24 Hr Forecast (1200Z Sep 14)... Tropical low centered in the eastern tropical Atlantic at 12N-37.5W

IOH 48 Hr Forecast (1200Z Sep 15)... 45 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 13N-42W

IOH 72 Hr Forecast (1200Z Sep 16)... 60 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 15N-46W

IOH 96 Hr Forecast (1200Z Sep 17)... 75 mph maximum sustained wind hurricane centered in the central tropical Atlantic at 17.5N-49W

IOH 120 Hr Forecast (1200Z Sep 18)... 95 mph maximum sustained wind hurricane centered in the central tropical Atlantic at 19N-54W

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

Formation chance through 48 hours... 70%

Formation chance through 7 days... 90%


...COMPUTER MODEL SUMMARY...

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


0000Z (Sep 13) CMC Model Run...

**For Major Hurricane Lee... passes just west of Bermuda at 54 hours... makes landfall on the southwest coast of Nova Scotia as a weakening but still strong frontal cyclone at 108 hours... center of gradually weakening frontal cyclone slides east-northeast across Nova Scotia through 120 hours.

**For Hurricane Margot... reaches 37N-45W at 120 hours as a weakened tropical storm

**For Area of Interest #34... tropical cyclone formation suggested near 14N-39.5W at 54 hours and reaches 22.5N-51W as a hurricane by 120 hours

**Tropical wave emerges from west coast of Africa at 36 hours... evolves into a tropical low near 8.8N-26.5W at 102 hours which becomes quasi-stationary thorugh 120 hours while dragged by additional tropical wave approaching from the east.

**Additional and strong tropical wave emerges from west coast of Africa at 162 hours


0000Z (Sep 13) ECMWF Model Run...

**For Major Hurricane Lee... passes just west of Bermuda at 54 hours and makes landfall at the Maine/New Brunswick border at 102 hours as a strong frontal cyclone... the gradually weakening but still strong frontal cyclone turns norhteast across southeastern Quebec and the northwest corner of the Gulf of St. Lawrence through 120 hours.

**For Hurricane Margot... makes a clockwise loop in the open central Atlantic and arrives to 32.5N-43W as a weakened tropical storm by 120 hours.

**For Area of Interest #34... tropical cyclone formation suggested near 19.5N-46.5W at 96 hours... reaches 20.8N-51.5W at 120 hours as a strengthening tropical storm.

**Additional and strong tropical wave emerges from west coast of Africa at 168 hours


0600Z (Sep 13) GFS Model Run...

**For Major Hurricane Lee... passes just west of Bermuda at 42 hours and makes landfall at the Maine/New Brunswick border at 84 hours as a strong frontal cyclone... the gradually weakening but still vigorous frontal cyclone turns northeast across the northern Gulf of St Lawrence and into the northwest coast of Newfoundland through 120 hours.

**For Hurricane Margot... reaches 41.5N-40.5W through 120 hours while maintaining at least strong tropical storm strength.

**For Area of Interest #34... tropical cyclone formation suggested near 15N-40.5W at 51 hours... tropical cyclone begins to strengthen near 17N-43.5W at 63 hours while having a dominant center instead of multiple centers... while moving northwest the strengthening tropical cyclone reaches 24N-53.5W as a hurricane by 120 hours.


0600Z (Sep 13) NAVGEM Model Run...

**For Major Hurricane Lee... passes just west of Bermuda at 42 hours and makes landfall at the Maine/New Brunswick border at 84 hours as a strong frontal cyclone... the gradually weakening but still vigorous frontal cyclone turns northeast across the northern Gulf of St Lawrence and into the northwest coast of Newfoundland through 120 hours.

**For Hurricane Margot... makes a clockwise loop in the open central Atlantic and arrives to 32N-41.5W as a strong hurricane by 120 hours.

**For Area of Interest #34... develops into a broad tropical storm centered near 14.5N-39.5W at 54 hours... the gradually strengthening broad tropical storm reaches 22N-54W at 120 hours

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