top of page
Home: Text

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 

Home: Text
Home: Blog2
Search
  • Writer's pictureNCHurricane2009

MY 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #75

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


...TUESDAY SEPTEMBER 12 2023 10:35 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... the United States east coast... and the Bahamas over the course of the next five days. After passing near Bermuda over the next 48 hours... Lee is expected to strike the eastern part of the northeastern United States... Nova Scotia... New Brunswick... and Prince Edward Island this weekend as an enlarging and still strong cyclone. See Lee section below for more information on expected impacts to land areas.


In addition... a pair of tropical waves of low pressure well to the southeast of Tropical Storm Margot continue to be closely-spaced and are interacting with each other. One of the waves is now expected to absorb the other and potentially develop into a tropical cyclone in the central tropical Atlantic over the next five days... see area of interest #34 and #35 sections below for details.


Elsewhere... satellite imagery shows a well-defined tropical wave of low pressure with strong thunderstorms that has recently shifted into western Africa from central Africa. This tropical wave will emerge from the west coast of Africa and into the eastern tropical Atlantic in about three days. It is not yet clear if upper winds in the eastern tropical Atlantic will be favorable or not for development as a high-latitude upper trough currently passing north of Margot 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. Therefore there are no additional areas of interest for tropical development in the Atlantic basin for the next five days.


MAJOR HURRICANE LEE... Lee... now located midway between the northeastern Caribbean Islands and Bermuda.. has spent much of the last 24 hours undergoing a slow eye wall replacement cycle where the new eye is notably larger in diameter. This cycle has caused the hurricane to weaken to a minimal category 3 with 115 mph maximum sustained winds. Although the hurricane has been moving northwestward... the stage is set for Lee to turn north any moment now due to the surface ridge weakness caused by the surface front now pushing offshore from the northeastern United States and the increase in upper southerly flow just west of the hurricane as a leading upper trough that had been over the eastern US has been kicked toward Lee by a trailing amplified upper trough over central North America. Because the northward turn has not occurred yet... my updated forecast track is shifted west and further from Bermuda. Also noting the other global models are begining to agree with the GFS on a faster northward acceleration and my updated track is faster to the north accordingly... however my updated track is not quiet as fast to the north as the recent 1200Z GFS as the other models still lag the GFS. Despite the above-mentioned west shift in my forecast track... between 48 and 72 hours there is some east lean in my forecast track as Lee gets kicked by the southeast side of the approaching central North America upper trough. Then between 72 and 96 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 central North America... potentially creating a cold core upper vortex just west of Lee whose northeast side bends the track of the hurricane. And finally between 96 and 120 hours there is a slight 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... on colorized infrared satellite pictures the inner core of the hurricane looks a little better organized as the new larger eye is becoming better established. And because the shear will not be too bad for another 24 hours I forecast potential strengthening in the short term. After 24 hours weakening is expected as shear increases when the approaching upper trough from central North America digs into Lee. Another factor that may aid in weakening is Lee's passage across the cool sea surface temperature wake caused by previous Hurricanes Franklin and Idalia in between 48 and 72 hours. Despite these negative factors (shear and cooled sea surface temperatures from the recent previous hurricanes)... the weakening rate of Lee is only expected to be gradual 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 96 hours once Lee reaches the cool northwest Atlantic waters well below 26 deg C... with the weakening rate of the frontal cyclone increasing between 96 and 120 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.


Regarding impact to land areas:

(1) 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 couple of days. Coastal surf will then increase across the coastal northeastern United States and Atlantic Canada (Nova Scotia... New Brunswick... and Newfoundland) by later in the week.

(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 watch is in effect as of this writing (the watch was issued at 11 AM EDT today). I recommend to finish preparations for tropical storm conditions (wind and coastal surf) by tomorrow night.

(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 at risk of seeing more direct impacts such as life-threatening coastal surf and damaging winds this weekend. 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. For southeastern Quebec... although the potential for notable wind appears low at this time... heavy rainfall will likely be a concern here.

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

0 Hr Position (1800Z Sep 12)... 115 mph maximum sustained wind major hurricane centered in the western Atlantic at 24.5N-66.2W

IOH 24 Hr Forecast (1800Z Sep 13)... 125 mph maximum sustained wind major hurricane centered southwest of Bermuda at 26.5N-67.5W

IOH 48 Hr Forecast (1800Z Sep 14)... 110 mph maximum sustained wind hurricane centered southwest of Bermuda at 30N-67.5W

IOH 72 Hr Forecast (1800Z Sep 15)... 95 mph maximum sustained wind hurricane centered northwest of Bermuda at 35N-66.5W

IOH 96 Hr Forecast (1800Z Sep 16)... 85 mph maximum sustained wind hurricane transitioning into a frontal cyclone while centered midway between Cape Cod Massachusetts and the southwest coast of Nova Scotia at 41.5N-67.5W

IOH 120 Hr Forecast (1800Z Sep 17)... 60 mph maximum sustained wind frontal cyclone centered on the coast of North America at the Maine/New Brunswick border at 45N-67W

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

5-day Position (1800Z Sep 17)... 45 mph maximum sustained wind frontal cyclone centered on the Gulf of St Lawrence coast of New Brunswick at 47.1N-64.5W


HURRICANE MARGOT... Margot has continued northward in the open central Atlantic along 40W longitude while remaining under the influence of upper southerly flow on the east side of the central Atlantic upper trough... and also while gravitated toward the surface ridge weakness associated with a surface front to the north. Because the upper trough is amplified there has been little westerly shear affecting Margot... thus it has been able to strengthen into a hurricane which reached a peak strength of 85 mph maximum sustained winds within the last 24 hours. At times the small core of the hurricane has been isolated from its outer bands by dry air that has wrapped into the circulation... it is probable the dry air is originating from the sinking motion caused by the western convergent side of the upper trough. Margot has in fact recently weakened to 80 mph maximum sustained winds from the disruption caused by the dry air. Noting the previous forecast track has done well and so the updated one is the same for the short-term. A westward bend in Margot’s track remains likely thru 48 hours as the high-latitude upper trough currently in the north-central Atlantic is passing north of Margot and will move the nearby surface front northeast and away from Margot... with the western convergence zone of the high-latitude upper trough then re-building the Atlantic surface ridge due north of Margot. The steering pictures gets complicated around 48 to 72 hours as northwesterly flow on the southwest side of the high-latitude upper trough tries to drag Margot eastward while the recovered Atlantic surface ridge tries to do the opposite. The conflicting steering then continues 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. Therefore I show Margot stalled in the 48 to 72 hour window... with a slight eastward adjustment to the stall position as the models now insist Margot’s northwest side will pull enough cool air to the south to make a local upper trough that may resist Margot’s westward progress. Beyond 72 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 trough gets pushed into Margot by what will be an upper vortex over Lee.


For intensity... Margot has another 24 hours in a low shear environment as the central Atlantic upper trough weakens further to a vortex to the southwest thanks to Margot’s thunderstorm latent heat release and the trough’s ongoing isolation from high-latitude cold air. However I show only slight strengthening and thus a lower intensity compared to the prior forecast due to the dry air noted in the prior paragraph and as the upper vortex may impinge on the southwestern outflow of the storm. The initial weakening after 24 hours is from shearing upper northwesterly flow on the southwest side of the passing high-latitude upper trough overspreading Margot... albeit the shear may be weakened by the formation of the local upper trough noted in the prior paragraph and so I only show slight initial weakening. By 72 and 96 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 120 hours Margot is likely to transition into a remnant frontal low while lifting north into cooler waters and while becoming supported by the eastern divergence zone of what remains of the central Atlantic upper trough 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 (1800Z Sep 12)... 80 mph maximum sustained wind hurricane centered in the central Atlantic at 31.7N-39.6W

IOH 24 Hr Forecast (1800Z Sep 13)... 90 mph maximum sustained wind hurricane centered in the central Atlantic at 33.5N-41.5W

IOH 48 Hr Forecast (1800Z Sep 14)... 80 mph maximum sustained wind hurricane centered in the central Atlantic at 35N-42.5W

IOH 72 Hr Forecast (1800Z Sep 15)... 65 mph maximum sustained wind tropical storm centered in the central Atlantic at 35N-42.5W

IOH 96 Hr Forecast (1800Z Sep 16)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 37.5N-42.5W

IOH 120 Hr Forecast (1800Z Sep 17)... Frontal cyclone centered in the north-central Atlantic at 42.5N-41W

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

Peak Strength (0600Z Sep 13)... 85 mph maximum sustained wind hurricane centered in the central Atlantic at 33.2N-40.2W

5-day Position (1800Z Sep 17)... 50 mph maximum sustained wind tropical storm centered in the central Atlantic at 40N-43W


AREA OF INTEREST #34... Of the pair of closely-spaced tropical waves of low pressure in the eastern tropical Atlantic... it is the western of the two that continues to remain the most organized and has become the focal point in recent NHC tropical weather outlooks for development potential in the days ahead. Through 1800Z the NHC TAFB surface analysis had the center of rotation of this wave near 12.5N-32.5W. However based on the curvature of the cloud bands in the region it appears the center of rotation is further west toward at least 35W longitude as of 0000Z. Because the models have converged on developing this wave... I have begun a tropical cyclone formation forecast with a specific track and intensity projection as outlined below. The forecast track for the next 36 hours should be slow to the west while this system continues to be dragged by the adjacent tropical wave to the east (Area of Interest #35) until it absorbs it... followed by a slow northwest track from 36 to 120 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 after day 5 the surface ridge is likely to re-build after Lee and Margot lift northward and away... potentially resulting in a more westward and less northward track in the longer range. 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 trough 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 by day 5 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 5 as this system will likely become a broad tropical low pressure and then an initially broad tropical cyclone while absorbing Area of Interest #35... 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.

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

0 Hr Position (0000Z Sep 13)... Tropical low centered in the eastern tropical Atlantic at 12.5N-35W

IOH 24 Hr Forecast (0000Z Sep 14)... Tropical low centered in the eastern tropical Atlantic at 12.5N-38W

IOH 48 Hr Forecast (0000Z Sep 15)... Tropical low centered in the central tropical Atlantic at 13N-41W

IOH 72 Hr Forecast (0000Z Sep 16)... 45 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 14N-44W

IOH 96 Hr Forecast (0000Z Sep 17)... 60 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 16N-47.5W

IOH 120 Hr Forecast (0000Z Sep 18)... 75 mph maximum sustained wind hurricane centered in the central tropical Atlantic at 18.5N-51W

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

Formation chance through 48 hours... 30%

Formation chance through 7 days... 80%


AREA OF INTEREST #35... The tropical wave of low pressure that has been passing south of the Republic of Cabo Verde Islands remains less organized than the adjacent wave to the west tagged as area of interest (AOI) #34 in this update. Likewise the models have now converged on a solution where AOI #34 absorbs this wave... with AOI #34 going on to develop. Also AOI #34 has become the only focus in the region for further development in the latest NHC tropical weather outlooks with the initial position of the NHC area of interest aligned with AOI #34 instead of the previous NHC outlooks where both AOI #34 and #35 were marked as discrete features. Therefore I have downgraded the odds of this wave's development to 0%... and this is my final statement on this area of interest on this blog.

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

IOH 24 Hr Outlook (0000Z Sep 14)... 0% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-30W)

******National Hurricane Center (hurricanes.gov) official outlook as of 8 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 12) CMC Model Run...

**For Major Hurricane Lee... centered just south of western Nova Scotia at 120 hours near 42.5N-66W

**For Hurricane Margot... reaches 38.5N-45W at 120 hours while weakening to a tropical storm

**For Area of Interest #34... tropical cyclone formation suggested near 13.5N-36.5W at 60 hours and reaches 21N-48W as a hurricane by 120 hours

**For Area of Interest #35... No development shown

**Tropical wave emerges from west coast of Africa at 66 hours... compact tropical cyclone formation suggested near 11N-20W at 120 hours


0000Z (Sep 12) ECMWF Model Run...

**For Major Hurricane Lee... located just north of Cape Cod Massachusetts at 120 hours while centered near 42N-70.5W

**For Hurricane Margot... reaches 37.5N-44W at 120 hours while weakening to a tropical storm

**For Area of Interest #34... tropical cyclone formation suggested near 18.5N-45W at 102 hours... tropical cyclone located near 21.5N-48W at 120 hours

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


1200Z (Sep 12) GFS Model Run...

**For Major Hurricane Lee... centered over New Brunswick at 120 hours

**For Hurricane Margot... reaches 42.5N-45W at 120 hours while weakening to a tropical storm

**For Area of Interest #34... tropical cyclone formation suggested near 15N-40.2W at 66 hours... tropical cyclone begins to strengthen near 19.9N-45.5W at 93 hours while having a dominant center instead of multiple centers... while moving northwest the strengthening tropical cyclone reaches 23.5N-49.5W as a hurricane.

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


0600Z (Sep 12) NAVGEM Model Run...

**For Major Hurricane Lee... centered over the southwest coast of Nova Scotia at 120 hours

**For Hurricane Margot... makes a clockwise loop in the open central Atlantic and arrives to 32.5N-38.5W as a strong hurricane

**For Area of Interest #34... arrives to 17.5N-50W as a broad tropical low by 120 hours.

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

18 views0 comments

Comments


bottom of page