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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 #78

Updated: Sep 18, 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...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.**********


…UPDATE… MONDAY SEPTEMBER 18 2023 9:45 AM EDT…

The National Hurricane Center upgraded Nigel in the open central Atlantic to an 80 mph maximum sustained wind hurricane as of 5 AM EDT.


While continuing northeast… the remnant frontal cyclone of Lee has entered the North Atlantic from Newfoundland and Labrador. Gusty winds are still occurring for southeast Labrador and northern Newfoundland… and coastal surf is ongoing for the east coast of Newfoundland and Labrador. Weather conditions will improve here throughout today as the remnant cyclone accelerates eastward and away. The following are reports of peak wind gusts seen across Atlantic Canada (from Environment Canada weather stations… weather.gc.ca/canada_e.html) and the eastern  part of the northeastern US (from National Weather Service weather stations… weather.gov) from the remnant cyclone of Lee over the weekend and into this morning. Reports below are in mph… Environment Canada station reports below were converted from kph to mph. Timestamps are local time at each location:

**Mountauk (eastern Long Island NY)… sustained 15… gust 26… 6:54 AM Sept 16

**New London (southeast CT)… sustained 21… gust 32… 1:56 PM Sept 16

**Worcester (central MA)… sustained 28… gust 48… 3:54 PM Sept 16

**Hyannis (Cape Cod MA)… sustained 21… gust 36… 4:57 AM Sept 16

**Portsmouth (southeast NH)… sustained 22… gust 33… 5:55 PM Sept 16

**Concord (central NH)… sustained 25…gust 41… 3:51 PM Sept 16

**Portland (southwest ME)… sustained 28… gust 44… 4:51 PM Sept 16

**Bar Harbor (southeast ME)… sustained 25… gust 39… 1:56 PM Sept 16

**Millinocket (east-central ME)… sustained 22… gust 47… 4:53 PM Sept 16

**Fredericton (central NB)… sustained 13… gust 23… 4:00 PM Sept 17

**St Stephen (southwest NB)… sustained 9… gust 19… 12:00 PM Sept 17

**Yarmouth (southwest NS)… sustained 18… gust 28… 1:00 PM Sept 17

**Halifax (central NS)… sustained 20… gust 30… 9:00 AM Sept 17

**Sydney (northeast NS)… sustained 27… gust 42… 9:00 AM Sept 17

**Charlottetown PE… sustained 13… gust 26… 12:00 PM Sept 17

**Gaspe (southeast QC)… sustained 11… gust 18… 4:00 PM Sept 17

**Blanc Sablon (southeast QC)… sustained 25… gust 33… 4:00 PM Sept 17

**Channel Port Aux Basques (southwest NL)… sustained 34… gust 48… 12:30 PM Sept 17

**Deer Lake (west-central NL)… sustained 16… gust 31… 1:30 PM Sept 17

**St Anthony (northern NL)… sustained 21… gust 36… 10:30 AM Sept 18

**Marys Harbour (southeast Labrador)… sustained 20… gust 39… 6:30 AM Sept 18

**Happy Valley-Goose Bay (south-central Labrador)… sustained 24… gust 34… 7:00 PM Sept 17

**Nain (northern Labrador)… sustained 22… gust 29… 6:00 PM Sept 17


...SUNDAY SEPTEMBER 17 2023 12:45 PM EDT...

Lee has transitioned into a remnant frontal cyclone now moving northeast across Atlantic Canada… see remnants of Lee section below for more information. Tropical Storm Margot in the open central Atlantic has collapsed into a remnant low as of 11 AM EDT today… see Margot section below for more information. See Tropical Storm Nigel section below for information on the new central Atlantic tropical storm located to the south of Margot.


Elsewhere... see area of interest #36 section below for an update on the tropical wave over western Africa which has potential to develop this upcoming week when it moves offshore into the eastern tropical Atlantic. Also some model runs indicate that a portion of the upper vorticity currently offshore of California may merge with a southern fracture of the current central North America upper trough to make a cut-off upper vortex over the Florida peninsula in about six days… with the eastern divergence zone of the upper vortex kicking off a surface subtropical disturbance with development potential just north of the northwestern Bahamas. As such… another area of interest north of the northwestern Bahamas and near the southeast United States coast may need to be declared in future updates.


REMNANTS OF LEE... Lee transitioned into a large and strong remnant frontal cyclone offshore of the northeastern US and Atlantic Canada on Saturday while moving over cooler waters that caused Lee to lose its thunderstorm core… while simultaneously maintaining its strength and size through non-tropical processes via the large eastern divergence zone of the northeastern US upper trough it’s interacting with. Around 8 PM EDT Saturday the center of the remnant cyclone made landfall just east of the New Brunswick/Maine border… and still had a strong intensity of 65 mph maximum sustained winds thanks to the aforementioned support of the upper trough. So far this Sunday morning the center of the cyclone curved northeastward across southern New Brunswick and is about to enter the Gulf of St Lawrence with the circulation having 50 mph maximum sustained winds. Going forward the center of the remnant cyclone through Monday will continue northeast across the Gulf of St Lawrence… then either over northern Newfoundland or southern Labrador while coming under the influence of the next upper trough now inbound from central North America… and will continue to be slow to weaken while divergence zone of this next upper trough also aids ex-Lee.


For the remainder of this weekend coastal surf… periods of heavy rainfall… and gusty winds with some damage potential will be impacts for New Brunswick… Nova Scotia… Prince Edward Island… southeastern Quebec… Newfoundland… and Labrador. This is my final statement on Lee on this blog as it is no longer a tropical cyclone… statements regarding the remnant cyclone’s impacts will be carried on the home page bulletins of this site going forward.


Update as of 11 AM EDT… the remnant cyclone of Lee was centered in the Gulf of St Lawrence with 45 mph maximum sustained winds.


TROPICAL STORM MARGOT (RECENTLY DOWNGRADED TO REMNANTS OF MARGOT)… While in the open central Atlantic… Margot has been swinging west away from the Azores under the influence of the Atlantic surface ridge as well as well as a warm core upper ridge to the north that has been built up by northward warm air transport on the east side of ex-Lee. Margot has lost its thunderstorms over the weekend so far and is barely a tropical storm as the outflow of the warm core upper ridge to the north and outflow of the low-latitude tropical upper ridge cell to the south (pumped up by Nigel’s thunderstorm latent heat release) are converging over Margot and hence suppressing Margot’s outflow. Over the next 48 hours the surface and upper ridge centers to the north will continue east in the mid-latitude westerlies such that Margot will curve north and then northeastward around the west side of the ridge centers. My updated forecast track is adjusted based on the fact that Margot is slightly southeast of my previous one. The forecast track by 24 hours takes Margot away from the suppressing upper convergence zone… and the wave of upper vorticity to the west (consisting of an upper vortex to the southwest that migrated from the central Atlantic and upper troughing currently interacting with ex-Lee) is weaker than previously forecasted and thus remains off to the west without disrupting Margot… leaving Margot to perhaps take advantage of low shear and outflow beneath the northern upper ridge cell. Therefore I hold on to Margot as a tropical storm thru 24 hours while indicating the possibility of re-strengthening. By 48 hours Margot’s northeast curving track takes it into cooler waters below 26 deg C… however Margot is likely to hang on as a non-tropical frontal low or cyclone as the supporting eastern divergence zone of the wave of upper vorticity to the west moves in. Because the wave of upper vorticity is weaker and less amplified… the upper flow is more westerly and less southerly and the models and my updated forecast track have hence shifted south for the track of Margot’s non-tropical remnants. The lower amplitude wave of upper vorticity also moves faster as typically seen with lower amplitude features which then allows Margot to be left behind by the wave… thus leaving Margot’s remnants to weaken under the convergence zone behind the wave while the remnants drift toward the Azores. However the Azores may still see coastal surf early this upcoming week and before the remnants weaken.


Update as of 11 AM EDT… my above discussion and forecast below were completed at 0600Z earlier this morning… since then Margot was downgraded to a 40 mph max sustained wind remnant low as Margot has so far failed to re-fire any thunderstorms. In the next 24 hours Margot may find better upper winds to re-fire thunderstorm as discussed above… however such an event is now likely to be too short lived for the NHC to re-upgrade Margot to a tropical system as it would soon thereafter move into cooler waters and lose thunderstorms. Therefore this will be planned my final statement on Margot on this blog as it is no longer a tropical cyclone.

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

0 Hr Position (0600Z Sep 17)... 40 mph maximum sustained wind tropical storm centered in the central Atlantic at 34N-41.4W

IOH 24 Hr Forecast (0600Z Sep 18)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 37N-42.5W

IOH 48 Hr Forecast (0600Z Sep 19)... Frontal cyclone centered in the northeastern Atlantic at 40N-38.5W

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

Loss of Tropical Cyclone Status (1800Z Sep 17)… 35 mph maximum sustained wind remnant low centered in the central Atlantic at 34.5N-42.7W


TROPICAL DEPRESSION FIFTEEN (RECENTLY UPGRADED TO TROPICAL STORM NIGEL)... The broad tropical depression in the open central Atlantic finally strengthened into Tropical Storm Nigel overnight and into Sunday morning. My forecast track is adjusted northward again as Nigel is well north of my previous forecast track… and thru 72 hours there will be a northward component to the westward track of Nigel as follows:

(1) A wave of upper vorticity to the west has setup consisting of an upper vortex to the west merging with upper troughing currently interacting with ex-Lee. Nigel is already north of the previous forecast while likely also dragged by the upper southerlies on the east side of this upper vorticity wave.

(2) Even though the western part of the Atlantic surface ridge recovers as ex-Lee and Margot lift northeastward… the ridge does not recover enough to prevent a northward angle of the forecast track. This is because the next upper trough in the mid-latitude westerlies... currently inbound from central North America... will drive a surface front into the western Atlantic.

(3) The surface ridge weakness associated with the western Atlantic front is now expected to be larger while the divergence zone of the aforementioned next upper trough is now sufficient in the latest modeling to produce a frontal cyclone along the front. Therefore Nigel is now forecast to recurve and accelerate northeastward by the end of the 5-day forecast period due to the expanded surface ridge weakness and strong upper southwesterly flow ahead of the upper trough.


Regarding intensity... Nigel is weaker than my previous forecast while the broad tropical cyclone has struggled to consolidate and so my updated intensity forecast is lower than the previous. Noting that Nigel has consolidated in the latest satellite imagery… however I do not show Nigel being a hurricane yet by 24 hours due to possible westerly shear that could be imparted by the wave of upper vorticity noted in the prior paragraph. By 48 hours the models dissipate the portion of upper vorticity near Nigel due to the storm’s latent heat release… and this is when I show consolidated Nigel strengthen briskly. Then by 72 hours I slow the strengthening rate as Nigel begins to become sheared by the recurving upper trough… with weakening then shown by 96+ hours as the shear worsens when the trough moves closer to Nigel. However the weakening rate should be gradual as Nigel becomes supported by the broad divergence zone of the trough… and by 120 hours as Nigel reaches cooler waters transition into a strong frontal cyclone supported by the upper trough should be completed.


The updated forecast track is further from the northern Lesser Antilles and so no notable coastal surf is possible from Nigel going forward. Coastal surf is still likely for Bermuda by Tuesday and Wednesday.


Update as of 11 AM EDT… my above discussion and forecast below were completed at 0600Z earlier this morning… since then Nigel has strengthened further to 60 mph maximum sustained winds. If current trends continue my intensity forecast below is likely too low and will need to be increased by my next update. The 11 AM NHC advisory package still calls for  Nigel to peak as a 115 mph maximum sustained wind major hurricane.

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

0 Hr Position (0600Z Sep 17)... 50 mph maximum sustained wind tropical storm centered in the central Atlantic at 23N-48.6W

IOH 24 Hr Forecast (0600Z Sep 18)... 65 mph maximum sustained wind tropical storm centered in the central Atlantic at 26N-53W

IOH 48 Hr Forecast (0600Z Sep 19)... 95 mph maximum sustained wind hurricane centered in the central Atlantic at 28N-57.5W

IOH 72 Hr Forecast (0600Z Sep 20)... 105 mph maximum sustained wind hurricane centered east of Bermuda at 32.5N-59W

IOH 96 Hr Forecast (0600Z Sep 21)… 85 mph maximum sustained wind hurricane centered in the central Atlantic at 36N-55W

IOH 120 Hr Forecast (0600Z Sep 22)… Frontal cyclone centered in the north-central Atlantic at 43N-44W

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

Peak Strength (1800Z Sep 19)… 115 mph maximum sustained wind major hurricane centered in the central Atlantic at 30.5N-55.4W

5-Day Position (0600Z Sep 22)… 80 mph maximum sustained wind hurricane centered in the north-central Atlantic at 44.5N-40W


AREA OF INTEREST #36... Over the weekend the tropical wave of low pressure that was moving into western Africa from central Africa was initially losing its organization while becoming less distinct on satellite pictures relative to another wave close to the west coast of Africa. However as of 0600Z today the wave re-gained distinction and organization near 10N-1W… and this has continued in the most recent satellite pictures as the wave moves westward. This wave will gain scrutiny for possible development as it later moves into the eastern tropical Atlantic as various model runs suggest it will develop. Currently upper winds in the eastern tropical Atlantic are not conducive for development due to suppressing upper vorticity at the southern base of the current eastern Atlantic upper trough. However in the days ahead the north Atlantic upper ridge cell initiated by the warm sector of ex-Lee will push the suppressing upper vorticity westward and away… allowing the current western Africa upper ridge cell with favorable low shear and outflow to expand into the eastern tropical Atlantic. My updated forecast track below delays the arrival of this wave into the eastern tropical Atlantic due to the 0600Z position of the wave relative to the previous forecast. For odds of tropical cyclone formation… I have increased them to 10% for day 4 (just offshore of Africa) and 30% by day 5 (near the Republic of Cabo Verde Islands) even though the collection of recent model runs in the model summary section below for the most part backed away from rapid development when the wave moves offshore… because the wave remains organized on recent satellite pictures. Note the Republic of Cabo Verde Islands may see heavy rainfall and gusty winds from this tropical wave by Thursday.

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

IOH 24 Hr Outlook (0600Z Sep 18)... 0% chance of tropical cyclone formation (western Africa near 11N-6W)

IOH 48 Hr Outlook (0600Z Sep 19)... 0% chance of tropical cyclone formation (western Africa near 11.5N-11W)

IOH 72 Hr Outlook (0600Z Sep 20)... 0% chance of tropical cyclone formation (near west coast of Africa near 12N-16W)

IOH 96 Hr Outlook (0600Z Sep 21)… 10% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-21W)

IOH 120 Hr Outlook (0600Z Sep 22)… 30% chance of tropical cyclone formation (south-southwest of the Republic of Cabo Verde Islands near 13N-26W)

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

Formation chance through 48 hours... 0%

Formation chance through 7 days... 40%


...COMPUTER MODEL SUMMARY...

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


1200Z (Sep 16) CMC Model Run...

**For Tropical Storm Margot... while circling in a clockwise loop reaches the waters west of the Azores near 38.5N-35W as a remnant low by 84 hours… remnant low moves into the Azores by 120 hours

**For Tropical Depression Fifteen… curves north to 35N-56W through 120 hours while becoming a hurricane

**For Area of Interest #36... tropical wave emerges from west coast of Africa at 84 hours... tropical cyclone formation suggested at 120 hours just south-southwest of the Republic of Cabo Verde Islands


1200Z (Sep 16) ECMWF Model Run...

**For Tropical Storm Margot... while circling in a clockwise loop reaches 38.5N-35W as a remnant low at 60 hours… remnant low located west-southwest of the Azores by 120 hours

** For Tropical Depression Fifteen… curves north to 37N-55W through 120 hours while becoming a hurricane

**For Area of Interest #36... tropical wave emerges from west coast of Africa at 78 hours... while evolving into a tropical low reaches 12N-28W by 120 hours


1800Z (Sep 16)… GFS Model Run...

**For Tropical Storm Margot... while circling in a clockwise loop reaches the waters just southwest of the Azores by 102 hours as a remnant low… remnant low drifts closer to the Azores through 120 hours

**For Tropical Depression Fifteen… curves north then northeast to 40N-50.5W through 120 hours while becoming a hurricane

**For Area of Interest #36... no development shown

**South part of current central North America upper trough and some upper vorticity currently offshore of California join to make a cut-off upper vortex over Florida by 144 hours… subtropical low just north of the western Bahamas in progress by 144 hours under the supportive eastern divergence zone of the upper vortex which strengthens into a subtropical cyclone centered just offshore of northeastern Florida by 168 hours.


1800Z (Sep 16) NAVGEM Model Run...

**For Tropical Storm Margot... while circling in a clockwise loop reaches the waters just southwest of the central Azores by 120 hours

**For For Tropical Depression Fifteen... curves north then northeast to 39N-52.5W through 120 hours while becoming a hurricane

**For Area of Interest #36... tropical wave emerges from west coast of Africa at 120 hours... develops into a tropical cyclone just northeast of the Republic of Cabo Verde Islands through 168 hours

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