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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 #66

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


...THURSDAY AUGUST 31 2023 2:00 AM EDT...

Three tropical cyclones are currently active in the Atlantic basin as follows:

(1) Hurricane Franklin is passing just north of Bermuda and will produce wide-reaching coastal surf for Bermuda... the US east coast from the mid-Atlantic to the northeast shoreline... and Atlantic Canada (Nova Scotia and Newfoundland) over the next few days. See Franklin section below for more information.

(2) Idalia has weakened to an inland tropical storm over the southeast US... and is now expected to turn eastward across the western Atlantic and toward Bermuda while lingering over the next few days. See Idalia section below for more information.

(3) Tropical Depression Eleven persists in the open central Atlantic... see TD Eleven section below for more information.


In addition... looking for possible development from other features as follows:

(1) See area of interest #27 section below for more information on an organizing tropical low pressure area currently centered over the Republic of Cabo Verde Islands

(2) See area of interest #28 section below for an update on a troipcal wave of low pressure now moving through the eastern half of the Caribbean.

(3) See area of interest #29 section below for the remnants of Gert which are attempting to make a comeback in the western Atlantic while located between Hurricane Franklin and Tropical Depression Eleven.


While pressed for time due to personal life activities... did not have time to do my traditional track... intensity... or probablities of tropical cyclone formation callouts for all six systems mentioned above. Instead I provided a general outlook for most of the six systems.


Also noting that METEOSAT satellite imagery (https://www.goes.noaa.gov/f_meteo.html) as of this writing shows a tropical wave of low pressure with strong thunderstorm activity over western Africa. Models suggest this wave may develop after it moves into the eastern tropical Atlantic in a few days... as such this wave may become yet another tropical area of interest for the Atlantic basin if these trends continue.


HURRICANE FRANKLIN... Franklin's appearance has changed quiet a bit during its eye wall replacement cycle which has resulted in a much larger eye. Franklin has weakened to a category 2 hurricane as of this writing due to the cycle... has not been able to recover strength while westerly shear imparted by the approaching north fracture of the eastern North America upper trough is increasing. There have been notable changes to forecast track projections in the computer model guidance over the last day... probably as the models have been initialized with a more amplified version of the northern upper trough fragment than previous forecasts predicted. The new data results in increased upper divergence over the currently developing Atlantic Canada frontal cyclone... resulting in a more intense frontal cyclone which then moves into southeastern Greenland. The west side of the more intense frontal cyclone then pulls cold air associated with the upper trough fragment closer to it... resulting in most of the upper trough concentrating toward the frontal cyclone and further away from Franklin. In turn this results in Franklin moving slower to the northeast in weaker upper-level steering... and the updated forecast track shown below reflects a slower forward speed but not quiet as slow as the current model consensus to wait and see if the models continue with current trends or not. The forecast track overall has Franklin continuing northeastward... passing just north of Bermuda by tonight and eventually the open north Atlantic in the long-term. Weakening is forecast going forward as southwesterly shear progressively increases with the approach of the aforementioned upper trough. I forecast transition into a non-tropical frontal cyclone by 48 hours as Franklin merges with the cold front associated with the upper trough and becomes supported by the upper divergence on the trough's east side. Noting some model runs (such as the ECMWF and NAVGEM examples in the model summary section below) have the remnant frontal cyclone of Franklin tracking more westward. These westward solutions have ex-Franklin pull enough cold air associated with the upper trough southward to make an amplified local upper trough... with ex-Franklin hooking more northward and less eastward around the east side of this amplified local upper trough. With the wide spread in the long-range track (some models more westward with ex-Franklin and others not)... the long-range outlook for ex-Franklin's track has higher than usual uncertainty.


Regarding impact to land areas:

(1) Bermuda has recently seen the arrival of Franklin's outer southern rain bands(http://www.weather.bm/radar.asp). Gusty tropical storm force winds have also reached the island... for instance an observation as of 8:08 PM local time showed a sustained 39 mph wind with a gust to 51 mph... and gusts to 51 mph have continued through 11:55 PM local time (http://www.weather.bm/observations.asp). The rainfall and gusty winds will abate by tomorrow as Franklin pulls away... with the coastal surf gradually fading thereafter.

(2) The mid-Atlantic and northeastern US coast... as well as the shores of Atlanic Canada (Nova Scotia and Newfoundland)... will see coastal surf over the next day or so. The period of coastal surf may linger for a longer period of time... particularly for Atlantic Canada... if ex-Franklin takes a more westward track in the long range as discussed above.


Update as of 11 PM EDT... Franklin has weakened further to 100 mph maximum sustained winds.

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

0 Hr Position (1800Z Aug 30)... 105 mph maximum sustained wind hurricane centered just northwest of Bermuda at 33.9N-66.9W

IOH 24 Hr Forecast (1800Z Aug 31)... 85 mph maximum sustained wind hurricane centered in the northwest Atlantic at 37N-59W

IOH 48 Hr Forecast (1800Z Sep 1)... Hurricane-force remnant frontal cyclone centered south-southeast of Newfoundland at 41N-48.5W

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

5-day Position (0000Z Sep 5)... 45 mph maximum sustained wind frontal low centered in the north-central Atlantic at 50.1N-35.5W


HURRICANE IDALIA (RECENTLY DOWNGRADED TO TROPICAL STORM IDALIA)... Idalia has weakened into a tropical storm from a hurricane while moving northeastward from southeastern Georgia and into the Carolinas. The lengthy eastern North America upper trough that has been pulling Idalia northeastward has broken into a northern upper trough fragment moving toward Hurricane Franklin and southern upper trough fragment being pinned in place over the southeastern US by the current amplified western US upper ridge. The eastern divergence zone of the southern upper trough fragment has slowed Idalia's post-landfall weakening rate. In fact as of 11 PM EDT the maximum sustained winds are estimated by the NHC to be 60 mph despite Idalia traveling over land over the last several hours. Idalia is expected to soon turn eastward into the Atlantic from the Carolinas... and the long term model guidance has notably shifted eastward and further offshore from the US east coast. This is due to the northern upper trough fragment being more amplified as noted in the above Hurricane Franklin section... and also as Hurricane Franklin is now forecast to move more slowly northeastward such that its low pressure circulation stays closer to Idalia and helps pull it eastward. The models and NHC official forecast insist on keeping Idalia a tropical feature instead of transitioning Idalia into a non-tropical remnant frontal low supported by the eastern divergence zone of the southern upper trough fragment. The recent NHC TAFB surface analyses show the nearby surface front has stalled instead of marching into Idalia as the southern upper trough fragment has stalled as noted above... therefore Idalia is indeed likely to keep its tropical status for a few more days.


The following is the outlook on Idalia going forward:

(1) Through 24 hours Tropica Storm Idalia shifts more quickly offshore from the Carolinas than previously forecast... while pulled more eastward by the more amplified northern upper trough fragment (this trough fragment is more amplified than previously forecast as noted in the above Hurricane Franklin section).

(2) Between 24 and 72 hours... Idalia is expected to shift east-southeast into the waters midway between the US east coast and Bermuda under the influence of a developing and expanding oblong surface ridge (this surface ridge will materialize across eastern North America and northwest Atlantic while supported by the back convergence zones of the aforementioned northern and southern upper trough fragments). In addition a recent northeastern Pacific upper vortex has moved into the northwestern US as an upper trough... and this upper trough will eventually be digging southeastward into the northwestern Atlantic around the east side of what is now the amplified western US upper ridge. This northwestern Atlantic upper trough will also help push Idalia east-southeast and also shear the tropical storm such that it is unlikely to re-strengthen during this timeframe. Because Franklin is now forecast to move more slowly northeast and hence be closer to Idalia... its low pressure circulation will also help pull Idalia eastward. A frontal low that eventually develops between Idalia and Franklin under the support of the incoming northwest Atlantic upper trough will also help pull Idalia eastward.

(3) By days 4 and 5 (96 and 120 hours)... the incoming northwestern Atlantic upper trough has potential to amplify as the current amplfied western US upper ridge moves into the eastern US and approaches... and also as the northwest side of Idalia helps pull cool air associated with the upper trough southward. Increased divergence and less shear on the east side of the amplifying upper trough may help to re-strengthen Idalia as the trough also begins to bend the track of the tropical storm east-northeastward toward Bermuda.


Regarding impact to land areas:

(1) Based on the latest doppler radar presentation... heavy rainfall with flash flooding potential will be a concern across northeastern South Carolina... central and eastern North Carolina... southeastern Virginia... and southeastern Maryland for tonight and early tomorrow. Surf will be a concern along the Atlantic coastline of this region over the next 24 hours. Gusty winds are occuring across eastern parts of the Carolinas based on National Weather Service station reports (weather.gov)... some instances of wind damage may occur here through the overnight. Directional wind shear between southerly flow on the east side of Idalia and the current upper southwesterly flow over Idalia may result in isolated tornadoes in the eastern parts of the Carolinas in the overnight.

(2) Interests in Bermuda should be aware that Idalia may be a re-strengthening tropical cyclone moving northeastward over or near the island in 4 to 5 days as discussed above. This could result in another round of heavy rainfall... gusty winds...and coastal surf not long after Franklin moves away.

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

5-day position (0000Z Sep 5)... 50 mph maximum sustained wind tropical storm centered just northeast of Bermuda at 33.5N-63W


TROPICAL DEPRESSION ELEVEN... The tropical depression in the open central Atlantic has been quasi-stationary near 28.5N-52.5W over the last several hours while trapped in a notch within the Atlantic surface ridge. The depression has not been able to strengthen perhaps as its western outflow remains restricted by the nearby upper trough fragment. The following is the outlook on Eleven going forward:

(1) Over the next 24 hours the upper air pattern improves as Franklin's upper anticyclone with low shear and upper outflow gets displaced eastward as Franklin is becoming sheared... and overspreads this system. The overspreading anticyclone will also displace the nearby upper trough fragment southward and away. The depression retains a healthy circular thunderstorm mass and it would not surprise me if this system strengthened into a 50 to 60 mph maximum sustained wind tropical storm underneath the improved upper air pattern in the next 24 hours. The northward motion should increase during the next 24 hours as southerly flow ahead of Franklin approaches.

(2) Between 24 and 48 hours... the upper trough that transitions Franklin into a frontal cyclone will also kick away the upper anticyclone over this system... leaving this system to experience northerly shear from the east end of the current western Atlantic upper anticyclone. Thus I anticipate weakening during this timeframe... with this system also curving northeastward as the regional flow becomes more westerly as the remnant frontal cyclone of Frankin passes to the north. The cold front driven by ex-Franklin should also overspread this system and make it less tropical by 48 hours.

(3) After 48 hours... this system could transition into a broad remnant frontal low positioned between Idalia and Franklin under the support of a northwestern Atlantic upper trough that dives in from its current northwestern US position. Or alternatively the remnants of this system loses its identity within a frontal low that forms in the region.

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

Loss of tropical cyclone status (1200Z Sep 1)... 35 mph maximum sustained wind remnant low centered in the central Atlantic at 33.9N-51.9W


AREA OF INTEREST #27... Satellite imagery over the last day has shown that the tropical wave of low pressure that has been moving into the Republic of Cabo Verde Islands has absorbed another adjacent wave to the southeast... and has maintained its organization instaed of excessively broadening during the absorption process while its low pressure spin has progressively become better oragnized over the islands. The current east Atlantic upper vortex is expected to shift south as upper vorticity being pushed by amplifying warm core North Atlantic upper ridging (the upper ridging is forecast due to the warm surface southerly flow ahead of Franklin as it transitions into a strong non-tropical frontal cyclone... and also due to warm southerly flow ahead of a frontal cyclone that develops over Atlantic Canada and heads into southeastern Greenland). The eastern divergence zone of this upper vorticity will intiate a surface ridge weakness that this system will move northwestward toward over the next five days... with the weakness then being maintained by the formation of a frontal low between Idalia and Franklin (see Idalia section above for more info on the origins of this frontal low). All in all a northwestward track into the open central Atlantic is anticipated through day 5. Due to the improved satellite organization of the tropical low... I agree with the NHC on increasing peak odds of tropical cyclone formation to 70%... particularly for the next 48 hours before the northwest track takes this system into more hostile southerly shear on the east side of the aforementioned east Atlantic upper vorticity.


Noting the Republic of Cabo Verde Islands may see additional heavy rain and gusty winds from this system over the next 24 hours regardless of tropical cyclone formation or not.

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

Formation chance through 48 hours...60%

Formation chance through 7 days (168 hours)...70%


AREA OF INTEREST #28...The tropical wave of low pressure that recently crossed the southern Lesser Antilles and is now moving swiftly westward through the eastern half of the Caribbean has overall seen a decrease in thunderstorms... albeit their was an attempt for some activity to redevelop around 1800Z Wednesday when the wave was passing north of the ABC Islands (Aruba Bonaire and Curacao) with this attempt falling apart in the hours afterwards. The inactivity of the wave has likely been brought about by the linear nature of the easterly flow on the south side of the western Atlantic upper anticyclone that lacks upper divergence... and for now I am cancelling this tropical wave as an area of interest for development (i.e. downgrading odds of tropical cyclone formation to 0%)... espeically since models continue to not develop this wave. Noting some of the upper vorticity associated with the upper trough between TD Eleven and AOI #29 (Ex-Gert) is forecast to move westward around the southeast side of the upper anticyclone... it is possible split flow upper divergence develops between the west side of the upper vorticity and south side of the upper anticyclone... and over this tropical wave... when the wave later moves into the western Caribbean. Should this wave show signs of taking advantage of the more divergent upper air pattern... will consider re-adding the wave as an area of interest in future updates.

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

Not in the official outlook


AREA OF INTEREST #29 (REMNANTS OF GERT)... The remarkable remnants of Gert in the western Atlantic have been hanging on over the last several days while drifting northward away from the northern Lesser Antilles and approximately along 60W longitude while gravitated toward the surface ridge weakness associated with Franklin. As of this writing the remnants are located near 27.5N-58W. The remnants have been kept suppressed from northerly shear on the east end of a warm core western Atlantic upper anticyclone pumped up by Hurricane Franklin's thunderstorm latent heat release (this anticyclone has become Franklin's outflow structure). At the same time the shear has not been high enough to totally destroy the remnant system of Gert. The NHC has recently added the remnants of Gert into their tropical weather outlook as it had earlier on Wednedsay produced concentrated thunderstorm activity near its center of rotation... probably as the remnants have become embedded in a boosting split flow upper divergence environment between the west side of the upper trough fragment to the east that has been interacting with TD Eleven and east side of the western Atlantic upper anticyclone. This is the twenty-ninth tropical Atlantic area of interest I have tracked on this site this year.


More recent satellite pictures show spiral banding in the remaining cloudiness and thunderstorms ongoing with this system... therfore I believe the odds of tropical cyclone formation are a bit higher than the NHC's 8 PM EDT outlook... I recommend 20% odds for the next 24 hours. My odds are still on the low side as this system will still have to contend with some ongoing northerly shear and competiton for surface inflow between Franklin close to the northwest and TD Eleven close to the east. By 48 hours the cold front driven by what will be the remnant frontal cyclone of Frankin should overspread this system and end its potential for tropical development. Ultimately the remnants of Gert by 72+ hours will likely be absorbed into the west side of a central Atlantic frontal low to develop between Idalia and Franklin (see Idalia section above for more info on the origins of this frontal low).


Update as of 2 AM EDT... the NHC has increased the odds of Gert's re-development to 30%.

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

Formation chance through 48 hours...10%

Formation chance through 7 days (168 hours)...10%


...COMPUTER MODEL SUMMARY...

Source...Tropical Tidbits (https://www.tropicaltidbits.com/analysis/models/).


0000Z (Aug 30) CMC Model Run...

**For Hurricane Franklin... passes just north of Bermuda at 24 hours... transitions into a frontal cyclone near 41.5N-50W at 66 hours... through 84 hours loses identity near 45.5N-37.5W to much larger frontal cyclone moving from Atlantic Canada to southeastern Greenland.

**For Hurricane Idalia... enters the Atlantic from southeastern North Carolina at 42 hours as a broad tropical storm supported by upper trough fragment to the west... through 72 hours the broad tropical storm drifts east-southeast to 32N-71.5W under the influence of upper westerlies in combination with an expanding oblong surface ridge building over eastern North America and northwest Atlantic... transitions into an elongated remnant low centered just southwest of Bermuda through 120 hours under the influence of an elongated divergence zone associated with an upper trough digging in from the northwest.

**For Tropical Depression Eleven... quasi-stationary through 30 hours while dissipating... the remnant trough later drifts north to 34.5N-51W through 90 hours where it begins to strengthen to the east of Idalia as a non-tropical frontal low supported by the divergence of an upper trough digging in from the northwest... frontal low strengthens into a frontal cyclone when it reaches 37N-52W by 120 hours

**For area of interest #27... broad tropical low moves northwest to 22.5N-32.5W through 120 hours.

**For area of interest #28... no development shown

**For area of interest #29... remnants of Gert not shown to redevelop

**Tropical wave emerges from west coast of Africa at 84 hours... develops into a tropical low near 13N-30.5W by 144 hours... develops into a tropical cyclone near 14.5N-35W by 168 hours.


0000Z (Aug 30) ECMWF Model Run...

**For Hurricane Franklin... passes just north of Bermuda at 27 hours... northwest side of Franklin pulls in cool air associated with passing upper trough to the north which makes a small amplified upper trough just west of Franklin by 81 hours while Franklin is located near 35N-55W... transitions into a powerful frontal cyclone supported by the eastern divergence zone of the local amplified upper trough while hooking northward to the waters south-southeast of Newfoundland (near 41.5N-52W) through 120 hours.

**For Hurricane Idalia... enters the Atlantic from the North Carolina/South Carolina border at 36 hours as a broad tropical storm supported by upper trough fragment to the west... through 96 hours the broad tropical storm drifts southeast to 29N-68.5W under the influence of an expanding oblong surface ridge building over eastern North America and northwest Atlantic in combination with an upper ridge expanding into the eastern US from the western US... through 120 hours the broad tropical storm begins to drift northeast toward the surface ridge weakenss associated with ex-Franklin while reaching 29N-65W (south of Bermuda).

**For Tropical Depression Eleven... drifts north to 31N-53W where it loses its identity to Franklin

**For area of interest #27... tropical low moves northwest to north-northwest through 120 hours and reaches 27.5N-32.5W at 120 hours

**For area of interest #28... no development shown

**For area of interest #29... remnant low of Gert moves north-northeast to 28N-58W through 27 hours... subsequently curves east-northeast to 30.5N-53W through 66 hours where it loses its identity to Franklin

**Tropical wave emerges from west coast of Africa at 84 hours and organizes into a tropical low near 11.5N-36W at 141 hours... develops into a tropical cyclone located near 12.2N-43W by 168 hours


0600Z (Aug 30) GFS Model Run...

**For Hurricane Franklin... passes just north of Bermuda at 18 hours... transitions into a frontal cyclone near 40.5N-51W at 60 hours... subsequently loses identity to much larger southeastern Greenland frontal cyclone while reaching 51.5N-22.5W at 108 hours

**For Hurricane Idalia... enters the Atlantic from Cape Fear North Carolina just before 30 hours as a broad tropical storm supported by upper trough fragment to the west... through 72 hours the broad tropical storm drifts east-southeast to 31.5N-69W under the influence of an expanding oblong surface ridge building over eastern North America and northwest Atlantic in combination with an upper ridge expanding into the eastern US from the western US... through 120 hours drifts east-northeast into Bermuda as a potentially strengthening tropical storm enhanced by the eastern divergence zone of an upper trough digging in from the northwest

**For Tropical Depression Eleven... movs northeast to 36N-49W through 66 hours where it merges with cold front driven by Franklin's remnant frontal cyclone... the remnant frontal low loses its identity along the cold front while located near 40N-40W at 114 hours

**For area of interest #27... broad tropical low moves northwest to 26.5N-36W through 120 hours.

**For area of interest #28... no development shown

**For area of interest #29... remnant low of Gert moves northeast to 31.5N-49W through 84 hours where it becomes absorbed by developing frontal low to the west (this frontal low is positioned east of Idalia and southwest of the remnant frontal low of TD Eleven and is along the cold front being driven by ex-Franklin)


0600Z (Aug 30) NAVGEM Model Run...

**For Hurricane Franklin... passes just north of Bermuda at 18 hours... northwest side of Franklin pulls in cool air associated with passing upper trough to the north which makes a small amplified upper trough just west of Franklin by 72 hours while Franklin is located near 39N-50W... transitions into a powerful frontal cyclone supported by the eastern divergence zone of the local amplified upper trough while hooking more northward in track and reaches 47N-44W at 120 hours

**For Hurricane Idalia... enters the Atlantic from the North Carolina/South Carolina border at 30 hours as a broad tropical storm supported by upper trough fragment to the west... a small portion of the upper trough fragment and the broad tropical storm move east-southeast to 31.5N-69.5W through 72 hours... the upper trough fragment amplifies into an upper vortex due to approach of amplified upper ridge moving from western to eastern US with lower shear and high divergence on the east side of the vortex helping the broad tropical storm re-strengthen into a hurricane near 31N-66W (just southwest of Bermuda) at 102 hours... the center of the hurricane continues east-northeast in the flow ahead of an upper trough digging in from the northwest and passes just south of Bermuda and reaches 32N-62.5W at 120 hours.

**For Tropical Depression Eleven... quasi-stationary through 30 hours while dissipating

**For area of interest #27... broad tropical low moves northwest to 26.5N-33.5W through 102 hours and dissipates shortly thereafter.

**For area of interest #28... no development shown

**For area of interest #29... remnants of Gert not shown to redevelop

**Tropical wave emerges from west coast of Africa at 108 hours and develops into an offshore tropical low near 14N-19.5W by 144 hours

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