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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 #64

*******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...SUNDAY AUGUST 27 2023 11:40 AM EDT...

As of 11 AM EDT Franklin has strengthened into a category 2 hurricane while achieving 100 mph maximum sustained winds. As of 11:15 AM EDT aircraft reconnaissance has found tropical depression ten centered in the northwest corner of the Caribbean has strengthened into Tropical Storm Idalia with 40 mph maximum sustained winds.


...SUNDAY AUGUST 27 2023 10:40 AM EDT...

Franklin has become a hurricane in the western Atlantic... and is expected to become a major hurricane that 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) during this upcoming week. See Franklin section below for more information. Elsewhere the northwest Caribbean tropical low is now tropical depression ten and will produce impacts to a corridor including the northeast Yucatan peninsula... western Cuba... and parts of the southeastern United States. See TD Ten section below for more information.


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

(1) See area of interest #23 section below for an update on the central Atlantic tropical low pressure being monitored for development as it continues northwest into open mid-latitude waters in the days ahead.

(2) See area of interest #27 section below for more information on a current western African tropical wave of low pressure which will encounter conducive upper winds as it later moves into the eastern tropical Atlantic over the next couple of days.

(3) See area of interest #28 section below for notes on a low-latitude central Atlantic tropical wave of low pressure heading for the Caribbean Sea over the next few days.


Note some of the forecasts below were completed at 0000Z and 0600Z earlier today... any changes that have occurred for each feature since then are noted in each feature’s section.


HURRICANE FRANKLIN... The upper vorticity that was deposited to Franklin’s north over the last 36 hours has consolidated into an upper vortex over the southeastern Bahamas. The tropical storm has responded by intensifying into the second hurricane of the 2023 Atlantic season while taking advantage of reduced westerly shear and also the divergence on the east side of the vortex. The divergence maximum appears to have allowed Franklin to consolidate into a smaller tropical cyclone. Noting the upper vortex has materialized at a further south position than previous forecasts... causing the hurricane to curve north and then westward around the northeast half of the upper vortex... and the hurricane is notably west of previous forecasts. For the next 48 hours... the updated forecast track below has less of a northward angle and more of a westward angle than prior forecasts as Franklin continues to arc around the north side of the further-south positioned vortex. By 72+ hours this causes Franklin to be further southwest when it begins to interact with an upper trough to approach from the Great Lakes region of North America... causing Franklin to be more aligned with more westerly flow toward the south side of the trough instead of more southwesterly flow on the east side of the trough. The models have responded to this by having a more east and less north angle to the long-term track... and hence a southward shift in the long long-term track projections. In fact the ECMWF is far south enough that it has Franklin shifting eastward across Bermuda instead of passing north of Bermuda. My updated forecast track below is in the middle of the long term model spread.


My updated intensity forecast is nudged upward due to Franklin's initial higher intensity and more compact structure which allows it to intensify more quickly. The further west 48-hour position in my updated track places Franklin closer to the shearing upper trough to approach from the Great Lakes... so I do not forecast Franklin to get above category 3 at this time... instead keeping the intensity flat between 48 and 72 hours as Franklin begins to experience shear. As the shearing trough gets closer... I forecast weakening by 96 hours and then transition into a non-tropical frontal cyclone by 120 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.


Regarding impact to land areas:

(1) Given the updated forecast track and intensity of Franklin... Bermuda will be subjected to notable coastal surf by Wednesday and Thursday as the hurricane passes to the north. Interests in Bermuda should continue to monitor the progress of Franklin as any southward shift in the track could place Bermuda under gusty winds on the storm's south side.

(2) The mid-Atlantic and northeastern US coast are likely to see coastal surf from Franklin by Tuesday through Thursday. Coastal surf will reach the shores of Atlanic Canada (Nova Scotia and Newfoundland) by late in the week.


Update as of 5 AM EDT... Franklin is stronger while now achieving 90 mph maximum sustained winds.

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

0 Hr Position (0000Z Aug 27)... 85 mph maximum sustained wind hurricane centered over the western Atlantic at 23.9N-68.2W

IOH 24 Hr Forecast (0000Z Aug 28)... 100 mph maximum sustained wind hurricane centered over the western Atlantic at 26N-71W

IOH 48 Hr Forecast (0000Z Aug 29)... 125 mph maximum sustained wind major hurricane centered over the western Atlantic at 28N-74W

IOH 72 Hr Forecast (0000Z Aug 30)... 125 mph maximum sustained wind major hurricane centered midway between the Carolinas and Bermuda at 31N-72W

IOH 96 Hr Forecast (0000Z Aug 31)... 100 mph maximum sustained wind hurricane centered just north of Bermuda at 35N-65W

IOH 120 Hr Forecast (0000Z Sep 1)... Hurricane-force remnant frontal cyclone centered south-southeast of Newfoundland at 41N-53.8W

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

Peak Strength (0000Z Aug 29)... 130 mph maximum sustained wind major hurricane centered over the western Atlantic at 29.2N-70.4W

5-day Position (0000Z Sep 1)... 85 mph maximum sustained wind hurricane centered south-southeast of Newfoundland at 41N-52.5W


TROPICAL DEPRESSION TEN... Over the last 36 hours the tropical low pressure spin in the western Caribbean Sea drifted north-northwest into the Yucatan channel (between the Yucatan peninsula and west tip of Cuba). By Saturday afternoon it had developed a small concentrated area of thunderstorms that allowed it to strengthen into tropical depression ten... with the depression since then developing an increasingly sprawling area of curved shower and thunderstorm bands. The depression has become quasi-stationary as the southwest Gulf of Mexico upper vortex that helped to lift it north has since moved away into central Mexico. The surface center has recently made a west-southwest orbit into the northeast coast of the Yucatan peninsula... I assume the surface center is cyclonically orbiting a mid-level center further south such that by 24 hours I forecast it to whirl southeast back into the northwest corner of the Caribbean. This system is waiting for the current US Gulf coast upper vorticity to merge with an upper trough to dive into the Great Lakes region of North America... with the merger resulting in a lengthy upper trough that pulls this system north-northeast by 48+ hours... especially as it becomes progressively stronger/taller to be steered by upper winds or alternatively transitions into a system supported by the divergence on the trough’s east side. Because this system has become a tropical depression early... my intensity forecast is higher than the NHC guidance as of 11 PM EDT and calls for a top-end category 1 hurricane before landfall with the southeastern US through Florida. I do not select an intensity higher than this as the upper trough may impart some disrupting shear. During and after landfall... the north part of the lengthy upper trough continues east toward Hurricane Franklin while the south part stays behind and supports this system with its eastern divergence zone... therefore this system is likely to only gradually weaken as it skirts across the southeastern US while transitioning into a less tropical system supported by the southern upper trough fragment. By day 5... the non-tropical remnants are likely to turn eastward and offshore from the North Carolina coast in the westerly flow between the northern and southern upper trough fragments... and with the westerly flow being neutral (no convergence but also lacking supportive divergence) the remnants are likely to also weaken. Regeneration back to a tropical system in the day 5 window would also be challenged by the shear caused by the upper westerlies.


Regarding impact to land areas:

(1) Periods of heavy rain with flooding potential... gusty winds... and coastal surf are expected for the northeast Yucatan peninsula and western Cuba over the next 48 hours as this system likely strengthens into a slow-moving tropical storm. Weather-permitting... preparations should be completed in the next 24 hours before conditions potentially deteriorate further... and exercise caution as weather conditions deteriorate. Take shelter indoors in the event gusty winds develop.

(2) I recommend interests across the Florida Keys... the Florida peninsula... the eastern panhandle of Florida... and southeastern Georgia begin preparing for an increased likelihood of gusty winds... coastal surf... and heavy rainfall to overspread the region by Wednesday. The most significant wind and coastal storm surge threat is anticipated for the northwestern part of the Florida peninsula and far eastern part of the Florida panhandle. Notable wind damage will likely spread inland across the northeastern part of the peninsula and southeastern Georgia.

(3) Interests across South Carolina... eastern and central North Carolina... southeastern Virginia... and southeast Maryland should be aware that this system could produce gusty winds... coastal surf... and heavy rain by Thursday.


Update as of 5 AM EDT... the NHC has increased their intensity forecast to show a 90 mph maximum sustained wind hurricane prior to landfall with Florida. Thru 8 AM EDT the center has pivoted back southeast into the northwest corner of the Caribbean as anticipated in the above track forecast notes. Eastern squalls of heavy rain have reached the Cayman Islands... flash flooding is possible here today if these trends continue.

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

0 Hr Position (0000Z Aug 27)... 35 mph maximum sustained wind tropical depression centered just offshore of the northeastern Yucatan peninsula at 21.1N-86.4W

IOH 24 Hr Forecast (0000Z Aug 28)... 45 mph maximum sustained wind tropical storm centered just offshore of the northeastern Yucatan peninsula at 20N-85.5W

IOH 48 Hr Forecast (0000Z Aug 29)...60 mph maximum sustained wind tropical storm centered over the western tip of Cuba at 22N-84.8W

IOH 72 Hr Forecast (0000Z Aug 30)... 95 mph maximum sustained wind hurricane centered just offshore of the northwest Florida peninsula coast at 28.5N-83.5W

IOH 96 Hr Forecast (0000Z Aug 31)... Frontal cyclone centered over southeastern North Carolina at 34.8N-78.8W

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

Peak Strength (0000Z August 30)... 80 mph maximum sustained wind hurricane centered offshore of the northwest Florida peninsula coast at 27.5N-84.8W

5-day position (0000Z Sep 1)... 40 mph maximum sustained wind tropical storm centered on the central North Carolina coast at 35.2N-76.7W


AREA OF INTEREST #23... The tropical wave of low pressure in the open central Atlantic that we have been monitoring for development over the last several days... now simply analyzed by the NHC TAFB as a tropical low pressure rotation... is continuing northwest around the southwest side of the steering Atlantic surface ridge. This system took longer to cross 25N-50W (arriving there at 0000Z instead of 12 hours earlier) than the previous forecast... and the updated one below is adjusted accordingly. The track forecast is essentially northwest... north... then northeast around the steering ridge’s west side. There is a pause (stalling) in the track between 24 and 48 hours due to a passing small blocking surface ridge that passes north of Franklin and this system which will be induced by the western convergence zone of a shortwave upper trough to eject from the northeast US. Regarding odds of tropical cyclone formation... the models as of late have dropped showing development. On the other hand an upper trough fragment has been left behind by the current northwest Atlantic upper trough... and the models insist that it will be amplified enough to keep shear low and aiding divergence on its east side high such that this system could get enhanced by the upper trough fragment. By day 3 the upper winds stay favorable as Franklin’s anticyclone (with low shear and outflow) gets displaced eastward from the hurricane by shear... with the anticyclone pushing the upper trough fragment southward and away while also overspreading this system. Due to the favorable upper wind outlook... I have only slightly dropped peak odds of tropical cyclone formation to 40% in this update despite the loss of computer model support. I end the outlook by day 4 with 0% odds as this system would likely be absorbed by the large surface low pressure field consisting of Franklin and also an Atlantic Canada frontal cyclone north of Franklin (induced by the upper trough recurving Franklin northeastward) approaching from the west if this system hasn’t developed by then.

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

IOH 24 Hr Outlook (0000Z Aug 28)... 20% chance of tropical cyclone formation (central Atlantic near 30N-54.5W)

IOH 48 Hr Outlook (0000Z Aug 29)... 40% chance of tropical cyclone formation (central Atlantic near 30N-54.5W)

IOH 72 Hr Outlook (0000Z Aug 30)... 40% chance of tropical cyclone formation (central Atlantic near 33N-54.5W)

IOH 96 Hr Outlook (0000Z Aug 31)... 0% chance of tropical cyclone formation (south-southeast of Newfoundland near 41N-52.5W)

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

Formation chance through 48 hours...0%

Formation chance through 7 days (168 hours)...0%


AREA OF INTEREST #27... Animation of METOESAT satellite imagery (https://tropic.ssec.wisc.edu/real-time/europe/movies/m7irn/m7irn_loop.html) shows a large tropical wave of low pressure has reached Western Africa from central Africa while having reached 11.5N-5W as of 0600Z earlier today. Regional tropical upper ridging covering the low-latitudes of Africa and eastern Atlantic with low shear and upper outflow is forecast to persist over the next few days and development of this wave remains possible when it later moves into the eastern tropical Atlantic. By the end of the 5-day forecast period... 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). Some increased northward angle in the west track of this wave is shown by day 5 as it potentially gets pulled by the upper vorticity... especially if it becomes a stronger/taller feature able to be steered by the upper levels. I agree with the NHC’s low peak 20% odds of tropical cyclone formation as the models are consistent on this wave emerging from Africa as a large feature which will need time to consolidate. Noting the Republic of Cabo Verde Islands may see heavy rain and gusty winds from this system by late tomorrow and Tuesday regardless of tropical cyclone formation or not.

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

IOH 24 Hr Outlook (0600Z Aug 28)... 0% chance of tropical cyclone formation (western Africa near 12N-12W)

IOH 48 Hr Outlook (0600Z Aug 29)... 0% chance of tropical cyclone formation (just offshore of Senegal near 13N-18W)

IOH 72 Hr Outlook (0600Z Aug 30)... 10% chance of tropical cyclone formation (over the southern Republic of Cabo Verde Islands near 14N-24W)

IOH 96 Hr Outlook (0600Z Aug 31)... 15% chance of tropical cyclone formation (eastern tropical Atlantic near 15N-29W)

IOH 120 Hr Outlook (0600Z Sep 1)... 20% chance of tropical cyclone formation (eastern tropical Atlantic near 16.5N-34W)

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

Formation chance through 48 hours...0%

Formation chance through 7 days (168 hours)...20%


AREA OF INTEREST #28... A tropical wave of low pressure was positioned near 9N-45W as of 1200Z this morning with a defined area of showers and thunderstorms that have often had some signs of organization over the last several hours. Although the wave may encounter some less favorable upper winds in the short-term... after it crosses the Lesser Antilles and enters the Caribbean in 72+ hours it will encounter better upper winds for it. Therefore I am in the process of adding this wave as an area of interest... the twenty-eighth I have tracked on this site this year. I have not had time to do a track forecast and probabilities of tropical cyclone formation for this update... will do so in a special update later today.


...COMPUTER MODEL SUMMARY...

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


1200Z (Aug 26) CMC Model Run...

**For Hurricane Franklin... reaches 30N-71W at 66 hours... subsequently curves east-northeast and passes just north of Bermuda at 102 hours... reaches 35.5N-59W at 120 hours

**For tropical depression ten... strengthens into a tropical storm in the southeastern Gulf of Mexico near 24N-86W at 66 hours... makes landfall over the Big Bend of the Florida panhandle as a strong tropical storm at 96 hours... transitions into a remnant frontal cyclone that moves across southern Georgia and eastern Carolinas through 126 hours

**For area of interest #23... no development shown

**For area of interest #27... strong tropical wave of low pressure emerges from the west coast of Africa at 36 hours and by 120 hours moves across the Republic of Cabo Verde Islands as a broad tropical low

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


1200Z (Aug 26) ECMWF Model Run...

**For Hurricane Franklin... reaches 30N-71.5W at 72 hours... curves east-northeast and east into Bermuda by 108 hours... continues to 32N-62.5W by 120 hours

**For tropical depression ten... while quasi-stationary strengthens into a tropical storm between the west tip of Cuba and NE corner of the Yucatan peninsula through 60 hours... subsequently moves north-northeast and makes landfall just east of the Big Bend of the Florida panhandle as a strong tropical storm at 102 hours... maintains strength as a tropical storm while center moves northeast across coastal Georgia and into the southern tip of South Carolina thru 120 hours

**For area of interest #23... no development shown

**For area of interest #27... strong tropical wave of low pressure emerges from the west coast of Africa at 36 hours and passes just north of the Republic of Cabo Verde Islands as a tropical low by 102 hours... tropical low located at 18.5N-26.5W at 120 hours

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


1800Z (Aug 26) GFS Model Run...

**For Hurricane Franklin... reaches 30N-71W at 60 hours... subsequently curves northeast and passes just north of Bermuda by 96 hours... reaches 41N-52.5W at 120 hours

**For tropical depression ten... while quasi-stationary strengthens into a tropical storm over the northeast corner of the Yucatan peninsula through 36 hours... subsequently accelerates north-northeast and makes landfall over the the Big Bend of the Florida panhandle while reaching hurricane strength at 93 hours... while moving northeast across southern Georgia and eastern South Carolina it weakens to a tropical storm through 120 hours

**For area of interest #23... no development shown

**For area of interest #27... strong tropical wave emerges from western Africa at 36 hours and moves across the Republic of Cabo Verde Islands as a broad tropical low by 96 hours... degenerates into an east-west elongated low pressure to the west of the islands through 120 hours

**For area of interest #28... Tropical wave currently at 42.5W longitude develops into a compact tropical low offshore of northeast Nicaragua near 15N-81W at 150 hours... makes landfall as a compact tropical cyclone just south of the Nicaragua/Honduras border at 162 hours


1800Z (Aug 26) NAVGEM Model Run...

**For Hurricane Franklin... reaches 29.8N-72.5W at 54 hours... curves east-northeast with center passing just north of Bermuda at 96 hours... continues east-northeast and reaches 35N-57.5W at 120 hours

**For tropical depression ten... while quasi-stationary strengthens into a tropical storm over the west tip of Cuba through 42 hours... subsequently accelerates into the north-northeast to the northwest Florida coast by 84 hours... continues east-northeast and enters the Atlantic from coastal Georgia at 96 hours... strengthens into an offshore hurricane while reaching 32.5N-75.5W

**For area of interest #23... no development shown

**For area of interest #27... strong tropical wave emerges from western Africa at 36 hours and passes over the Republic of Cabo Verde Islands as a broad tropical low through 96 hours... center of broad low reaches 17.5N-29W by 120 hours

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

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