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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 #62

*******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 24 2023 5:40 PM EDT...

For now the active Atlantic tropics have seen some reduction in activity while now down to two named systems in the region... see remnants of Emily (Area of Interest #25) and Tropical Storm Franklin sections below for more details. Note by early this upcoming week Franklin is expected to strenghten into a strong western Atlantic hurricane and produce coastal surf for Bermuda and for the US east coast from the mid-Atlantic to the northeast shoreline.


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 wave of low pressure being monitored for development as it continues northwest into open mid-latitudes waters in the days ahead.

(2) Animation of METOESAT satellite imagery (https://tropic.ssec.wisc.edu/real-time/europe/movies/m7irn/m7irn_loop.html) shows a western Africa tropical wave of low pressure which has quickly moved from 2.5E longitude to about 11W longitude over the last day... with the western side of the wave producing disorganized thunderstorms along the west coast of Africa as of late. Another tropical wave of low pressure which is large in size is over central Africa while having moved from about 16E to 12E longitude over the last day. Over the next several days regional tropical upper ridging with low shear and outflow is forecast to persist... and model consensus showing the current central African wave developing when it later moves into the eastern Atantic in 5+ days in increasing. Will add this tropical wave as another area of interest in my next full update if these trends continue.

(3) A tropical low pressure with development potential may emerge over the western Caribbean within the next five days... and move toward the Cayman Islands... western Cuba... the northwestern Bahamas... and/or south Florida. See area of interest #26 section below for more information.


Also noting the remnant low pressure of what was Tropical Storm Gert has been lingering stationary to the east of the northern Lesser Antilles while trapped in weak steering between ex-Emily (Area of Interest #25) to the northeast and Tropical Storm Franklin to the northwest... it has survived up to this point as the shearing upper vorticity in the region has retrograded westward and away while pushed around by the ongoing central US upper ridge. As Franklin moves in closer over the next 48 hours... its upper outflow is expected to re-intensify the shear over remnant low of Gert and the surface inflow of Franklin will steal from the surface inflow of ex-Gert. Therefore the remnant low of Gert is still expected to dissipate without making a comeback.


TROPICAL STORM FRANKLIN... In the last 24 hours Franklin has been successful with its northward passage across Hispaniola (Haiti and the Dominican Republic) as it has remained intact and is already re-strengthening from 40 mph maximum sustained winds while the center is passing over the waters just east of the eastern Bahamas. As of 11 AM EDT the re-strengthening trend has already brought Franklin to 60 mph maximum sustained winds per aircraft reconaissance data.


The upper trough and western Atlantic surface cold front that pulled Franklin across Hispaniola is beginning to leave behind the tropical storm. After being left behind... their will be effectively no surface steering as a series of shortwave upper troughs and associated surface frontal depressions to push in from the northeastern United States will prevent the Atlantic surface ridge from re-building in the western Atlantic... while at the same time the frontal depressions stay too far to influence Franklin. So then we turn to the upper-levels for steering... espeically since Franklin is forecast to stay a sufficiently strong/tall feature to be pulled by upper-level winds. Indeed in the upper-levels the departing upper trough will leave behind an upper vortex just to Franklin's north by 24 hours... with the forecast track below showing Franklin arcing eastward...northward... and then northwestward around the east half of the vortex over the next 96 hours. The latest model data shows the upper vortex being further south... allowing Frankiln to arc northwestward around the northeast corner of the vortex instead of simply going straight north around the east side of a further north positioned vortex. Therefore even though Franklin has been close to the previous forecast track... the long-term track requires some westward adjustment to reflect a northwestward bend in the track anticipated in the 48 to 96 hour window. By 96 hours one of the frontal depressions ejecting from the northeastern US is forecast to be over Atlantic Canada while the western convergence zone of this depression's upper trough makes a small surface ridge over the northeastern US. Another frontal depression and its upper trough to approach from the Great Lakes region of North America during this same time appears it will be the system that finally accelerates Franklin northeastward into the high-latitude westerlies in the long range. However from 96 to 120 hours the forecast track is straight north as the passing small surface ridge to the north delays the eastward bend in the track.


The short-term intensity of Franklin will be regulated by the upper vortex mentioned in the previous paragraph. In addition to being further south... the latest model data also has the vortex initially more elongated east-to-west which expands the region of unfavorable westerly shear on the south side of the vortex... therefore I delay the timeframe for the anticipated additional strengthening. However Franklin as of 11 AM EDT has acheived a higher initial strength than I previously forecast... and so despite the delay the longer-term intensity forecast ends up being the same as the previous. Essentially the intensity forecast shows Franklin taking advantage of reduced westerly shear and also the divergence on the east side of the upper vortex in the 72 to 96 hour window such that I project the storm to ramp up into a category 2 hurricane. As Franklin lifts northward and away from the vortex at 120 hours... it will still be in a low shear environment as the upper trough to approach from the Great Lakes region will still be too far away to shear Franklin. At the same time the upper vortex will now be too far away to impede the southwestern outflow of the storm. Therefore I conclude the 5-day (120 hour) forecast window by showing Franklin strengthening further into a category 3 major hurricane. If this verifies... this would mean Franklin would become the first major hurricane of the 2023 Atlantic season.


Regarding impact to land areas:

(1) For the eastern Bahamas... some current light westerly shear in Franklin's environment is keeping the strongest thunderstorms (gusty winds and heavy rains) to the east of the storm center and hence also east of the islands. Coastal surf will be the primary impact before Franklin moves away from the eastern Bahamas by tomorrow.

(2) The westward shift in the longer-range forecast track keeps Franklin's center further away from Bermuda for the early part of this upcoming week. With the current forecast track and intensity however... Bermuda will be subjected to notable coastal surf by Monday and Tuesday. Interests in Bermuda should continue to monitor the progress of Franklin as any eastward shift in the track could place Bermuda under some gusty winds on the storm's east side.

(3) The mid-Atlantic and northeastern US coast are likely to see coastal surf from Franklin by early this upcoming week.

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

0 Hr Position (1200Z Aug 24)... 50 mph maximum sustained wind tropical storm centered just east of the eastern Bahamas at 21.9N-70.4W

IOH 24 Hr Forecast (1200Z Aug 25)... 60 mph maximum sustained wind tropical storm centered over the western Atlantic at 22.8N-67.5W

IOH 48 Hr Forecast (1200Z Aug 26)... 60 mph maximum sustained wind tropical storm centered over the western Atlantic at 24N-65.5W

IOH 72 Hr Forecast (1200Z Aug 27)... 85 mph maximum sustained wind hurricane centered over the western Atlantic at 26N-66.5W

IOH 96 Hr Forecast (1200Z Aug 28)... 110 mph maximum sustained wind hurricane centered west-southwest of Bermuda at 30.5N-69W

IOH 120 Hr Forecast (1200Z Aug 29)... 125 mph maximum sustained wind major hurricane centered west-northwest of Bermuda at 35N-69W

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

5-day Position (1200Z Aug 29)... 105 mph maximum sustained wind hurricane centered west-northwest of Bermuda at 34.5N-67.5W


AREA OF INTEREST #23... In visible satellite animation... the eastern Atlantic tropical wave of low pressure that has recently moved into the central Atlantic continues to display a broad area of rotation centered near 18.5N-41W as of 1200Z. Although the wave is now producing a larger area of thunderstorms... the activity is south of the center of rotation due to northerly shear imparted by the southwest side of the current northeast Atlantic upper trough. Based on the 1200Z position of this system... the previous forecast track is holding and so the updated one below is a continuation of the previous. The westward forecast track has some northward angle overall as this system is forecast to move toward the surface ridge weakness caused by the remnants of Emily (Area of Interest #25). After 24 hours ex-Emily and the western Atlantic frontal system/upper trough curving Emily northward are forecast to lift northeastward and away... around the amplified warm air mass upper ridge currently in the north Atlantic which will later progress toward the northeast Atlantic. However a northward angle in the forecast track is kept thru day 3 due to the likely influence of Franklin's surface circulation...and by day 4 a complete turn to the north is anticipated in the southerly flow ahead of Franklin. By day 5 the steering picture gets muddy as this system gets trapped between a small surface ridge passing north of Franklin and the Atlantic surface ridge to the east. For now the models show more of an upper trough fragment being left behind by the current western Atlantic frontal system... to the east of Franklin's outflow and in this system's environment. The models resolve the day 4 to 5 steering pattern by turning this system eastward with this upper trough fragment... while transitioning this system into a feature supported by the eastern divergence zone of the trough fragment.


Regarding odds of tropical cyclone formation... the more-reliable GFS and ECMWF models have trended back toward trying to develop this system in the longer range as it interacts with the upper trough fragment in 5+ days. In addition the thunderstorm activity has increased and this system will soon move away from the shearing upper northerly winds. However I have only cautiously raised peak odds of tropical cyclone formation to a cautious 30% as this system will still encounter some challenging upper wind profiles through day 5 as follows:

(1) By 48 hours this system will soon move toward the small upper trough currently interacting with ex-Emily (Area of Interest #25). However by then the cool core small upper trough is forecast to be decaying due to prolonged isolation from high-latitude cold air. Thus only light southerly shear... which is not completely prohibitive to development but still potentially disrupting... is anticipated from the decaying upper trough.

(2) By 3 to 5 days this system may be challenged by northwesterly shear imparted by Hurricane Frank's eastern outflow and the aforementioned upper trough fragment to drop in to the east of the outflow. Although the GFS/ECMWF consensus as of this writing show some development on the east side of the upper trough fragment... this assumes the fragment is amplified enough to reduce the amount of overhead shear. Because this is during the day 5 window when model errors tend to be larger... waiting to see if this trend holds before assuming this system has a higher chance of long-range development than I currently show below.

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

IOH 24 Hr Outlook (1200Z Aug 25)... 15% chance of tropical cyclone formation (central tropical Atlantic near 19.5N-45W)

IOH 48 Hr Outlook (1200Z Aug 26)... 30% chance of tropical cyclone formation (central Atlantic near 22.5N-50W)

IOH 72 Hr Outlook (1200Z Aug 27)... 30% chance of tropical cyclone formation (central Atlantic near 25N-54W)

IOH 96 Hr Outlook (1200Z Aug 28)... 30% chance of tropical cyclone formation (central Atlantic near 30N-54W)

IOH 120 Hr Outlook (1200Z Aug 29)... 30% chance of tropical cyclone formation (central Atlantic near 30.5N-51W)

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

Formation chance through 48 hours...20%

Formation chance through 7 days (168 hours)...50%


AREA OF INTEREST #25 (REMNANTS OF EMILY)... The remnants of what was Tropical Storm Emily is in the open central Atlantic continuing northward in the southerly flow between the Atlantic surface ridge to the east and approaching western Atlantic cold front to the west. The remnants continue to interact with the eastern divergence zone of a small upper trough in the region (not to be confused with the larger-scale upper trough associated with the aforementioned cold front) which has helped ex-Emily produce thunderstorms. However as of late the thunderstorm activity is weaker and less organized on colorized infrared satellite pictures... and on visible satellite animation the low-level cloud motions show a north-south elongated rotation approximately centered at 30N-49W... instead of a well-defined center needed for tropical cyclone formation (note this approximate center is a little east of the previous forecast... my updated one is nudged in that direction). The elongation is a result of the upper divergence region being elongated. Therefore my confidence that ex-Emily will make a comeback as a tropical cyclone before merging with the incoming cold front is decreasing... and I have now switched to showing probabilities of tropical cyclone formation instead of an intensity forecast. Going forward the upper outflow and associated surface pressure falls of an abrupt thunderstorm burst in the elongated envelope of rotation could help consolidate ex-Emily into a tropical cyclone... or alternatively ex-Emily simply stays elongated and uneventfully merges with the cold front. I vote a 50% chance of either scenario happening... which is reflected by my 50% chance of tropical cyclone formation over the next 24 hours. After that time ex-Emily will transition into a remnant non-tropical frontal cyclone supported by the eastern divergence zone front's upper trough. The remnant cyclone is expected to curve northeastward then eastward into the northeast Atlantic while rounding the northwest side of the current north Atlantic upper ridge as that upper ridge also shifts east into the northeast Atlantic. Noting that the upper divergence maximum of the front's upper trough should produce another broad frontal low over or near Iceland by day 4 which will likely absorb the remnant cyclone of Emily... therefore Emily most likely will not move into the British Isles as a distinct entity.


Update as of 2 PM EDT... the NHC in their tropical weather outlook has reduced odds of tropical cyclone formation from 70% to 50%.

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

IOH 24 Hr Outlook (1200Z Aug 25)... 50% chance of tropical cyclone formation (central Atlantic near 38N-47.5W)

IOH 48 Hr Outlook (1200Z Aug 26)... 0% chance of tropical cyclone formation (north Atlantic near 47N-40W)

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

Formation chance through 48 hours...50%

Formation chance through 7 days (168 hours)...50%


AREA OF INTEREST #26... When Franklin was in the Caribbean... surface pressures in the Caribbean immediately west of the storm and across Central America were kept low by upper divergence on the southeast side of a string of elongated northwestern Caribbean upper vorticity. This upper vorticity has since moved on to the southwestern Gulf of Mexico while pushed around the central US upper ridge... which has allowed the western extent of the tropical upper ridging in the Atlantic to expand into the Caribbean. The outflow at the west extent of the upper ridging has recently promoted an increase in thunderstorms in the vicinity of the Central American eastern Pacific coast... specifically around the Nicaragua/Honduras border region. Some model runs forecast a tropical cyclone to develop from this activity as the activity organizes into a tropical low and lifts north across the western Caribbean. As a result... within the last day the NHC has added an area of interest for the western Caribbean in their tropical weather outlook. This marks the twenty-sixth tropical Atlantic area of interest tracked on this site this year.


Any tropical low pressure area that develops over Nicaragua or Honduras should be initially quasi-stationary as it would be embedded in an expansive surface ridge weakness caused by passing frontal depressions to the north over the eastern US combined with Franklin in the western Atlantic to the northeast. As such the track forecast below shows a quasi-stationary system over the next 72 hours. By 96+ hours the southward-diving shortwave upper trough currently over the eastern US will be pushed into the eastern Gulf of Mexico by the ongoing central US upper ridge. This should result in a north-northeastward lift of this area of interest across the western Caribbean as whatever tropical low is present should transition into a feature supported by the divergence on the southeast side of the eastern Gulf upper vorticity. Regarding odds of tropical cyclone formation... models are mixed with some showing development and others not. Among the more reliable GFS and ECMWF camp... the ECMWF shows development of a bonafide tropical cyclone that moves from the western Caribbean and into the southeastern corner of the Gulf of Mexico while the GFS is the polar opposite by not even showing a tropical low consolidating. In the upper-levels... the ECMWF has the eastern Gulf upper vorticity covering a smaller area while the GFS goes with larger... perhaps then the GFS sees the larger upper vorticity as being repressive toward development while having the south extent of the vorticity squashing some of the western Caribbean upper outflow. I have assigned a low 20% odds of tropical cyclone formation by day 5 due to the mixed model support. Will assign higher odds of development in future updates if the model consensus for development increases... and/or a more distinct tropical low pressure circulation develops in the region.


The immediate concern from this area of interest will be possible excess rainfall and resulting flooding over the next few days for Nicaragua... Honduras... and El Salvador... especially if a quasi-stationary tropical low develops over the region. Interests in the Cayman Islands... western Cuba... south Florida... and the northwestern Bahamas should be aware of this area of interest in case an organizing tropical disturbance emerges over the next five days.

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

IOH 24 Hr Outlook (1200Z Aug 25)... 0% chance of tropical cyclone formation (over Honduras near 15N-87.5W)

IOH 48 Hr Outlook (1200Z Aug 26)... 0% chance of tropical cyclone formation (over Honduras near 15N-87.5W)

IOH 72 Hr Outlook (1200Z Aug 27)... 0% chance of tropical cyclone formation (over Honduras near 15N-87.5W)

IOH 96 Hr Outlook (1200Z Aug 28)... 0% chance of tropical cyclone formation (western Caribbean near 17N-86W)

IOH 120 Hr Outlook (1200Z Aug 29)... 20% chance of tropical cyclone formation (northwest Caribbean between the Cayman Islands and the Isle of Youth of western Cuba near 21N-82.5W)

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

Formation chance through 48 hours...10%

Formation chance through 7 days (168 hours)...60%


...COMPUTER MODEL SUMMARY...

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


0000Z (Aug 24) CMC Model Run...

**For Tropical Storm Franklin... drifts east-northeast to 23N-68W through 60 hours where it begins to strengthen briskly... while drifting north strengthens into a hurricane which reaches 28N-70W through 120 hours

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

**For area of interest #25... the remnants of Emily redevelop into a tropical cyclone near 38N-49W through 36 hours shortly after which time it merges with cold front... as a remnant frontal cyclone accelerates northeast to 53N-31.5W through 90 hours... subsequently weakens to a remnant frontal low that turns east and while offshore of the British Isles is absorbed by a larger frontal low developing over Iceland at 114 hours

**For area of interest #26... a better-defined tropical low develops just north of Honduras at 36 hours which drifts north into the Yucatan channel (between the west tip of Cuba and northeast corner of the Yucatan peninsula) by 78 hours... develops into a tropical cyclone over the Florida Keys at 102 hours which makes landfall on the southwest coast of the Florida peninsula at 120 hours.

**Tropical wave emerges from west coast of Africa at 36 hours and develops into a tropical low near 11.5N-20.5W at 54 hours... tropical cyclone formation suggeted at 84 hours near 13.8N-28.8W at 84 hours... becomes a compact hurricane which reaches 14N-38.5W through 120 hours

**Additional strong tropical wave of low pressure emerges from the west coast of Africa at 120 hours and quickly evolves into a large tropical cyclone east-southeast of the Republic of Cabo Verde Islands and near 15N-20W at 132 hours... tropical cyclone moves across the Republic of Cabo Verde Islands through 156 hours and is centered just west of the islands by 168 hours.


0000Z (Aug 24) ECMWF Model Run...

**For Tropical Storm Franklin... drifts east-northeast to 22.6N-67.5W at 36 hours where it begins to strengthen briskly... subsequently hooks northwest and then north through 120 hours while reaching hurricane strength and arrives to 30N-71W

**For area of interest #23... turns northwest to 30N-52.5W through 132 hours where it develops into a tropical cyclone

**For area of interest #25... the remnant low of Emily develops into a compact tropical cyclone near 42.5N-35W at 54 hours just before it merges with cold front... subsequently the remnant frontal cyclone quickly fades to a remnant frontal low that becomes absorbed by larger frontal low developing southwest of Iceland at 108 hours while located near 52N-26W

**For area of interest #26... tropical low becomes better defined just south of the Yucatan channel (between the west tip of Cuba and northeast corner of the Yucatan peninsula) by 78 hours and develops into a tropical cyclone on the northwest of Cuba at 114 hours... tropical cyclone drifts north into the waters just west of the Florida Keys through 126 hours.

**Strong tropical wave of low pressure emerges from the west coast of Africa at 114 hours and rapidly develops into a tropical cyclone offshore of Mauritania at 126 hours


0600Z (Aug 24) GFS Model Run...

**For Tropical Storm Franklin... drifts east-northeast to 24.5N-65.5W by 63 hours where it begins to strengthen briskly... subsequently arcs north-northwest and then northward and passes just west of Bermuda as a hurricane through 114 hours... hurricane centered west-northwest of Bermuda near 32.5N-69W at 120 hours

**For area of interest #23... turns northwest to 31N-52.5W through 120 hours where it evolves into a more consolidated tropical low

**For area of interest #25... remnant low of Emily merges with cold front and transitions into a frontal cyclone at 45 hours while located near 44N-35W... subsequently the remnant cyclone fades to a remnant frontal low that becomes absorbed by larger frontal low developing between Greenland and Iceland at 90 hours while located near 55N-24W

**For area of interest #26... no development shown

**Strong tropical wave emerges from western Africa at 87 hours and moves across the Republic of Cabo Verde Islands as a broad tropical low by 123 hours


0000Z (Aug 24) NAVGEM Model Run...

**For Tropical Storm Franklin... drifts east-northeast to 22.5N-68W by 36 hours where it begins to strengthen briskly... subsequently turns north while strengthening into a large and intense hurricane whose center arrives just west of Bermuda through 120 hours.

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

**For area of interest #25... remnant low of Emily redevelops into a tropical cyclone located near 35N-51.5W at 36 hours... subsequently the remnant frontal cyclone accelerates northeastward into the northeast Atlantic and becomes absorbed by a developing frontal low southwest of Iceland at 108 hours while located near 55N-18W

**For area of interest #26... no development shown

**Strong tropical wave emerges from western Africa at 102 hours and passes over the Republic of Cabo Verde Islands as a broad tropical low through 132 hours... center of broad tropical low located near 15N-30W at 168 hours

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