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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 #61

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


...WEDNESDAY AUGUST 23 2023 2:30 PM EDT...

For now the active Atlantic tropics have seen a little reduction in activity while now down to three named systems in the region... see remnants of Emily (Area of Interest #25)... Tropical Storm Franklin... and remnants of Harold sections below for more details. Note Franklin and Harold are impacting land areas... and Franklin could produce notable impacts to Bermuda by early this upcoming week... more information on the impacts is provided in the respective sections below.


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

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

(2) Computer models are mixed on possible development from tropical waves of low pressure to follow behind area of interest #23 by moving into the eastern Atlantic from Africa...all while the regional tropical upper ridge with low shear and upper outflow persists over the next several days. Current satellite imagery shows a tropical wave moving into western Africa while at 2.5E longitude as of this writing and another tropical wave over central Africa at 16E longitude. Will upgrade either wave to an area of interest if needed in future updates.

(3) Some recent model runs suggest that the elongated area of upper vorticity over the northwestern Caribbean may generate a broad tropical low pressure area over the western Caribbean with its southeastern divergence zone. Upper winds would also become more conducive over time for such a broad low pressure area as the upper vorticity retrogrades westward and away while pushed by the central US upper ridge... allowing for Atlantic tropical upper ridging with lower shear and upper outlfow to expand into the Caribbean. There are currently no signs of a low pressure area materializing in the western Caribbean... should this change during future updates will add an area of interest here only if needed.


TROPICAL STORM FRANKLIN... Yesterday afternoon... around 5 PM EDT... aircraft reconaissance found the surface circulation of Franklin... which was located south of Hispaniola (Haiti and the Dominican Republic)... had become disorganized with a broad center seperated further west of the thunderstorm activity and a second center developing closer to the thunderstorms. The recon measurements also found Franklin had weakened to 40 mph maximum sustained winds. This was probably an effect of the elongated divergence zone of the string of upper vorticity to the northwest resulting in some elongation of Franklin's surface circulation. The westerly shear and disruption from this upper vorticity has relaxed while the upper vorticity has begun to retrograde westward and away thanks to the strength of the current central US upper ridge. Accordingly Franklin overnight and through this morning has been slowly regaining organization with the surface center consolidating back toward the thunderstorms... with a corresponding gradual increase in the organization of the thunderstorms. Franklin also regained 50 mph maximum sustained winds. The center has recently made landfall over the southwest corner of the Dominican Republic while it continues north under the influence of the surface ridge weakness associated with the current western Atlantic cold front... and as of 11 AM EDT Franklin has weakened back down to 40 mph due to the landfall.


Franklin is only a tad east of the previous forecast... my updated one shown below is nudged eastward accordingly. After today's passage across Hispaniola... Franklin is expected to lift northeastward through 48 hours while chasing the surface ridge weakness associated with the western Atlantic cold front... after which time the cold front and its upper trough leave Franklin behind. 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 during the 5-day forecast window. Indeed in the upper-levels the upper trough that leaves Franklin behind will also leave behind an upper vortex just to Franklin's north at 48 hours... with the forecast track below showing Franklin arcing northeastward and then northward around the east side of the vortex in the 48 to 96 hour window. For the 96 to 120 hour window... Franklin will be close enough to one of the aforementioned surface frontal depressions to accelerate north toward the associated surface ridge weaknes... and a northward acceleration is projected during that timeframe.


Regarding intensity... by 24 hours I anticipate Franklin to only slowly recover back to its pre-Hispaniola landfall strength as it recovers from the land interaction with the mountanious terrain of Hispaniola. Then thru 48 hours I do not show any additional strengthening with the arrival of westerly shear on the south side of the upper vortex mentioned at the end of the prior paragraph. Due to the eastward-nudged forecast track... Franklin arrives into lower westerly shear and supportive eastern divergence zone of the upper vortex sooner and so in my updated forecast below the anticipated long-term strengthening begins earlier. Models also agree that the latent heat release of Franklin's thunderstorms will weaken the disrputive cool core upper vortex by 96 hours... and moreover by 120 hours Franklin accelerates northward and away from what will be remaining of the upper vortex. During this time Franklin will also be passing over an area of rather warm 30 deg C water temps. Therefore by day 5 (120 hours) I project Franklin will have strengthened to a top-end category 2 hurricane. The NHC advisory at 11 AM EDT also has a similar idea and brings Franklin to a mid-range category 2.


Regarding impact to land areas:

(1) As Franklin moves north across Hispaniola (Haiti and the Dominican Republic)... an expanding area of strong showers and thunderstorms on colorized infrared satellite imagery covers all of the Dominican Republic and eastern Haiti. Potentially dangerous flash flooding and mudslides kicked off by the heavy rain are the primary concern here as Franklin has weakened to a minimal tropical storm where gusty winds and coastal surf are only secondary concerns at this point.

(2) Preparations for Franklin in the eastern Bahamas should be completed by tonight. Although Franklin has weakend to a minimal tropical storm due to its landfall with Hispaniola... when the center arrives to the waters just east of the islands by early tomorrow the lingering westerly wind shear levels in the region are not strong enough to prevent Franklin from re-strengthening... and there is a small chance of gusty winds and coastal surf should Franklin recover as shown in the forecast below.

(3) Interests in Bermuda should closely monitor the progress of Franklin for possible severe impacts by early Monday. Franklin is currently forecast to approach the region as a strong hurricane.

(4) The mid-Atlantic and northeastern US coast may see coastal surf from Franklin by early this upcoming week should it strengthen into a strong offshore hurricane as currently forecast.

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

0 Hr Position (1200Z Aug 23)... 50 mph maximum sustained wind tropical storm centered over the southwestern corner of the Dominican Republic at 17.9N-71.2W

IOH 24 Hr Forecast (1200Z Aug 24)... 50 mph maximum sustained wind tropical storm centered just east of the eastern Bahamas at 21.5N-70.8W

IOH 48 Hr Forecast (1200Z Aug 25)... 50 mph maximum sustained wind tropical storm centered over the western Atlantic at 22.8N-67.5W

IOH 72 Hr Forecast (1200Z Aug 26)... 70 mph maximum sustained wind tropical storm centered over the western Atlantic at 24N-65.5W

IOH 96 Hr Forecast (1200Z Aug 27)... 95 mph maximum sustained wind hurricane centered over the western Atlantic at 26N-65.5W

IOH 120 Hr Forecast (1200Z Aug 28)... 110 mph maximum sustained wind hurricane centered just south of Bermuda at 30.5N-65.5W

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

5-day Position (1200Z Aug 28)... 105 mph maximum sustained wind hurricane centered in the western Atlantic at 31.1N-67.6W


REMNANTS OF HAROLD... Over the last 24 hours Harold has weakend to an inland remnant low pressure while moving into the eastern part of the Texas/Mexico border region... and as of late its west-northwest track around the southwestern edge of the steering eastern North America surface ridge has kicked the remnant low into southwestern Texas. Doppler radar shows the rainfall has been on the western side of the remnant system... and as of this writing the rainfall has transfered from southwestern Texas and into south-central New Mexico. The remnant low pressure is forecast to soon dissipate due to ongoing land interaction. Refer to your local forecasts at the National Weather Service (available at weather.gov) and your local news media for any flood advisories across southwestern Texas and southern New Mexico caused by the rainfall. This is my final statement on Harold on this blog as it is no longer a tropical cyclone.


AREA OF INTEREST #23... In visible satellite animation... the eastern Atlantic tropical wave of low pressure continues to display a broad area of rotation centered near 17N-36.5W as of 1200Z. A small area of thunderstorms is further southeast... however the curvature in the thunderstorm activity suggests a secondary center could be developing near 16N-35W. For now using the broad center at 17N-36.5W for the initial position... therefore the updated forecast track below is quiet similar to 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). By 48+ 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 4 due to the likely influence of Franklin's surface circulation...and by day 5 a complete turn to the north is anticipated in the southerly flow ahead of Franklin. My longer term forecast track is nudged eastward over the previous as my updated forecast track for Franklin was adjusted in that direction. Regarding odds of tropical cyclone formation... most models continue to not develop this system as it nears what is forecast to be a strong Hurricane Franklin... probably as Franklin steals surface inflow from this system and perhaps also shears this system with its upper outflow. Also the shower and thunderstorm activity in the circulation of this system remains anemic... likely from ingestion of dry Saharan air to the east. Therefore I have once again lowered peak odds of tropical cyclone formation in this update. I reserve peak odds of development to after 48 hours as the aforementioned warm air mass upper ridge pushes the south part of the current northeastern Atlantic upper trough toward this system thru 24 hours... which will allow the southwest part of the upper trough to impart some northerly shear over this system in the short-term. The fact that the small area of showers and thunderstorms mentioned above are on the south side of the broad area of rotation is a sign that the northerly shear has begun. On a final note... by days 3 and 4 this system will be approaching the small upper trough interacting with ex-Emily (see Area of Interest #25... ex-Emily... section below for more info on the small upper trough). 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 prohibitive to development... is anticipated from the decaying upper trough.

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

IOH 24 Hr Outlook (1200Z Aug 24)... 0% chance of tropical cyclone formation (central tropical Atlantic near 18.5N-41W)

IOH 48 Hr Outlook (1200Z Aug 25)... 10% chance of tropical cyclone formation (central tropical Atlantic near 19.5N-45W)

IOH 72 Hr Outlook (1200Z Aug 26)... 20% chance of tropical cyclone formation (central Atlantic near 22.5N-50W)

IOH 96 Hr Outlook (1200Z Aug 27)... 20% chance of tropical cyclone formation (central Atlantic near 25N-54W)

IOH 120 Hr Outlook (1200Z Aug 28)... 20% chance of tropical cyclone formation (central Atlantic near 30N-54W)

******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)...30%


AREA OF INTEREST #25 (REMNANTS OF EMILY)... Continuing to track the remnants of Emily as upper winds could become more conducive for its redevelopment as this system curves north across the open central Atlantic in the next 48 hours. Ex-Emily is making its northward turn as expected in the flow out ahead of the surface cold front and upper trough that have been pushing into the western Atlantic from eastern Canada. Some of the mid-latitude upper vorticity that has been hanging out over the western Atlantic has transitioned into a small upper trough that has been shoved toward ex-Emily by the larger scale upper trough entering from eastern Canada. The eastern divergence zone of the smaller upper trough has helped ex-Emily re-build thunderstorm activity. Visible satellite animation shows a less-defined surface center than yesterday... with broad cyclonic turning in the low clouds suggesting the center of rotation as of 1200Z was near the southwestern edge of the thunderstorm activity... or near 26N-49W. This is southwest of the previous forecast track... and so my updated one is adjusted in that direction accordingly. Going forward... its possible that Emily simply degenerates into an elongated north-south surface trough that becomes absored by the incoming cold front... as the smaller upper trough will have an elongated upper divergence zone. Or alternatively Emily could re-generate into a tropical cyclone with the initial help from the smaller upper trough... followed by arrival into the southwest edge of the current north Atlantic upper ridge where wind shear is lower and upper outflow is higher. On the one hand the surface center of Emily is less defined than yesterday as noted above... leaning toward the idea of elongation into a surface trough. On the other hand thunderstorm activity has notably increased in the last 24 hours... and the percentage of global models showing Emily coming back as a tropical cyclone has increased. Therefore I am continuing to provide a specific track and intenisty forecast assuming ex-Emily will indeed make its comeback... and have also nudged up the intensity forecast. Note that by 72+ hours Emily is expected to merge with the cold front and 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 Atlanitc while rounding the northwest side of the aforementioned north Atlantic upper ridge. Noting that the upper divergence maximum of the front's upper trough should produce another broad frontal low over Iceland by day 5 which will likely absorb the remnant cyclone of Emily... therefore Emily most likely will not move into the British Isles as a distinct entity.

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

0 Hr Position (1200Z Aug 23)... Tropical low centered in the central Atlantic at 26N-49W

IOH 24 Hr Forecast (1200Z Aug 24)... Tropical low centered in the central Atlantic at 31N-50W

IOH 48 Hr Forecast (1200Z Aug 25)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 38N-48.5W

IOH 72 Hr Forecast (1200Z Aug 26)... Frontal cyclone centered in the north Atlantic at 47N-41W

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

Formation chance through 48 hours...60%

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


...COMPUTER MODEL SUMMARY...

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


0000Z (Aug 23) CMC Model Run...

**For Tropical Storm Franklin... degenerates into an east-west elongated trough over the next 24 hours while lifting northward across Haiti... re-organizes into a tropical low over the easternmost Bahamas at 30 hours... curves eastward and re-gains tropical cyclone status near 22.5N-69.5W at 48 hours and then acquires hurricane strength near 23N-66.5W at 78 hours... the hurricane subsequently curves northward into the waters south-southwest of Bermuda through 120 hours while reaching 28N-65.5W

**For area of interest #23... tropical cyclone formation suggested near 24.5N-45W at 90 hours... drifts west-northwest as a weak tropical cyclone through 120 hours while reaching 26N-46.2W

**For area of interest #25... the remnants of Emily redevelop into a tropical cyclone near 33.5N-50W at 54 hours... later merges with cold front and accelerates northeastward as a remnant frontal cyclone while reaching 53N-28.5W at 120 hours

**Tropical wave emerges from the west coast of Africa at 60 hours and develops into a tropical low near 13N-32.5W at 120 hours... tropical cyclone formation suggested near 13.5N-35W at 126 hours... tropical cyclone located near 14N-44W at 168 hours

**Additional strong tropical wave of low pressure emerges from the west coast of Africa at 144 hours... evolves into large tropical low pressure just offshore of the Mauritania/Senegal border at 168 hours

**Tropical low develops in the western Caribbean Sea near 17.5N-85W at 72 hours... while generally stationary evolves into a tropical cyclone through 108 hours... tropical cyclone drifts north to 19.5N-85W through 120 hours


0000Z (Aug 23) ECMWF Model Run...

**For Tropical Storm Franklin... drifts north across Haiti and begins to organize just east of the easternmost Bahamas through 30 hours... while drifting east-northeast to 24N-65.5W through 78 hours strengthens into a hurricane... subsequently the hurricane turns north-northwest to 28.5N-68.8W through 120 hours

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

**For area of interest #25... remnant low of Emily merges with cold front near 42.5N-45.5W at 78 hours... as a remnant frontal low accelerates northeastward to 53N-32W through 120 hours

**Strong tropical wave emerges from western Africa at 126 hours and moves into the Republic of Cabo Verde Islands by 162 hours as a broad tropical low


0600Z (Aug 23) GFS Model Run...

**For Tropical Storm Franklin... crosses northward through the western Dominican Republic through 15 hours then becomes better organized over the easternmost Bahamas by 24 hours... subsequently turns eastward in track and reaches 23.5N-65.5W at 75 hours... while subsequently curving northward strengthens into a hurricane that reaches the waters west-southwest of Bermuda near 30.2N-67.5W by 120 hours

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

**For area of interest #25... remnant low of Emily redevelops into a tropical cyclone near 30.5N-50W at 21 hours... later merges with cold front and accelerates northeastward to 47.5N-40W by 84 hours as a remnant frontal cyclone... the frontal cyclone weakens to a frontal low and then loses identity to larger/stronger Iceland frontal low by 120 hours while located west of the British Isles

**Strong tropical wave emerges from western Africa at 114 hours and moves into the Republic of Cabo Verde Islands by 144 hours as a broad tropical low


0600Z (Aug 23) NAVGEM Model Run...

**For Tropical Storm Franklin... crosses northward through the western Dominican Republic through 12 hours and passes just east of the eastern Bahamas by 24 hours... subsequently curves east while strengthening into a hurricane near 22.5N-66W at 48 hours... while strengthening further into a large and intense hurricane curves north into the waters southwest of Bermuda through 126 hours while reaching 28.8N-67.5W

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

**For area of interest #25... remnant low of Emily re-develops into a tropical cyclone near 31N-51.2W at 30 hours and gains hurricane strength while merging with cold front near 40.5N-49.5W at 66 hours... as a remnant frontal cyclone curves northeastward and then eastward to 56.5N-18.8W through 120 hours

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