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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 #89

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


...SUNDAY OCTOBER 1 2023 3:30 PM EDT...

The primary focus for the Atlantic tropics at this time are a pair of central Atlantic tropical cyclones... see Tropical Storm Philippe and Rina sections below for more details on the two cyclones. Philippe has potential to bring impacts to the northern Lesser Antilles and Bermuda in the days ahead. Elsewhere... a frontal cyclone in the northwestern Atlantic has not acquired tropical characteristics thus far... see area of interest #42 section below for more information.


TROPICAL STORM PHILIPPE... I guess with Philippe its not a surprise that its forecast track has shifted again. Initially was expecting Philippe to be stalled while equally tugged by Rina passing to the north and the surface ridge weakness associated with area of interest (AOI) #42 to the northwest. Instead it appears Rina has weakened enough and/or is now far enough away such that Philippe has developed a westward drift... soon to be a west-northwest drift... toward the northern Lesser Antilles and the surface ridge weakness of AOI #42. Philippe will still turn north during the 5-day forecast period while interacting with AOI #42 and its associated upper trough. Note that during the forecast period the upper trough splits into southwestern and northeastern halves... and the short-term more westward position of Philippe has larger longer term consequences as well as Philippe will now miss the northeastward acceleration with the northeastern upper trough and instead be interacting with the southwestern upper trough. For intensity... I have downgraded the short-term intensity forecast as the shorter term westward track now puts Philippe in direct oppostion with the southeastward moving wave of upper vorticity that has arrived from its previous position northeast of the eastern Bahamas. The wave of upper vorticity has already pushed Philippe's thunderstorms more southeastward from its swirl center... and with Philippe and the wave of upper vorticity moving in opposite directions this effect will be worsened such that I now predict Philippe to barely be a tropical storm at 24 hours. By 48 hours Philippe will be positioned northwest of the wave of upper vorticity and out ahead of the upper trough associated with AOI #42... still in an environment of westerly shear but with increased upper divergence between northwesterlies streaming into the wave of upper vorticity and southwesterlies ahead of the upper trough. With the help of the upper divergence at 48 hours I forecast Philippe to redevelop thundrestorms closer to its center and regain some strength. The upper trough will then undergo its southwestern and northeastern split beyond 48 hours... with the southwestern split upper trough lifting Philippe north. As it does so... the southwestern upper trough will become increasingly amplified due to ongoing amplified upper ridging over eastern North America... which will gradually reduce the westerly shear over Philippe and hence allow Philippe to intensify. However the shear will never be zero and so I forecast Philippe to not exceed category 1 hurricane status through 96 hours. Between 96 and 120 hours... an amplified central North America upper trough and its strong surface frontal cyclone finally have enough oomph to break through the eastern North America upper ridge and push the upper trough near Philippe eastward... and in turn Philippe turns northeastward with the nearby upper trough while remaining a strong/tall enough system to be coupled with upper winds. With the nearby upper trough being shoved east toward Philippe... some increase in westerly shear over Philippe can be expected and so I lower the intensity forecast in the 96 to 120 hour window.


With the updated forecast... Philippe's center now has an opportunity to pass very close to the northern Lesser Antilles within the next 48 hours. As such tropical storm advisories have begun for some of the islands in the northern Lesser Antilles... gusty winds and coastal surf are possible here. Philippe will pass Bermuda to the southeast by Thursday... but still could be near enough such that Bermuda may see coastal surf during that time.

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

0 Hr Position (1200Z Oct 1)... 50 mph maximum sustained wind tropical storm centered east of the northern Lesser Antilles at 16.1N-58.7W

IOH 24 Hr Forecast (1200Z Oct 2)... 40 mph maximum sustained wind tropical storm centered just east of the northern Lesser Antilles at 17.5N-60.5W

IOH 48 Hr Forecast (1200Z Oct 3)... 45 mph maximum sustained wind tropical storm centered just northeast of the northern Lesser Antilles at 20N-61W

IOH 72 Hr Forecast (1200Z Oct 4)... 60 mph maximum sustained wind tropical storm centered in the western Atlantic at 23N-61W

IOH 96 Hr Forecast (1200Z Oct 5)... 80 mph maximum sustained wind hurricane centered southeast of Bermuda at 27.5N-61W

IOH 120 Hr Forecast (1200Z Oct 6)... 75 mph maximum sustained wind hurricane centered in the central Atlantic at 30N-57.5W

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

5-Day Position (1200Z Oct 6)... 85 mph maximum sustained wind hurricane centered in the central Atlantic at 29.5N-59W


TROPICAL STORM RINA... Rina in the open central Atlantic has been continuing northwestward in the flow on the north side of Philippe... and will soon turn north and northeastward in the flow ahead of area of interest (AOI) #42 and its upper trough. The updated forecast track in the short-term is nudged northward due to Rina's initial position relative to my prior forecast. In an environment of hostile northwesterly shear Rina has hung on to minimal tropical storm status (40 mph maximum sustained winds) by devloping an east-west linear band of nearby thunderstorms to the southeast of its cloud swirl center. A mid-latitude warm core upper ridge axis is present due to warm surface southerly flow ahead of AOI #42... however a look at the latest 200 mb upper wind profile shows the upper ridge has not amplified enough to reduce the westerly shear over Rina. That means Rina will not catch a break from westerly shear for the remainder of its life cycle... especially while interacting with the upper trough associated with AOI #42. However the northeastward acceleration of the storm which is more in alignment with the shearing upper winds... and boosting upper divergence on the southeast side of the upper trough... may help Rina hang on for longer and this is what I show in my forecast below. However my updated forecast shows no strengthening as the northward-nudged updated forecast track puts Rina closer to the upper trough and hence more hostile westerly shear. By 72 hours the upper trough will be splitting into southwestern and northeastern halves... with Rina caught in linear upper westerlies on the south side of the northeastern upper trough that have a lack of divergence... thus I forecast Rina to collapse around that time under the combo of shear and lack of upper divergence.

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

0 Hr Position (1200Z Oct 1)... 40 mph maximum sustained wind tropical storm centered in the central Atlantic at 25.3N-54.8W

IOH 24 Hr Forecast (1200Z Oct 2)... 40 mph maximum sustained wind tropical storm centered in the central Atlantic at 28.5N-56W

IOH 48 Hr Forecast (1200Z Oct 3)... 40 mph maximum sustained wind tropical storm centered in the central Atlantic at 34N-53.5W

IOH 72 Hr Forecast (1200Z Oct 4)... Dissipating remnant low in the central Atlantic centered at 35N-46W

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

Loss of Tropical Cyclone Status (0000Z Oct 2)... 35 mph maximum sustained remnant low centered in the central Atlantic at 26.8N-55.2W


AREA OF INTEREST #42... A classical non-tropical low pressure system is in progress midway between the northeastern United States coast and Bermuda. The surface frontal cyclone... which was near 37.5N-67.6W as of 1200Z... has wrapped in cold air associated with its parent upper trough to make a local cold core upper vortex that is about to stack over the cyclone. The overhead upper vortex is providing a low shear environment over the surface frontal cyclone... and combined with sufficiently warm waters was previously concerned that the surface cyclone could produce core thunderstorms and tropical characteristics. However only scattered showers have developed near the core of the surface cyclone thus far. Going forward... the strength of the ongoing surface ridge protruding from eastern Canada will tend to keep the surface cyclone from accelerating eastward with the upper vortex... thus the surface cyclone is forecast to end up beneath the west side of the upper vortex where it will be pulled southeastward by the vortex (I have nudged the forecast track eastward due to the 1200Z position of the surface cyclone relative to the prior forecast). And with suppressing upper convergence beneath the west side of the upper vortex... subtropical development is unlikely going forward and I have assigned a 0% chance of subtropical cyclone development. Beyond 24 hours... noting the upper vortex will merge with upper vorticity diving southeastward from its current northeastern Canada position... creating a southwest-northeast tilted upper trough. The elongated and tilted upper trough's divergence zone will result in a southwest-to-northeast elongation of whatever remains of the surface low pressure circulation. In the long range... the tilted upper trough splits into southwestern and northeastern halves... with the divergence zone of the northeastern upper trough transforming a part of the elongated surface circulation into a frontal cyclone that moves east-northeast into the north Atlantic.


Noting the pressure gradient between the surface frontal cyclone of the eastern US and surface ridge protruding from eastern Canada is still driving winds blowing toward shore... resulting in coastal surf for parts of the eastern US. Coastal flood advisores are in effect for southwestern Connecticut... southeastern New York including Long Island... New Jersey... Delaware... southeastern Maryland... and southeastern Virgnia as of this writing. As the surface low moves southeast over the next 24 hours as discussed above... surf generated by this system may later reach the shores of Bermuda.


This is my planned final statement on this area of interest on this blog as subtropical development is not anticipated going forward.

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

IOH 24 Hr Outlook (1200Z Oct 2)... 0% chance of subtropical cyclone formation (north-northeast of Bermuda near 35N-64W)

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

Not in the official outlook


...COMPUTER MODEL SUMMARY...

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


0000Z (Oct 1) CMC Model Run...

**For Tropical Storm Philippe... moves west-northwest and passes just north of the northern Lesser Antilles through 48 hours... subsequently accelerates north-northeast while strengthening into a hurricane and reaches 30N-56W at 120 hours.

**For Tropical Storm Rina... weakens to a remnant low in the next 12 hours while located near 25.5N-54.5W... remnant low then accelerates northeastward in the flow ahead of area of interest #42 and passes just north of the Azores at 102 hours and becomes absorbed by area of interest #42 shortly thereafter

**For Area of Interest #42... frontal cyclone offshore of northeastern US moves southeast to the waters north of Bermuda and near 35N-64.5W through 36 hours while weakening to a frontal low... frontal low subsequenlty shifts east and splits into a southwestern and northeastern half through 54 hours... southwestern frontal low quickly dissipates while norhteastern frontal low ejects east-northeast toward northeast Atlantic as a frontal cyclone through 84 hours.

**Broad tropical low materialies over the western Caribbean... Honduras... El Salvador... Guatemala... eastern Pacific... Belize... southeastern Mexico... and eastern Bay of Campeche through 168 hours


0000Z (Oct 1) ECMWF Model Run...

**For Tropical Storm Philippe... moves east-northwest and passes just northeast of the northern Lesser Antilles through 54 hours... subsequently is turned north through 120 hours while initially moving toward surface ridge weakness caused by area of interest #42 and then later the southwestern fracture of upper trough associated with AOI #42 and reaches 28N-62.5W at 120 hours as a tropical storm

**For Tropical Storm Rina... weakens to a remnant low in the next 24 hours while located near 26N-55.5W at 24 hours... remnant low then turns north-northeast in the flow ahead of area of interest #42 and is absorbed by AOI #42 while located near 31N-52.5W at 48 hours

**For Area of Interest #42... frontal cyclone offshore of northeastern US moves southeast to the waters north of Bermuda and near 35N-65.5W through 30 hours while weakening to a frontal low... frontal low subsequenlty shifts east and splits into a southwestern and northeastern half through 42 hours... southwestern frontal low quickly dissipates while norhteastern frontal low ejects east-northeast toward northeast Atlantic as a frontal cyclone through 90 hours.


0600Z (Oct 1) GFS Model Run...

**For Tropical Storm Philippe... moves west-northwest to the waters just east-northeast of the Lesser Antilles through 51 hours where it begins to intensify... subsequently accelerates north-northeast while strengthening into a hurricane and reaches 29N-57W at 120 hours.

**For Tropical Storm Rina... weakens to a remnant low near 29.5N-55.5W at 30 hours... subsequently turns northeast in flow ahead of area of interest #42 and is absorbed by AOI #42 while located near 33N-51.5W at 48 hours.

**For Area of Interest #42... frontal cyclone offshore of northeastern US moves southeast to the waters north of Bermuda and near 34.5N-64W through 33 hours while weakening to a frontal low... frontal low subsequenlty shifts east and splits into a southwestern and northeastern half through 45 hours... southwestern frontal low quickly dissipates while norhteastern frontal low ejects east-northeast toward northeast Atlantic as a frontal cyclone through 84 hours.


0600Z (Oct 1) NAVGEM Model Run...

**For Tropical Storm Philippe... moves west-northwest to the waters just east-northeast of the Lesser Antilles through 30 hours where it begins to intensify... subsequently accelerates northward and then northeastward while becoming a hurricane and reaches 30.8N-47.5W at 120 hours.

**For Tropical Storm Rina... weakens to a remnant low in the next 12 hours while located near 25.5N-55W... subsequently turns northeast in the flow ahead of area of interest #42 and is absorbed by AOI #42 while located near 31N-52.5W at 36 hours.

**For Area of Interest #42... frontal cyclone offshore of northeastern US moves east-southeast to the waters northeast of Bermuda and near 35N-62.5W through 30 hours while weakening to a frontal low... frontal low subsequenlty shifts east and splits into a southwestern and northeastern half through 42 hours... southwestern frontal low quickly dissipates while norhteastern frontal low ejects east-northeast toward northeast Atlantic as a frontal cyclone through 72 hours.

**Tropical wave emerges from west coast of Africa at 120 hours and organizes into a tropical low near 10.8N-20.2W at 168 hours.

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