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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 #91

*******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 OCTOBER 4 2023 12:57 PM EDT...

Tropical Storm Philippe's impacts to the northeastern Caribbean islands... mainly Puerto Rico and the Virgin Islands... will dwindle through the rest of today as the tropical storm continues lifting northward. Philippe will bring impacts to Bermuda by Friday night and Atlantic Canada and northeatern United States by this weekend... see Philippe section below for more details. Elsewhere... models have converged on showing a deep-layer cyclone northwest of the Azores over the next five days which could acquire tropical characteristics... this marks the forty-third tropical Atlantic area of interest I have tracked on this site this year... see area of interest #43 section below for more details.


Also watching for two possible tropical Atlantic areas of interest that could emerge over the next 7 days as follows:

(1) The current amplified upper trough over central North America is now approaching Philippe. Over the next 7 days the tail end of the surface cold front driven by this upper trough could settle below a tropical upper ridge cell to be positioned either over Mexico and/or the western Caribbean... with the upper ridge cell’s low shear and outflow favoring thunderstorm development. Therefore the tail end of the surface front could evolve into a western Caribbean... northern Central America... southeastern Mexico... and/or Bay of Campeche tropical disturbance by day 7.

(2) Tropical development in the eastern Atlantic and offshore of Africa as of late has been suppressed by eastern Atlantic upper vorticity. However over the next 7 days the deep-layer cyclone to setup northwest of the Azores (area of interest #43) is forecast to sweep the suppressing upper vorticity out of the region... and some global model runs continue to suggest a tropical wave of low pressure to emerge from Africa may try to develop in the eastern Atlantic within the next 7 days. However there are currently no well-defined or organized tropical waves of low pressure in satellite pictures over Africa or the eastern tropical Atlantic to declare an area of interest at this time.


TROPICAL STORM PHILIPPE... Infrared satellite images showing Philippe re-organizing from 1520Z October 3 to 0720Z October 4... the center of Philippe is marked with black crosshairs in each image. From 1520Z to 2130Z on October 3 northwesterly shear shed off the initial canopy of thunderstorms over the Lesser Antilles which then dissipated. From 2130Z October 3 to 0730Z October 4 Philippe fired a new and better organized canopy of thunderstorms closer to the storm center:

The center of Philippe went more west and less north than previous forecasts... taking the center across the northernmost Lesser Antilles and northernmost Virgin Islands on October 3. Even while treating Philippe as a shallower/weaker system suffering from ongoing westerly shear... I expected Philippe to turn more north toward the surface ridge weakness of what is now the oblong north Atlantic frontal low. Instead it appears the effect of the strong eastern North America surface ridge was under-estimated. The southwest-to-northeast titled upper trough associated with the oblong frontal low has already begun to split into southwestern and northeastern halves due to the strength of the eastern North America upper ridge... with Philippe to interact with the southwestern upper trough for the duration of its life cycle. Even if we assume Philippe remains a weak/shallow cyclone from shear... a northward turn should still occur as the divergence zone of the southwestern upper trough produces a northward-curving surface low pressure field due west of Philippe. Indeed the center fixes in recent NHC advisories suggest Philippe has already begun moving straight north near 65.5W longitude. Regarding storm structure... westerly shear completely ripped off the storm's initial thunderstorm canopy through 2130Z October 3 and Philippe weakened to 45 mph maximum sustained winds. Since then a new thunderstorm canopy has blossomed near the storm center which has allowed the storm to keep its 45 mph maximum sustained wind strength in the sheared environment.


The southwestern upper trough will become increasingly amplified due to amplification of the neighboring eastern North America upper ridge... which will gradually reduce the westerly shear over Philippe and hence allow Philippe to intensify while the storm moves northward. Philippe is behind my previous intensity forecast and therefore my updated one is notably lowered... and calls for Philippe to barely become a category 1 hurricane through 48 hours. During the middle of the forecast period... an amplified central North America upper trough and its strong surface frontal cyclone will have enough oomph to break through the eastern North America upper ridge. Previously it was thought the southwestern upper trough near Philippe would then merge with the incoming North America upper trough... however the lastest model guidance now shows the upper trough near Philippe being swung east then north around the North America upper trough. The initial east swing pushes the nearby upper trough and its southwesterly shear into Philippe sooner which is why I also do not show a strength above minimal category 1 at 48 hours. And even though Philippe is southwest of the previous forecast track... Philippe will be more strongly steered by the nearby upper trough than previously thought as the trough's eastward swing moves the trough closer to Philippe... thus I show a north-northeast acceleration through 72 hours that takes Philippe's center just east of Bermuda and has it catch back up to the latitudinal positions of the previous forecast track. From 48 to 72 hours Philippe suffers from a one-two pucnh of cooled sea surface temperatures caused by the August-September western Atlantic hurricanes (Franklin... Lee... Idalia) and a jump in southerly shear as the nearby upper trough digs into the south side of Philippe. However I only show slight weakening as the southerly shear is mitigated by Philippe's fast north-northeast speed which is in alignment with the upper southerly winds... and the amount of upper divergence ahead of the nearby upper trough supports Philippe holding on to high-end tropical storm strength. By 96 hours and while moving over even cooler water... Philippe is expected to transition into a strong landfalling non-tropical frontal cyclone supported by the aforementioned upper divergence. The landfall of the center will most likely be over Nova Scotia... however note some model runs suggest a landfall as far west as New Brunswick or Maine. By 120 hours the nearby upper trough and incoming North America upper trough merge into a large upper vortex west of Philippe... so Philippe's remnant frontal cyclone is expected to hook northwest across Quebec while pulled in by the northeast quadrant of the upper vortex. The more western landfall positions may be some model runs having the upper vortex materialize sooner and hence hook Philippe westward sooner.


Regarding impact to land areas:

(1) For Puerto Rico and the Virgin Islands... gusty winds have come to an end. Rainfall and coastal surf will come to an end over the next few hours as Philippe continues lifting northward and away.

(2) The latest forecast track projections have Philippe's center barreling northward over or near Bermuda by late Friday... I recommend preparing now for possible hurricane-force wind and coastal storm surge as Philippe has potential to strengthen over the next 48 hours. Tropical storm adivsories are in effect for Bermuda as of this writing.

(3) The coastal sections of the northeastern United States will experience surf generated by Philippe by this weekend. The most likely region in the northeastern United States to see more direct impacts such as strong gusty winds on Sunday is both coastal and inland sections of Maine.

(4) The coastal sections of Atlantic Canada will experience surf generated by Philippe by this weekend. The most likely region in Atlantic Canada to see more direct impacts such as strong gusty winds on Sunday and Monday is both coastal and inland sections of Nova Scotia... New Brunswick... Prince Edward Island... and the southern half of Quebec.

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

0 Hr Position (1200Z Oct 4)... 45 mph maximum sustained wind tropical storm centered north of Puerto Rico and the Virgin Islands at 20.5N-65.5W

IOH 24 Hr Forecast (1200Z Oct 5)... 60 mph maximum sustained wind tropical storm centered in the western Atlantic at 23.5N-65.5W

IOH 48 Hr Forecast (1200Z Oct 6)... 75 mph maximum sustained wind hurricane centered south of Bermuda at 28N-64.5W

IOH 72 Hr Forecast (1200Z Oct 7)... 70 mph maximum sustained wind tropical storm centered in the northwest Atlantic at 36N-63W

IOH 96 Hr Forecast (1200Z Oct 8)... Frontal cyclone centered over central Nova Scotia at 45N-63.8W

******National Hurricane Center (hurricanes.gov) official forecast as of 5 AM EDT***************************

Peak Strength (1800Z Oct 6)... 60 mph maximum sustained wind tropical storm centered over Bermuda at 32N-65W

Loss of Tropical Cyclone Status (0600Z Oct 8)... 60 mph maximum sustained wind frontal cyclone centered just offshore of western Nova Scotia at 43.1N-66.5W


AREA OF INTEREST #43... The southwest-to-northeast tilted upper trough associated with the current oblong north Atlantic surface frontal low is alraedy splitting into southwestern and northeastern halves. The northeastern upper trough is expected to continue into the northeastern Atlantic and send most of the oblong frontal low toward Iceland and the British Isles. By 24 hours the divergence zone of the upper trough will trigger a new surface frontal low to the northwest of the Azores... with the southern part of the upper trough amplifying into a cut-off cold-core upper vortex under the following influences:

(1) The cold air associated with the upper trough is pulled southward by the new frontal low

(2) Adjacent amplification of warm core upper ridging to the west caused at first by the warm southerly flow on the west side of the current eastern North America surface ridge... followed by the thunderstorm latent heat release of Philpppe... followed by warm southerly flow on the east side of what would be Philippe's remnant frontal cyclone or alternatively another frontal cyclone that takes Philippe's place to be generated by the amplified upper trough over North America.


The new surface frontal low will at first intensify into a frontal cyclone supported by the increasing divergence on the east side of the materializing upper vortex... and then whirl into the center of the upper vortex where it will begin a gradual decay at 48+ hours thanks to a lack of divergence at the upper vortex's core. The gradually decaying deep-layer cyclone (consisting of the upper vortex and slowly-weakening surface frontal cyclone) is expected to drift southward under the influence of the above-mentioned upper ridging to the west. During the decay phase the core of the deep-layer cyclone may acquire thunderstorms and tropical characteristics despite 20 to 22 deg C waters along the forecast track... as the upper vortex is forecast to be quiet cold during much of the 5-day forecast period (200 mb heights of the upper vortex expected to be as low as 1170 dekameters... looking for 1200 dekameters or less for tropical development at these water temps). For this update I am already assigning a peak 30% odds of subtropical cyclone formation due to the rather cold de-stabilizing temps of the forecast upper vortex and as all of the major global models are currently in agreement with the deep-layer cyclone setup happening. Regardless of whether or not the deep-layer cyclone acquires tropical characteristics... expected a prolong period of coastal surf for the Azores over the next five days.

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

IOH 24 Hr Outlook (1200Z Oct 5)... 0% chance of subtropical cyclone formation (northeast Atlantic near 45N-35W)

IOH 48 Hr Outlook (1200Z Oct 6)... 10% chance of subtropical cyclone formation (northeast Atlantic near 45N-34W)

IOH 72 Hr Outlook (1200Z Oct 7)... 30% chance of subtropical cyclone formation (northeast Atalntic near 44N-34W)

IOH 96 Hr Outlook (1200Z Oct 8)... 30% chance of subtropical cyclone formation (northeast Atalntic near 43N-34W)

IOH 120 Hr Outlook (1200Z Oct 9)... 30% chance of subropical cyclone formation (northeast Atlantic near 42N-34W)

******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM 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 4) CMC Model Run...

**For Tropical Storm Philippe... accelerates northward while becoming a hurricane whose center passes over Bermuda at 66 hours... makes landfall over western Nova Scotia at 108 hours while transitioning into a frontal cyclone... frontal cyclone continues north across New Brunswick and southeastern Quebec through 120 hours

**For area of interest #43... through 54 hours the northeastern half of the upper trough associated with the current oblong north Atlantic frontal low becomes a very cold and amplified upper trough in the northeast Atlantic in response to amplified upper ridging over eastern North America... the northeastern half of the oblong frontal low intensifies into a frontal cyclone positioned just south of Iceland by 54 hours under the support of the eastern divergence zone of the northeast Atlantic upper trough while the upper trough's divergence zone also produces a new southern frontal cyclone near 45N-34W... the southern frontal cyclone and southern half of the upper trough evolve into a deep-layer cyclone with possible tropical characteristics near 42.5N-36W by 120 hours

**Tropical wave emerges from west coast of Africa at 90 hours and organizes into a broad tropical low that passes south of the Republic of Cabo Verde Islands through 126 hours... tropical low reaches 11N-32.5W at 168 hours.


0000Z (Oct 4) ECMWF Model Run...

**For Tropical Storm Philippe... accelerates northward with the center passing just east of Bermuda at 66 hours... while transitioning into a remnant frontal cyclone the center makes landfall over the southeast corner of Maine just after 108 hours... remnant frontal cyclone whirls northwestward across southern Quebec through 120 hours.

**For Area of Interest #43... through 42 hours the northeastern half of the upper trough associated with the current oblong north Atlantic frontal low becomes a very cold and amplified upper trough in the northeast Atlantic in response to amplified upper ridging over eastern North America... the northeastern half of the oblong frontal low intensifies into a frontal cyclone positioned just northwest of the British Isles by 42 hours under the support of the eastern divergence zone of the northeast Atlantic upper trough while the upper trough's divergence zone also produces a new southern frontal cyclone with multiple centers near 45N-31.5W... the southern frontal cyclone and southern half of the upper trough consolidate into a deep-layer cyclone with possible tropical characteristics near 45.5-35W by 120 hours


0600Z (Oct 4) GFS Model Run...

**For Tropical Storm Philippe... weaknes to a remnant low near 21.5N-66W at 18 hours... redevelops into a compact tropical cyclone near 26.2N-64W at 48 hours that passes east of Bermuda and near 31.8N-61W at 66 hours... subsequently becomes absorbed by a frontal cyclone developing to its west while the frontal cyclone and Philippe move into Nova Scotia at 96 hours.

**For Area of Interest #43... through 51 hours the northeastern half of the upper trough associated with the current oblong north Atalntic frontal low becomes a very cold and amplified upper trough in the northeast Atlantic in response to amplified upper ridging over eastern North America... the northeastern half of the oblong frontal low intensifies into a frontal cyclone positioned just north of the British Isles by 51 hours under the support of the eastern divergence zone of the northeast Atlantic upper trough while the upper trough's divergence zone also produces a new southern frontal cyclone with multiple centers near 45N-32W... the southern frontal cyclone and southern half of the upper trough consolidate into a deep-layer cyclone with possible tropical characteristics near 40.8N-34W by 120 hours

**Tropical wave emerges from west coast of Africa at 78 hours and evolves into a compact tropical cyclone near 7.5N-20W at 114 hours... compact tropical cyclone reaches 10N-30W at 168 hours


0000Z (Oct 4) NAVGEM Model Run...

**For Tropical Storm Philippe... accelerates northward with the center passing just west of Bermuda at 60 hours... while transitioning into a remnant frontal cyclone the center makes landfall just east of the Maine/New Brunswick border just after 96 hours... remnant frontal cyclone whirls northwestward across southern Quebec through 120 hours.

**For Area of Interest #43... through 48 hours the northeastern half of the upper trough associated with the current oblong north Atalntic frontal low becomes a very cold and amplified upper trough in the northeast Atlantic in response to amplified upper ridging over eastern North America... the northeastern half of the oblong frontal low intensifies into a frontal cyclone positioned just north of the British Isles by 48 hours under the support of the eastern divergence zone of the northeast Atlantic upper trough while the upper trough's divergence zone also produces a new southern frontal cyclone near 46N-34.5W... the southern frontal cyclone and southern half of the upper trough consolidate into a deep-layer cyclone with possible tropical characteristics near 43.5N-34W by 120 hours

**Tropical wave emerges from west coast of Africa at 132 hours with tropical cyclone formation suggested just southeast of the Republic of Cabo Verde Islands through 168 hours

**Tail end of surface cold front associated with the upper trough that pulls Philippe into eastern Canada gradually evolves into a western Gulf of Mexico tropical cyclone near 23.5N-95W by 168 hours

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