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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 #93

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


...FRIDAY OCTOBER 6 2023 3:15 PM EDT...

Tropical Storm Philippe has transitioned into a remnant frontal low moving northward across Bermuda... see remnants of Philippe section below for more information. Elsewhere... a deep-layer cyclone has materialized northwest of the Azores and could acquire tropical characteristics in the days ahead... see area of interest #43 section below for more details. And finally a tropical wave of low pressure currently over western Africa will be moving into favorable atmospheric conditions across the eastern tropical Atlantic by this weekend and through this upcoming week. Recent global model runs insist on developing this tropical wave into a tropical cyclone... see area of interest #44 section below for more information.


Also noting the current amplified upper trough over central North America will spend the next few days driving the tail end of its surface cold front beneath 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 over the next six days.


REMNANTS OF PHILIPPE... Tropical Storm Philippe in the western Atlantic continued lifting northward toward Bermuda while steered within the east side of a western Atlantic frontal low being generated by the divergence zone of a nearby upper trough. As it did so it fired a strong thunderstorm complex to the east of its cloud swirl center overnight that allowed it to keep tropical characteristics. Through 11 AM EDT the thunderstorm complex has become well-removed to the east of the cloud swirl center... and the NHC has declared that Philippe has already transitioned into a remnant frontal low now in competition with the neighboring frontal low to the west. For Bermuda... the peak wind gust logged so far was 40 mph at at 4:36 AM local time... and more recently sustained winds have been hovering between 25 and 29 mph (http://www.weather.bm/observations.asp). Additional gusty winds and coastal surf will be possible for Bermuda for the remainder of this afternoon... with improving conditions this evening as Philippe continues northward and away. Doppler radar shows the heavy rainfall has ended for Bermuda as the thunderstorm complex has been shoved well east of Philippe's center and as the drier south half of Philippe's circulation is rotating in (http://www.weather.bm/tools/graphics.asp?name=500KM%20PPI&user=).


Going forward... ex-Philippe and the adjacent western Atlantic frontal low will be in competition with each other. The adjacent western Atlantic frontal low is aligned with the nearby upper trough's upper divergence maximum so its conceivable ex-Philippe simply becomes absorbed by the western Atlantic frontal low. Regardless of which circulation comes out on top... we will be having a western Atlantic frontal low that intensifies into a frontal cyclone under the support of the divergence zone of the nearby upper trough... followed by the divergence zone of the amplified upper trough now incoming from central North America. The western Atlantic frontal cyclone then makes landfall either over Nova Scotia... New Brunswick... or Maine and either continues northwestward and inland as the dominant feature or becomes absorbed by another frontal cyclone developing over southern Quebec (the southern Quebec frontal cyclone would also be developing with the support of the North American upper trough's divergence zone). Expect coastal surf to increase for the northeastern United States and Atlantic Canada this weekend. By Sunday strong gusty winds accompany the coastal surf for Nova Scotia... Prince Edward Island... New Brunswick... Maine... and Quebec. Through early this upcoming week gusty winds continue for Quebec and spread westward to eastern Ontario and the Great Lakes region of North America (surf across the Great Lakes and Hudson Bay will also be generated by the gusty winds). This is my final statement on Philippe on this blog as it is no longer a tropical cyclone... starting tomorrow impacts from the remnants of Philippe will be carried on the home page bulletins of this site... particularly if the remnant circulation holds on as the dominant circulation while moving across the northwest Atlantic and eastern North America.


AREA OF INTEREST #43... The large surface frontal low northwest of the Azores has in a classical manner intensified into a frontal cyclone with the support of its parent upper trough's eastern divergence zone. More recently southward cool air transport on the frontal cyclone's west side has amplified the south half of the upper trough into a cold core upper vortex... with the frontal cyclone beginning to whirl into a position beneath the core of the upper vortex. The upper vortex and frontal cyclone will continue on as a quasi-stationary deep-layer cyclone over the next several days while cut-off from the mid-latitude upper westerlies by persistent warm core upper ridging to the west. The upper ridging continues on with surface warm southerly flow ahead of ex-Philipppe or alternatively the frontal cyclone(s) that take ex-Philippe's place. The deep-layer cyclone will be undergoing a gradual decay phase as the surface frontal cyclone slowly weakens below the core of the upper vortex where upper divergence is lacking. Forecast track below is the same as previous as the deep-layer cyclone undergoes a south-southwest drift through 72 hours under the influence of the amplified upper ridging. By 96 hours a north fragment of the current North American upper trough skips over the north side of the upper ridging and attempts to drag the deep-layer cyclone northeastward. However noting that around 120 hours the upper trough fragment leaves behind the deep-layer cyclone... and so it would be waiting for the arrival of the next high-latitude upper trough for some time after 120 hours before moving again.


Regarding odds of subtropical cyclone formation... recent sea-surface temperature analysis from the NHC (https://www.nhc.noaa.gov/sst/) shows the waters near the core of the deep-layer cyclone have cooled to 18 deg C. However the above-described forecast track still brings the core of the deep-layer cyclone across 20 to 22 deg C waters through 72 hours... and then back northeastward toward the 20 deg C isotherm around 120 hours. Also the overhead upper vortex is expected to remain rather cold over the next five days to support instability and possible development of core thunderstorms and tropical characteristics (200 mb heights of the upper vortex are currently at around 1170 dekameters... only warming to 1185 dekameters through day 5 as the upper vortex remains isolated from fresh cold air injections... and looking for 1200 dekameters or less for tropical development in the 20 to 22 deg C sea surface temperature range). Because the core of the deep-layer cyclone has not yet developed much shower and thunderstorm activity... I am not raising peak odds of subtropical cyclone formation above 30% in this update cycle... and reserve those peak odds for when the cyclone sees its warmest water temps.


Regardless of whether or not the deep-layer cyclone acquires tropical characteristics... expect a prolonged 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 (1800Z Oct 7)... 20% chance of subtropical cyclone formation (northeast Atlantic near 44.5N-34W)

IOH 48 Hr Outlook (1800Z Oct 8)... 30% chance of subtropical cyclone formation (northeast Atlantic near 43N-35W)

IOH 72 Hr Outlook (1800Z Oct 9)... 30% chance of subtropical cyclone formation (northeast Atlantic near 42N-35.5W)

IOH 96 Hr Outlook (1800Z Oct 10)... 25% chance of subtropical cyclone formation (northeast Atlantic near 43.5N-34W)

IOH 120 Hr Outlook (1800Z Oct 11)... 20% chance of subtropical cyclone formation (northeast Atlantic near 44N-31W)

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

Not in the official outlook


AREA OF INTEREST #44... Animation of satellite imagery (https://tropic.ssec.wisc.edu/real-time/europe/movies/m7irn/m7irn_loop.html) suggests a tropical wave of low pressure over western Africa has moved from 6N-0W to 7N-7W over a 24-hour period spanning 1800Z yesterday to 1800Z today. The thunderstorm activity collapsed and then reformed off to the west-northwest and closer to the west coast of Africa during this time... it is possible the wave re-organizes further west-northwest into this activity and therefore my updated forecast track points have been nudged north and west to reflect this. Even if the wave were to vault into offshore eastern tropical Atlantic waters in the short-term... I show a slow down in the westward speed of the wave between 24 and 48 hours as the wave deals with the surface ridge weakness caused by area of interst (AOI) #43. The models then show the surface ridge over Europe building southwestward into the eastern Atlantic as the south part of the upper vortex associated with AOI #43 becomes a shortwave upper trough whose western convergnce zone helps the surface ridge expansion. The eastern Atlantic surface ridge then remains intact for some time as the outflow over this tropical wave clashes with the outflow of the central Atlantic mid-latitude upper ridge to create a zone of upper convergence. As such a steady westward track around the surface ridge is shown after 48 hours. By 120+ hours some of the energy associated with the current North American upper trough shifts toward the central Atlantic... with the divergence zone of this energy creating a surface ridge weakness that this system will likely move northwestward toward in the long range.


Regarding odds of tropical cyclone formation... upper winds over the offshore eastern tropical Atlantic waters are become more conducive for development as the upper ridge cell that was over Africa... featuring low shear and upper outflow... has been able to expand over offshore waters in the wake of retreating upper vorticity that was in the eastern Atlantic. Moreover the models continue to develop this tropical wave... therefore I agree with the NHC in increasing peak odds of tropical cyclone formation to 50%.

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

IOH 24 Hr Outlook (1800Z Oct 7)... 0% chance of tropical cyclone formation (west coast of Africa near 8N-14W)

IOH 48 Hr Outlook (1800Z Oct 8)... 10% chance of tropical cyclone formation (offshore of western Africa near 9N-17.5W)

IOH 72 Hr Outlook (1800Z Oct 9)... 20% chance of tropical cyclone formation (eastern tropical Atlantic near 9.5N-22.5W)

IOH 96 Hr Outlook (1800Z Oct 10)... 30% chance of tropical cyclone formation (eastern tropical Atlantic near 10N-27.5W)

IOH 120 Hr Outlook (1800Z Oct 11)... 50% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-32W)

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

Formation chance through 48 hours... 0%

Formation chance through 7 days... 50%


...COMPUTER MODEL SUMMARY...

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


0000Z (Oct 6) CMC Model Run...

**For Tropical Storm Philippe... accelerates northward with center passing just west of Bermuda at 18 hours and transitions into an elongated frontal cyclone near 35.5N-68W at 36 hours... remnant frontal cyclone center makes landfall over southeastern Maine at 54 hours and at 66 hours merges with another frontal cyclone devloping to its immediate west over southern Quebec

**For area of interest #43... elongated frontal cyclone consolidates into a single center near 45N-31.5W at 12 hours... frontal cyclone then takes multiple cyclonic laps beneath its parent upper vortex while potentially acquiring tropical characteristics and arrives to 43N-30W by 120 hours.

**For area of interest #44... tropical wave emerges from west coast of Africa at 42 hours with tropical cyclone formation suggested near 10.5N-31.5W at 126 hours... while approaching hurricane strength the tropical cyclone curves northwest to 17N-38W through 168 hours.


0000Z (Oct 6) ECMWF Model Run...

**For Tropical Storm Philippe... accelerates north with center passing over Bermuda just after 18 hours... subsequently absorbed by western Atlantic frontal low developing to its immediate west at 30 hours.

**For area of interest #43... elongated frontal cyclone consolidates into a single center near 45N-31.5W at 12 hours... frontal cyclone subsequently takes large cyclonic loop beneath its parent upper vortex while potentially acuqiring tropical characteristics and reaches 40.8N-31.5W at 120 hours.

**For area of interest #44... no development shown


0600Z (Oct 6) GFS Model Run...

**For Tropical Storm Philippe... maintains a compact tropical core within east side of developing western Atlantic frontal low with center of tropical core passing just east of Bermuda at 15 hours... subsequently transitions into a remnant frontal cyclone that makes landfall at the Maine/New Brunswick border at 48 hours... frontal cyclone subsequently accelerates northwest across the inland part of the border and across central Quebec through 66 hours... remnant frontal cyclone subsequently weakens to a frontal low while below core of upper vortex where upper divergence is lacking and meanders in a cyclonic loop in the vicinity of the Quebec/Ontario border through 120 hours.

**For area of Interest #43... frontal cyclone subsequently takes large cyclonic loop beneath its parent upper vortex while potentially acuqiring tropical characteristics and reaches 43N-33.5W at 120 hours.

**For area of interest #44... tropical wave emerges from west coast of Africa at 30 hours with compact tropical cyclone formation suggested near 9.2N-26W at 102 hours... strengthening compact tropical cyclone subsequently accelerates north-northwest to 18.5N-35.5W through 168 hours.


0600Z (Oct 6) NAVGEM Model Run...

**For Tropical Storm Philippe... center passes just west of Bermuda at 12 hours while gradually intensifying... subsequently transitions into an intensifying frontal cyclone whose center makes landfall just east of the Maine/New Brunswick border at 54 hours... frontal cyclone subsequently accelerates northwest across central Quebec through 102 hours... remnant frontal cyclone subsequently weakens to a frontal low while below core of upper vortex where upper divergence is lacking and meanders in a cyclonic loop in the vicinity of the Quebec/Ontario border through 120 hours.

**For Area of Interest #43... frontal cyclone subsequently takes large cyclonic loop beneath its parent upper vortex while potentially acuqiring tropical characteristics and reaches 45.5N-26.5W at 120 hours.

**For area of interest #44... tropical wave emerges from west coast of Africa at 12 hours with tropical cyclone formation suggested near 12.5N-33.5W at 138 hours... while staying a weak tropical cyclone moves west-northwest to 15N-38W through 120 hours.

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