*******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 OCTOBER 5 2023 5:41 PM EDT...
Tropical Storm Philippe continues lifting northward across the western Atlantic and will bring impacts to Bermuda by tomorrow and Atlantic Canada and northeastern United States by this weekend... see Philippe section below for more details. Elsewhere... a deep-layer cyclone is materialzing 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 over western Africa has become better defined near 6N-0W which the models insist on developing when it later moves into the eastern tropical Atlantic... see area of interest #44 section below for more information.
Elsewhere... 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.
TROPICAL STORM PHILIPPE... Philippe in the western Atlantic is lifting northward toward Bermuda while steered within the east side of a surface low pressure field and nearby upper trough whose divergence zone is generating the surface low pressure field. The tropical storm actually weakened to 40 mph maximum sustained winds about 24 hours ago perhaps as the tropical storm was becoming broader with a more relaxed surface pressure gradient while merging with said surface low pressure field. More recently Philippe has strengthened back to 50 mph maximum sustained winds as the eastern warm core upper ridging/outflow generated by Philippe's thunderstorm latent heat release and divergence zone of the nearby upper trough are working together to help Philippe and the broad surface low pressure field. It could be argued that Philippe has transitioned into a larger and more subtropical cyclone as its strength is now derived by both tropical processes (the aforementioned eastern outflow) and non-tropical processes (the divergence zone of the nearby upper trough). Going forward the amplified upper trough over central North America will continue to approach... with the smaller upper trough near Philippe pivoting eastward and then northward around the North American upper trough. As such my updated forecast track has Philippe accelerating north-northeastward through 48 hours while remaining coupled to the divergence zone of the smaller upper trough. Between 48 and 72 hours the smaller upper trough in Philippe's environment merges with the incoming North American upper trough to make a large upper vortex whose northeastern quadrant draws Philippe northwestward into southeastern Canada. Because Philippe has moved faster to the north and is also west of the previous forecast... my updated forecast track now takes the center of the storm directly into Bermuda instead of just east of Bermuda and a little sooner. Even though Philippe at 48 hours will be dealing with a one-two punch 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 storm... I still show gradual strengthening of the storm through that time 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 gaining high-end tropical storm strength. By 72 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 this past 0600Z GFS model run prefers a more western landfall toward the Maine/New Brunswick border while insisting the currently broad circulation of Philippe consolidates further west. Not long after 72 hours... the models insist that another frontal cyclone developing over southern Quebec with the support of the North American upper trough will absorb Philippe's remnant frontal cyclone.
Regarding impact to land areas:
(1) Philippe has been moving faster to the north... which means tropical storm force coastal surf and gusty winds will arrive on Bermuda earlier on Friday instead of later. Preparations in Bermuda for tropical storm conditions should finish by tonight. Due to the enlarged storm structure... heavy rainfall will arrive well in advance of the storm center and later this afternoon.
(2) 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. Gusty winds further west across the remainder of the northeastern United States and Great Lakes region (and also surf for the Great Lakes region) to occur Sunday and early next week will be more associated with another frontal cyclone that develops over southern Quebec.
(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 early next week is both coastal and inland sections of Nova Scotia... New Brunswick... Prince Edward Island... southeastern Quebec. Gusty winds further west across southwestern Quebec and Ontario will be more associated with another frontal cyclone that develops over southern Quebec.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Oct 5)... 50 mph maximum sustained wind tropical storm centered in the western Atlantic at 26.2N-66.3W
IOH 24 Hr Forecast (1800Z Oct 6)... 60 mph maximum sustained wind tropical storm centered just south of Bermuda at 30.5N-65.5W
IOH 48 Hr Forecast (1800Z Oct 7)... 65 mph maximum sustained wind tropical storm centered in the northwest Atlantic at 37.5N-63W
IOH 72 Hr Forecast (1800Z Oct 8)... Frontal cyclone centered over the Gulf of St Lawerence coast of New Brunswick at 47N-65W
******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************
Peak Strength (0000Z Oct 7)... 60 mph maximum sustained wind tropical storm centered north-northwest of Bermuda at 34.2N-66.6W
Loss of Tropical Cyclone Status (0000Z Oct 8)... 60 mph maximum sustained wind frontal cyclone centered offshore of western Nova Scotia at 41.8N-66W
AREA OF INTEREST #43... The divergence zone of the current north Atlantic upper trough is triggering a new and intensifying surface frontal low with multiple centers to the northwest of the Azores. The bulk of the upper trough is forecast to amplify 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 west side of the new frontal low
(2) Adjacent amplification of warm core upper ridging to the west caused by the thunderstorm latent heat release of Philippe and warm southerly surface flow ahead of Philpppe. Philippe is forecast to become absorbed by another frontal cyclone that develops over southern Quebec... with warm southerly flow ahead of the absorbing frontal cyclone continuing the warm core upper ridging to the west.
The new surface frontal low will at first rapidly 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 24+ 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) from 24 to 96 hours is expected to drift south-southwestward under the influence of the above-mentioned upper ridging to the west... and my updated forecast track below reflects the more west slant in the south drift shown in recent model runs. During this 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... only warming to 1175 dekameters as the upper vortex remains isolated from fresh cold air injections... and looking for 1200 dekameters or less for tropical development at these water temps). For this update I have not raised peak odds of subtropical cyclone formation above 30% as some model runs suggest the surface layer of this system may never shed its elongated multiple-center structure... and a single center is needed for official subtropical cyclone status. The elongated multi-center structure of the new surface frontal low is already being caused by the elongated divergence zone of the current upper trough... and recent models have the upper trough evolving into a more oblong instead of circular upper vortex which will continue the elongated upper divergence zone. Note that by 120 hours a north fragment of the current North American upper trough is forecast to skip over the north side of the amplified upper ridging to the west and will try to pull the surface layer of the deep-layer cyclone northeastward with the surface cold front generated by the divergence zone of the upper trough fragment. A northeastward drift of this system is likely to continue beyond 120 hours as the upper vortex of the deep-layer cyclone is also likely to become pulled by the upper trough fragment.
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 (1800Z Oct 6)... 10% chance of subtropical cyclone formation (northeast Atlantic near 45N-34W)
IOH 48 Hr Outlook (1800Z Oct 7)... 30% chance of subtropical cyclone formation (northeast Atlantic near 44.5N-34W)
IOH 72 Hr Outlook (1800Z Oct 8)... 30% chance of subtropical cyclone formation (northeast Atlantic near 43N-35W)
IOH 96 Hr Outlook (1800Z Oct 9)... 30% chance of subtropical cyclone formation (northeast Atlantic near 42N-35.5W)
IOH 120 Hr Outlook (1800Z Oct 10)... 30% chance of subtropical cyclone formation (northeast Atlantic near 43.5N-34W)
******National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT***************************
Not in the official outlook
AREA OF INTEREST #44... Satellite image as of 1800Z of a tropical wave of low pressure near the south-facing coast of western Africa now being monitored for potential development when it later moves offshore in a few days:
Satellite imagery suggests a western Africa tropical wave of low pressure with a small area of curved thunderstorm banding was positioned near 6N-0W as of 1800Z. Various model runs suggest this tropical wave may develop in a few days when it moves into and across the eastern tropical Atlantic... this marks the forty-fourth tropical Atlantic area of interest tracked on this site this year. Although development in the eastern Atlantic has been suppressed over the last several days by upper vorticity... a shift in the upper air pattern is coming as about half of the eastern Atlantic upper vorticity will soon be swept northeastward and away by the upper vortex associated with area of interest (AOI) #43... and the other half of the upper vorticity will retrograde westward and away under the influnece of the current central Atlantic mid-latitude upper ridge cell. The retreating upper vorticity will allow the current western Africa upper ridge cell... with low shear and upper outflow... to expand into the eastern tropical Atlantic and thus keep conditions favorable for this tropical wave to possibly develop. During the five day forecast period... the expanding eastern tropical Atlantic upper ridge's outflow will clash with the outflow of the current central Atlantic mid-latitude upper ridge cell... creating upper convergence that allows for a southwestward expansion of a surface ridge from Europe that will keep the track of whatever develops from this tropical wave westward. Due to the favorable upper wind outlook and insistence in the models that this wave may develop... I agree with the NHC in already assigning peak 30% odds of tropical cyclone formation for this new area of interest during the forecast period.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 6)... 0% chance of tropical cyclone formation (western Africa near 7N-5W)
IOH 48 Hr Outlook (1800Z Oct 7)... 0% chance of tropical cyclone formation (western Africa near 7.5N-10W)
IOH 72 Hr Outlook (1800Z Oct 8)... 0% chance of tropical cyclone formation (offshore of western Africa near 8N-15W)
IOH 96 Hr Outlook (1800Z Oct 9)... 15% chance of tropical cyclone formation (eastern tropical Atlantic near 8.5N-20W)
IOH 120 Hr Outlook (1800Z Oct 10)... 30% chance of tropical cyclone formation (eastern tropical Atlantic near 9N-25W)
******National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT***************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 30%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).
0000Z (Oct 5) CMC Model Run...
**For Tropical Storm Philippe... accelerates northward while gradually strengthening into a stronger tropical storm whose center passes just west of Bermuda bewtween 36 and 42 hours... makes landfall over western Nova Scotia at 78 hours while transitioning into a frontal cyclone... through 90 hours swings northwestward across New Brunswick and southwestern Quebec while merging with another frontal cyclone developing to its immediate west.
**For area of interest #43... new frontal cyclone with multiple centers solidifies northwest of the Azores and near 45N-30W through 18 hours... through 120 hours frontal cyclone makes mutliple cyclonic laps beneath its parent upper vortex while still having multiple centers and is positioned near 45.5N-31.2W at 120 hours
**For area of interest #44... tropical wave emerges from west coast of Africa at 66 hours and evolves into a tropical low near 10N-23W at 96 hours... tropical low reaches 11.2N-35W at 168 hours.
0000Z (Oct 5) ECMWF Model Run...
**For Tropical Storm Philippe... accelerates northward while gradually strengthening into a stronger tropical storm whose center passes just west of Bermuda bewtween 36 and 42 hours... makes landfall over western Nova Scotia just after 78 hours while transitioning into a frontal cyclone... through 90 hours swings northwestward across New Brunswick and southwestern Quebec while merging with another frontal cyclone developing to its immediate west.
**For area of interest #43... new frontal cyclone with multiple centers solidifies northwest of the Azores and near 45N-30W through 18 hours... while cyclonically whirling beneath its parent upper vortex the frontal cyclone consolidates into a single center near 47N-33.5W at 66 hours... the single center dives south to 41.5N-35W through 120 hours while potentially acquiring tropical characteristics
**For area of interest #44... no development shown
0600Z (Oct 5) GFS Model Run...
**For Tropical Storm Philippe... degenerates into a subtropical low with multiple centers at 30 hours while located south of Bermuda near 30N-66W... one of the western centers intensifies into a non-tropical frontal cyclone that makes landfall at the Maine/New Brunswick border at 72 hours... continues northwestward across the inland part of the border and into southeastern Quebec at 81 hours where it merges with another frontal cyclone developing to its immediate west.
**For area of Interest #43... new frontal cyclone with multiple centers solidifies northwest of the Azores and near 45N-31W through 12 hours... while cyclonically whirling beneath its parent upper vortex the frontal cyclone consolidates into a single center near 46.5N-35W at 63 hours... the single center continues whirling cyclonically through 120 hours while potentially gaining tropical characteristics and reaches 44N-30W
**For area of interest #44... tropical wave emerges from west coast of Africa at 63 hours and evolves into a tropical low near 8N-26W at 117 hours... tropical cyclone formation suggested near 11.2N-34W at 168 hours.
0600Z (Oct 5) NAVGEM Model Run...
**For Tropical Storm Philippe... accelerates northward while gradually strengthening into a stronger tropical storm whose center passes over Bermuda just after 30 hours... makes landfall over western Nova Scotia at 78 hours while transitioning into a frontal cyclone... frontal cyclone continues northwest into the inland Maine/New Brunswick border at 90 hours and then westward across southern Quebec and into the Quebec/Ontario border through 120 hours
**For Area of Interest #43... new frontal cyclone with multiple centers solidifies northwest of the Azores and near 45.5N-31W through 18 hours... while cyclonically whirling beneath its parent upper vortex the frontal cyclone consolidates into a single center near 45.5N-35.5W at 66 hours... the single center continues whirling cyclonically through 120 hours while potentially gaining tropical characteristics and reaches 42.5N-30W
**For area of interest #44... tropical wave emerges from west coast of Africa at 66 hours and evolves into a tropical low near 10N-20W at 102 hours... tropical cyclone formation suggested near 10N-26W at 138 hours with strengthening tropical cyclone suggested near 12N-29.5W by 168 hours.