*******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 26 2022 4:54 AM EDT...
See area of interest #41 section below for an update on the current subtropical low pressure area that has recently lifted northward from Bermuda. A second subtropical low pressure area is also forming southwest of Bermuda and is expected to approach the island late this week and into the weekend... see area of interest #42 section below for more information on the second subtropical low.
Elsewhere... the interaction of multiple features is expected to generate a slow-moving tropical low pressure area in the southeastern Caribbean Sea over the next five days... see area of interest #43 section below for more information.
New to this site this year... I will be sequentially numbering up areas of interest for possible Atlantic tropical development. In this scheme... will reset back to #1 at the start of next year (January 2023). The current area of interest in this blog post are designated #41 to #43 as the other numbers were used in previous birdseye view posts. This scheme is to reduce confusion as Atlantic tropical activity increases during the peak of the hurricane season... when multiple simultaneous areas of interest begin and end which previously required shuffling around the area of interest numbers from update to update.
AREA OF INTEREST #41... The subtropical surface low that has been located over/near Bermuda over the last 24 hours has undergone a meteorologically interesting evolution. For much of Tuesday the swirl center that was seen in Bermuda doppler radar has gone on to lift northward away from the island and was visible during daylight satellite as a remarkably small cloud swirl featuring occasional thunderstorm activity. The swirl is embedded in an area of upper divergence ahead of an upper trough fragment to the west... perhaps explaining how it has been able to fire thunderstorm activity despite being over 25 deg C water (tropical development typically occurs over 26+ deg C waters). As a result this system has been hanging on as an area of interest in the NHC tropical weather outlook.
The small swirl of interest is moving north in southerly flow between a surface ridge to the east and an area of dropping surface pressures to the west associated with the divergence maximum of the aforementioned upper trough fragment. Because the small swirl is not beneath the divergence maximum it will soon lose its identity to the area of dropping surface pressures to the west... with the overall area of dropping surface pressures transitioning into a less tropical low pressure system that moves toward southeastern Canada in the next 24 hours. Although it is harder to tell with nighttime infrared satellite... it appears the swirl is beginning to lose its identity beneath a small east-west band of thunderstorms that recently developed in its vicinity. With this outlook... I assign 0% odds of tropical cyclone formation. Note that the remnant less tropical low pressure area over southeastern Canada and the associated upper trough fragment is forecast to become absorbed by the stronger current central US frontal low and its upper trough once the two systems collide by 48 hours.
This will be my planned final statement on this area of interest on this blog. As of 2 AM EDT the NHC has also dropped tropical development odds of this system to 0%.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Oct 27)... 0% chance of tropical cyclone formation (northwestern Atlantic and offshore of western Nova Scotia near 41N-65.5W)
AREA OF INTEREST #42... The south portion of the current upper trough in the western Atlantic is becoming cut-off from the mid-latitude westerlies by an eastern Canada warm core upper ridge... bolstered by the warm surface southerly flow ahead of the current central Canadian frontal cyclone. The eastern divergence zone of the cut-off upper trough has generated a new surface subtropical low pressure area near 27N-70W per the latest NHC TAFB surface analysis and CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=). Due to the amplified nature of the cut-off upper trough... upper divergence on the east side of the trough is expected to be sufficiently high and wind shear is expected to be sufficiently low to support possible evolution of the new subtropical surface low into a subtropical cyclone. Forecast track in the outlook below is initially northeastward toward the direction of Bermuda... and adjustments have been made by blending the current position of the new subtropical surface low with the forecast location of the upper trough's divergence maximum from this past 1800Z GFS model run. The longer range forecast track toward days 4 and 5 is uncertain due to competing steering influences. Some model solutions promote a westward drift under the influence of a blocking surface ridge to build to the north and in the wake of the current central US and Canadian frontal systems... and others prefer an eastward drift while having the subtropical surface low dragged by a north fracture of the current northeast Pacific upper trough (just offshore of SW Canada and NW US) and the associated surface ridge weakness it will sustain with its eastern divergence zone once it rapidly swings east across North America and into the Atlantic. My current solution is to stall this system just southwest of Bermuda at days 4 and 5 under the competing steering influences.
I ramp up subtropical development odds to a peak of 25% through day 3 as the supporting cut-off upper trough potentially acquires a northwest-to-southeast tilt which will induce a better-defined maximum of upper divergence needed for the formation of a consolidated surface circulation. I have not raised peak development odds above the 25% mark in this update as the GFS is currently the only global model showing subtropical cyclone formation... however should this system become better organized and/or should other models join the GFS then will raise development odds in future updates. By days 4 and 5 the aforementioned upper trough energy from the northeast Pacific is expected to drag the cut-off upper trough associated with this system eastward and away... leaving this system underneath potentially broad and shearing upper westerly flow in the wake of these upper features... especially so if it stalls or drifts west in the long range. So even though the updated forecast track in the outlook below just keeps this sysetm over warm 26 deg C water during this timeframe... I still elect to taper down development odds from the 25% peak due to the potential shear. However I also do not drop the odds to 0% either as the shear could be moderate instead of high depending on how much anticyclonic curvature occurs in the upper flow in the wake of the departing upper troughing. The subtropical designation is used in the outlook below through day 4 to indicate the potential for this system becoming a hybrid... supported by the upper divergence on the east side of the cold core upper troughing while at the same time aided by warm core outflow associated with thunderstorm latent heat release and the outflow warm core upper ridging forecast to be located just east of the upper trough. The subtropical designation is switched to tropical by day 5 as the cold core upper troughing moves east and away as discussed above.
Per the updated forecast... potential impacts (heavy rain... gusty winds... and coastal surf) to Bermuda will likely arrive in the later part of this week and persist thorugh the weekend due to a potentially erratic and slow track that develops under conflicting steering influences. Interests here should remain aware of this system and monitor changes with its forecast in the coming days... a stronger system and/or closer track toward the island will result in more notable impacts.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Oct 27)... 10% chance of subtropical cyclone formation (western Atlantic near 27N-70W)
IOH 48 Hr Outlook (0600Z Oct 28)... 20% chance of subtropical cyclone formation (western Atlantic near 28.8N-69W)
IOH 72 Hr Outlook (0600Z Oct 29)... 25% chance of subtropical cyclone formation (southwest of Bermuda near 30.5N-68W)
IOH 96 Hr Outlook (0600Z Oct 30)... 15% chance of subtropical cyclone formation (southwest of Bermuda near 31N-68W)
IOH 120 Hr Outlook (0600Z Oct 31)... 15% chance of tropical cyclone formation (southwest of Bermuda near 31N-68W)
AREA OF INTEREST #43... The interaction between a surface tropical wave of low pressure currently crossing the Lesser Antilles... the outflow of a tropical upper ridge cell developing between the cut-off upper trough associated with area of interest (AOI) #42 and central Atlantic upper vortex to the northeast... and the southeastern divergence zone of the cut-off upper trough associated with AOI #42 is forecast to potentially generate a broad tropical low pressure in the southeastern Caribbean Sea within the next five days. Various model runs also continue to forecast possible tropical cyclone formation from the broad tropical low... therefore the NHC has added the aforementioned surface tropical wave as an area of interest in their 5-day tropical weather outlook. This marks the forty-third tropical Atlantic area of interest I have tracked on this blog this year.
Over the next five days... any broad tropical low pressure area that develops in the southeastern Caribbean Sea is likely to at first drift slowly westward as the surface easterly trade winds have been weakened in the region by a sprawling area of western Atlantic surface low pressure in part associated with AOI #42. Although not shown explicitly by any of the current model runs as of this writing... anything that develops more quickly could become stronger/taller and couple with the upper southerly/southwesterly flow ahead of the cut-off upper trough tied to AOI #42 and on the northwest side of the upper ridge cell... brining this system toward the northeastern Caribbean Islands anywhere from the eastern Dominican Republic... Puerto Rico... to the Virgin Islands. At this time I agree with the current 5-day model consensus of a further south and slow westward track in the weak easterly surface trade winds as an initially weaker/shallower system appears more likely for two reasons... (1) a southeastern Caribbean Sea tropical low has not formed yet and will need some time to form first which is why 48-hour odds of development are set to 0%... (2) the cut-off upper trough tied to AOI #42 could induce westerly wind shear through days 3 and 4 especially if this system consolidates closer to the trough which is why I have low development odds of 10% to 20% in that timeframe. By day 5 I agree with the NHC on higher 30% development odds as the cold core cut-off upper trough weakens while remaining isolated from high-latitude cold air while also shifting eastward and away... allowing for the low shear/outflow environment of the upper ridge cell to expand. To reflect a potentially stronger/taller system by that timeframe... I nudge the track forecast northward on day 5 while coupling this system to the upper flow on the west side of the expanding upper ridge cell.
What happens after day 5 will depend on the strength of a low-latitude upper trough to slide across the southeastern US... this trough will be a merger between the south part of the current northeast Pacific upper trough offshore of the northwestern US and the south part of yet another upper trough that slides across North America by day 5... with the strength/position of the southeastern US upper trough depending on the strength/postion of adjacent warm upper ridiging immediately to its west which in turn depends on how the warm sector of frontal systems several hundred miles to the west exactly evolves. Based on the latest input data... the models over the last 24 hours have trended toward a weaker/less amplified southeastern US upper trough... however that could change again. Here are three examples of what could happen beyohd day 5... it is highly uncertain at this time which one will occur:
(1) A stronger/more amplified southeastern US upper trough will keep the area of western Atlantic surface low pressure stronger with its eastern divergence zone and also keep a blocking surface ridge over the Gulf of Mexico stronger with its western convergence zone. The blocking ridge would halt westward progress... with this system turning north toward the northeastern/north-central Caribbean islands and points north while attracted to the stronger western Atlantic surface low pressure field.
(2) A weaker/less amplified southeastern US upper trough will correspondingly result in a weaker Gulf of Mexico surface ridge and weaker western Atlantic surface low pressure field. The surface ridge however would be enough to recover the surface easterly trade winds and coax this system on a more westward track toward the central and western Caribbean in the long range.
(3) Should this system in fact end up more north in the next five days as discussed in the prior paragraph... a turn toward the northeastern/north-central Caribbean islands and points north will be possible regardless of the strength of the southeastern US upper trough as the more north initial position will place it closer to the western Atlantic Atlantic surface low pressure field and also closer to the mid-latitude upper westerlies which would help steer it should it be stronger/taller.
I recommend the following interests be aware of this system for possible impacts (heavy rains... gusty winds... and coastal surf) within the next five days as follows:
(1) The ABC Islands (Aruba Bonaire and Curacao) and north coast of Venezuela should a more south track occur.
(2) The eastern Dominican Republic... Puerto Rico... and the Virgin Islands should a more north track occur.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Oct 27)... 0% chance of tropical cyclone formation (southeastern Caribbean Sea near 11.5N-64.5W)
IOH 48 Hr Outlook (0600Z Oct 28)... 0% chance of tropical cyclone formation (southeastern Caribbean Sea near 12N-65W)
IOH 72 Hr Outlook (0600Z Oct 29)... 10% chance of tropical cyclone formation (southeastern Caribbean Sea and just east of the ABC Islands near 12N-66W)
IOH 96 Hr Outlook (0600Z Oct 30)... 20% chance of tropical cyclone formation (southeastern Caribbean Sea and just east of the ABC Islands near 12N-67W)
IOH 120 Hr Outlook (0600Z Oct 31).. 30% chance of tropical cyclone formation (just north-northeast of the ABC Islands near 12.5N-68W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Oct 25) CMC Model Run...
**For area of interest #41... transitions into a larger non-tropical low near 37.5N-69.5W at 24 hours... current central US frontal low accelerates northeastward and absorbs the remnant non-tropical low while it moves across southeastern Canada through 54 hours.
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low near 30N-65.5W at 72 hours... surface low moves northeast into Bermuda by 96 hours and then drifts east to 32N-63.5W through 120 hours.
**For area of interest #43... tropical wave currently at 60W longitude evolves into a broad tropical low in the central Caribbean Sea and just offshore of northern Colombia by 120 hours.
1200Z (Oct 25) ECMWF Model Run...
**For area of interest #41... transitions into a larger non-tropical low near 35N-67.5W at 12 hours... current central US frontal low accelerates northeastward and absorbs the remnant non-tropical low while it moves across southeastern Canada through 54 hours.
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low just west of Bermuda at 72 hours... drifts southeast to 30N-66W through 120 hours.
**For area of interest #43... no development shown
1800Z (Oct 25) GFS Model Run...
**For area of interest #41... transitions into a larger non-tropical low near 36N-69W at 12 hours...current central US frontal low accelerates northeastward and absorbs the remnant non-tropical low while it moves across southeastern Canada through 42 hours.
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low near 28N-67W at 45 hours... surface low forecast to evolve into a subtropical cyclone near 30N-68.5W at 63 hours... begins to slowly weaken while drifing westward to 30.2N-70W through 120 hours.
**For area of interest #43... tropical wave currently at 60W longitude evolves into a tropical low just east of the ABC Islands (Aruba Bonaire and Curacao) at 123 hours.
1800Z (Oct 25) NAVGEM Model Run...
**For area of interest #41... transitions into a larger non-tropical low near 36N-69W at 12 hours... current central US frontal low accelerates northeastward and absorbs the remnant non-tropical low while it moves across southeastern Canada through 48 hours.
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low near 22.5N-66.5W at 54 hours... surface low drifts north to 27N-66W through 96 hours... surface low subsequently drifts west and weakens to a surface trough near 27.5N-68.5W at 108 hours.
**For area of interest #43... tropical wave currently at 60W longitude evolves into a tropical low just north of the ABC Islands (Aruba Bonaire and Curacao) at 90 hours... strengthens into a tropical cyclone which reaches 14.5N-71W at 120 hours.