*******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.**********
...TUESDAY OCTOBER 25 2022 3:40 AM EDT...
See area of interest #41 section below for an update on the current subtropical low pressure center passing over Bermuda. A second subtropical low pressure area is also expected to approach Bermuda from the southwest with potentially notable impacts arriving later this week... see area of interest #42 section below for more information on the forecast second feature.
Elsewhere... an upper ridge cell is forecast to expand over the southeastern Caribbean Sea in between the upper trough associated with area of interest (AOI) #42 and central Atlantic upper vortex. Meanwhile the tropical wave of low pressure currently at 55W longitude is expected to slow down underneath the upper ridge cell due to the sprawling surface ridge weakness to be associated with AOI #42 which will weaken the steering easterly surface flow. Models have recently trended toward developing this tropical wave in the southeastern Caribbean Sea due to the potential low shear and upper outflow of the upper ridge cell. This tropical wave is currently not marked as an area of interest as the model support is relatively new... and it remains to be seen if the models switch back to a less favorable picture or not. For example less favorable wind shear will be higher if the upper ridge cell is displaced further south should the upper trough associated with AOI #42... followed by the southern fracture of the current northeast Pacific upper trough to approach from the southern United States... dig further south. This tropical wave will likely be added as an area of interest in future updates if the currently more favorable model solutions hold.
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 and #42 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 swirl center of the subtropical surface low pressure system that has been approaching Bermuda from the east has passed just south of the island based on the latest doppler radar imagery from the Bermuda weather service (http://www.weather.bm/). So far measured sustained winds on the island have not exceeded 17 mph. Since special update #137A the thunderstorm activity at the center of circulation... as well as the activity to the north bolstered by the upper outflow of the warm core deep-layer ridge in the region... have weakened. This is a sign that this system is likely moving west-northwest into less favorable thermodynamic conditions... a combination of moving into waters below 26 deg C combined with upper air temps too warm to support instability over the cooler water. The NHC has recently dropped tropical cyclone formation odds to 60% from 70%. In this update I have lowered my short-term (6-hour) odds of tropical cyclone formation to below 50% as the thermodynamic conditions that lie ahead will not be improving going forward and this system has not responded well to the current thermodynamic conditions. I drop development odds to 0% by 24 hours as this system is forecast to transition into a less tropical system to be supported by the upper divergence of the north fracture of the upper trough that has recently exited the eastern US. The forecast track is nudged southward due to the current position of this system's center of circulation on Bermuda doppler radar. For Bermuda... expect the potential for scattered thunderstorms this morning... with weather conditions improving later today. Attention will now be turning to an additional subropical low pressure system forecast to develop to the southwest later this week... see area of interest #42 section below for more information on that system.
This will be my planned final statement on this area of interest on this blog... unless the situation changes or it somehow continues to be mentioned in the NHC tropical weather outlook by my next update.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 6 Hr Outlook (1200Z Oct 25)... 40% chance of tropical cyclone formation (just west-southwest of Bermuda near 31.8N-66.2W)
IOH 24 Hr Outlook (0600Z Oct 26)... 0% chance of tropical cyclone formation (western Atlantic near 34N-70W)
AREA OF INTEREST #42... The south portion of the current upper trough that has recently emerged into the western Atlantic from the US east coast is expected to become cut-off from the mid-latitude westerlies by warm core upper ridging that is currently amplifying to the northwest... courtesy of the warm sector of the frontal cyclone that has recently entered central Canada from the north-central US. 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 generate a potentially organizing subtropical surface low pressure area. Forecast track in the outlook below is initially northeastward toward the direction of Bermuda and is based on the forecast location of the upper divergence maximum from this past 0000Z GFS model run. As such the initial part of the forecast track has a south and west adjustment. In the longer-range the forecast track is also slower to the northeast than previously shown as a blocking surface ridge to build to the north... in the wake of the aforementioned central Canadian frontal cyclone and its upper trough... is forecast to be stronger per the latest model data. There is a split in the ultimate destination of this system beyond the 5-day window. The ECMWF and NAVGEM lean toward a continued northeast track while this system is dragged by a north fracture of the current northeast Pacific upper trough and the associated surface ridge weakness it will sustain with its eastern divergence zone. The CMC and GFS give more weight to the blocking surface ridge and turn this system on a westward drift.
Initial odds of subtropical cyclone formation are set to 0% as the region of upper divergence on the east side of the upper trough is expected to be too elongated to support a consolidated surface low pressure spin. I raise development odds in the longer range once the 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. While the NHC has recently added this area of interest to their tropical weather outlook and has already ramped up peak odds of subtropical cyclone formation to 30%... I maintain my previous 25% peak odds instead of raising them as not all models agree on the upper trough taking a tilted oreintation... with those solutions resulting in an ongoing elongated area of upper divergence that results in an elongated and less organized surface system. By 120 hours I begin to trim down development odds from the peak as this system track north into waters below 26 deg C. The subtropical designation is used in the outlook below to indicate the potential for this system becoming a hybrid... supported by the upper divergence on the east side of the cold core upper trough 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.
Due to the updated slower forecast track... potential impacts (heavy rain... gusty winds... and coastal surf) to Bermuda will more likely arrive in the later part instead of the mid-part of this week. 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 26)... 0% chance of subtropical cyclone formation (western Atlantic near 25N-69.5W)
IOH 48 Hr Outlook (0600Z Oct 27)... 10% chance of subtropical cyclone formation (western Atlantic near 25N-68.5W)
IOH 72 Hr Outlook (0600Z Oct 28)... 20% chance of subtropical cyclone formation (western Atlantic near 27.5N-68.5W)
IOH 96 Hr Outlook (0600Z Oct 29)... 25% chance of subtropical cyclone formation (southwest of Bermuda near 30N-66.5W)
IOH 120 Hr Outlook (0600Z Oct 30)... 15% chance of subtropical cyclone formation (just west of Bermuda near 32N-66W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Oct 24) CMC Model Run...
**For area of interest #41... transitions into a larger non-tropical low near 34.5N-68.5W at 36 hours... subsequently accelerates north with the non-tropical remnant low becoming absorbed by incoming cold front to the west while arriving to the Maine/Canada border at 66 hours (this cold front forecast to be driven by the current north-central US frontal cyclone over the next few days)
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low near 29.5N-66.2W at 96 hours... after reaching 30.5N-67.5W at 126 hours begins to turn west.
**Tropical wave currently at 55W longitude evolves into a broad tropical low in the central Caribbean Sea near 15N-71.5W at 150 hours.
1200Z (Oct 24) ECMWF Model Run...
**For area of interest #41... transitions into a larger non-tropical low near 36.5N-70W at 42 hours... subsequently accelerates north with the non-tropical remnant low becoming absorbed by incoming frontal low to the west while arriving just east of the Maine/Canada border at 66 hours (this frontal low forecast to emerge from southern split of current north-central US frontal cyclone)
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low just southwest of Bermuda at 90 hours... after its center passes just west of Bermuda the surface low continues drifting northeast and reaches 33.5N-63W at 120 hours.
0000Z (Oct 25) GFS Model Run...
**For area of interest #41... transitions into a larger non-tropical low near 35N-70W at 27 hours...subsequently accelerates north with the non-tropical remnant low becoming absorbed by incoming cold front to the west while arriving to the Maine/Canada border at 54 hours (this cold front forecast to be driven by the current north-central US frontal cyclone over the next few days)
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low near 29N-67W at 75 hours... surface low strengthens to a subtropical cyclone near 31N-69W at 102 hours... subtropical cyclone drifts west-southwest to 30.5N-70W through 123 hours.
**Tropical wave currently at 55W slows down while entering the eastern Caribbean Sea due to expansive surface ridge weakness caused by area of interest (AOI) #42... in an improving upper air pattern between the upper trough associated with AOI #42 to the northwest and upper vortex to the northeast gradually evolves into a slow-moving tropical cyclone near 12.5N-65W by 123 hours.
1800Z (Oct 24) NAVGEM Model Run...
**For area of interest #41... transitions into a larger non-tropical low near 35N-66.5W at 30 hours... subsequently accelerates north with the non-tropical remnant low becoming absorbed by incoming frontal low to the west while arriving into the Gulf of St. Lawrence at 72 hours (this frontal low forecast to emerge from southern split of current north-central US frontal cyclone)
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low near 24N-66.5W at 78 hours... drifts north in track and passes just west of Bermuda by 120 hours.
**Tropical wave currently at 55W evolves into a tropical low in the southeastern Caribbean Sea near 12.5N-63.8W at 60 hours... tropical low turns northwest into surface ridge weakness caused by area of interest #42 with the center passing between Puerto Rico and the Dominican Republic at 96 hours... turns more north in track and passes east of the eastern Bahamas near 22N-69W at 120 hours as a tropical cyclone.