*******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 27 2022 5:29 AM EDT...
See area of interest #42 section below for an update on the slow-moving subtropical low pressure area developing to the southwest of Bermuda. A tropical wave of low pressure currently traversing through the eastern Caribbean Sea continues to be monitored for signs of development in the days ahead... 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 #42 and #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 #42... The upper trough in the western Atlantic that has been cut-off from the mid-latitude westerlies has been generating an area of low surface pressure with its eastern divergence zone. 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=) the surface low pressure area has become less organized while transitioning into a north-south elongated surface trough due to the elongated nature of the upper trough's eastern divergence zone. However noting that the upper trough is taking a northwest-to-southeast tilt while it attempts to link with with another upper trough currently moving through the Great Lakes region of North America... with the tilt expected to induce a maximum of upper divergence that will aid in the consolidation of the surface low pressure area. As such the forecast track over the next 48 hours is based on the location of the upper divergence maximum from this past 1800Z GFS model run. There is also a slight westward adjustment during this timeframe as models have come into agreement that a blocking surface ridge to build to the north and in the wake of the Great Lakes upper trough will keep the consolidated surface circulation pinned toward the west. After 48 hours... the north fracture of the current western US upper trough is expected to slide into the northwest Atlantic. Models have also come into agreement that this feature and the surface ridge weakness it will create with its divergence zone will help drag the surface circulation eastward in the 48+ hour window despite the presence of the blocking surface ridge... therefore my updated forecast track is adjusted eastward in the longer range accordingly.
Regarding odds of subtropical cyclone formation... the NHC had raised odds of development to 50% and has recently tapered odds down to 40% perhaps due to the current disorganization of the system noted in the prior paragraph. I do agree that an increase in development odds is warranted as the other global models have recently joined the GFS in showing a better-defined surface circulation forming in the next 48 hours thanks to the maximum of upper divergence that the supporting western Atlantic upper trough is on its way to developing. To acknowledge the current disorganization of this system... I have dropped short term odds of development and have not quiet raised odds as high as the NHC has... settling in this update for a 35% peak. The tilt of the supporting western Atlantic upper trough that will be responsible for the helpful upper divergence maximum will also come to an end fairly quickly by 48+ hours as the north side of the upper trough tries to link with the north fragment of the current western US upper trough once that fragment races into the Atlantic... this is also another consideration for my slightly lower odds relative to the NHC. For the 72 and 96 hour window... the aforementioned upper trough fragment will help finally pull the western Atlantic upper trough eastward... however due to the strength of the blocking surface ridge mentioned in the prior paragraph the surface circulation is not expected to vault eastward with the upper trough... resulting in a pattern of upper westerly wind shear. Models are in agreement that the shear will be strong enough to inhibit tropical development... and while decoupling with the upper trough the surface circulation will lose support from the upper trough's eastern divergence zone... resulting in forecast weakening of the surface circulation. Therefore in this update I have lowered my odds of subtropical cyclone formation for the 72 and 96 hour window... ending the outlook at 96 hours with 0% odds. On a final note regarding the outlook below... I use a subtropical instead of tropical designation due to this system's potential to 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.
For Bermuda... this system has potential to produce periods of heavy rainfall through the weekend. Depending on the peak strength that this system attains around 48 hours... a short period of coastal surf may occur. At this time wind is not expected to be a notable impact as forecasts continue to indicate hostile upper-level wind conditions that will cause the surface circulation to weaken as it later slides eastward toward Bermuda.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Oct 28)... 0% chance of subtropical cyclone formation (western Atlantic near 28.8N-69W)
IOH 48 Hr Outlook (0600Z Oct 29)... 35% chance of subtropical cyclone formation (western Atlantic near 30.5N-69W)
IOH 72 Hr Outlook (0600Z Oct 30)... 10% chance of subtropical cyclone formation (southwest of Bermuda near 30.5N-68W)
IOH 96 Hr Outlook (0600Z Oct 31)... 0% chance of subtropical cyclone formation (just southwest of Bermuda near 30.5N-66.5W)
AREA OF INTEREST #43... The surface tropical wave of low pressure in the eastern Caribbean Sea has not yet slowed down in its westward track while already reaching 67.5W longitude per the latest NHC TAFB surface analysis... and this is also supported by the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=). Meanwhile upper divergence on the southeast side of the upper trough associated with area of interest (AOI) #42 has been producing rounds of thunderstorms across the northeastern Caribbean islands while the outflow of the upper ridge cell in the southeastern Caribbean has supported thunderstorm activity close to the north coast of Venezuela. However satellite animation is not suggesting an increase in surface rotation to the east of the tropical wave and within this activity... and the CIMSS 850 mb vorticity product agrees. Therefore it appears the potential for Caribbean tropical development is shifting further west... and models have been trending toward that direction. Therefore my updated forecast track in the outlook below has a notable wesward shift compared to my previous outlook.
Due to the surface ridge weakness associated with AOI #42... it does seem reasonable that the tropical wave of low pressure will eventually slow down its westward speed through day 4 as the models have been hinting at. I have lowered short-term odds of tropical cyclone formation... and have also avoided raising longer term odds above 30% in this update cycle... as their has been no progress so far in an organzing tropical low pressure rotation forming and the more west position of the seedling tropical wave places it closer to westerly wind shear associated with the upper trough of AOI #42. Eventually the shear is forecast to relax as the upper trough weakens from its ongoing isolation from high-latitude cold air... with the upper trough also eventually shifting eastward and away... allowing the southeastern Caribbean upper ridge cell to expand northwestward. Because the core of the expanding upper ridge (where shear is low and upper outflow is maximum) will be located further south toward the South American coastline... the forecast track in the outlook below shows a further south system moving along 12N latitude. Also noting a couple of other steering factors that favor a westward track staying in proximity to this latitude for the longer term:
(1) Upper troughing is expected to increase over the southeastern US during the latter part of the forecast period... a merger between the south part of the current western US upper trough and the south part of yet another upper trough that slides across North America. This upper troughing is expected to push the current Mexico upper ridge into the northwestern Caribbean... with the northwestern upper ridge cell promoting an ongoing westward track even if this system were to become stronger/taller. If the northwestern upper ridge cell merges with the southeastern Caribbean upper ridge cell... this will also embed this system in a vast area of upper anticyclonic flow with no net effect in steering this system (therefore a merged expansive upper ridge cell will not be able to pull this system north either)
(2) Models have also continued to trend with weaker southeastern US upper troughing (the 1800Z GFS even suggested the upper troughing by 0600Z November 2 splitting into one piece of energy heading into the western Atlantic and another lagging behind over the south-central US instead of a cohesive single piece of stronger energy as shown before). This will result in a weaker western Atlantic surface low pressure field to be supported by the eastern divergence zone of the upper troughing such that the surface low pressure field will struggle to pull this system north. This will also result in a weaker eastern US/Gulf of Mexico surface ridge to be supported by the western convergence zone of the upper troughing... however this surface ridge will still be strong enough to recover the steering surface easterly trade winds. A slightly faster westward track by day 5 in the outlook below is a reflection of the recovering surface trades.
Due to the shift in the latest forecast... here are updates regarding the impact to land areas:
(1) The potential for gusty winds and heavy rains directly from this system have decreased for the Virgin Islands... Puerto Rico... the eastern Dominican Republic... and the north-central and northeastern coast of Venezuela.
(2) The ABC Islands (Aruba Bonaire and Curacao)... northwest coast of Venezuela... and the Guajira peninsula of northern Colombia should watch for the potential development of heavy rainfall and gusty winds within the next three days.
(3) Interests in Central America should be aware of this system as the latest model trends hint at a long-range track of this system toward the area.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Oct 28)... 0% chance of tropical cyclone formation (ABC Islands near 12N-69W)
IOH 48 Hr Outlook (0600Z Oct 29)... 0% chance of tropical cyclone formation (just northeast of the Guajira peninsula of northern Colombia near 12N-70.5W)
IOH 72 Hr Outlook (0600Z Oct 30)... 10% chance of tropical cyclone formation (just northwest of the Guajira peninsula of northern Colombia near 12N-72.5W)
IOH 96 Hr Outlook (0600Z Oct 31)... 20% chance of tropical cyclone formation (south-central Caribbean Sea near 12N-74.5W)
IOH 120 Hr Outlook (0600Z Nov 1)... 30% chance of tropical cyclone formation (south-central Caribbean Sea near 12N-77.5W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Oct 26) CMC Model Run...
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low near 30.5N-67.5W at 42 hours... drifts west-northwest to 31.5N-69.5W through 66 hours... turns east in track and passes just south of Bermuda through 102 hours... reaches 31.5N-61.2W by 120 hours.
**For area of interest #43... eastern Caribbean tropical wave currently at 66W longitude evolves into tropical low in the central Caribbean near 13N-76W at 114 hours... tropical cyclone formation suggested near 14.5N-79.5W at 144 hours.
1200Z (Oct 26) ECMWF Model Run...
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low near 29N-68W at 42 hours... drifts north-northwest to 31N-69.5W through 78 hours... drifts east-southeast to 30N-68W through 108 hours... drifts northeast to a position west-southwest of Bermuda and near 31N-67.5W through 126 hours.
**For area of interest #43... eastern Caribbean tropical wave currently at 66W longitude evolves into tropical low in the central Caribbean near 13.8N-70.2W at 96 hours... tropical low drifts northwest to 14.5N-71.5W through 120 hours.
1800Z (Oct 26) GFS Model Run...
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low near 25.5N-67.5W at 21 hours... surface low continues north to 30.5N-68.5W through 48 hours where subtropical cyclone formation forecast... subtropical cyclone turns northwest to 31.8N-69.5W through 69 hours... while weakening to a remnant low drifts east-southeast to 31N-67.5W through 102 hours... remnant low turns northeast and reaches a position just northwest of Bermuda through 120 hours.
**For area of interest #43... Interaction of tropical wave currently at 66W... outflow of southeastern Caribbean upper ridge cell... and divergence on southeast side of cut-off upper trough assoicated with AOI #42 produces a tropical low near 13.5N-67.5W at 81 hours... tropical low drifts northwest while strengthening to a tropical cyclone reaching 15N-70W through 120 hours.
1800Z (Oct 26) NAVGEM Model Run...
**For area of interest #42... eastern divergence zone of cut-off upper trough in the western Atlantic produces a surface low near 24.5N-67W at 12 hours... surface low continues north-northwest to 30N-68.5W through 36 hours where subtropical cyclone formation is forecast... subtropical cyclone continues north-northwest to 32.5N-69W through 72 hours... afterwards drifts east-northeast while weakening to a remnant low with the remnant low passing just north of Bermuda at 114 hours... remnant low reaches 34N-64W at 120 hours.
**For area of interest #43... eastern Caribbean tropical wave currently at 66W longitude evolves into tropical low south of the Dominican Republic and located near 16N-70W at 78 hours... while moving northwest across the Dominican Republic and Haiti the tropical low weakens to a surface trough through 102 hours... surface trough redevelops into a tropical low between eastern Cuba and the central Bahamas at 126 hours.