*******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.**********
...SATURDAY OCTOBER 29 2022 7:14 AM EDT...
See area of interest #42 section below for an update on the subtropical low pressure area now positioned just west of Bermuda. See area of interest #43 section below for an update on the currently slow-moving tropical disturbance currently located in the eastern Caribbean Sea.
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... A well-defined surface subtropical low pressure area has developed southwest of Bermuda over the last 24 hours... with this feature drifting north-northeast to a position due west of Bermuda as of late. The surface low has formed under the supportive eastern divergence zone of the upper trough in the western Atlantic that has been cut-off from the mid-latitude westerlies over the last few days. Going forward... the surface low will be interacting with the strong surface ridge to the north which will make it difficult for the surface low to move eastward... while at the same time the current shortwave upper trough approaching from the northeastern US will try to accelerate the western Atlantic upper trough and the surface low eastward. Models remain in agreement that the approaching shortwave upper trough and the surface ridge weakness it will create with its divergence zone will have more influence relative to the surface ridge... resulting in a net eastward drifting motion of the surface low. Therefore my updated forecast track in the outlook below continues to show an eastward motion... however the track forecast points are adjusted considering that the surface low is currently northeast of the previous forecast.
Regarding potential for subtropical cyclone formation... the upper wind environment will become increasingly hostile as the western Atlantic upper trough will begin to weaken and de-amplify while it remains cut-off from high-latitude cold air which will result in increasing wind shear. In addition the shortwave upper trough from the northeastern US will also approach in a de-amplified state... with the shear also being exacerbated by the surface ridge to the north preventing the surface low from rapidly accelerating eastward with the upper westerly flow. Given that subtropical cyclone formation has not yet occurred and the bleak upper wind forecast... the NHC as of late has lowered odds of subtropical cyclone formation to 20%. I have also lowered odds of development... but not quiet as far as the NHC... as the surface low has developed thunderstorm activity just north of the center and therefore have settled for a 30% peak in the development odds in this update cycle. I end the outlook by 48 hours while dropping development odds to 0% as the shear is forecast to be excessive for tropical development by that time. In the long range... the eastward-drifting surface low is forecast to transition into a less tropical low pressure system to be supported by the divergence zone of the shortwave upper trough to approach from the northeastern US... as that shortwave continues east across the Atlantic. On a final note regarding the outlook below... I use a subtropical instead of tropical designation as this system and its associated thunderstorm activity is being aided by an upper trough unlike a fully tropical system.
For Bermuda... this system has potential to produce periods of heavy rainfall and possibly gusty winds over the next 24 hours depending on how much subtropical development occurs.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Oct 30)...30% chance of subtropical cyclone formation (just west of Bermuda near 32N-65.5W)
IOH 48 Hr Outlook (0600Z Oct 31)...0% chance of subtropical cyclone formation (east of Bermuda near 32N-62.5W)
AREA OF INTEREST #43... A surface trough of low pressure and associated area of scattered showers and thunderstorms persists in the eastern Caribbean Sea while supported by the outflow of the nearby tropical upper ridge cell to the southeast. Overall this tropical disturbance is expected to continue west across the Caribbean Sea... at first slowly over the next 48 hours due to the surface ridge weakness associated with AOI #42. There are a couple of factors that favor a westward track as follows:
(1) Upper troughing is expected to increase over the southeastern US during the latter part of the forecast period... a merger between the current south-central 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 Central American 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.
(2) The western convergence zone of the upper troughing to settle over the southeastern US is expected to build a surface ridge over the eastern US and Gulf of Mexico. The surface ridge will recover the steering surface easterly trade winds in the Caribbean... the forecast track in the outlook below shows an increasing forward speed at 3+ days as a reflection of the recovering trades. A south bend in the forecast track by day 5 is a reflection of the forecast strength of the surface ridge expected during that timeframe.
It is interesting to note the models still prefer a more north track towards Jamaica instead of Central America while suggesting a consolidated center forming further north along the surface trough axis. However the most concentrated thunderstorm activity on this disturbance remains toward the south. Also the upper trough associated with AOI #42 is forecast to weaken while remaining cut-off from high-latitude cold air while the upper trough is also forecast to shift east and away... allowing the upper ridge cell to the southeast to expand in its wake. The outflow maximum of this expanding upper ridge cell will also be located further to the south... therefore I have maintained a further south track in this update cycle.
Regarding odds of tropical cyclone formation... the NHC has been gradually increasing development odds and as of this writing suggest a 70% peak by day 5. This is at odds with the latest model consensus which has backed off on showing development as the northward trends in the model consensus brings this system closer to shearing upper westerlies associated with the upper trough tied to AOI #42 in the short-term... and then closer to a string of shearing and outflow suppressing central Caribbean upper vorticity that seperates from this upper trough and becomes trapped between the northwestern and southeastern Caribbean upper ridge cells mentioned in the prior paragraph. Due to the possiblity of this system encountering less favorable upper winds further north should it in fact consolidate in that direction... I retain a lower 40% peak odds of development in this update cycle. By days 4 and 5 it is likely that the string of disrputive central Caribbean upper vorticity dissipates while it remains cut-off from cold air... therefore my peak 40% odds of development are reserved for that timeframe.
Regarding the impact to land areas:
(1) 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 couple of days.
(2) Interests in Central America should be aware of this system as it has potential to track toward the region under improving upper-level wind conditions by 5+ days.
(4) Although the latest model consensus remains shifted northward toward Jamaica instead of Central America in the long range... the models have also correspondingly backed off in the intensity forecast. As discussed in the previous paragraph upper-level winds toward the north are expected to be less favorable for tropical cyclone formation... therefore signficant gusty wind and heavy rain impacts to Jamaica appear unlikely at this time.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Oct 30)... 10% chance of tropical cyclone formation (just north of the western ABC Islands near 13N-69.5W)
IOH 48 Hr Outlook (0600Z Oct 31)... 20% chance of tropical cyclone formation (just north-northeast of the Guajira peninsula of northern Colombia near 13N-71W)
IOH 72 Hr Outlook (0600Z Nov 1)... 30% chance of tropical cyclone formation (south-central Caribbean Sea near 13N-74W)
IOH 96 Hr Outlook (0600Z Nov 2)... 40% chance of tropical cyclone formation (south-central Caribbean Sea near 13N-78W)
IOH 120 Hr Outlook (0600Z Nov 3)... 40% chance of tropical cyclone formation (east of Nicaragua near 12N-81W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z (Oct 29) CMC Model Run...
**For area of interest #42... surface low drifts north-northwest to 32.5N-66.5W through 12 hours... afterwards drifts east as a weaker and less tropical low that passes just north of Bermuda at 42 hours... remnant non-tropical low accelerates east-southeast and while located near 31.5N-56W at 96 hours becomes absorbed by developing frontal low to the northeast.
**For area of interest #43... tropical low forms just northeast of the ABC Islands at 12 hours... tropical cyclone formation suggested near 14.8N-70.5W at 30 hours... moves west-northwest into Jamaica as a weak and compact tropical cyclone by 84 hours... passes through the Cayman Islands as a weak and compact tropical cyclone by 102 hours... turns west-southwest in track and begins to strengthen in the western Caribbean near 18.2N-85W at 126 hours
1200Z (Oct 28) ECMWF Model Run...
**For area of interest #42... surface low drifts north-northwest to 32N-67.5W through 18 hours... subsequently turns east with the center passing over Bermuda at 48 hours... subsequently moves east-northeast as a broadening and less tropical remnant low that reaches 36N-54W through 120 hours.
**For area of interest #43... tropical low forms near 15N-72.5W at 54 hours... tropical low weakens to a trough south of the Cayman Islands at 102 hours
0000Z (Oct 29) GFS Model Run...
**For area of interest #42... surface low drifts north-northwest to 32.2N-67.5W through 12 hours... subsequently turns east with the center passing just north of Bermuda at 36 hours... subsequently evolves into a complex and less tropical remnant low by 45 hours with the original center located just northeast of Bermuda and a second northwestern center near 35N-66W induced by the divergence maximum of a shortwave upper trough that ejects from the northeastern US... northwestern center becomes the dominant center while strengthening and passes just north of Bermuda at 60 hours... remnant non-tropical center of this system accelerates east and reaches 36N-48.5W at 120 hours.
**For area of interest #43... tropical low forms near 14.8N-66.5W at 24 hours... weakens to a trough southeast of Jamaica at 90 hours.
**Upper troughing increases over the southeastern US as current upper trough over the south-central US merges with south side of additional upper trough that moves across North America through 84 hours... upper troughing moves offshore into western Atlantic through 168 hours with split flow upper divergence between the south side of the upper troughing and east side of Caribbean upper ridging produces a southern Caribbean tropical low near 12N-79W.
0000Z (Oct 29) NAVGEM Model Run...
**For area of interest #42... surface low drifts north-northwest to 32.5N-68.5W through 12 hours... subsequently turns east while transitioning into a more elongated and less tropical low pressure that passes just north of Bermuda at 48 hours... remnant non-tropical low reaches 35N-49W at 120 hours.
**For area of interest #43... tropical low forms near 15N-69.5W at 12 hours... tropical cyclone formation suggested at 42 hours as the tropical low drifts north-northwest toward the Dominican Republic... weakens to a remnant low while moving across the western Dominican Republic through 66 hours... remnant low turns west and passes just south of the eastern Bahamas at 84 hours... redevelops into a tropical depression that moves into eastern Cuba through 120 hours.