*******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.**********
...FRIDAY OCTOBER 28 2022 5:24 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. See area of interest #43 section below for an update on the also 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... The upper trough in the western Atlantic that has been cut-off from the mid-latitude westerlies continues to generate an area of low surface pressure with its eastern divergence zone. The area of low surface pressures continues to be structured as a north-south oriented surface trough... however the latest satellite imagery suggests a more consolidated surface circulation is developing near 29N-69W where the upper divergence maximum of the northwest-southeast tilted upper trough is located. For the outlook below... the forecast track in the next 24 hours remains the same as previous while projecting the surface circulation to shift north instead of northeast with the upper westerly flow due to the strength of the surface ridge approaching from the Great Lakes region of North America which will act as a blocking surface during the forecast period that will make it difficult for the surface circulation to move east. After 24 hours... the north fracture of the current central US upper trough is expected to slide into the northwest Atlantic. Most models remain in 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 24+ hour window despite the presence of the blocking surface ridge... therefore the longer range portion of the forecast track in the outlook below also remains the same while continuing to show an eastward drift.
Regarding odds of subtropical cyclone formation... the NHC as of this writing has lowered odds of development to 30% perhaps as the consolidating surface circulation has not fully formed yet... and the amount of time for upper-level winds to be conducive for subtropical development will be short-lived as the supporting western Atlantic upper trough will quickly lose its northwest-southeast tilt and associated upper divergence maximum while it tries to link with the north fragment of the central US upper trough as that fragment races into the Atlantic. In this update I prefer to retain a peak of 35% odds instead of lowering the odds as the consolidated surface circulation appears to be becoming well-defined quickly enough to still keep the door open for subtropical cyclone formation. For the 48 and 72 hour window... the aforementioned upper trough fragment from the north-central US 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 from 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 I taper down odds of subtropical cyclone formation from the peak during this window of time... ending the outlook at 72 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 24 hours... a short period of coastal surf may occur. 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 29)... 35% chance of subtropical cyclone formation (western Atlantic near 30.5N-69W)
IOH 48 Hr Outlook (0600Z Oct 30)... 10% chance of subtropical cyclone formation (southwest of Bermuda near 30.5N-68W)
IOH 72 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 transitioned into a slow-moving surface trough supported by the outflow of the nearby tropical upper ridge cell to the southeast and an area of upper divergence to the northwest associated with the upper trough tied to area of interest (AOI) #42. The latest satellite imagery suggests the surface trough has an associated comma-shaped region of cloudiness and thunderstorms covering eastern Venezuela... the Lesser Antilles... and the eastern Caribbean waters east of the surface trough. The activity is displaced east of the surface trough due to westerly shear imparted by the aforementioned upper trough. Based on the hook of the comma shaped cloud system... it could be argued that the maximum spin of the surface trough is a bit east of the previous forecast track presented in my previous update... therefore my updated forecast track in the outlook below is adjusted in that direction.
Overall this tropical disturbance is expected to continue west across the Caribbean Sea... at first slowly over the next 72 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 south part of the current 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 days 4 and 5 as a reflection of the recovering trades.
It is interesting to note the models have shifted north in track towards Jamaica instead of Central America while suggesting a consolidated center forming further north along the surface trough axis. However the hook of the current comma shaped cloud system which would be traditionally used for marking the location of maximum spin is already further 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 while at the same time adjusting the forecast track just slightly northward out of respect of the latest model consensus.
Regarding odds of tropical cyclone formation... the NHC has been gradually increasing development odds and as of this writing suggest a 60% peak by day 5. This is at odds with the latest model consensus which has backed off on showing development as the northward shift in the model solutions 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. While balancing the possiblity of this system encountering less favorable upper winds further north should it in fact consolidate in that direction... and the better organized comma shaped cloud pattern the disturbance is now displaying... I have also raised peak odds of tropical cyclone formation but only to 40% in this update cycle. By day 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 day 5.
Regarding the impact to land areas:
(1) Wind shear is expected to displace the heaviest weather associated with this system over eastern and central Venezuela as well as the Lesser Antilles over the next couple of days... flash flooding in this region cannot be ruled out.
(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 it has potential to track toward the region under improving upper-level wind conditions by 5+ days.
(4) Although the latest model consensus has 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 29)... 0% chance of tropical cyclone formation (just northeast of the ABC Islands near 12.5N-68.5W)
IOH 48 Hr Outlook (0600Z Oct 30)... 10% chance of tropical cyclone formation (just north of the western ABC Islands near 13N-69.5W)
IOH 72 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 96 Hr Outlook (0600Z Nov 1)... 30% chance of tropical cyclone formation (south-central Caribbean Sea near 13N-74W)
IOH 120 Hr Outlook (0600Z Nov 2)... 40% chance of tropical cyclone formation (south-central Caribbean Sea near 13N-78W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Oct 27) CMC Model Run...
**For area of interest #42... surface low forms just west of Bermuda at 24 hours and remains stationary through 48 hours... drifts southeast with the center passing just south of Bermuda by 66 hours... while located at 31N-57.5W at 114 hours becomes absorbed by developing frontal low to the east.
**For area of interest #43... tropical low forms near 14N-69.5W at 42 hours... tropical cyclone formation forecast east-southeast of Jamaica and near 17N-75W at 102 hours... weak tropical cyclone moves west-northwest across Jamaica through 120 hours.
1200Z (Oct 27) ECMWF Model Run...
**For area of interest #42... broad surface low forms just west of Bermuda at 54 hours... through 90 hours drifts southeast while weakening to a surface trough located just southwest of the island
**For area of interest #43... tropical low forms near 14.5N-70W at 60 hours... tropical low weakens to a trough just southeast of Jamaica at 126 hours.
1800Z (Oct 27) GFS Model Run...
**For area of interest #42... compact surface low forms near 29.5N-67.5W through 12 hours... turns northeast and east and moves across Bermuda through 69 hours while becoming less tropical and more elongated... continues east as a broad non-tropical low which reaches 32N-59.5W through 120 hours.
**For area of interest #43... tropical low forms near 14.5N-68.8W through 54 hours... weakens to a trough southeast of Jamaica through 120 hours.
1800Z (Oct 27) NAVGEM Model Run...
**For area of interest #42... surface trough drifts north to position just west of Bermuda through 48 hours... subsequently drifts west then northwest and dissipates near 35N-70W at 102 hours.
**For area of interest #43... tropical low forms near 14N-66W at 36 hours... tropical cyclone formation suggested just south of the eastern Dominican Republic at 66 hours... moves north-northwest across the eastern Dominican Republic as a weak tropical cyclone and begins to strengthen over the easternmost Bahamas by 102 hours... strengthening tropical cyclone forecast to stall over/near the easternmost Bahamas through 120 hours.