*******Note that forecasts 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 25 2024 2:05 PM EDT...
In the mid-latitudes of the eastern Atlantic... a surface trough of low pressure positioned along 27.5N latitude has materialized due to the divergence zone of upper vorticity that has been slowly working its way in from the central Atlantic. The surface trough has recently whirled westward to 40W longitude and beneath the core of the upper vorticity where boosting upper divergence is lacking. The surface trough is expected to move northwest into the open central Atlantic in the flow between the developing deep-layer ridge to the north and out ahead of an approaching surface cold front being driven by ex-Oscar... on this track... there is a brief window for the surface trough to undergo tropical development within the next 48 hours after escaping the suppressive convergence beneath the upper vorticity and before moving into cooler waters and merging with the incoming surface cold front. However given the short window of time for conditions conducive to tropical development... I have not upgraded the surface trough to an area of interest for tropical development at this time.
For the Caribbean Sea... continuing to watch for possible tropical development in the days ahead... see area of interest #44 section below for details.
AREA OF INTEREST #44... Over the last few days various model runs have hinted at tropical development in the Caribbean Sea. Today concentrated and persistent thunderstorm activity has developed offshore of Panama and Costa Rica with the support of outflow provided by the regional upper ridge/anticyclone. Surface convergence provided by tropical waves currently in the central Caribbean and east of the southern Lesser Antilles... provided by the arrival of an upper air divergence zone associated with upper vorticity currently offshore of western North America which will be parked over the Bahamas and northern Caribbean region by day 5... may further agitate weather in the central Caribbean region in the days ahead. And finally the NAVGEM has recently joined the GFS in suggesting some kind of development within the next week. Therefore have added an area of interest for possible tropical development in the central Caribbean... this is the forty-fourth such area of interest tracked on this site this year.
There are multiple possibilities regarding how the current thunderstorm cluster offshore of Panama and Costa Rica and aforementioned surface tropical waves of low pressure interact with the upper wind field in the days ahead... the outlook below is my current best stab at how I think the situation evolves:
(1) Over the next 48 hours I forecast the activity offshore of Panama and Costa Rica to persist due to the ongoing upper outflow... with the surface tropical wave currently in the central Caribbean arriving from the east. I currently forecast the surface wave to evolve into a tropical low in this region in the short-term.
(2) Beyond 48 hours... I forecast the tropical low to gradually evolve into a southwest-northeast tilted surface trough in the central Caribbean supported by split flow upper divergence between the aforementioned regional upper anticyclone and incoming upper vorticity that arrives into the Bahamas and northern Caribbean. During this time the tropical wave of low pressure currently east of the southern Lesser Antilles is likely to merge with the surface trough. My track forecast in the outlook below therefore reflects the idea of a tropical low offshore of Panama/Costa Rica gradually transitioning into a southwest-northeast tilted surface trough positioned toward the day-5 location of the aforementioned split flow upper divergence.
(3) I currently set my peak odds of tropical cyclone formation to a low 30% as a well-defined low-level spin is currently not in progress as seen in the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=). The low odds are also reflect the idea that this system could increasingly become large/broad in nature without a well-defined center due to the expansive upper outflow region of the upper anticyclone combined with the arrival of the upper divergence zone tied to the forecast day-5 northern Caribbean/Bahamas upper vorticity... and also due to this system potentially being a merger between multiple surface tropical waves as outlined above. For the 5-day window I set peak odds at 96 hours... after which time I trim the odds down due to increasing westerly shear associated with the incoming upper vorticity. Noting that my peak odds are not lower than 30% as this disturbance will have a preceding 4 days in a lower shear environment.
Given the current outlook... I recommend interests in eastern Nicaragua... eastern Honduras... and Jamaica monitor the progress of this area of interest in the days ahead.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 26)... 0% chance of tropical cyclone formation (offshore of Panama and Costa Rica near 10N-81W)
IOH 48 Hr Outlook (1200Z Oct 27)... 10% chance of tropical cyclone formation (offshore of Panama and Costa Rica near 10N-81W)
IOH 72 Hr Outlook (1200Z Oct 28)... 20% chance of tropical cyclone formation (offshore of southern Nicaragua near 11.5N-81.5W)
IOH 96 Hr Outlook (1200Z Oct 29)... 30% chance of tropical cyclone formation (offshore of the Nicaragua/Honduras border near 15N-82W)
IOH 120 Hr Outlook (1200Z Oct 30)... 20% chance of tropical cyclone formation (southwest of Jamaica near 16N-79.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT*************************
Not in the official outlook
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Oct 25) CMC Model Run...
**For area of interest #44... no development shown
0000Z (Oct 25) ECMWF Model Run...
**For area of interest #44... no development shown
0600Z (Oct 25) GFS Model Run...
**For area of interest #44.. tropical low forms in the south-central Caribbean near 12N-80.5W at 126 hours... while quasi-stationary becomes a tropical cyclone by 141 hours... while intensifying into a hurricane begins to move east-northeast while in a cyclonic orbit with deep-layer cyclonic flow associated with a subtropical disturbance to the north and reaches 15N-75W by 168 hours
**Upper vorticity shown to separate from southeast side of current upper vortex south of Alaska in next 24 hours... through 78 hours the upper vorticity dives southeast across the western and central US (in the flow on the back side of the current and eastward-shifting central North America upper trough) and arrives into the southeastern US... the upper vorticity then continues southeast into the western and central Bahamas where its eastern divergence zone triggers a surface low over the southeastern Bahamas by 132 hours... through 168 hours the surface low cyclonically whirls into the central Bahamas and toward the core of the upper vorticity while possibly becoming a subtropical cyclone.
1200Z (Oct 25) NAVGEM Model Run…
**For area of interest #44... rather road surface low pressure field materializes across central and western Caribbean... extending into the southeastern Bahamas through 150 hours... the lowest surface pressures become concentrated in the waters between Cuba and the central Bahamas through 168 hours
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