*******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.*********
...UPDATE...FRIDAY OCTOBER 18 2024 1:17 PM EDT...
The surface and upper air charts valid for October 17 have been added below.
...THURSDAY OCTOBER 17 2024 3:10 PM EDT...
For areas of interest being monitored for tropical development... have resumed issuing 24-hourly points for my outlooks as Atlantic tropical activity is calm enough and my personal life activity is back to a level where I can do so (this is different from the last several posts where I issued shorthand outlooks more similar in format to the National Hurricane Center). Their remain three areas of interest for possible Atlantic tropical development as follows:
(1) A central Atlantic tropical wave of low pressure which continues to have development potential while moving into the northern Caribbean Islands over the next three days... see area of interest #40 section below for details.
(2) A broad area of low pressure moving into the northwestern Caribbean which may gradually develop within the next couple of days in the waters offshore of Honduras and Belize and before landfall... see area of interest #42 section below for details.
(3) A currently developing surface frontal cyclone between the mid-Atlantic United States and Bermuda which has a short window of time to acquire some tropical characteristics... see area of interest #43 section below for details.
AREA OF INTEREST #40... The surface tropical wave of low pressure that continues to churn west across the central tropical Atlantic... and toward the northern Caribbean Islands... continues to show signs of organization with curved thunderstorm bands around its surface swirl center. The track of this system has been steady to the west around 17N latitude (with swirl center passing near 17N-55W as of 1200Z today)... and will potentially bend more north toward 18N latitude in the next 24 hours while rounding the southwest edge of the steering Atlantic surface ridge. The track then continues west into the northern Caribbean Islands through day 3 as the strong eastern US surface ridge begins to expand into offshore western Atlantic waters. Regarding development potential... in the short-term it appears the organized thunderstorm bands have been pushed to the northwest side of the surface swirl by southeasterly shear related to recent developments with the sprawling mid-ocean upper anticyclone/ridge. The strongest part of the upper anticyclone has been weighted toward the eastern Atlantic... with the stronger part of the anticyclone sending much of the central Atlantic to east Caribbean upper vorticity towards the north (instead of continuously west and away from the surface tropical wave of interest) which has allowed the now north-south oriented axis of upper vorticity to split the anticyclone into one in the eastern Atlantic and another in the western Caribbean. In turn southeasterly shear imparted by the southwest quadrant of the eastern Atlantic upper anticyclone has increased over the surface tropical wave. However in the next 48 hours the shear should reduce... and upper outflow over the surface wave should remain optimal... as the two upper anticyclones are allowed to rejoin as the northern part of the upper vorticity is swept away by the upper trough now moving offshore from eastern North America and as the southern part of the upper vorticity fades from prolonged isolation from high-latitude cold air. Therefore I still forecast greater than 50% odds of tropical cyclone formation for the surface wave through 48 hours. By 72 hours northerly wind shear increases due to the approach of what will be the southwest cut-off tail of the current eastern North America upper trough... and combined with landfall with Hispaniola (Haiti and the Dominican Republic) I lower development odds to 0%. In the long range surface ridging over the eastern US remains strong enough to push this system west-southwest into and across the northwestern Caribbean Sea... a track that also takes this toward lower shear and increased outflow underneath ongoing western Caribbean upper anticyclonic flow (the surface ridging over the eastern US & western Atlantic is expected to remain intact in the long range due to the western convergence zone of the aforementioned southwest cut-off tail of the current eastern North America upper trough... as that tail of upper vorticity becomes re-enforced by packets of energy deposited into it by passing high-latitude upper troughs). Therefore if this system remains intact enough after passing the rugged terrain of Hispaniola... may have to extend my outlook points beyond October 20 to cover potential northwestern Caribbean development of this area of interest in future updates.
Regarding impact to land areas... expect heavy rainfall with flash flood potential (and mudslide potential in mountainous terrain)... gusty winds... and coastal surf for the northern Lesser Antilles... Virgin Islands... Puerto Rico... and the Dominican Republic from Friday through this weekend even if this system does not quiet become a tropical cyclone (Friday for more eastern locations... weekend for more western locations). Impacts to Haiti will likely be limited to heavy rainfall as this system likely weakens and becomes disrupted by interaction with the Dominican Republic beforehand. It is too early to know about impacts in the northwestern Caribbean beyond Haiti... as that will depend on how intact this system is after its interaction with Hispaniola.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 18)... 70% chance of tropical cyclone formation (just northeast of the northern Lesser Antilles near 18N-61W)
IOH 48 Hr Outlook (1200Z Oct 19)... 60% chance of tropical cyclone formation (Puerto Rico near 18N-66W)
IOH 72 Hr Outlook (1200Z Oct 20)... 0% chance of tropical cyclone formation (south coast of the Dominican Republic near 18N-71W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 30%
Same probabilities issued by NHC at 2 PM EDT
AREA OF INTEREST #42... The sprawling central Caribbean surface tropical low has lifted northward across the waters just east of Nicaragua and Honduras... instead of west for an early landfall with these locations... due to the surface ridge weakness associated with area of interest (AOI) #43. However as that area of interest and associated upper trough now departing eastern North America shift east and away... the strong eastern US surface ridge will take over the steering and shift this system west across the northwestern Caribbean waters offshore of Honduras and Belize. My outlook below has been updated with this new forecast track. Upper-level winds are expected to remain conducive for tropical development as westerly shear overtop this disturbance... induced by the northwest side of the current western Caribbean upper anticyclone... drops as the upper anticyclone is allowed to re-expand in the wake of the departing aforementioned upper trough. Combined with the GFS model once again developing this system... longer time over warm Caribbean water on the updated forecast track... and ongoing signs of organization with curved thunderstorm bands defining the broad tropical low.... I have raised my peak odds of tropical cyclone formation to 50%. I lower odds of tropical cyclone formation to 0% by 72 hours due to land interaction with Belize... Guatemala... and southeastern Mexico. It is possible that the best-defined center of this broad system then attempts to develop over offshore Bay of Campeche or eastern Pacific waters beyond that time as regional upper winds remain favorable... as such may have to extend my outlook points beyond October 20 to cover potential Bay of Campeche development of this area of interest in future updates (meanwhile any eastern Pacific tropical development is not covered on this site... information on eastern Pacific activity is on the NHC site... hurricanes.gov).
Given the updated outlook... interests in northern Central America (Honduras... Belize... and Guatemala) as well as the southeastern Mexico provinces of southern Quintana Roo... southern Campeche... Tabasco... Chiapas... eastern Veracruz... and eastern Oaxaca should be on guard for possible tropical cyclone impacts including heavy rainfall... gusty winds... and coastal surf through early next week... with impacts arriving earlier (Friday and this weekend) for locations further east and later (early next week) for locations further west.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 18)... 40% chance of tropical cyclone formation (offshore of eastern Honduras near 17N-84.5W
IOH 48 Hr Outlook (1200Z Oct 19)... 50% chance of tropical cyclone formation (offshore of northern Belize near 17N-87W)
IOH 72 Hr Outlook (1200Z Oct 20)... 0% chance of tropical cyclone formation (inland southeastern Mexico just west of northwestern Guatemala near 17N-91.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 20%
NHC increased 48-hour and 7-day probabilities to 30% as of 2 PM EDT
AREA OF INTEREST #43... For the upper trough now departing eastern North America into the western Atlantic... the southwest tail part of the upper trough is becoming cut-off into a band of upper vorticity due to the strength of the current eastern US deep-layer ridge. Divergence on the east side of the upper vorticity band is strong enough to generate a rapidly forming surface frontal cyclone (currently a new frontal low) offshore of the mid-Atlantic United States. Over the next 24 hours the frontal cyclone pulls in the coldest part of the upper vorticity directly over itself... resulting in the upper vorticity and surface frontal cyclone becoming vertically stacked where the surface frontal cyclone will begin a classical post-mature decay phase due to a lack of divergence directly beneath the core of the upper vorticity. However during this decay phase the surface system will be parked over warm Gulf stream waters still running at 26 deg C... and the temps of the overhead upper vorticity are cold enough to add instability needed for thunderstorms. Therefore upgrading this system to an area of interest for possible tropical development. Beyond 24 hours... the upper layers of the eastern US deep-layer ridge begin to erode from approaching energy associated with high-latitude upper troughs... however the surface layer of the ridge remains strong enough to capture the surface low... sending the surface low south into Bermuda through 48 hours... then southwest beyond that time. This track decouples the surface low from the coldest de-stabilizing temps of the overhead upper vorticity as the upper vorticity continues to shift east... and also exposes the decaying surface low to northerly wind shear and suppressive upper convergence on the back west side of the shifting upper vorticity. I have assigned a low 20% chance of tropical development as the conditions ideal for tropical activity are already gone by 48+ hours... and I assess this system is more likely to be subtropical instead of fully tropical due to the short window of time of ideal conditions which greatly limits the potential for any core thunderstorm activity lasting long enough to generate warm core upper outflow needed for fully tropical status.
Regardless of tropical development or not... this system is likely to generate coastal surf for Bermuda and the mid-Atlantic coast of the United States within the next couple of days. Direct impacts to Bermuda such as gusty winds and heavy rain appear unlikely as the surface low will be far along in its decay phase... with shower and thunderstorm generation likely being capped by aforementioned upper convergence as this system slides across Bermuda.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 18)... 20% chance of subtropical cyclone formation (northwestern Atlantic near 37.5N-69.5W)
IOH 48 Hr Outlook (1200Z Oct 19)... 10% chance of subtropical cyclone formation (just north of Bermuda near 35N-65W)
IOH 72 Hr Outlook (1200Z Oct 10)... 0% chance of subtropical cyclone formation (just southwest of Bermuda near 31N-66W)
*****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 17) CMC Model Run...
**For area of interest #40... passes across the northern Caribbean Islands including Cuba and the Cayman Islands through 114 hours... develops into a tropical low thereafter which drifts southwest toward Honduras through 168 hours
**For area of interest #42... no development shown
**For area of interest #43... surface low reaches peak strength midway between Massachusetts and Bermuda through 36 hours... subsequently dives south while weakening with the center passing just east of Bermuda by 66 hours... subsequently turns southwest into the waters southwest of Bermuda through 90 hours while dissipating
0000Z (Oct 17) ECMWF Model Run...
**For area of interest #40... no development shown
**For area of interest #42... no development shown
**For area of interest #43... surface low reaches peak strength midway between Massachusetts and Bermuda through 42 hours... subsequently dives south while weakening with the center passing just east of Bermuda between 63 and 66 hours... subsequently turns southwest into the waters southwest of Bermuda through 90 hours while dissipating
0600Z (Oct 17) GFS Model Run...
**For area of interest #40... no development shown
**For area of interest #42... possible tropical cyclone formation suggested by 60 hours as center makes landfall at the Belize/Mexico border... inland remnant low continues WSW into southeastern Mexico (toward Isthmus of Tehuantepec) and dissipates by 90 hours
**For area of interest #43... surface low reaches peak strength midway between Massachusetts and Bermuda through 36 hours... subsequently dives south while weakening with the center passing over Bermuda at 63 hours... subsequently turns southwest into the waters southwest of Bermuda through 84 hours while dissipating
0600Z (Oct 17) NAVGEM Model Run...
**Not available at above-mentioned source
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