*******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 SEPTEMBER 19 2024 1:07 AM EDT...
After Gordon degenerates into a remnant low in the open central Atlantic... it appears multiple areas of interest for possible Atlantic basin tropical development are beginning to appear... one of which is ex-Gordon itself which has a chance to make a comeback... see area of interest #29 section below for ex-Gordon. The following is more information on the areas of interest in addition to ex-Gordon:
(1) For the eastern tropical Atlantic... dry Saharan air has capped development for recent disturbances that have rolled offshore from Africa. However the regional tropical upper ridge axis featuring low shear and outflow is expected to persist... and some recent model runs indicate that additional tropical waves of low pressure that roll offshore from western Africa in 5+ days may develop. Therefore may need to add an area of interest in the eastern tropical Atlantic in future updates.
(2) In the mid-latitudes of the central Atlantic... a frontal low has recently drifted west to 30N-55W while undergoing a fujiwhara interaction with ex-Gordon. The frontal low is expected to be quasi-stationary here over the next few days while under conflicting steering between ex-Gordon to the east and any western Atlantic frontal lows that will be generated by the current large-scale eastern US upper vorticity. Although thunderstorm activity has recently increased just north of the center... two rounds of wind shear are currently expected to suppress this system's future tropical development... the first round from the currently approaching upper vorticity just to the west... and the second round when much of the current eastern US upper vorticity finally moves into the western Atlantic. However should future wind shear forecasts shift to just a little less wind shear... that may be enough to consider upgrading this frontal low to an area of interest for possible tropical development in future updates.
(3) Watching to see if any frontal lows that develop in the mid-latitudes of the western Atlantic in the days ahead... under the divergence zone of the large-scale eastern US upper vorticity... will acquire tropical characteristics... especially if any portion of the upper vorticity develops into a mid-latitude western Atlantic cut-off upper vortex featuring an eastern zone of low shear and increased upper divergence. Meanwhile models are converging on the southernmost portion of the upper vorticity diving south toward the western Caribbean and triggering a tropical disturbance there... see area of interest #30 section below for more information.
AREA OF INTEREST #29 (REMNANTS OF GORDON)... Looks like we are starting over with Gordon... after it once was thought that the tropical cyclone could strengthen in more favorable upper winds while moving north in the open central Atlantic... instead we are left with a northward-moving north-south elongated remnant low that now faces the prospect of less favorable than previously thought upper-level winds. The remnant low of Gordon is expected to curve northeast over the next 48 hours while completing a fujiwhara interaction with an adjacent frontal low to the northwest that is now positioned near 30N-55W. During this time a deep-layer north Atlantic cyclone is expected to materialize well north of ex-Gordon from the merger between the current north Atlantic frontal low... an upper trough that has recently exited eastern Canada... and another upper trough currently over eastern Canada. The low-level warm southerly flow on the southeast side of the deep-layer cyclone is expected to result in a warm-core deep-layer ridge between ex-Gordon and the deep-layer cyclone. To the west of ex-Gordon is approaching upper vorticity that recently separated from the large-scale eastern US upper vorticity... it was previously thought this upper vorticity would respond to the amplifying deep-layer ridge by amplify into an upper vortex that would keep shear low in ex-Gordon's environment. Instead the latest model runs show the approaching upper vorticity becoming stretched into a band by the amplifying deep-layer ridge... with the band spreading on top of ex-Gordon resulting in both increasing shear and suppressed upper outflow in the next 48 hours... thus I hold 0% odds of tropical cyclone formation during this time. Between 48 and 72 hours the upper vorticity band is expected to fade from prolonged isolation from high-latitude cold air... potentially allowing ex-Gordon to make a comeback in the lower shear/upper outflow environment of the deep-layer ridge's south side... with ex-Gordon also moving west-northwest while steered by the southwest edge of the deep-layer ridge's surface layer. Thus I assign a low 10% odds of tropical cyclone formation for that time... as the GFS and ECMWF model are no longer interested in re-developing Gordon while the usually less reliable CMC is the only model in the model summary section below that re-develops Gordon... and need to see how healthy ex-Gordon looks after it survives the next 48 hours of unfavorable upper-level winds before agreeing to assign higher odds for the 48 to 72 hour window. After 72 hours the north Atlantic deep-layer cyclone and eastern US upper vorticity finally team up to kick the deep-layer ridge east while driving a large-scale western Atlantic surface front toward ex-Gordon... with ex-Gordon turning north then northeast in the flow between the approaching front and deep-layer ridge. Wind shear over ex-Gordon gradually increases through 120 hours due to large scale upper southwesterly flow ahead of the merger between the eastern US upper vorticity and north Atlantic deep-layer cyclone... however I still allow for 10% odds of tropical cyclone formation at 96 hours as the shear levels may not be high enough yet to hinder development. I drop odds of development back to 0% by 120 hours with the increased shear... movement northeast into cooler waters... and absorption by the approaching western Atlantic surface front.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 20)... 0% chance of tropical cyclone formation (central Atlantic near 24N-47W)
IOH 48 Hr Outlook (0000Z Sep 21)... 0% chance of tropical cyclone formation (central Atlantic near 26N-44W)
IOH 72 Hr Outlook (0000Z Sep 22)... 10% chance of tropical cyclone formation (central Atlantic near 27.5N-46W)
IOH 96 Hr Outlook (0000Z Sep 23)... 10% chance of tropical cyclone formation (central Atlantic near 32N-46W)
IOH 120 Hr Outlook (0000Z Sep 24)... 0% chance of tropical cyclone formation (central Atlantic near 38.5N-41.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT*************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 50%
AREA OF INTEREST #30... The south part of the large-scale upper vorticity over the eastern United States... currently over Florida... is expected to dive south toward the western Caribbean over the next 72 hours under the influence of the current Mexico warm core upper ridge which will amplify across the eastern United States in warm southerly flow ahead of a series of frontal lows to move north across western North America. By 72 hours the eastern divergence zone of the upper vorticity is currently expected to increase thunderstorm activity and drop surface pressures in the western Caribbean. In between 72 to 120 hours (days 3 to 5) the upper vorticity then splits into two pieces... with the southwestern piece retrograding westward and away into the southwestern Gulf of Mexico under the influence of the eastern United States upper ridge and the remainder of the upper vorticity continuing east toward ex-Gordon (area of interest #29). An expanding upper anticyclone... featuring low shear and outflow... is expected to materialize between the two pieces of upper vorticity which will continue to support dropping surface pressures and thunderstorms... and a tropical disturbance with tropical cyclone formation potential is likely to materialize. Through day 5... I assign a low 20% peak odds of tropical cyclone formation as the models tend to develop this system just after day 5. My low odds of development are also a reflection of land interaction along my current track forecast which pushes this system slowly west toward the Belize/Mexico border toward day 5... under the influence of a remainder narrow surface ridge that persists along the United States east coast in the eastern convergence zone of the eastern United States upper ridge. I recommend interests along the Caribbean coast of Belize and the Yucatan to monitor the progress of this area of interest in the days ahead... for possible tropical cyclone impacts late this weekend.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 20)... 0% chance of tropical cyclone formation (between Florida and Cuba near 24N-81W)
IOH 48 Hr Outlook (0000Z Sep 21)... 0% chance of tropical cyclone formation (southeast of the Isle of Youth of western Cuba near 20.5N-82W)
IOH 72 Hr Outlook (0000Z Sep 22)... 0% chance of tropical cyclone formation (western Caribbean Sea near 18.8N-85W)
IOH 96 Hr Outlook (0000Z Sep 23)... 10% chance of tropical cyclone formation (offshore of the southern Yucatan peninsula near 18.8N-96W)
IOH 120 Hr Outlook (0000Z Sep 24)... 20% chance of tropical cyclone formation (south coast of the Yucatan peninsula and just north of the Belize/Mexico border near 18.8N-86W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT*************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 30%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
1200Z (Sep 18) CMC Model Run...
**For Area of Interest #29... remnants of Gordon regains tropical cyclone status near 27N-44W at 48 hours… subsequently meanders in a clockwise loop then turns northwest and weakens back into a remnant low near 28.5N-46.5W at 102 hours… remnant low subsequently turns north and loses identity to incoming surface front to the west.
**For area of interest #30… tropical low develops just east of Nicaragua by 102 hours with tropical cyclone formation suggested just offshore of eastern Honduras at 120 hours… while continuing to strengthen the tropical cyclone center passes between the west tip of Cuba and northeast corner of the Yucatan peninsula at 156 hours… while gaining hurricane strength moves into the south-central Gulf of Mexico by 168 hours
**Central Atlantic frontal low currently NW of AOI #29 moves SW then west to 26N-60W through 90 hours… subsequently turns northeast and becomes a tropical cyclone while reaching 35N-47.5W through 168 hours
1200Z (Sep 18) ECMWF Model Run...
**For Area of Interest #29... remnants of Gordon move northeast… then northwest… then north over next few days without redevelopment shown
**For area of interest #30… rather broad tropical low slowly develops through 168 hours which moves northwest into the Yucatan peninsula and southwest Gulf of Mexico
**Broad tropical low emerges from west coast of Africa at 156 hours and reaches 13N-20W by 168 hours while potentially strengthening into a tropical depression
1800Z (Sep 18) GFS Model Run...
**For Area of Interest #29... remnants of Gordon move northeast… then northwest… then north over next few days without redevelopment shown
**For area of interest #30… broad tropical low develops north of Honduras from 105 to 114 hours… tropical cyclone formation suggested just southwest of the Cayman Islands by 147 hours… center of strengthening tropical cyclone moves toward the waters between west tip of Cuba and northeast corner of the Yucatan peninsula through 168 hours
**Through 120 hours large portion of current eastern US upper vorticity evolves into a cut-off upper vortex diving east-southeast toward Bermuda while its divergence zone triggers a surface cyclone that whirls into the core of the upper vortex which possibly becomes a subtropical cyclone centered WSW of Bermuda… surface cyclone weakens while drifting ESE into the waters just south of Bermuda through 168 hours due to a lack of divergence beneath the core of the upper vortex
**Tropical wave emerges from west coast of Africa at 96 hours… evolves into a tropical low that reaches 15N-37W through 168 hours
1800Z (Sep 18) NAVGEM Model Run...
**Not available at above-mentioned source
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