*******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 SEPTEMBER 20 2024 1:15 PM EDT...
In the open central Atlantic... continuing to see if the remnant low of Gordon will make a comeback in the days ahead... see area of interest #29 section below for more details. Attention is also turning toward Honduras... Belize... the Yucatan peninsula... and surrounding southern Gulf of Mexico and Caribbean waters for possible tropical cyclone formation with impacts to land areas... see area of interest #30 section below for more information. In addition two these two areas of interest... monitoring the following:
(1) The former frontal low quasi-stationary near 25N-55W has been upgraded to a tropical low with potential for tropical development in the days ahead... see area of interest #31 section below for more details.
(2) For the eastern tropical Atlantic... the tropical wave of low pressure that was near 32.5W longitude has since been cancelled in the NHC TAFB surface analysis... however it appears in satellite pictures there is a broad surface trough of low pressure in the region resulting from the merger between this wave and another wave to the east that rolled off of Africa on September 15. Based on the cyclonic curvature of cloudiness with scattered thunderstorms near the west coast of Africa... it appears another such tropical wave will soon exit the west coast and merge with the surface trough. The surface trough is not showing signs of development due to regional dry Saharan air. However there are model runs that insist that additional waves of low pressure that roll offshore from Africa... in 3+ days... may develop underneath the persistent regional tropical upper ridge axis. Therefore may need to add an area of interest in the eastern tropical Atlantic in future updates.
(3) The current upper vorticity entering the western Atlantic from the eastern United States is forecast to stack with the current northwest Atlantic frontal low... resulting in a deep-layer cyclone in the days ahead. The deep-layer cyclone is forecast to dive southeast toward Bermuda in response to the amplification of an upper ridge over the eastern United States while its east side potentially absorbs area of interest #31 (see area of interest #30 section below for more information on the eastern United States upper ridge). Will watch to see if the surface layer of the cyclone acquires tropical characteristics on its southeast dive into toward warmer waters... and declare an area of interest for Bermuda and vicinity in future updates if needed.
AREA OF INTEREST #29 (REMNANTS OF GORDON)... In the open central Atlantic... ex-Gordon has turned increasingly northeast due to the steering provided by the adjacent surface low to the west (now area of interest #31) and a string of upper vorticity that has spread overtop ex-Gordon while stretched and pushed by the developing warm core deep-layer ridge to the northwest. Due to the southwest-northeast tilt of the upper vorticity... southwesterly wind shear has increased over ex-Gordon which has pulled the thunderstorms east and away from ex-Gordon's surface low pressure center and I assign a 0% chance of tropical cyclone formation through 24 hours. After that time the shear relaxes... upper outflow over ex-Gordon increases... and the track reverses to a west turn through 48 hours as the upper vorticity string fades from prolonged isolation from high-latitude cold air which allows the passing deep-layer ridge to the north to take over ex-Gordon's steering and upper-level wind pattern. In between 48 and 96 hours ex-Gordon is then forecast to take an increasingly north then northeast turn as the steering deep-layer ridge gets pushed east by the current northwest Atlantic frontal low and its upper vorticity... with ex-Gordon rounding the west side of the eastward-shifting ridge. I have increased my peak odds of tropical cyclone formation to 20% within this window as the latest model runs show less shear with the upper-layers of the deep-layer ridge's west side still covering ex-Gordon through 72 hours (instead of previous model runs which had linear and hence shearing upper southwesterly flow associated with the upper vorticity tied to the approaching northwestern Atlantic frontal low covering ex-Gordon). I did not select higher odds than 20% 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 also need to see how healthy ex-Gordon looks after it survives the next 24 hours of unfavorable upper-level winds before agreeing to assign higher peak odds. By 96 hours ex-Gordon moves into cooler waters... and also merges with a surface front linking the approaching northwest Atlantic frontal low to a deep-layer north Atlantic cyclone... thus I end my outlook at that time by dropping development odds back to 0%.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 21)... 0% chance of tropical cyclone formation (central Atlantic near 27N-42.5W)
IOH 48 Hr Outlook (1200Z Sep 22)... 10% chance of tropical cyclone formation (central Atlantic near 29N-44W)
IOH 72 Hr Outlook (1200Z Sep 23)... 20% chance of tropical cyclone formation (central Atlantic near 32.5N-45W)
IOH 96 Hr Outlook (1200Z Sep 24)... 0% chance of tropical cyclone formation (central Atlantic near 37.5N-40W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 20%
AREA OF INTEREST #30... The south part of the large-scale upper vorticity that is now edging into the Atlantic from the eastern United States... which has been pushed south into the east coast of the Yucatan peninsula by the amplifying Mexico warm core upper ridge... is beginning to produce a Caribbean area of disturbed weather just east of Nicaragua and Honduras with its eastern upper divergence zone... however tropical cyclone formation is not expected in the near-term due to wind shear also induced by the upper vorticity. After 48 hours the wind shear begins to relax due to the following upper-level wind evolution... (1) the Mexico warm core upper ridge continues to amplify across the eastern United States due to warm southerly flow ahead of a series of forecast central North America frontal lows... (2) The upper ridge pushes the upper vorticity over the Yucatan westward and away into the southwestern Gulf of Mexico... (3) the remainder of the upper vorticity near the United States east coast continues east and away toward areas of interest #31 and #29... (4) a shear-reducing and outflow enhancing upper anticyclone develops and expands over this disturbance and in between the two pieces of departing upper vorticity. I currently forecast whatever surface low pressure field that develops to move slowly west toward Belize or the southeast coast of Mexico's Yucatan peninsula while pushed by the weak steering provided by the remainder and narrow east US coast surface ridge that will be supported by the eastern convergence zone of the eastern US upper ridge. After landfall with Belize and the Yucatan... in 5+ days I currently expect a northwest turn toward the southern Gulf of Mexico while this system edges toward the ridge weakness associated with one of the forecast central North America frontal lows. For the next five days... I assign a low 20% peak odds of tropical cyclone formation as the models tend to develop this system after day 5. My low odds of development are also a reflection of the land interaction with Belize and the Yucatan along my current track forecast... and I dip the odds back to 0% on day 5 when this system is most likely to be inland. However note that in future updates the 5-day position will likely be over Gulf of Mexico waters and so I expect to issue higher long term odds of development for this area of interest in future updates. I recommend interests along the Caribbean coasts of Honduras... Belize... and the Yucatan to monitor the progress of this area of interest in the days ahead... for possible tropical cyclone impacts (gusty winds and coastal surf) late this weekend through early next week. This system may also bring prolonged periods of heavy rainfall with flash flooding potential to coastal and inland areas as well.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 21)... 0% chance of tropical cyclone formation (just offshore of the Nicaragua/Honduras border near 15.2N-82.5W)
IOH 48 Hr Outlook (1200Z Sep 22)... 0% chance of tropical cyclone formation (northeast coast of Honduras near 16N-84.5W)
IOH 72 Hr Outlook (1200Z Sep 23)... 10% chance of tropical cyclone formation (just offshore of north-central Honduras near 16.2N-85.8W)
IOH 96 Hr Outlook (1200Z Sep 24)... 20% chance of tropical cyclone formation (just offshore of Belize near 17N-87.5W)
IOH 120 Hr Outlook (1200Z Sep 25)... 0% chance of tropical cyclone formation (inland Belize/ Guatemala/ Mexico border intersection near 17.5N-89.1W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 40%
AREA OF INTEREST #31... The frontal low that has been parked near 25N-55W has lost air mass contrasts across it... and because it has also fired occasional thunderstorms near its center it has been upgraded to a tropical low that the NHC is now monitoring for possible tropical cyclone formation... this marks the thirty-first area of interest tracked on this site this year. Through 48 hours the tropical low is likely to be quasi-stationary while in conflicting steering between ex-Gordon (area of interest #29) to the east and current northwestern Atlantic frontal low. After that time the northwest Atlantic frontal low dives southeast toward this area of interest... causing this area of interest to lift north then northwest while pulled into the northeast side of the frontal low where it could then become absorbed by the frontal low. Regarding odds of tropical cyclone formation... the upper wind forecasts have shifted toward less southwesterly wind shear... giving another reason its plausible that the tropical low was upgraded to an area of interest. Within the next 48 hours the southwesterly shear levels have potential to drop as the upper vorticity string currently in the tropical low's environment drifts west and away under the influence of the same deep-layer ridge that will be steering ex-Gordon (area of interest #29). The models have shifted toward a more amplified signature associated with the upper vorticity tied to the incoming northwestern Atlantic frontal low... and the upper-level wind profile becomes more conducive for potential tropical development by 72 hours while this system is exposed to less linear upper southwesterly flow on the east side of the incoming upper vorticity that also features increased divergence. Due to the fact the global models are shy to develop this system... and the fact the tropical low currently does not have a well-defined center in visible satellite animation and also lacks thunderstorms near its center... I agree with the NHC's low peak 20% odds of tropical cyclone formation. I assign my peak odds of development in the 72 to 96 hour window when the upper-level wind profile is at its best as discussed above... and dip below that peak by 120 hours when this system is at increased risk of being absorbed by the incoming northwestern Atlantic frontal low if it hasn't developed into a tropical cyclone by then.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 21)... 10% chance of tropical cyclone formation (central Atlantic near 25N-55W)
IOH 48 Hr Outlook (1200Z Sep 22)... 10% chance of tropical cyclone formation (central Atlantic near 25N-55W)
IOH 72 Hr Outlook (1200Z Sep 23)... 20% chance of tropical cyclone formation (central Atlantic near 27.5N-55W)
IOH 96 Hr Outlook (1200Z Sep 24)... 20% chance of tropical cyclone formation (central Atlantic near 32N-55W)
IOH 120 Hr Outlook (1200Z Sep 25)... 10% chance of tropical cyclone formation (northeast of Bermuda near 35N-60W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 20%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Sep 20) CMC Model Run...
**For Area of Interest #29... remnants of Gordon regains tropical cyclone status near 26.5N-42W at 18 hours... weakens back to a remnant low near 26.5N-44W at 48 hours... remnant low subsequently turns north and loses identity to incoming surface front to the west.
**For area of interest #30... organizes into a large tropical low that moves into the Yucatan peninsula through 120 hours... large tropical low proceeds to organize into a large tropical storm centered just west-northwest of the Yucatan peninsula through 156 hours... while quasi-stationary the large tropical storm begins to take on an elongated north-south structure through 168 hours.
**For area of interest #31... drifts west then accelerates northeast and by 132 hours merges with incoming surface front to the west (without tropical cyclone formation beforehand) while located near 36N-45.5W... remnant frontal low located near 36N-41W by 168 hours
**Tropical wave emerges from west coast of Africa at 72 hours and passes over the southern Republic of Cabo Verde Islands as a tropical low by 102 hours... tropical low reaches 16.5N-41W by 168 hours
**Additional tropical wave emerges from west coast of Africa at 126 hours and passes over the northern Republic of Cabo Verde Islands as a tropical low through 168 hours.
0000Z (Sep 20) ECMWF Model Run...
**For Area of Interest #29... remnants of Gordon drift northeast... then turns west then north over the next few days without redevelopment shown
**For area of interest #30... broad tropical low centered over the southwest coast of the Yucatan peninsula slowly materializes through 168 hours
**For area of interest #31... through 84 hours becomes gradually absorbed by current northwestern Atlantic frontal low that dives slowly southeast
**Broad tropical low emerges from west coast of Africa at 120 hours and moves into the Republic of Cabo Verde Islands through 162 hours while potentially becoming a tropical depression.
0600Z (Sep 20) GFS Model Run...
**For Area of Interest #29... remnants of Gordon move east… then northwest… then north over next few days without redevelopment shown
**For area of interest #30... broad tropical low develops just north of Honduras through 102 hours... tropical cyclone develops within northeast side of the broad tropical low and swings northwest into the northeastern corner of the Yucatan peninsula through 144 hours... tropical cyclone strengthens further through 168 hours while moving northwest across the south-central Gulf of Mexico
**For area of interest #31... initially is quasi-stationary then through 168 hours makes a large counter-clockwise arc around the current northwest Atlantic frontal low while gradually losing its identity to the frontal low
0600Z (Sep 20) NAVGEM Model Run...
**Not available at above-mentioned source
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