*******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.**********
...MONDAY JULY 24 2023 7:00 PM EDT...
Hurricane Don has transitioned to a non-tropical remnant low pressure over the cool north-central Atlantic waters... see remnants of Don section below for more information.
Elsewhere... monitoring two areas of interest for possible tropical development in the Atlantic basin in the days ahead as follows:
(1) See area of interest #14 section below for an update on the central Atlantic tropical low pressure now closing in on the Lesser Antilles and Caribbean Sea.
(2) See area of interest #16 section below for a new western Atlantic surface trough of low pressure being monitored by the National Hurricane Center for possible development. This trough is forecast to swing toward the northwestern Bahamas and southeastern United States coastline later this week and into the weekend... and is the sixteenth tropical Atlantic area of interest tracked on this site this year.
REMNANTS OF DON... For such a long-lived tropical cyclone... there is not much to say about Don now. While continuing to anticyclonically curve around the northwestern periphery of the steering North Atlantic deep-layer ridge... Don has curved northeastward and then east-northeastward offshore of Newfoundland and into cooler north-central Atlantic waters. Due to the cooler waters... the hurricane has since weakened to a tropical storm and then a gale-force remnant low pressure swirl while having lost thunderstorms in its circulation. The shortwave upper trough currently over southeastern Canada will spend the next 24 hours ejecting eastward across the north Atlantic while generating a large surface frontal cyclone to the north of Don with its eastern divergence zone... with Don eventually losing its identity within this cyclone. This is my final statement on Don on this blog as it is no longer a tropical cyclone.
AREA OF INTEREST #14... The tropical low pressure in the central tropical Atlantic has weakened to a open tropical wave of low pressure. However since then the tropical wave has moved into lower concentrations of dry Saharan air... and combined with the help of the outflow of the tropical upper ridge in the region there has been a marked increase in the size and intensity of the associated thunderstorm field. Regarding forecast track for this disturbance... this system in the short-term will continue west with little northward heading under the influence of the recently expanded surface layer of the north Atlantic deep-layer ridge. By days 3 to 5 the northward angle is increased once this system rounds the southwestern periphery of the steering surface layer of the ridge. Regarding odds of tropical cyclone formation... the increased thunderstorm activity and an improved upper wind forecast favor this system. Specifically the recently developed wall of western Atlantic upper ridging is no longer forecast to push the current suppressing central Atlantic upper vorticity into the Caribbean and path of this disturbance. Therefore I have maintained a peak 40% odds of tropical cyclone formation from the previous update... but have delayed the timing of the peak odds to later in the 5-day forecast as the tropical wave will need time to re-strengthen into a tropical low with a well-defined center. I have not chosen development odds higher than 40% as the computer models continue to avoid developing this disturbance.
Due to the recent expansion of the thunderstorm activity of this disturbance... much of the Lesser Antilles are likely to see gusty winds and heavy rainfall in the next 24 hours regardless of tropical cyclone formation or not. I also recommend interests in Jamaica should also be aware of this disturbance as it could pass over the region by Friday.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jul 25)... 20% chance of tropical cyclone formation (southern Lesser Antilles near 13N-61W)
IOH 48 Hr Outlook (1800Z Jul 26)... 30% chance of tropical cyclone formation (eastern Caribbean Sea near 13.5N-66W)
IOH 72 Hr Outlook (1800Z Jul 27)... 40% chance of tropical cyclone formation (central Caribbean Sea near 15N-72W)
IOH 96 Hr Outlook (1800Z Jul 28)... 40% chance of tropical cyclone formation (just south of Jamaica near 16N-77.5W)
IOH 120 Hr Outlook (1800Z Jul 29)... 40% chance of tropical cyclone formation (southwest of the Cayman Islands near 17N-82.5W)
******National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT*****************************
Formation chance through 48 hours...20%
Formation chance through 7 days (168 hours)...20%
AREA OF INTEREST #16... An area of split flow divergence between the current western Atlantic upper ridge and central Atlantic upper vorticity... marked in the above birdseye view chart... has generated a surface trough of low pressure near 25N-65W. The steering surface layer of the current north Atlantic deep-layer ridge has recently been expanding westward due to the southeastern convergence zone of the western Atlantic upper ridge. Therefore the northward turn of the surface trough will not immediately occur... instead the surface trough will continue west-northwestward around the expanded surface layer of the ridge and toward the northwestern Bahamas and northeastern Florida coast through 72 hours. Once it reaches the western periphery of the expanded ridge... a turn to the north and then northeast... paralleling the southeastern US coast from Georgia to the Carolinas... is anticipated in the 96+ hour window. The forecast track of the surface trough takes it below the upper layers of the western Atlantic upper ridge where low wind shear and upper outflow may make conditions conducive for tropical development... and the NHC has added this feature into their tropical weather outlook. I agree with the NHC on a low peak 20% odds of tropical cyclone formation as the computer model support showing development is lacking. Because there is already an area of low-level concentrated spin in the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=)... my 24 hour odds of tropical cyclone formation are above 0%. And for day 5 I lower odds from the peak due to potential for increased land interaction and as this system may become aligned with the suppressive western convergence zone of a shortwave upper trough associated with the ongoing upper trough regime over eastern North America.
Interests in the northwestern Bahamas... and the southeastern US coast from northeastern Florida to southeastern North Carolina should be aware of this disturbance should it attempt to develop... which could result in increased rainfall and gusty winds later this week and into the weekend.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jul 25)... 10% chance of tropical cyclone formation (western Atlantic near 26N-70W)
IOH 48 Hr Outlook (1800Z Jul 26)... 20% chance of tropical cyclone formation (just east of the northwestern Bahamas near 26.5N-75W)
IOH 72 Hr Outlook (1800Z Jul 27)... 20% chance of tropical cyclone formation (just offshore of northeastern Florida near 27.5N-79W)
IOH 96 Hr Outlook (1800Z Jul 28)... 20% chance of tropical cyclone formation (just offshore of Georgia near 31.5N-80.2W)
IOH 120 Hr Outlook (1800Z Jul 29)... 10% chance of tropical cyclone formation (coastal northeastern South Carolina near 33N-79W)
******National Hurricane Center (hurricanes.gov) official outlook as of 2 PM EDT*****************************
Formation chance through 48 hours...0%
Formation chance through 7 days (168 hours)...20%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Jul 24) CMC Model Run...
**For Tropical Storm Don... continues east-northeast and weakens to a remnant trough near 49N-37.5W at 24 hours
**For area of interest #14... no development shown
**For area of interest #16... no development shown
0000Z (Jul 24) ECMWF Model Run...
**For Tropical Storm Don... continues east-northesat and weakens to a remnant rough near 49.5N-34W at 30 hours
**For area of interest #14... no development shown
**For area of interest #16... no development shown
1200Z (Jul 24) GFS Model Run...
**For Tropical Storm Don... continues east-northeast and weakens to a remnant trough near 49N-34W at 18 hours
**For area of interest #14... no development shown
**For area of interest #16... no development shown
**Tropical wave currently over western Africa gradually evolves into a tropical low as it later moves across the central tropical Atlantic... tropical low forecast to be just north of the northern Lesser Antilles by 168 hours.
0600Z (Jul 24) NAVGEM Model Run...
**For Tropical Storm Don... continues east-northeast and weakens to a remnant trough near 50N-37W at 18 hours
**For area of interest #14... no development shown
**For area of interest #16... no development shown
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