*******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.**********
...TUESDAY JUNE 20 2023 11:45 AM EDT...
The following is a special update on recent tropical activity in the Atlantic as I am currently on vacation. While on vacation I will continue to issue special updates on active disturbances or tropical cyclones when possible... meanwhile refer to the National Hurricane Center website hurricanes.gov (hurricanes dot gov) for up to the minute latest information on the Atlantic tropics.
Satellite image as of 1330Z June 20 showing Tropical Storm Bret… other current areas of interest (AOIs)… along with a simplified surface analysis of surface low pressures (Ls)… high pressure ridges (Hs)… and fronts (red lines) based on the NHC TAFB surface analysis at the time:
TROPICAL STORM BRET… On colorized infrared satellite pictures… Bret has struggled to maintain a core of thunderstorms and instead there is broken regions of thunderstorms in the circulation. This could be an indication that dry Saharan air and perhaps competition with the adjacent tropical wave to the east (Area of Interest #8) could be negative influences on Bret despite the tropical storm currently being over warm 28 deg C waters and beneath the low shear and upper outflow environment of the tropical upper ridge cell in the region. Bret was initially moving faster to the west than previously forecast and therefore the updated forecast track below is adjusted accordingly… bringing Bret into the Lesser Antilles a day sooner (on Friday). Intensity-wise I continue to avoid forecasting hurricane strength due to the above-mentioned observations… and because by 48 hours Bret will begin to encounter some northerly shear from the east side of the Caribbean upper ridge cell and southwest side of the low-latitude central Atlantic upper vorticity (the low-latitude central Atlantic upper vorticity has stopped retrograding westward and away while now merging with the current northwestern Atlantic upper vorticity). Also noting as of 11 AM EDT the NHC has cancelled hurricane strength from their official forecast. By 96 hours the northward warm air transport ahead of the current eastern US frontal system will have amplified the Caribbean upper ridge cell… with this cell causing a chunk of the central Atlantic upper vorticity to retrograde southwest into the Lesser Antilles. Because Bret’s forecast track has been adjusted westward… this now puts the storm on a collision course with the suppressing upper vorticity chunk and thus I dissipate Bret into a remnant tropical wave by 96 hours. Also noting the GFS… CMC… and ECMWF are trending toward this idea.
Interests in the central and northern Lesser Antilles should be aware of Bret as it will likely bring periods of heavy rainfall… coastal surf… and gusty winds by Friday. Keep in touch with up to the minute latest forecasts by visiting the NHC site (hurricanes.gov).
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Jun 20)… 40 mph maximum sustained wind tropical storm centered at 11.7N-44.7W
IOH 24 Hr Forecast (1200Z Jun 21)… 60 mph maximum sustained wind tropical storm centered at 12.5N-51W
IOH 48 Hr Forecast (1200Z Jun 22)… 60 mph maximum sustained wind tropical storm centered east of the Lesser Antilles at 13.5N-56W
IOH 72 Hr Forecast (1200Z Jun 23)… 50 mph maximum sustained wind tropical storm centered over the central Lesser Antilles at 14.5N-61W
IOH 96 Hr Forecast (1200Z Jun 24)… Remnant tropical wave in the eastern Caribbean Sea at 66W longitude
******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************
Peak strength (1200Z Jun 22)… 65 mph maximum sustained wind tropical storm centered at 13.6N-57.3W
Loss of Tropical Cyclone Status (1200Z Jun 25)… Dissipation in the central Caribbean Sea
AREA OF INTEREST #8… To the east of Tropical Storm Bret… an additional strong tropical wave of low pressure has gained organization overnight and is now at high risk of tropical cyclone formation. As of late the thunderstorm activity has waned but the remaining cloud deck resembles a classic rotating tropical system with a better-defined center compared to before. I agree with the NHC on similarly high peak odds of tropical cyclone formation in my updated outlook below… but wait till 48 hours to show the peak odds due to the current lack of widespread thunderstorms in the circulation.
Noting that the current northwestern and central Atlantic upper vorticity will merge and create a surface ridge weakness with the combined eastern divergence zones… the forward speed in my outlook below is slowed in response to this weakness in the 48 to 72 hour window. Later the current Caribbean upper ridge cell is forecast to amplify which will tilt the upper vorticity into a southwest-northeast configuration… with the northwestern convergence zone of the tilted vorticity helping to recover the Atlantic surface ridge. As a result I return to a faster forward speed in the 72 to 96 hour window. With a high likelihood of development… this system is likely to be strong/tall enough to be bent northward in track as it nears the tilted upper vorticity axis… and this north bend is shown in my track forecast below for the 96 to 120 hour window. It is also for this timeframe I begin to drop development odds from the peak as this system encounters southwesterly shear from the upper vorticity axis.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jun 21)… 40% chance of tropical cyclone formation (eastern tropical Atlantic near 10.2N-37.5W)
IOH 48 Hr Outlook (1200Z Jun 22)… 70% chance of tropical cyclone formation (central tropical Atlantic near 10.7N-41.5W)
IOH 72 Hr Outlook (1200Z Jun 23)… 70% chance of tropical cyclone formation (central tropical Atlantic near 11.8N-45.5W)
IOH 96 Hr Outlook (1200Z Jun 24)… 70% chance of tropical cyclone formation (central tropical Atlantic near 12.7N-51W)
IOH 120 Hr Outlook (1200Z Jun 25)… 60% chance of tropical cyclone formation (central tropical Atlantic near 14.5N-55.5W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Formation chance through 48 hours...70%
Formation chance through 7 days (168 hours)...80%
AREA OF INTEREST #9… An additional tropical wave of low pressure over interior Western Africa is producing widespread thunderstorms in the vicinity of 8.5N-2W. The CMC and GFS models have begun to pick up on possible development with this feature as it later emerges into the eastern tropical Atlantic… and the upper air pattern is forecast to be stubbornly favorable with the persistence of the low shear and upper outflow environment supplied by the tropical upper ridge cell in the region. Therefore I have added this tropical wave as an area of interest for potential development… however I am starting with low odds of cyclone formation through day 5 as it will have yet to have spent much time over the favorable eastern tropical Atlantic conditions.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 72 Hr Outlook (1200Z Jun 23)… 0% chance of tropical cyclone formation (vicinity of west coast of Africa near 10N-15W)
IOH 96 Hr Outlook (1200Z Jun 24)… 10% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-19W)
IOH 120 Hr Outlook (1200Z Jun 25)… 15% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-24W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 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 (Jun 20) CMC Model Run...
**For Tropical Storm Bret… weakens to a tropical low while crossing the Lesser Antilles through 60 hours… subsequently weakens to a tropical wave while moving across the Caribbean
**For Area of Interest #8… tropical cyclone formation forecast near 13.5N-46W at 84 hours… subsequently curves northwest while staying a weak tropical cyclone and reaches 22N-53W at 126 hours
**For Area of Interest #9… additional tropical wave emerges from west coast of Africa at 66 hours… compact tropical cyclone formation suggested near 10N-30W at 138 hours
0000Z (Jun 20) ECMWF Model Run...
**For Tropical Storm Bret… crosses the central Lesser Antilles at 66 hours after which time it weakens into a remnant low and then tropical wave while moving into the Caribbean Sea
**For Area of Interest #8… tropical cyclone formation suggested near 11N-36W at 30 hours… curves west-northwest in track and reaches 17.5N-53W at 120 hours as a compact tropical storm
**For Area of Interest #9… No development shown
0600Z (Jun 20) GFS Model Run...
**For Tropical Storm Bret… crosses the central Lesser Antilles at 75 hours after which time it weakens to a tropical depression in the eastern Caribbean at 93 hours and remnant tropical wave in the central Caribbean at 108 hours
**For Area of Interest #8… tropical cyclone formation suggested near 11.5N-45W at 72 hours… while curving west-northwest weakens to a remnant low near 16N-54.5W at 117 hours
**For Area of Interest #9… additional tropical wave emerges from west coast of Africa at 66 hours… evolves into a tropical low near 10N-32.5W at 141 hours
0600Z (Jun 20) NAVGEM Model Run...
**For Tropical Storm Bret… crosses the central Lesser Antilles as a hurricane at 84 hours and approaches the south coast of the Dominican Republic at this strength through 120 hours
**For Area of Interest #8… tropical cyclone formation suggested near 11.5N-44W at 72 hours… curves west-northwest and reaches 17N-56W as a tropical storm at 120 hours
**For Area of Interest #9… No development shown
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