*******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 JUNE 23 2023 7:15 PM EDT...
The following is a special update on recent tropical activity in the Atlantic as I am currently on vacation. Note that the forecasts below were generated at 1200Z earlier today… however I could not release this update until now due to vacation activities today. 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 23 showing Tropical Storms Bret and Cindy… 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. Blue-dashed line is used to mark the location of upper vorticity axis:
TROPICAL STORM BRET… The center of Bret passed through the St Vincent region of the Lesser Antilles islands overnight. Shear imparted by upper vorticity over the eastern Caribbean Sea weakened Bret to 60 mph maximum sustained winds before the center crossed the islands. However the shear is not severe enough to completely separate the thunderstorms from the center as the upper vorticity is amplified enough to produce southerly winds over Bret instead of more severe westerly winds that would otherwise have been directly opposed to Bret’s current westward track. However once the tropical storm crosses 65W longitude… where the axis of the upper vorticity is… it will encounter northerly shear but also suppressing upper convergence on the back side of the upper vorticity and southeast side of the current upper ridge axis spanning the western Caribbean and western Atlantic. This suppressive upper air environment is expected to dissipate Bret as it continues west across the Caribbean over the next 48 hours. Worse for Bret… only the western Atlantic portion of the warm core upper ridge axis will amplify where the maximal northward warm air transport is located in association with the flow ahead of the stalled eastern US frontal system… which means the eastern Caribbean upper vorticity will retrograde westward and chase Bret while pushed around the amplified west Atlantic upper ridge cell. This means Bret will be trapped in the suppressive upper convergence regime on the west side of the retrograding upper vorticity.
Bret has been tracking more west instead of west-northwest and also at a higher speed… and my updated forecast track is adjusted accordingly. Trailing thunderstorm activity on the east side of Bret is biased to the southeast side of the storm and will likely bring periods of heavy rainfall to the southern half of the Lesser Antilles over the next several hours. Any coastal surf affecting the Virgin Islands… Puerto Rico… and the Lesser Antilles should diminish as Bret weakens going forward.
Update as of 5 PM EDT… Bret has become less organized due to the negative effects of wind shear… and has weakened to 50 mph maximum sustained winds
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Jun 23)… 60 mph maximum sustained wind tropical storm centered in the eastern Caribbean Sea at 13.4N-63.6W
IOH 24 Hr Forecast (1200Z Jun 24)… 30 mph maximum sustained wind tropical depression centered in the central Caribbean Sea at 13.5N-70W
IOH 48 Hr Forecast (1200Z Jun 25)… Remnant tropical wave in the south-central Caribbean Sea at 77W longitude
******National Hurricane Center (hurricanes.gov) official forecast as of 5 PM EDT***************************
Loss of Tropical Cyclone Status (1800Z Jun 25)… Dissipation in the south-central Caribbean Sea
TROPICAL STORM CINDY… Tropical depression four in the central tropical Atlantic has managed to gradually strengthen into Tropical Storm Cindy as of 11 PM EDT. Cindy continues to have a small area of thunderstorms over and just west of the center as this system has a recent history of struggling to produce widespread activity… perhaps an indication that regional dry Saharan air continues to affect this system. With a high likelihood of additional development… Cindy is likely to be strong/tall enough to be bent northward in track as it nears the southwest-northeast tilted upper vorticity axis that lies ahead… and a north turn is shown in the forecast below after 24 hours. In addition to steering provided by the tilted upper vorticity axis… a northward turn will also be helped by the surface layer as divergence zones on the east side of the upper vorticity axis and approaching eastern US upper trough (to be finally kicked toward the Atlantic by the current western US upper trough energy) begin to limit the western extent of the Atlantic surface ridge. My updated track forecast points below are nudged northwestward compared to the previous based on Cindy’s current position relative to the previous forecast.
Regarding intensity…atmospheric conditions for the next 24 hours are expected to be favorable for development with the low shear and upper outflow of the expansive tropical upper ridge cell currently in the region… however given the history of this system only gradually intensifying within the regional dry Saharan air will continue with a gradual strengthening rate. The latest GFS model upper wind field for the long term continues to trend with a weaker upper vorticity axis located further west… which means a longer time before this system encounters shear and when it does the shear will be less. Therefore I have increased the forecast peak intensity for 12Z June 25 with a gradual decay rate under the shear depicted afterwards. By days 4 and 5 there are indications that the cold core upper vorticity axis… due to prolonged isolation from high-latitude cold air… will begin to break up into upper vortices. The GFS trends with a further east track while showing Cindy becoming enhanced by the eastern divergence zone of one of the dissipating upper vortices. The remaining models suggest Cindy will quickly weaken and become shallow by day 3 such that it cannot couple with the dissipating upper vortex… such that the Atlantic surface ridge pushes Cindy more northwest into the south side of the dissipating upper vortex where westerly shear is higher… finishing off Cindy for good before it can take advantage of the better upper air pattern after the upper vortex dissipates in 5+ days. My long-term forecast splits the difference between the GFS and non-GFS solutions for both track and intensity… holding on to Cindy thru day 5 as a tropical cyclone but not aggressively re-intensifying Cindy in the better upper air pattern in 5+ days as the GFS does. However if it turns out the GFS is right then the forecast re-strengthening rate for 5+ days may need to be upped in future updates.
Given the current track and intensity forecast… this system could bring coastal surf to the northern Lesser Antilles by Sunday and Monday.
Update as of 5 PM EDT… after strengthening further to 50 mph max sustained winds at 11 AM… Cindy’s thunderstorms have become weaker and disorganized likely due to the regional dry Saharan air… and Cindy has stopped strengthening at this time.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Jun 23)… 45 mph maximum sustained wind tropical storm centered at 12.1N-46.9W
IOH 24 Hr Forecast (1200Z Jun 24)… 60 mph maximum sustained wind tropical storm centered at 13.5N-52.2W
IOH 48 Hr Forecast (1200Z Jun 25)… 65 mph maximum sustained wind tropical storm centered at 16N-56W
IOH 72 Hr Forecast (1200Z Jun 26)… 45 mph maximum sustained wind tropical storm centered just northeast of the northern Lesser Antilles at 20N-59W
IOH 96 Hr Forecast (1200Z Jun 27)… 35 mph maximum sustained wind tropical depression centered at 24N-61W
IOH 120 Hr Forecast (1200Z Jun 28)… 45 mph maximum sustained wind tropical storm centered southeast of Bermuda at 29N-62W
******National Hurricane Center (hurricanes.gov) official forecast as of 5 PM EDT***************************
Peak Strength (0600Z Jun 24)… 60 mph maximum sustained wind tropical storm centered at 14.5N-51.2W
Loss of Tropical Cyclone Status (1800Z Jun 28)… Dissipation well south of Bermuda
AREA OF INTEREST #9… The disturbance offshore of Africa consisting of a duplex of closely-spaced tropical waves of low pressure appears to have consolidated into a single wave near 7.5N-22.5W based on the latest satellite imagery which shows some rotating organized showers and thunderstorms in this area. The NHC TAFB surface analysis seems to agree with this while in recent hours holding the western of the two waves in the former duplex stationary at this location instead of moving both waves in the duplex westward in tandem. The forecast coordinates in the updated outlook below is adjusted toward the
current 7.5N-22.5W position… and moving this disturbance along at the typical 5W longitude per day pace. Given the signs of organization with the showers and thunderstorms… I have slightly raised peak odds of tropical cyclone formation to 20% as of this update. Noting that current North Atlantic upper vorticity will be pushed southeastward toward the eastern tropical Atlantic. However the latest forecast coordinates below means the disturbance is now likely to escape the reaches of the suppressing upper vorticity while heading toward sprawling tropical upper ridging (low shear/upper outflow) in the central tropical Atlantic. Despite this… keeping development odds low until computer model support develops for this disturbance… or if observations in future updates warrant higher odds.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jun 24)… 5% chance of tropical cyclone formation (eastern tropical Atlantic near 8.5N-27.5W)
IOH 48 Hr Outlook (1200Z Jun 25)… 15% chance of tropical cyclone formation (eastern tropical Atlantic near 9.5N-32.5W)
IOH 72 Hr Outlook (1200Z Jun 26)… 20% chance of tropical cyclone formation (eastern tropical Atlantic near 10N-37.5W)
IOH 96 Hr Outlook (1200Z Jun 27)… 20% chance of tropical cyclone formation (central tropical Atlantic near 10.5N-42.5W)
IOH 120 Hr Outlook (1200Z Jun 28)… 20% chance of tropical cyclone formation (central tropical Atlantic near 10.5N-42.5W)
******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 (Jun 23) CMC Model Run...
**For Tropical Storm Bret… weakens to a tropical wave while moving across the central Caribbean through 54 hours
**For Tropical Storm Cindy… passes just northeast of the Lesser Antilles at 60 hours while weakening to a tropical depression… weakens to a remnant trough northeast of the eastern Bahamas at 102 hours
**For Area of Interest #9… no development shown
0000Z (Jun 23) ECMWF Model Run...
**For Tropical Storm Bret… weakens to a tropical wave while moving across the central Caribbean through 66 hours
**For Tropical Storm Cindy… passes northeast of the Lesser Antilles as a tropical storm through 66 hours… weakens to a remnant low near 22.5N-64.5W at 90 hours
**For Area of Interest #9… No development shown
0600Z (Jun 23) GFS Model Run...
**For Tropical Storm Bret… weakens to a tropical wave in the south-central Caribbean through 39 hours
**For Tropical Storm Cindy… passes well northeast of the Lesser Antilles at 57 hours while weakening to a remnant low… regenerates into a compact tropical cyclone near 23.5N-59W at 84 hours which curves north to 26.2N-59.8W through 120 hours while strengthening to a high-end tropical storm
**For Area of Interest #9… No development shown
0600Z (Jun 23) NAVGEM Model Run...
**For Tropical Storm Bret… weakens to a depression in the central Caribbean near 15.5N-72W at 42 hours and regains tropical storm strength just south of Jamaica at 72 hours… curves northwest into the Cayman Islands at 96 hours and approaches western Cuba at hurricane strength through 126 hours
**For Tropical Storm Cindy… passes just northeast of the Lesser Antilles at 66 hours and reaches 24N-69W at 120 hours while weakening to a tropical depression
**For Area of Interest #9… No development shown
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