MY 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #27D (Special Update)

*******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 JUNE 22 2023 3:15 PM 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 1230Z June 22 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… Bret continues to barrel westward toward the central Lesser Antilles while having strengthened further to just below hurricane force… while acquiring 70 mph maximum sustained winds. Upper vorticity just to the north is retrograding southwestward toward the eastern Caribbean Sea and into Bret’s path due to the forcing of amplifying upper ridging over the Caribbean and western Atlantic. Shear from the upper vorticity already appears to be negatively affecting Bret while displacing the strongest part of the thunderstorm canopy to the northeast of the center… and Bret is not expected to strengthen further. However as of this writing a hurricane watch is in effect for the St Lucia region of the central Lesser Antilles in case Bret strengthens a little more before the shear worsens for Bret. After crossing the Lesser Antilles and entering the Caribbean… it is imminent that Bret will slide underneath and collapse under the lack of divergence beneath the retrograding upper vorticity by 48+ hours. Even if Bret manages to successfully cross through the upper vorticity… suppressing upper convergence on the southeast side of the aforementioned upper ridging awaits. The CMC… GFS… and ECMWF models all dissipate Bret into a remnant tropical wave of low pressure by 72 hours.

Interests in the central Lesser Antilles should have completed preparations by now as periods of coastal surf… gusty winds… and heavy rainfall will arrive tonight and into Friday. Some wind damage near where the strongest winds/center of circulation passes is likely. Coastal surf and periods of heavy rainfall is also likely for the northern Lesser Antilles. Coastal surf may also reach the shores of the Virgin Islands and Puerto Rico from the south.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (1200Z Jun 22)… 70 mph maximum sustained wind tropical storm centered east of the Lesser Antilles at 13.6N-57W

IOH 24 Hr Forecast (1200Z Jun 23)… 60 mph maximum sustained wind tropical storm centered just west of the central Lesser Antilles at 15N-62W

IOH 48 Hr Forecast (1200Z Jun 24)… 30 mph maximum sustained wind tropical depression centered southwest of Puerto Rico at 15.5N-68W

IOH 72 Hr Forecast (1200Z Jun 25)… Remnant tropical wave in the central Caribbean Sea at 75W longitude

******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************

Loss of Tropical Cyclone Status (1200Z Jun 25)… Dissipation in the central Caribbean Sea

TROPICAL DEPRESSION FOUR… The vigorous central Atlantic tropical wave of low pressure that has been following Bret has finally managed to strengthen into a tropical cyclone as of 5 AM EDT today… and is designated tropical depression four. The new tropical cyclone has 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. The current northern and central Atlantic upper vorticity is merging and creating a surface ridge weakness with the combined eastern divergence zones… the result of this weakness is the forward speed of this system is a little bit slower than the typical 5W per day longitude for tropical systems in this region. As the current warm core western Atlantic to Caribbean upper ridging continues to amplify (due to northward warm air transport ahead of the current eastern US frontal system)… the upper ridging will tilt the aforementioned 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 a faster forward speed is expected in the 24 to 48 hour window. With a high likelihood of additional 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 a north turn is shown in the forecast below after 48 hours. In addition to steering provided by the tilted upper vorticity axis… a northward turn will also be promoted at 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.

Regarding intensity…atmospheric conditions for the next 48 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 struggling to maintain thunderstorms for now I gradually ramp up the intensity. My updated intensity forecast is a bit lower than my previous as this system is taking longer than I previously anticipated to become a tropical storm. The latest GFS model upper wind field for the long term is trending toward 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 delayed the weakening phase in the updated forecast below. By day 5 there are some indications that the cold core upper vorticity axis… due to prolonged isolation from high-latitude cold air… may begin to break up into upper vortices… with this system potentially surviving while becoming enhanced by divergence on the east side of one such vortex. Therefore I hold on to this system as a tropical cyclone through day 5.

Given the current track and intensity forecast… this system could bring coastal surf to the northern Lesser Antilles not long after Bret passes… by Sunday and Monday.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (1200Z Jun 22)… 35 mph maximum sustained wind tropical depression centered at 10.9N-41.1W

IOH 24 Hr Forecast (1200Z Jun 23)… 50 mph maximum sustained wind tropical storm centered at 11.8N-45.5W

IOH 48 Hr Forecast (1200Z Jun 24)… 60 mph maximum sustained wind tropical storm centered at 12.8N-51W

IOH 72 Hr Forecast (1200Z Jun 25)… 60 mph maximum sustained wind tropical storm centered at 15N-55.5W

IOH 96 Hr Forecast (1200Z Jun 26)… 45 mph maximum sustained wind tropical storm centered just east of the northern Lesser Antilles at 18.5N-59W

IOH 120 Hr Forecast (1200Z Jun 27)… 35 mph maximum sustained wind tropical depression centered at 22.5N-60W

******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************

Peak Strength (1200Z Jun 24)… 60 mph maximum sustained wind tropical storm centered at 15.5N-52.2W

5-Day Position (1200Z Jun 27)… 35 mph maximum sustained wind tropical depression centered at 24N-65.2W

AREA OF INTEREST #9… The latest disturbance to emerge into the eastern tropical Atlantic from western Africa now consists of a duplex of closely-spaced tropical waves of low pressure… one western one now located well offshore and well south-southwest of the Republic of Cabo Verde Islands… and a second eastern one located on the west coast of Africa… with each wave having a cluster of showers and thunderstorms. The CMC and GFS models on June 20th were latched onto the eastern wave developing when I introduced this system as an area of interest… therefore the forecast coordinates in the updated outlook below is adjusted toward the current position of the eastern wave and moving this wave along at the typical 5W longitude per day pace. I have also lowered the 5-day peak odds of tropical cyclone formation to 15% as there is little organization to the thunderstorm activity. Low odds also make sense due to lack of computer model support and as a portion of the current north Atlantic upper vorticity is forecast to be pushed southeastward toward the eastern tropical Atlantic by high-latitude upper ridging by day 4. I wait till day 5 to issue the peak development odds… when the wave will be escaping the influence of the upper vorticity and heading toward more sprawling tropical upper ridging (low shear/upper outflow) in the central tropical Atlantic.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1200Z Jun 23)… 0% chance of tropical cyclone formation (offshore of the west coast of Africa near 8.5N-19W)

IOH 48 Hr Outlook (1200Z Jun 24)… 0% chance of tropical cyclone formation (eastern tropical Atlantic near 9.5N-24W)

IOH 72 Hr Outlook (1200Z Jun 25)… 10% chance of tropical cyclone formation (eastern tropical Atlantic near 10N-29W)

IOH 96 Hr Outlook (1200Z Jun 26)… 10% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-34W)

IOH 120 Hr Outlook (1200Z Jun 27)… 15% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-39W)

******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 22) CMC Model Run...

**For Tropical Storm Bret… crosses the central Lesser Antilles at 24 hours… subsequently weakens to a tropical wave while moving across the central Caribbean through 60 hours

**For Tropical Depression Four… passes just northeast of the Lesser Antilles at 90 hours shortly after which time it weakens to a remnant trough

**For Area of Interest #9… evolves into a tropical low near 10N-44W at 96 hours and approaches the central Lesser Antilles in this state through 162 hours

0000Z (Jun 22) ECMWF Model Run...

**For Tropical Storm Bret… crosses the central Lesser Antilles at 24 hours after which time it weakens to a central Caribbean remnant low through 84 hours…

**For Tropical Depression Four… passes well northeast of the Lesser Antilles as a tropical storm through 90 hours… weakens to a remnant low near 21.5N-62W at 108 hours

**For Area of Interest #9… No development shown

0600Z (Jun 22) GFS Model Run...

**For Tropical Storm Bret… crosses the central Lesser Antilles at 24 hours… subsequently weakens to a tropical wave while moving across the central Caribbean through 60 hours

**For Tropical Depression Four… passes well northeast of the Lesser Antilles at 84 hours while weakening to a remnant low… regenerates into a compact tropical cyclone near 22.5N-59.5W at 102 hours which curves north to 24N-61W through 126 hours

**For Area of Interest #9… No development shown

0000Z (Jun 22) NAVGEM Model Run...

**For Tropical Storm Bret… crosses the central Lesser Antilles at 30 hours and curves north into the southwest tip of Haiti and east tip of Cuba through 120 hours

**For Tropical Depression Four… passes well northeast of the Lesser Antilles as a tropical storm through 96 hours and reaches 22N-61.2W at 120 hours

**For Area of Interest #9… No development shown