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BIRDSEYE VIEW POSTS

Since 2012 on the now retired Weather Underground blogs, I have been posting annotated "birdseye view" charts of the Atlantic basin, with a detailed explanation and forecasting that references the chart. From there you may know me as "NCHurricane2009." While I now do these "birdseye view" posts here, I will continue to do comments at Yale Climate Connections via Disqus where the former Weather Underground community has moved to. Feel free to reply to me there, at my Disqus feed at this link, or via e-mail at IOHurricanes@outlook.com 

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MY 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #27C (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.**********


...WEDNESDAY JUNE 21 2023 7:25 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 0910Z June 21 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 appears to have overcome some of its previous difficulties while once again accelerating faster to the west… increasing its separation from and thus reducing its competition with the adjacent tropical disturbance to the east (Area of Interest #8). The tropical storm appears to have also finally fought of the regional dry Saharan air while firing off and maintaining a central area of thunderstorms which has allowed it to strengthen over the last several hours. Once again my updated forecast track is nudged westward due to Bret’s faster pace. Going forward the northward warm air transport ahead of the current eastern US frontal system will amplify the current warm core Caribbean upper ridge cell… with this cell causing a chunk of the central Atlantic upper vorticity to retrograde southwest into the Lesser Antilles and eastern Caribbean. Given the above observations of Bret becoming better organized… it is more likely to be a stronger/taller system when it first encounters the retrograding upper vorticity and thus I have also made a slight north adjustment to the forecast track. I have raised the intensity forecast for Bret and hold on to it as a tropical cyclone for a bit longer… especially with the GFS upper wind field also trending toward a smaller area of disrupting retrograding upper vorticity when compared to yesterday’s runs. However it is still imminent that Bret will be dealing with some northerly shear from the east side of the amplifying Caribbean upper ridge cell by 24 hours… and then slide underneath and collapse under the lack of divergence beneath the upper vorticity by 72 hours. Even if Bret manages to successfully cross through the upper vorticity… suppressing upper convergence on the southeast side of the Caribbean upper ridge cell awaits. The CMC… GFS… and ECMWF models all dissipate Bret into a remnant tropical wave of low pressure by 96 hours.


Interests in the central and northern Lesser Antilles should now be preparing for periods of coastal surf… gusty winds… and heavy rainfall to arrive by late Thursday and into Friday. Some wind damage near where the strongest winds/center of circulation passes is possible. Coastal surf may also reach the shores of the Virgin Islands and Puerto Rico from the south.


Update as of 5 AM EDT… Bret has strengthened further to 60 mph maximum sustained winds.

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

0 Hr Position (0600Z Jun 21)… 50 mph maximum sustained wind tropical storm centered at 12.6N-50.9W

IOH 24 Hr Forecast (0600Z Jun 22)… 65 mph maximum sustained wind tropical storm centered east of the Lesser Antilles at 13.5N-56.2W

IOH 48 Hr Forecast (0600Z Jun 23)… 60 mph maximum sustained wind tropical storm centered just west of the central Lesser Antilles at 14.8N-61.2W

IOH 72 Hr Forecast (0600Z Jun 24)… 30 mph maximum sustained wind tropical depression centered south of Puerto Rico at 15.5N-67W

IOH 96 Hr Forecast (0600Z Jun 25)… Remnant tropical wave in the north-central Caribbean Sea at 73W longitude

******National Hurricane Center (hurricanes.gov) official forecast as of 5 AM EDT***************************

Peak strength (1800Z Jun 21)… 65 mph maximum sustained wind tropical storm centered at 13.1N-53.3W

Loss of Tropical Cyclone Status (0600Z Jun 26)… Dissipation in the western Caribbean Sea


AREA OF INTEREST #8The vigorous central Atlantic tropical wave of low pressure that has been following Bret has struggled to produce thunderstorm activity for much of the last 24 hours… perhaps an indication that regional dry Saharan air has penetrated the circulation. Despite this the remaining cloud deck has remained organized while maintaining the semblance of a tropical low pressure swirl… and thunderstorm activity as of late is re-building. Therefore for this update I am assuming imminent tropical cyclone formation and have begun a track and intensity forecast as outlined below.


Noting that the current northwestern and central Atlantic upper vorticity will soon merge and create a surface ridge weakness with the combined eastern divergence zones… the forward speed in the track forecast below is slowed in response to this weakness for the first 48 hours. 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 48 to 72 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 72 to 120 hour window. Atmospheric conditions for the next 72 hours are expected to be favorable for development with the low shear and upper outflow of the expansive tropical upper ridge cell… however given the history of this system struggling to maintain thunderstorm for now I gradually ramp up the intensity forecast. Because of the long 72 hour window of favored atmospheric conditions the gradual rate still brings this system just below hurricane force. A subsequent decay is then projected for 96+ hours as this system encounters southwesterly shear from the aforementioned upper vorticity axis.


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 (0600Z Jun 21)… Tropical low centered at 10N-37W

IOH 24 Hr Forecast (0600Z Jun 22)… 40 mph maximum sustained wind tropical storm centered at 10.5N-41W

IOH 48 Hr Forecast (0600Z Jun 23)… 60 mph maximum sustained wind tropical storm centered at 11.5N-45W

IOH 72 Hr Forecast (0600Z Jun 24)… 70 mph maximum sustained wind tropical storm centered at 12.5N-50.5W

IOH 96 Hr Forecast (0600Z Jun 25)… 60 mph maximum sustained wind tropical storm centered at 14N-55W

IOH 120 Hr Forecast (0600Z Jun 26)… 50 mph maximum sustained wind tropical storm centered just east of the northern Lesser Antilles at 16N-59W

******National Hurricane Center (hurricanes.gov) official outlook as of 2 AM EDT***************************

Formation chance through 48 hours...70%

Formation chance through 7 days (168 hours)...80%


AREA OF INTEREST #9 An additional strong tropical wave of low pressure is currently located over western Africa and is en route to the eastern tropical Atlantic. Due to the vigor of the wave as indicated by ongoing widespread thunderstorms and the stubbornly favorable upper wind pattern consisting of low shear and upper outflow supplied by the tropical upper ridge cell in the region… I am maintaining the wave as an area of interest for possible development. The tropical wave appears to be in the process of re-organizing toward the west where a batch of offshore thunderstorms is located… therefore I have shifted the forecast track westward while also raising odds of tropical cyclone formation as the offshore activity is already showing signs of organization. However I cap my peak odds at a low 25% due to lack of computer model support and as a portion of the current northwest Atlantic upper vorticity is forecast to be pushed southeastward toward the eastern tropical Atlantic by high-latitude upper ridging. By 120 hours the approaching upper vorticity may limit the outflow of the regional tropical upper ridge cell… note that I taper down from the peak odds during this timeframe.

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

IOH 48 Hr Outlook (0600Z Jun 23)… 5% chance of tropical cyclone formation (offshore of the west coast of Africa near 10N-17.5W)

IOH 72 Hr Outlook (0600Z  Jun 24)… 15% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-22.5W)

IOH 96 Hr Outlook (0600Z Jun 25)… 25% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-27.5W)

IOH 120 Hr Outlook (0600Z Jun 26)… 20% chance of tropical cyclone formation (eastern tropical Atlantic near 11.5N-32.5W)

******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/)


1200Z (Jun 20) CMC Model Run...

**For Tropical Storm Bret… weakens to a tropical low while crossing the Lesser Antilles through 54 hours… subsequently weakens to a tropical wave while moving across the Caribbean

**For Area of Interest #8… evolves into a tropical low that passes northeast of the Lesser Antilles through 132 hours

**For Area of Interest #9… compact tropical cyclone formation suggested near 10N-40W at 126 hours


1200Z (Jun 20) ECMWF Model Run...

**For Tropical Storm Bret… crosses the central Lesser Antilles at 60 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… passes northeast of the Lesser Antilles through 132 hours without further development

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


0000Z (Jun 21) GFS Model Run...

**For Tropical Storm Bret… crosses the central Lesser Antilles at 51 hours after which time it weakens to a tropical depression in the eastern Caribbean at 66 hours and remnant tropical wave in the central Caribbean at 87 hours

**For Area of Interest #8… tropical cyclone formation suggested near 11N-44W at 51 hours… while curving west-northwest weakens to a remnant low northeast of the Lesser Antilles at 117 hours

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


1800Z (Jun 20) NAVGEM Model Run...

**For Tropical Storm Bret… crosses the central Lesser Antilles as a hurricane at 60 hours and passes south of Haiti at this strength through 120 hours

**For Area of Interest #8… tropical cyclone formation suggested near 13.5N-52W at 84 hours…  curves west-northwest and reaches 17.5N-56.5W as a tropical storm at 120 hours

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

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