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 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #35

*******Note that forecasts 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 29 2021 1:18 PM EDT...

See remnants of Danny section below for a final statement on this tropical system which has weakened to a remnant low pressure overnight over Georgia. Also see area of interest sections below for multiple areas of interest being monitored for tropical development in the Atlantic basin...which include:


(1) Area of interest #1...vigorous tropical wave of low pressure now traversing the central tropical Atlantic...the Lesser Antilles islands could be affected by tomorrow evening...and Haiti...Jamaica...the Cayman Islands...and Cuba could be affected later this week.


(2) Area of interest #2...a rapidly organizing tropical wave of low pressure in the eastern tropical Atlantic which could affect the Lesser Antilles islands by Saturday or Sunday.


Elsewhere...a small upper ridge has formed over Texas and the western Gulf of Mexico...in relative higher pressures between the upper vortex over the northeastern Gulf of Mexico and the upper vortex now over northeastern Mexico. A tropical disturbance with a vigorous thunderstorm cluster...supported by the outflow of the small upper ridge...appears to be forming in the western Gulf of Mexico and offshore of northeastern Mexico. However satellite animation of low-level clouds suggests the surface rotation is already moving onshore in northeastern Mexico...and this disturbance could bring heavy rainfall with flash flooding potential over the Mexican provinces of Tamaulipas and northern Veracruz if the offshore heavy thunderstorm activity spreads onshore. Conditions for additional development here will soon decline as the northeastern Gulf of Mexico upper vortex gets pushed southwest into the heart of the Gulf of Mexico as the Texas portion of the upper ridge amplifies in warm southerly flow ahead of the persistent central US frontal system. The further southwest position of the upper vortex will subsequently suppress upper outflow in the western Gulf.


And finally...a tropical wave of low pressure in the northwestern Caribbean Sea is seeing its thunderstorms enhanced by the eastern divergence zone of the upper vortex in the northeastern Gulf of Mexico...and the divergence zone of the upper vortex is also helping to produce activity further north in the eastern Gulf of Mexico. As discussed in the previous paragraph...the upper vortex is forecast to shift southwestward...which will allow the tropical Atlantic upper ridge to expand northwestward in its wake. Although models do not forecast any development at the present time...it is possible a tropical disturbance develops in the northwestern Caribbean Sea or eastern Gulf of Mexico in the coming days while taking advantage of low shear and outflow beneath the expanding tropical Atlantic upper ridge...and also potentially taking advantage of the eastern divergence zone of the upper vortex as well. Anything that does develop would tend to move northwest around the southwest side of the Atlantic surface ridge.


REMNANTS OF DANNY...Danny is coming to a quick end while weakening from its landfall into to a remnant surface trough of low pressure over Georgia. The remnant surface trough is producing cloudiness and showers over the Appalachian mountains of the Carolinas...while the mid-level spin of Danny has decoupled from the remnant surface trough thanks to the easterly shear induced by the upper vortex to the south. The mid-level spin is seen on doppler radar producing a spiral band of showers and thunderstorms over northern Alabama. With the weather associated with Danny being none other than typical garden-variety summertime showers and thunderstorms...and with Danny no longer a tropical cyclone...this is my final statement on Danny on this blog. This is my final statement on Danny on this blog as it is no longer a tropical cyclone.


AREA OF INTEREST #1...The vigorous tropical wave of low pressure in the central tropical Atlantic has somewhat come back to life overnight as organized thunderstorm bands have redeveloped at the north apex of the wave. However with the history of this wave struggling with dry Saharan air...and latest satellite animation not showing a closed spin...I have only slightly raised my peak 5-day odds of development to 30%. Other than the dry air...conditions for development are otherwise favorable due to warm waters along the forecast track (26+ deg C)...coupled with low shear and upper outflow beneath the tropical upper ridge in the region. The cold core upper vorticity in the western Atlantic will continuously shrink while cut-off from high-latitude cold air...therefore wind shear will remain low even as the tropical wave crosses the Caribbean Sea from days 2 through 5.


The forecast track is due west within the deep-layered easterly flow on the south sides of the Atlantic surface ridge and tropical upper ridge...followed by an increasing north angle in the track by days 2 to 5 as the tropical wave rounds the southwest side of the Atlantic surface ridge. I maintain a brisk forward speed in the track (as do the computer models) as the wave has been weaker and less amplified...and lower amplitude waves in the atmosphere tend to move faster. The forecast track brings this system to the Lesser Antilles by tomorrow afternoon and evening...and then toward Haiti...Jamaica...the Cayman Islands...and Cuba by days 3 to 5. All of these land areas could see heavy rainfall and gusty winds even if a tropical cyclone does not form...especially if the wave maintains its current thunderstorm bands while taking advantage of the forecast favorable conditions in the Caribbean Sea.

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

IOH 24 Hr Outlook (1200Z Jun 30)...10% chance of tropical cyclone formation (east of the Lesser Antilles near 13N-56W)

IOH 48 Hr Outlook (1200Z Jul 1)...20% chance of tropical cyclone formation (eastern Caribbean Sea near 14N-62.5W)

IOH 72 Hr Outlook (1200Z Jul 2)...30% chance of tropical cyclone formation (south of the Dominican Republic near 16.5N-69.2W)

IOH 96 Hr Outlook (1200Z Jul 3)...30% chance of tropical cyclone formation (between southwestern Haiti and Jamaica near 17.8N-75.5W)

IOH 120 Hr Outlook (1200Z Jul 4)...30% chance of tropical cyclone formation (between Cuba and the Cayman Islands near 20.5N-81W)


AREA OF INTEREST #2...Infrared satellite images showing the rapid formation of an organized tropical low pressure spin overnight (circled in red) within the tropical wave in the eastern Atlantic:

The eastern Atlantic tropical wave of low pressure...located east of area of interest #1...has been interesting to watch over the last 12 hours while it rapidly developed an organized low pressure spin with spiral thunderstorm banding near 8N-35W. As such it has been promptly added into the National Hurricane Center tropical weather outlook as of 8 AM EDT. Much like area of interest #1...this tropical wave over the next five days will move westward within the deep-layered easterly flow on the south side of the tropical Atlantic upper ridge and Atlantic surface ridge...and will be in an environment conducive to further development with warm sea surface temperatures and expansive upper ridging with low shear and upper outflow...barring any dry saharan air intrusions from the north. The computer models over the last couple of days have switched to favoring this wave over area of interest #1...and that could be due to predictions of the leading wave in area of interest #1 keeping the atmosphere moist and thus mitigating the effect of the dry saharan air layer for this wave. Given the help of the leading wave in area of interest #1...the favorable conditions that lie ahead...and the healthier initial structure (low pressure with spiral bands) of this wave over area of interest #1...I already have 60% odds of tropical cyclone formation by days 3 to 5. I do not have as high odds for development in the short term as recent true-color satellite animation suggests the spin of the tropical wave is somewhat broad instead of tight...thus it will need time to consolidate. This tropical wave poses a bigger concern for the southern Lesser Antilles as it appears to have more potential for development...with the forecast below bringing this wave into the islands by Sunday. A lot of the models bring this wave into the islands as soon as Saturday...the forward speed of the wave will depend on whether it stays stronger or if it de-amplifies (lower amplitude featuers move faster in atmospheric flow...higher amplitude abd stronger features move slower).

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

IOH 24 Hr Outlook (1200Z Jun 30)...25% chance of tropical cyclone formation (eastern tropical Atlantic near 8.5N-40W)

IOH 48 Hr Outlook (1200Z Jul 1)...40% chance of tropical cyclone formation (central tropical Atlantic near 9N-45W)

IOH 72 Hr Outlook (1200Z Jul 2)...60% chance of tropical cyclone formation (central tropical Atlantic near 9.5N-50W)

IOH 96 Hr Outlook (1200Z Jul 3)...60% chance of tropical cyclone formation (east of Trinidad and the southern Lesser Antilles near 10N-56W)

IOH 120 Hr Outlook (1200Z Jul 4)...60% chance of tropical cyclone formation (southern Lesser Antilles near 12N-61W)


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)


0000Z CMC Model Run...

**For area of interest #1...crosses the Lesser Antilles as an amplified tropical wave at 42 hours...develops into a compact tropical low pressure located just east-northeast of eastern Honduras at 102 hours...no tropical cyclone formation shown while moving across Honduras through 120 hours.

**For area of interest #2...crosses the southern Lesser Antilles as a weak low-amplitude wave at 90 hours...tropical wave becomes more amplified over the southeastern Caribbean Sea at 102 hours...tropical wave begins to approach the southeast coast of Jamaica by 120 hours.


0000Z ECMWF Model Run...

**For area of interest #1...crosses the Lesser Antilles without further development just before 48 hours...no tropical cyclone formation shown

**For area of interest #2...crosses the Lesser Antilles between 72 and 96 hours while moving rapidly west-northwest as a compact tropical low pressure...tropical low pressure dissipates south of the Dominican Republic by 120 hours and no tropical cyclone formation shown


0600Z GFS Model Run...

**For area of interest #1...crosses the Lesser Antilles as a weak tropical wave at 39 hours...no tropical cyclone formation shown

**For area of interest #2...tropical cyclone formation shown near 7.8N-40.5W at 36 hours...intensifies into a compact hurricane near 10.8N-50.5W at 66 hours...compact and intense hurricane passes just south of Barbados and crosses the southern Lesser Antilles island chain at 90 hours...compact and intense hurricane located south of Haiti and the Dominican Republic near 16N-72W at 120 hours.


0600Z NAVGEM Model Run...

**For area of interest #1...crosses the southern Lesser Antilles as a weak tropical wave at 42 hours...no tropical cyclone formation shown as the tropical wave progresses across the Caribbean

**For area of interest #2...crosses the southern Lesser Antilles as a weak tropical wave at 96 hours...develops into a tropical low pressure south of Jamaica (14.5N-78W) by 132 hours

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