BIRDSEYE VIEW POSTS

Since 2012 on the Weather Underground (www.wunderground.com) 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 via Disqus on Weather Underground at www.wunderground.com/cat6. You can see my Disqus feed at this link for my latest comments. Feel free to reply to me with your disqus account or e-mail at IOHurricanes@outlook.com 

 
 
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MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #31

*******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.**********


...FRIDAY JUNE 25 2021 1:25 PM EDT...

See area of interest sections below for multiple areas being monitored for tropical development in the Atlantic basin. These areas of interest include:


(1) Area of interest #1...upper vortex and surface low in the vicinity of the Azores

(2) Area of interest #2...tropical wave of low pressure in the eastern tropical Atlantic

(3) Area of interest #3...surface trough of low pressure located north-northeast of the Lesser Antilles...supported by upper vorticity in the region


Elsewhere...the tail end of a frontal zone has been left behind offshore of the southeastern United States...with shower and thunderstorm activity being aided by the divergence zone of an upper trough fragment also left behind in the area. So far not enough thunderstorm activity and resultant latent heat release has not developed...therefore there is a lack of warm upper ridging aloft which is keeping wind shear induced by the cold core upper trough fragment elevated. Therefore tropical development here is not anticipated.


AREA OF INTEREST #1...An upper vortex and surface frontal low are currently centered just north of the western Azores near 40N-30W. The surface frontal low...which formed yesterday under the supportive eastern divergent side of the upper vortex...has whirled to a position directly below the upper vortex...essentially creating a deep-layered low pressure system. The surface frontal low which comprises the surface layer of the deep-layered circulation will no longer be able to strengthen as it is directly below the upper vortex center where there is a lack of divergence...and as shower and thunderstorm activity has not developed over the center as the upper vortex is not quiet cold enough to produce instability as the water temps at 40N latitude are barely in the low 20-deg C range. However I have not yet cancelled this area of interest as the ECMWF and now the CMC are suggesting potential for subtropical development as the deep-layered low pressure system interacts with the northwest Atlantic upper trough and surface cold front approaching from the west.


Models are in agreement that a portion of the northwest Atlantic upper trough will become a shortwave trough that orbits around the south side of the deep-layered low pressure system over the next 24 hours. If the CMC and ECMWF are correct...that means a compact surface low will be birthed on the south side of the northwest Atlantic upper trough's cold front...or on the southwest side of the deep-layered low pressure...with the support of the divergence zone of the orbiting shortwave. The further south position of the compact surface low would place it firmly in low-20 deg C water temps...and combined with the cold (potentially destabilizing) upper air temps of the deep-layered low and upper divergence of the orbiting shortwave there is still a window of opportunity for thunderstorms and tropical characteristics to develop with the compact surface low. Therefore in my updated outlook below I have slightly raised odds of subtropical cyclone formation from 5% to 10% for the next 24 hours. After that time...the deep-layered low pressure system is expected to slide west under the influence of the north Atlantic upper ridge all while the upper shortwave and compact surface low orbit northward through the Azores and around the east side of the deep-layered low pressure. By 48 hours...this would place the compact surface low over cooler waters north of the Azores...which is when I drop odds of subtropical development to 0%.


Because the surface layer of the deep-layered low will no longer be able to strengthen as noted above...it no longer has potential to bring notable weather to the Azores. However...if a compact orbiting surface low with tropical characteristics develops as the ECMWF and CMC suggest...the Azores could see a brief period of gusty winds Saturday afternoon or evening.

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

IOH 24 Hr Outlook (1200Z Jun 26)...10% chance of subtropical cyclone formation (southwest of the western Azores near 37.5N-34W)

IOH 48 Hr Outlook (1200Z Jun 27)...0% chance of subtropical cyclone formation (northeast Atlantic near 42.5N-30W)


AREA OF INTEREST #2...The vigorous tropical wave of low pressure in the eastern tropical Atlantic appears to have kicked off a dry saharan air surge to the northwest that may have been self-defeating. The northwest side of the tropical wave's low pressure spin now lacks thunderstorm activity while ingesting the dry air surge...while the southeast half of the spin has developed thunderstorm activity supported by the southern outflow of the tropical upper ridge in the region. Perhaps while being initialized with this latest data...all of the global models have now backed off in showing tropical cyclone formation. As the tropical wave continues west within the deep-layered easterly flow on the south sides of the Atlantic surface ridge and tropical upper ridge over the next five days...it will remain in a low shear and upper outflow environment...with its track staying far south enough such that it stays over 26+ deg C warm waters. I have dropped odds of tropical cyclone formation 50% to 30% (and the NHC has recently dropped odds of development from 40% to 20%) due to the current observations of dry saharan air. However because the wave is still vigorous with a closed surface spin and at least has thunderstorms in one half of the closed spin...it remains to be seen if it can mix out the dry air and develop with the aformentioned favorable water temps and atmospheric conditions (low shear...upper outflow)...and so this area of interest for tropical development is not yet cancelled.

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

IOH 24 Hr Outlook (1200Z Jun 26)...0% chance of tropical cyclone formation (eastern tropical Atlantic near 9N-25.5W)

IOH 48 Hr Outlook (1200Z Jun 27)...10% chance of tropical cyclone formation (eastern tropical Atlantic near 9.5N-30.5W)

IOH 72 Hr Outlook (1200Z Jun 28)...20% chance of tropical cyclone formation (eastern tropical Atlantic near 10N-35.5W)

IOH 96 Hr Outlook (1200Z Jun 29)...30% chance of tropical cyclone formation (central tropical Atlantic near 10.5N-41W)

IOH 120 Hr Outlook (1200Z Jun 29)...30% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-46.5W)


AREA OF INTEREST #3...The central Atlantic upper vortex located north-northeast of the Lesser Antilles continues to produce thunderstorm activity with the aid of its eastern divergence zone. The surface trough of low pressure that it birthed recently with this divergence zone has moved westward to a position below the upper vortex center where there is a lack of divergence. ASCAT passes only show a weak kink in the surface wind field associated with the surface trough...however just above the surface the CIMSS 850 mb vorticity product shows a somewhat defined spin near 26N-59W (http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=vor&zoom=&time=). With the surface trough direclty below the upper vortex center where divergence tends to be lacking...it would seem the potential for tropcial development of the surface trough would be over. However the 0600Z GFS model run from this morning suggested the upper vortex would become stretched west-to-east and even split into two halves due to amplification of the upper ridge over the southern US into the northwest Atlantic (the amplification of the warm upper ridge will be driven by the current warm sector of the northeastern Canadian frontal cylcone and also another Canadian frontal system to follow behind). If in fact the upper vortex splits in half...this would allow for an area of low shear and upper divergence in between...therefore I have extended my outlook on this system through 4 days (96 hours) to indicate the possiblity of this surface trough developing further in that environment. However I only have low 10% odds of development as the upper vortex would have to split in half as the GFS showed and this is not guaranteed...for example if the upper vortex simply stretches out into one continuous string of vorticity then upper winds would not be conducive for development with a lack of divergence overhead. Upper convergence to the north of the stretching upper vortex and southeast side of the amplifying northwest Atlantic upper ridge will keep the Atlantic surface ridge weighted to the west with no weakness...thus the forecast track below shows the west-weighted surface ridge pushing the surface trough west-northwest toward the waters offshore of the northwest Bahamas and northeast Florida. By day 4...the latest GFS run shows the upper vortex halves rejoining...resulting in the loss of upper divergence...thus I drop odds of development to 0% by that time.

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

IOH 24 Hr Outlook (1200Z Jun 26)...10% chance of tropical cyclone formation (western Atlantic near 27N-64W)

IOH 48 Hr Outlook (1200Z Jun 27)...10% chance of tropical cyclone formation (western Atlantic near 28N-70W

IOH 72 Hr Outlook (1200Z Jun 28)...10% chance of tropical cyclone formation (northeast of the western Bahamas near 28.5N-75W)

IOH 96 Hr Outlook (1200Z Jun 29)...0% chance of tropical cyclone formation (offshore of northeastern Florida near 30N-80W)


...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...Broad frontal low currently centered at 40N-30W develops a new tight center on its southwest side near 36.5N-35W while absorbing the north Atlantic cold front approaching from the west...compact circulation swings east into the Azores by 36 hours while gradually weakening...circulation subsequently drifts slowly north out ahead of cold front to be driven into the far north Atlantic by the current NE Canada frontal cyclone and reaches 45N-32W by 120 hours where it becomes absorbed by the front.

**For area of interest #2...no tropical cyclone formation shown

**For area of interest #3...no tropical cyclone formation shown


0000Z ECMWF Model Run...

**For area of interest #1...Broad frontal low currently centered at 40N-30W develops a new tight center on its southwest side between 0 and 24 hours while absorbing the north Atlantic cold front approaching from the west...compact circulation becomes a subtropical cyclone centered at 35.5N-32W at 24 hours...weakens to a remnant low by 48 hours while swinging north to 43.5N-29W...remnant low swings west to 40.2N-36W by 72 hours...remnant low subsequently drifts slowly north out ahead of cold front to be driven into the far north Atlantic by the current NE Canada frontal cyclone and reaches 44N-31W at 120 hours.

**For area of interest #2...no tropical cyclone formation shown

**For area of interest #3...no tropical cyclone formation shown


0600Z GFS Model Run...

**For area of interest #1...broad frontal low currently centered at 40N-30W drifts slowly west while absorbing north Atlantic cold front approaching from the west and arrives to 39N-35W by 60 hours...subsequently drifts slowly north out ahead of cold front to be driven into the far north Atlantic by the current NE Canada frontal cyclone and reaches 46.5N-33W at 117 hours where it becomes absorbed by the front.

**For area of interest #2...no tropical cyclone formation shown

**For area of interest #3...no tropical cyclone formation shown


0600Z NAVGEM Model Run...

**For area of interest #1...broad frontal low currently centered at 40N-30W drifts slowly west while absorbing north Atlantic cold front approaching from the west and arrives to 40.2N-36W by 66 hours...subsequently drifts slowly north out ahead of cold front to be driven into the far north Atlantic by the current NE Canada frontal cyclone and reaches 43.5N-31W at 108 hours where it becomes absorbed by the front.

**For area of interest #2...tropical wave maintains tropical low pressure spin and arrives to 13.5N-54W at 120 hours.

**For area of interest #3...no tropical cyclone formation shown

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