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 #28

*******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 22 2021 10:27 PM EDT...

See Claudette section below for a final statement on the remnants of the former tropical storm…which is offshore of Nova Scotia. See area of interest sections below for multiple areas being monitored for development.


Elsewhere…the tail end of the cold front being driven into the western Atlantic by the current northeast Canada frontal cyclone will likely leave behind a surface trough of low pressure offshore of the Carolinas over the next day or so…to be supported by the divergence zone of an upper trough fragment to also be left behind over the southeast coastal US. If the surface trough develops enough thunderstorm activity and resultant latent heat release…it could increase warm upper ridging aloft that would reduce the shearing effects of the upper trough fragment…and the 1800Z GFS model run has hinted at this as of this evening. Therefore yet another area Interest may be declared offshore of the Carolinas over the next 48 hours.


REMNANTS OF CLAUDETTE...Tropical Storm Claudette within the last 24 hours lost its closed surface spin while moving into the northwest Atlantic waters offshore of Nova Scotia. This was probably due to the fact Claudette was not a particularly strong tropical storm…coupled with the fast northeast track of Claudette taking away from northerly flow on its west side that would have otherwise kept the circulation closed (meanwhile the fast northeast track has enhanced the southerly flow on the east side of the circulation). The remnant low is not quiet as far northeast as I previously forecast…therefore it has been able to take advantage of some upper divergence out ahead of the large North American upper trough to the west and maintain its existence. It is possible that the remnants produce gusty winds and choppy seas offshore of Nova Scotia and Newfoundland over the next few hours…albeit it could be argued these offshore conditions are also attributed to the strong low pressure field of the surface cold front being driven into the Atlantic by the aforementioned upper trough. This is my final statement on Claudette on this blog as it is no longer a tropical cyclone.


AREA OF INTEREST #1…The National Hurricane Center continues to monitor a tropical wave of low pressure in the central Atlantic for further development as the wave continues to take advantage of low shear and upper outflow beneath low-latitude upper ridging currently present…and in fact its shower and thunderstorm field has grown in size over the last 24 hours. More recently…as of 0000Z…a small circular thunderstorm cluster has fired near the center of spin at 12.5N-55W. Therefore I have increased short-term odds of development to 15% over the next 24 hours.


The southwest portion of the current northwest Atlantic upper trough is being pushed southward toward this tropical wave by the amplifying upper ridging over in the west Atlantic (this ridging is supported by the warm sector of the current NE Canada frontal low). This portion of the upper trough will drive increasing westerly shearing winds over the wave by 24+ hours…and thus I trim odds of development down to 0% by 48 hours. Therefore the chances that this wave will be a tropical cyclone (depression or storm) while passing the southern Lesser Antilles just after 24 hours remains low even if short-term development occurs tonight…however the wave may bring enhanced rainfall if the wave’s thunderstorms becomes enhanced by the eastern divergence zone of the arriving upper trough energy.

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

IOH 24 Hr Outlook (1800Z Jun 23)…15% chance of tropical cyclone formation (just east of the southern Lesser Antilles near 13N-59W)

IOH 48 Hr Outlook (1800Z Jun 24)…0% chance of tropical cyclone formation (eastern Caribbean Sea near 14N-63W)


AREA OF INTEREST #2…The northeast portion of the current northwest Atlantic upper trough is forecast to become a cut-off cold upper vortex that becomes pushed southeastward into the Azores by the amplifying upper ridging over the west Atlantic (this ridging is supported by the warm sector of the current NE Canada frontal low). The surface frontal low currently supported by the divergence zone of the upper trough is forecast to regenerate southeastward while supported by the divergence zone of the upper vortex…or alternatively the current frontal low will dissipate while a new one forms to the southeast. Although water temps around the Azores are in the low 20 deg C range…the upper vortex could become cold enough to support thunderstorms and acquisition of tropical characteristics for the surface frontal low to be supported by the upper vortex. However I have low 10% odds of subtropical cyclone formation as the 200 mb height of the upper vortex is forecast to be around 1200 dekameters…would like to see a colder upper vortex with a height of below 1200 dekameters for more confidence in subtropical development at these water temps. Forecast positions in the Outlook below are based on the positions of the forecast cut-off upper vortex over the next five days from today’s 1800Z GFS model run. By 120 hours I trim off development odds down to 5% as the surface frontal low by then will have whirled directly below the upper vortex center where there is a lack of divergence…which will cause it to gradually weaken by that time if it does not develop before then.


Regardless of subtropical development or not…if the surface frontal low becomes strong enough gusty winds and coastal sea swells will be possible for the Azores in the 2 to 4 day timeframe.

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

IOH 24 Hr Outlook (1800Z Jun 23)…0% chance of subtropical cyclone formation (northeast Atlantic near 50N-26W)

IOH 48 Hr Outlook (1800Z Jun 24)…0% chance of subtropical cyclone formation (northeast Atlantic near 44N-26W)

IOH 72 Hr Outlook (1800Z Jun 25)…10% chance of subtropical cyclone formation (western Azores near 39N-30W)

IOH 96 Hr Outlook (1800Z Jun 26)…10% chance of subtropical cyclone formation (western Azores near 39N-30W)

IOH 120 Hr Outlook (1800Z Jun 27)…5% chance of subtropical cyclone formation (northeast Atlantic 40.5N-35W)


AREA OF INTEREST #3…Conditions in the eastern tropical Atlantic have improved for potential development as dry Saharan air has been weakened by tropical waves of low pressure emerging from Africa that are producing widespread thunderstorm activity. Models forecast that the upper ridge in the region keeping shear low and outflow high will be in place for the next several days…and are also in agreement that the tropical wave currently over central Africa will emerge into the eastern tropical Atlantic while developing into a tropical low pressure spin. Therefore I have introduced this wave as an area of interest for tropical development with such a strong model signature and consensus remaining in place. My peak odds of development are currently at a low 20% as none of the models however explicitly forecast a tropical cyclone…and as climatology does not usually favor development in this region in June. In particular…it is also possible that the vigorous wave kicks up some dry Saharan air from NW Africa and ingests it as it moves into the eastern tropical Atlantic.

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

IOH 24 Hr Outlook (1800Z Jun 23)…0% chance of tropical cyclone formation (Western Africa near 9N-6W)

IOH 48 Hr Outlook (1800Z Jun 24)…0% chance of tropical cyclone formation (Western Africa near 9N-11W)

IOH 72 Hr Outlook (1800Z Jun 25)…0% chance of tropical cyclone formation (just offshore of western Africa near 9N-16W)

IOH 96 Hr Outlook (1800Z Jun 26)…10% chance of tropical cyclone formation (eastern tropical Atlantic near 9N-21W)

IOH 120 Hr Outlook (1800Z Jun 27)…20% chance of tropical cyclone formation (eastern tropical Atlantic near 9.5N-26W)


...COMPUTER MODEL SUMMARY...

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


1200Z CMC Model Run...

**For area of interest #1...no tropical cyclone formation shown

**For area of interest #2...surface frontal low arrives just west of the Azores by 72 hours….drifts east into the western Azores by 102 hours…drifts northwest to 40N-30W by 120 hours.

**For area of interest #3…tropical wave reaches the eastern Atlantic near 9N-19W by 72 hours…maintains a broad closed surface spin while reaching 9.5N-31W by 120 hours.


1200Z ECMWF Model Run...

**For area of interest #1...no tropical cyclone formation shown

**For area of interest #2...surface frontal low arrives just northwest of the Azores by 72 hours….cyclonically loops over the western Azores through hours.

**For area of interest #3…tropical wave reaches the eastern Atlantic near 11N-19W by 72 hours…maintains a broad closed surface spin thru 96 hours...closed spin opens to a wave at 34W longitude by 120 hours.


1800Z GFS Model Run...

**For area of interest #1...no tropical cyclone formation shown

**For area of interest #2...surface frontal low arrives just west of the Azores by 72 hours….cyclonically loops in this region through 120 hours.

**For area of interest #3…tropical wave reaches the eastern Atlantic near 9N-19W by 66 hours…maintains a closed spin thru 120 hours while arriving to 11N-33W

**Surface low left behind by cold front at a location offshore of the Carolinas at 27 hours…drifts north toward New Jersey coast thru 66 hours.

1200Z NAVGEM Model Run...

**For area of interest #1...no tropical cyclone formation shown

**For area of interest #2...surface frontal low arrives over the western Azores by 78 hours….cyclonically loops at this location through 120 hours.

**For area of interest #3…tropical wave reaches the eastern Atlantic near 11N-18W by 72 hours…develops a large closed spin by 96 hours at a location SE of the Republic of Cabo Verde Islands…center of spin reaches 11.5N-30W at 120 hours.

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