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 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #91

*******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 AUGUST 14 2020 11:30 AM EDT...

See Tropical Storm Josephine section below for the only active tropical cyclone in the Atlanic basin. See area of interest section below for a surface low pressure located just offshore of North Carolina being monitored for tropical development. Elsewhere...the 0600Z NAVGEM model run from August 11 suggested thunderstorm activity in the southern Caribbean Sea could organize and develop in response to the outflow of a local upper ridge cell forming and expanding in the wake of the currently slowly weakening western Atlantic upper trough...and indeed thunderstorm activity in this region has flared up this morning...with additional support from a surface tropical wave of low pressure moving into the region. However the thunderstorm activity is currently not organized...therefore tropical cyclone formation is not expected before the tropical wave makes landfall in Central America. However heavy rainfall maybe possible over the Central American nations of Honduras...El Salavador...Nicaragua...and Costa Rica over the next day or so. This system will likely develop after crossing Central America and entering the eastern Pacific...and since the eastern Pacific is outside of the Atlantic coverage provided on this website...see the National Hurricane Center eastern Pacific tropical weather outlook (at hurricanes.gov) for details on eastern Pacific activity.


TROPICAL STORM JOSEPHINE...Over the last 24 hours Josephine has been hanging on to minimal tropical storm status with 40 to 45 mph maximum sustained winds despite large thunderstorm flare ups aided by the outflow of a tropical upper ridge cell in the region. This is because the flare ups have continued to be biased to the northwest of the surface center thanks to some southeasterly shear also induced by the cell of upper ridging...and I speculate that the shear has allowed for some dry saharan air to the east to make its way toward Josephine's center which has not been able to protect itself from the dry air while remaining on the edge of the thunderstorm bursts rather than being fully under the bursts. None of today's model runs show Josephine strengthen...but instead weakening into a remnant tropical wave or surface trough of low pressure while passing just north of the northeastern Caribbean islands. This weakening is to be caused by stronger westerly shear to be induced by the upper trough currently spanning the Gulf of Mexico and western Atlantic. Thus I forecast Josephine to weaken to a remnant low pressure by 72 hours...but it is possible that Josephine weakens to a remnant low sooner. Regarding the track forecast...I have nudged the track points northward due to the current position of Josephine. A curve to the north in the track is shown after 48 hours as the current frontal zone over the eastern United States will erode the west side of the steering Atlantic surface subtropical ridge.

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

0 Hr Position (1200Z Aug 14)...40 mph maximum sustained wind tropical storm centered at 15.3N-53.3W

IOH 24 Hr Forecast (1200Z Aug 15)...40 mph maximum sustained wind tropical storm centered just east of the northern Lesser Antilles at 17N-59W

IOH 48 Hr Forecast (1200Z Aug 16)...30 mph maximum sustained wind tropical depression centered just north of the Virgin Islands at 20.5N-64.5W

IOH 72 Hr Forecast (1200Z Aug 17)...Remnant surface low pressure centered in the western Atlantic at 24.5N-67W


AREA OF INTEREST #1...A surface cold front and its associated upper trough have recently entered the northwestern Atlantic from the northeastern United States. Just out ahead of this front...a surface low pressure system with well-organized thunderstorm bands continues to flourish while moving offshore from North Carolina and into the northwestern Atlantic. This feature is supported by upper outflow from upper ridging associated with the warm air ahead of the front. The thunderstorm bands mainly cover the east half of the surface low pressure circulation while the remainder of the circulation is less active due to cooler dry air behind the incoming front. However given the highly organized nature of the thunderstorm bands and how close they are to the center of circulation...I give this system a very high 80% chance of tropical cyclone formation in the next 24 hours before the cold front overruns the circulation and makes this system less tropical in nature. Regardless of its tropical or non-tropical status...this system is forecast to strengthen in the short-term as the divergence zone of the upper trough associated with the front also overspreads the circulation...potentially bringing coastal sea swells and rip currents to the mid-Atlantic and northeastern United States coast...as well as the Nova Scotia coast. Regarding track...this system will continue east-northeast across the open northwestern and then open northern Atlantic while swept up by the front. The center of circulation appears to be consolidating at 36N-74W...a little northeast of my previous forecast track...so my updated track points are nudged northeastward accordingly. After 48 hours...as this system passes south of Newfoundland and heads into the open north Atlantic...it appears this system will weaken while a much larger and more powerful frontal cyclone takes hold in the northeast Atlantic. This has to do with the evolution of the front's upper trough...which will at first become streteched southwest-to-northeast due to a building upper ridge over eastern Canada and in the short-term provide upper divergence to support and maintain this system. But after 48 hours...the northeast part of the upper trough will amplify into a tremendous upper vortex as the eastern Canada upper ridge continues to amplify adjacent to it...producing the larger surface northeastern Atlantic frontal cyclone with its expansive eastern upper divergence zone...with this frontal cyclone likely to absorb this system.

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

IOH 24 Hr Outlook (1200Z Aug 15)...80% chance of tropical cyclone formation (northwestern Atlantic near 38N-70W)

IOH 48 Hr Outlook (1200Z Aug 16)...0% chance of tropical cyclone formation (northwestern Atlantic near 41N-63W)


...COMPUTER MODEL SUMMARY...

Source...Tropical Tidbits (https://www.tropicaltidbits.com/analysis/models/)


0000Z CMC Model Run...For Tropical Storm Josephine...opens into a remnant trough of low pressure just northeast of the Bahamas in 84 hours. For area of interest #1...low pressure currently just offshore of North Carolina moves east-northeast into the northwestern Atlantic strengthens into a strong elongated low pressure in the vicinity of 38.5N-61.5W by 60 hours (elongated nature indicates system is non-tropical and frontal in nature)


0000Z ECMWF Model Run...For Tropical Storm Josephine..,weakens to a remnant tropical wave just east-northeast of the northern Lesser Antilles near 17.5N-58W in 24 hours. For area of interest #1...low pressure currently just offshore of North Carolina moves east-northeast into the northwestern Atlantic strengthens into a strong elongated low pressure in the vicinity of 42.5N-54.5W by 72 hours (elongated nature indicates system is non-tropical and frontal in nature)


0600Z GFS Model Run...For Tropical Storm Josephine...opens into a remnant tropical wave just north of the Lesser Antilles near 20N-62W in 42 hours. For area of interest #1...low pressure currently just offshore of North Carolina moves east-northeast into the northwestern Atlantic strengthens into a strong elongated low pressure in the vicinity of 40.5N-59W by 60 hours (elongated nature indicates system is non-tropical and frontal in nature)


0600Z NAVGEM Model Run...For Tropical Storm Josephine...opens into a remnant trough of low pressure just northeast of the Bahamas in 90 hours. For area of interest #1...low pressure currently just offshore of North Carolina moves east-northeast into the northwestern Atlantic strengthens into a strong elongated low pressure in the vicinity of 41.5N-60W by 60 hours (elongated nature indicates system is non-tropical and frontal in nature)

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