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 #128

*******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 SEPTEMBER 22 2020 12:11 PM EDT...

See Hurricane Teddy....Tropical Depression Beta...and Tropical Storm Paulette for the three currently active tropical cyclones in the Atlantic basin. See area of interest section below for the tail end of a cold front moving into Cuba being monitored for tropical development. Elsewhere in the open central Atlantic to the northeast of Tropical Storm Wilfred's remnants...a surface trough of low pressure with thunderstorms has developed in the northeastern divergence zone of the cut-off upper vortex that sheared apart Wilfred. However development here is not likely as the upper trough interacting with Hurricane Teddy will slide eastward and absorb the cut-off upper vortex by 48 hours...creating upper southwesterly flow in the region that will likely increase wind shear unfavorable to tropical development.


HURRICANE TEDDY...While interacting with a large upper trough that ejected from eastern North America...Teddy has accelerated northward while passing east of Bermuda and entering the northwestern Atlanic in the last day. Initially the trough disrputed the west side of Teddy and caused it to weaken to category 1 90 mph maximum sustained winds yesterday evening...but in the overnight aircraft reconaissance found Teddy intensified back to category 2 status with 105 mph maximum sustained winds due to the tremenodus upper divergence zone on the east side of the upper trough. Part of the reason for the impressive upper divergence zone is Teddy's west side has pulled cold air associated with the upper trough southward...thus making the upper trough more amplified. The more amplified nature of the upper trough is also exhibited in Teddy's track which has bent more westward while accelerating as the upper trough is amplified enough to whirl Teddy into itself...positioning the hurricane northwest of my previous forecast track. The acceleration in the track is caused by a strengthening jet between the cold upper trough and warm upper ridge to the east as Teddy's stronger than expected circulation has been able to bring the cold and warm air masses closer to each other than previously projected. However I have only adjusted the track westward as Teddy will slow down its northward acceleration once it whirls to a positon west of the jet and closer to the upper trough axis. Some weakening is anticipated before Teddy's center makes landfall in Nova Scotia as the upper trough axis does not have as much supportive divergence as the east side of the upper trough...but the weakening rate will be slow as Teddy will experience some supportive divergence on the east side of a second upper trough currently approaching from central North America. The intensity forecast is raised back to where it was in birdseye view post #124 given Teddy's current intensity...raising the prospects of hurricane force winds from Teddy over Nova Scotia even though it loses tropical characteristics in the next 24 hours due to cooler waters and ongoing interactions with upper troughs.


The wind field of Teddy has expanded due to the size of the upper divergence zone of the incoming upper trough which is dropping surface pressures over a wide area...and also because of the pressure gradient between Teddy and surface ridge over the eastern United States supported by the increasing upper convergence zone of the amplifying upper trough. This is resulting in a large amount of water getting pushed in the western Atlantic...so coastal sea swells and rip currents will remain a problem for the United States east coast...Bermuda...and Atlantic Canada coasts till Teddy crosses Atlantic Canada and moves into the far north Atlantic. Due to the forecast landfall point in Nova Scotia and large size of Teddy's wind field...I recommend preparations for damaging winds should be rushed to completion in eastern Maine...New Brunswick...Nova Scotia...Prince Edward Island...and Newfoundland. The worst wind damage is expected over Nova Scotia and Prince Edward Island. The southerly and easterly onshore push of water on the east and north side of Teddy will cause coastal storm surge problems for parts of Nova Scotia...Prince Edward Island...Quebec...New Brunswick...and Newfoundland.

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

0 Hr Position (1200Z Sep 22)...105 mph maximum sustained wind hurricane centered in the northwestern Atlantic at 39.3N-63.5W

IOH 24 Hr Forecast (1200Z Sep 23)...85 mph maximum sustained wind non-tropical remnant gale centered over Nova Scotia at 45N-63W


TROPICAL STORM BETA (RECENTLY DOWNGRADED TO TROPICAL DEPRESSION BETA)...In some way Beta is coupling to upper-level steering after the center made landfall in Matagorda Bay Texas as the storm has not moved much since the landfall...due to upper westerly flow from an incoming upper trough over the southwestern United States trying to push Beta eastward...but with the eastward progress being blocked so far by the strong surface ridge over the eastern United States. My forecast track assumes Beta will transition into a less tropical remnant low pressure supported by the eastern divergence zone of the incoming upper trough...with stronger upper southwesterly flow induced by the arrival of the trough pushing Beta's center northeastward away from Matagorda Bay and toward the Galveston Bay/Houston area in the next 24 hours. My updated forecast track is nudged west of the previous one due to Beta's currently more west position...perhaps because the tropical storm has weakened and become shallow enough to be kept more west by the surface ridge over the eastern United States. Don't let the current lack of thunderstorm intenisty in Beta's circulation fool you...there is still a rainfall flooding threat for southeast Texas and southern Louisiana in the coming days...especially if Beta's thunderstorms intensify in the divergence zone of the incoming upper trough. Even with Beta's current lack of thunderstorm intensity...it has already caused rainfall flooding in southeast Texas including the Houston area. When encountering a flooded roadway...do not drive into the floodwater to avoid accidental drowning!


11 AM EDT update...the National Hurricane Center has downgraded Beta to a tropical depression. This does not change the severity of the rainfall flood threat...just an indication that the winds in Beta have dropped below tropical storm force due to the landfall.

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

0 Hr Position (1200Z Sep 22)...40 mph maximum sustained wind tropical storm centered just inland from Matagorda Bay Texas at 28.8N-96.8W

IOH 24 Hr Forecast (1200Z Sep 23)...Remnant low pressure centered just inland over southeastern Texas at 30.5N-95W


TROPICAL STORM PAULETTE...It appears developing deep-layered ridging to the west driven by warm air advection (northward warm air transport) on Teddy's east side is stronger than previously anticipated as Teddy's intensity is higher than previous forecasts...see Teddy section for details. The warm air transport from Teddy is amplifying the warm north Atlantic upper ridge to the west...with increasing convergence on the east side of the strengthening upper ridge supporting surface ridging. Paulette has slowed down its eastward speed as the deep-layered ridging is trying to capture the storm...and models have picked up on the stronger ridging by now turning Paulette westward around the south side of the ridge later in the forecast period...only the GFS is the last holdout showing Paulette continuing east. My updated track forecast is adjusted accordingly and is a compromise between the GFS and the NAVGEM-CMC-ECMWF camps...showing a slower eastward track for the next 24 hours...then a southeastward drift by 48 hours as the ridge tries to reverse the track of Paulette westward.


Evidence that Paulette's thunderstorms last night were supported by the eastern divergence zone of the overhead 200 mb upper vorticity has increased as the slower eastward track has caused Paulette to slip out of this zone while the upper vorticity continues at a faster eastward pace...and behold the thunderstorm activity in Paulette's circulation has dissipated and the tropical storm has weakened from 60 to 40 mph maximum sustained winds as of 11 AM EDT this morning. This is because the tropical storm is over waters in the low 20s of deg C and the upper vorticity is also not cold enough to help Paulette fire thunderstorms at these water temperatures...so my assessment is that Paulette will be dependant on 200 mb upper divergence going forward. In the next 24 hours the GFS shows a portion of the current north Atlantic upper trough diving southward around the amplifying deep-layered ridge and toward Paulette...providing another round of divergence on the east side of this energy. Therefore I assume Paulette will redevelop thunderstorms by 24 hours and hang on as a tropical depression. By 48 hours the forecast track removes Paulette from this 200 mb divergence zone as the energy splits into two parts...one that retrogrades southwestawrd away from Paulette around the deep-layer ridge...and another that slides eastward away from Paulette into Europoe. This is also when the GFS rapidly weakens Paulette...so I assume by 48 hours Paulette will have weakened to a remnant low pressure. The updated track is nudged northward further away from Madeira island in the short term due to Paulette's current position...and the intensity is adjusted downward due to Paulette's current intensity. This reduces the potential for the island to see direct gusty winds and heavy rains from Paulette. However Madeira and the Canary Islands will likely see rainfall from a thick band of clouds east of Paulette being driven by the eastern divergence zone of the upper vorticity in the area.

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

0 Hr Position (1200Z Sep 22)...40 mph maximum sustained wind tropical storm centered in the eastern Atlantic at 35N-22.3W

IOH 24 Hr Forecast (1200Z Sep 23)...35 mph maximum sustained wind tropical depression centered north of Madeira Island at 35N-17.5W

IOH 48 Hr Forecast (1200Z Sep 24)...Remnant low pressure centered east of Madeira Island at 33.5N-15W


AREA OF INTEREST #1....The National Hurricane Center continues to monitor the tail end of a western Atlantic cold front shifting southward into Cuba (this same front is also merging with Hurricane Teddy). As Beta transitions into a less tropical system in the vicinity of southern Louisiana in the coming days...it will push the warmest air in the Gulf of Mexico southeastward toward Cuba...resulting in a warm upper ridge directly over the decaying front such that the decaying front might evolve into a tropical disturbance with thunderstorms aided by the outflow and low shear of the upper ridge. After 24 hours...whatever disturbance develops over Cuba would shift northwestward across the eastern Gulf of Mexico around the southwest side of the eastern United States surface ridge. For the next few days...I have lowered peak odds of development only at a very low 5% until there are signs of a disturbance developing along the front. There will also be only a narrow window of time for development as any disturbance that develops would soon enter shearing upper southwesterly winds on the northwest side of the Cuba upper ridge.

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

IOH 24 Hr Outlook (1200Z Sep 23)...0% chance of tropical cyclone formation (over Cuba near 22.5N-80W)

IOH 48 Hr Outlook (1200Z Sep 24)...5% chance of tropical cyclone formation (southeastern Gulf of Mexico offshore of western Cuba near 24N-84W)

IOH 72 Hr Outlook (1200Z Sep 25)...0% chance of tropical cyclone formation (eastern Gulf of Mexico near 26.5N-86W)


...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 Hurricane Teddy...makes landfall over eastern Nova Scotia in 42 hours. For Tropical Storm Beta...drifts slowly eastward back over the northwestern Gulf of Mexico and southeast Texas coast as a broadening low pressure that loses its identity in the vicinity of the Texas/Louisiana border in 108 hours. For Tropical Storm Paulette...stalls just northwest of Madeira island in 48 hours...accelerates weswtard under influence of surface ridge incoming from the northwestern Atlantic...weakens to a surface trough on the south side of the ridge near 32.5N-26W at 72 hours. For area of interest #1...no tropical cyclone formation shown.


0000Z ECMWF Model Run....For Hurricane Teddy...makes landfall over eastern Nova Scotia in between 24 and 48 hours. For Tropical Storm Beta...stationary near Matagorda Bay Texas for 24 hours...remnant low pressure accelerates northeastward into northwestern Alabama by 72 hours...weakens to a surface trough over northern Georgia by 96 hours. For Tropical Storm Paulette...stalls just northwest of Madeira island in 48 hours...accelerates weswtard under influence of surface ridge incoming from the northwestern Atlantic while weakening to a remnant low pressure (remnant low located at 31N-35W at 120 hours). For area of interest #1...no tropical cyclone formation shown.


0600Z GFS Model Run...For Hurricane Teddy...makes landfall over eastern Nova Scotia at 36 hours. For Tropical Storm Beta...stationary just east of Matagorda Bay Texas for 24 hours...remnant low pressure drifts eastward into Louisiana where it weakens to a surface trough in 78 hours. For Tropical Storm Paulette...weakens rapidly midway between Portugal and Madeira island by 54 hours...dissipated by 60 hours. For area of interest #1...no tropical cyclone formation shown.


0600Z NAVGEM Model Run...For Hurricane Teddy...makes landfall over eastern Nova Scotia at 36 hours. For Tropical Storm Beta...drifts eastward back into the northwestern Gulf of Mexico by 36 hours...drifts northawrd and makes landfall in southern Louisiana by 78 hours...remnant low loses identity at Mississippi/Louisiana border at 96 hours. For Tropical Storm Paulette...turns southward to the west of the Canary Islands by 48 hours...accelerates westward under influence of surface ridge incoming from the northwestern Atlantic and weakens to a surface trough near 30N-23W at 60 hours. For area of interest #1...no tropical cyclone formation shown.

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