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 #126

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


...SUNDAY SEPTEMBER 20 2020 4:25 PM EDT...

Satellite Image from 1950Z (red indicates tropical cyclone or remnants of tropical cyclone...with T marking Teddy...W marking Wilfred..B marking Beta. Green indicates an area of interest in the National Hurricane Center Tropical Weather Outlook. Yellow indicates an area of interest not in the National Hurricane Center Tropical Weather Outlook.):

NHC TAFB Surface Analysis 1200Z:


GFS Model Upper Level Winds 1200Z:



See Hurricane Teddy...Tropical Storm Beta...and Tropical Depression Wilfred sections below for all three currently active tropical cyclones in the Atlantic basin. See area of interest sections below for multiple disturbances being monitored for tropical or subtropical cyclone formation...one of which is the remnant circulation of Hurricane Paulette currently located just southwest of the Azores.

Note that the forecasts for Teddy and Beta were completed earlier in the day and have a 1200Z timestamp...while the forecasts for the other systems were completed recently with 1800Z timestamps.

HURRICANE TEDDY...In the last day Teddy has weakened further to a category 2 hurricane as yet another eye wall replacement cycle may have been starting according to the 11 PM EDT NHC advisory from last night...followed by the arrival westerly shear that has displaced the stronger thunderstorm activity to the east. This shear has arrived about 24 hours earlier than I anticipated. Looking at the 0600Z and 1200Z GFS model upper level wind fields...it appears the shear is due to an axis of warm upper ridging to the west that rivals the warm core upper anticyclone of Teddy...generated by warm southerly flow ahead of the front associated with the large upper trough approaching from eastern North America.

The biggest concern with Teddy is how it will affect Bermuda not long after Paulette already struck the island. As a still strong hurricane coupled to upper-level steering...Teddy jogged more west and less north while rounding the north side of western Atlantic upper vorticity...requiring me to nudged the forecast track points southwestward. At some point and relatively soon...Teddy will be recurved northward in track due to the approach of the large upper trough currently exiting eastern North America which should still allow the center of Teddy to pass east of Bermuda tomorrow. However the center may pass a little closer to the island with the west nudge in the track forecast....so Bermuda will see coastal storm surge along with some potentially damaging tropical storm force winds caused by the western rain bands of Teddy....interests here should use today to finish preparing for these impacts. It’s possible that the current shear relaxes as the upper ridge axis mentioned in the prior paragraph passes overhead...with Teddy possibly also gaining some support from the eastern divergence zone of the incoming upper trough (early afternoon update...there is already evidence of reduced shear as Teddy is quickly regaining symmetry in its thunderstorm cloud distribution). But I vote for now the upper trough will be more disruptive than beneficial...thus my 24 hour forecast point shows Teddy being a little weaker (also because Teddy will pass over cooler water upwelled by Paulette).

Between 24 and 48 hours...the northerly surface flow on the west side of Teddy will amplify the incoming cold core upper trough by pushing cold air southward...with increasing divergence on the east side of the amplifying upper trough in turn helping Teddy. This mechanism will make Teddy increasingly less tropical...but with the forecast amplification of the upper trough there will likely be a tremendous amount of upper divergence on the east side of the upper trough such that we are faced with Teddy transitioning into a powerful non-tropical frontal cyclone at strong tropical storm force category by 72 hours. With Teddy initially being a strong hurricane roaming the western Atlantic...and then becoming a large powerful non-tropical cyclone with winds becoming further widespread by a pressure gradient between Teddy and a strengthening surface ridge to be supported by the western convergence zone of the amplifying upper trough...expect sea swells and rip currents to continue reaching the northeastern Caribbean Islands...the Bahamas...United States east coast...and Atlantic Canada coast over the next few days. The track by 72 hours will be influenced by another upper trough to pivot across North America...which in today’s 0600Z GFS model guidance remains less amplified...and so when it phases with the amplified upper trough to be interacting with Teddy...it won’t cause Teddy’s trough to be as amplified. Therefore I still prefer a landfall point toward eastern Nova Scotia as the slightly less amplified upper trough will not pull Teddy as far to the west. I recommend interests in eastern Maine...New Brunswick...Nova Scotia...Prince Edward Island...and Newfoundland to continue preparing for impacts from what will be the non-tropical remnant cyclone of Teddy...which will include damaging wind arriving by late Tuesday and Wednesday....the worst of which would be over Nova Scotia and Prince Edward Island if the current track forecast holds. 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 20)...105 mph maximum sustained wind hurricane centered southeast of Bermuda at 28.3N-62.8W

IOH 24 Hr Forecast (1200Z Sep 21)...100 mph maximum sustained wind hurricane centered just southeast of Bermuda at 30.5N-62.8W

IOH 48 Hr Forecast (1200Z Sep 22)...85 mph maximum sustained wind hurricane centered in the northwestern Atlantic at 37.5N-61.5W

IOH 72 Hr Forecast (1200Z Sep 23)...70 mph maximum sustained wind non-tropical remnant gale centered over eastern Nova Scotia at 45N-61.5W

TROPICAL STORM BETA...Beta’s westward turn has been slower and further to the north thus far. The slow forward speed west has been from the western convergence zone of the southwestern lobe of the upper trough over eastern North America which has extended the central United States surface ridge southwestward...with the southwestern lobe of the ridge blocking west progress. Also Beta is strong and hence tall enough to be slowed by the upper southwesterly flow ahead of the upper trough’s southwest lobe. The latest upper wind analyses shown in the models suggest the southwest lobe of the upper trough has recently dissipated from Beta’s thunderstorm latent heat release...so the blocking effects that were in play should fade and allow Beta to move faster toward the Texas coast in the next 24 hours. A second upper trough to pass over North America will be too far north to play a role with Beta...which leaves the question of how Beta interacts with a third upper trough to move into the southwestern US. Because Beta is taking longer to reach the coast...it won’t weaken as much from land interaction before this third upper trough hits it...so Beta will be strong/tall enough to be turned slowly northeastward by the third trough and jammed against the central Unites States surface ridge...resulting in a slow motion along the Texas coast and toward the southwest Louisiana coast after 24 hours. Given the current position of Beta...my updated track is actually adjusted northeastward along a path just inland from the coastline after 24 hours.

Beta has struggled with rather dry air seen in water vapor satellite and over south Texas...earlier generated by the western convergence zone of the now dissipated southwest lobe of the upper trough in the region. This has prevented Beta from strengthening thus far despite the reduction in shear amid the upper trough lobe dissipation...and it is curious that the dry air is still there despite the upper trough lobe and its western convergence zone now being gone. Perhaps there remains residual westerly upper flow in the immediate wake of the upper trough lobe which is colliding with the western outflow of Beta...resulting in the persistence of the dry sinking air over south Texas. My intensity forecast is lowered from the previous...but assumes Beta can still become a minimal category 1 hurricane in the next 24

hours once it’s warm core upper outflow expands further and turns the residual upper westerlies over south Texas into a more divergent anticyclonic flow that will allow for some rising motion and moistening away of the dry air. The further north track increases land interaction and places Beta more into the shearing upper westerlies from the upper trough to pivot into the southwestern US...so I forecast dissipation into a remnant low sooner.

Interests along the Texas coast should be finishing preparations for tropical storm and possible hurricane force conditions (damaging winds...coastal storm surge...and heavy rainfall with flooding potential)...and when shopping during preparation to also frequently hand sanitize and wear a mask to reduce your risk of contracting the COVID-19 virus amid the outbreak in the region. Although there is some uncertainty in the exact track of Beta...weather conditions could deteriorate as early as tonight. Think of a hotel or family/friend residence if you live along a vulnerable section of coastline...in the event you may have to relocate for example if storm surge becomes a problem...as a public storm shelter may not be as ideal to controlling your exposure to COVID-19. Interests further north along the southwest Louisiana coast are under tropical storm advisories and should also be finishing preparation. The slow track forecast will become a problem for severe rainfall flooding along the Texas and southwest Louisiana coasts and areas inland....especially if Beta develops strong thunderstorm complexes supported by the divergence zone of the upper trough to approach from the southwestern US. The greatest wind and storm surge threat at this time appears to have shifted northward away from the southern and toward central Texas coast due to the more north current position of Beta.

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

0 Hr Position (1200Z Sep 20)...60 mph maximum sustained wind tropical storm centered in the western Gulf of Mexico at 27.2N-93W

IOH 24 Hr Forecast (1200Z Sep 21)...75 mph maximum sustained wind hurricane centered just offshore of Texas at 27.5N-96W

IOH 48 Hr Forecast (1200Z Sep 22)...50 mph maximum sustained wind tropical storm centered just inland from the eastern Texas coast at 29N-96W

IOH 72 Hr Forecast (1200Z Sep 23)...Remnant low pressure centered just inland and along the Texas/Louisiana border at 30.5N-94W

TROPICAL DEPRESSION WILFRED...Wilfred has weakened to a large and broad...also disorganized...tropical depression due to shear induced by cut-off upper vorticity that lies just to the northwest. This shear has gotten stronger as the vorticity got pushed southward into Wilfred by expanding warm upper ridging in the central and north Atlantic re-enforced by Teddy's thunderstorm latent heat release and also later to be enforced by the warm southerly flow on the east side of Teddy after Teddy transitions to non-tropical. This warm upper ridging will also push a chunk of the upper vortex associated with Paulette's remnant cyclone southward which will re-enforce the shearing upper vorticity. Wilfred took a track more westward perhaps as it has weakened and become shallow enough to no longer be steered by the shearing upper winds and entirely steered now by the surface ridge to the north. Thus my updated track is shifted westward....and I expect a north angle in track to resume from a surface ridge weakness to the northwest courtesy of Hurricane Teddy. Expect dissipation to a remnant low in the next 24 hours...and like just we saw with Vicky’s remnant low I expect Wilfred’s remnant low pressure to also dissipate beneath the western convergence zone of the upper vorticity which will tend to keep surface pressures higher.

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

0 Hr Position (1800Z Sep 20)...35 mph maximum sustained wind tropical depression centered in the tropical Atlantic at 16N-45.5W

IOH 24 Hr Forecast (1800Z Sep 21)...Remnant low pressure centered in the tropical Atlantic at 18N-48W

AREA OF INTEREST #1 (REMNANTS OF PAULETTE)...What was Hurricane Paulette remains a post mature non tropical low pressure centered in the eastern Atlantic at 35N-30W slowly weakening beneath its parent upper vortex. Paulette and the upper vortex are drifting southward in the northerly flow on the east side of amplifying upper ridging to the west. The upper vortex in the next 24 hours is forecast to become stretched southwest-to-northeast by the strength of the upstream upper ridging to be re-enforced by Hurricane Teddy’s latent heat release...followed by warm air advection on the east side of Teddy when it becomes a remnant frontal cyclone. This will leaves Paulette to stall beneath the stretched upper vorticity axis by 24 hours. The currently forecast stall location is in warm 26 deg C sea surface temperatures...and so I have continued to raise my odds of subtropical cyclone formation from Paulette's remnant upward to now 75%...especially as Paulette is already producing a circular clump of showers now in its west side and it has not yet quiet made it to the 26 deg C waters. Odds are trimmed donward with time as Paulette will continue to weaken with time under the cut-off upper vorticity if it does not develop into a subtropical cyclone early on....and by 48+ the upper vorticity and Paulette will be pushed eastward toward cooler waters near the Canary Islands by the upper ridging expanding to the west and also by the north fracture of the upper trough currently exiting eastern North America...according to the 0600Z GFS model run. The GFS has moved up the timing and speed of the eastward acceleration...so I now forecast Paulette to cross the Canary Islands as soon as Tuesday evening. Coastal sea swells...gusty winds...and heavy rains are possible here if Paulette retains strength by re-acquiring tropical characteristics...especially if it can develop a warm core upper outflow that sustains it low surface pressure.

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

IOH 24 Hr Outlook (1800Z Sep 21)...75% chance of subtropical cyclone formation (eastern Atlantic near 33N-30W)

IOH 48 Hr Outlook (1800Z Sep 22)...30% chance of subtropical cyclone formation (west of the Canary Islands near 30N-25W)

IOH 72 Hr Outlook (1800Z Sep 23)...0% chance of subtropical cyclone formation (east of the Canary Islands near 32.5N-15W)

AREA OF INTEREST #2....The swirl of low pressure currently over south Florida near 26.5N-81.5W reminds us that a cold front is an elongated trough of low pressure with air mass contrasts on either side supported by the eastern divergence zone of a mid-latitude upper trough. While separating from the front and upper trough...this new low pressure will move westward into the Gulf of Mexico over the next day or so...initially on a south angle due to the strength of the surface ridge over the eastern and central US...then on a slight north angle while gravitated towards the low pressure field of Tropical Storm Beta...all while passing below a favorable Gulf of Mexico upper ridge with low shear and upper outflow. I give low odds of tropical cyclone formation however due to the dominating low level inflow of Beta which this system will have to compete with...but my odds are slightly higher than the NHC outlook given how well defined the swirl of low pressure is on satellite pictures. I then drop the odds to 0% by 48 hours as this system gets too close to Beta’s dominating inflow.

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

IOH 24 Hr Outlook (1800Z Sep 21)...20% chance of tropical cyclone formation (eastern Gulf of Mexico near 25.5N-86W)

IOH 48 Hr Outlook (1800Z Sep 22)...0% chance of tropical cyclone formation (central Gulf of Mexico near 26.5N-91W)

...COMPUTER MODEL SUMMARY...

Temporarily cancelled to avoid further delays in completing this post.

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