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 #121

Updated: Sep 17

*******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 15 2020 2:17 PM EDT...

See Hurricane Paulette...Hurricane Sally...Tropical Storm Teddy...and Tropical Storm Vicky for the four 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.


HURRICANE PAULETTE...Despite Paulette becoming overspread by southwesterly upper flow ahead of an upper trough approaching from eastern North America...it does not have the look of a sheared hurricane as the thunderstorm bands continue to be symmetric around the center. This can be attributed to the fast northeast acceleration provided by the deep-layer southwesterly steering flow (from the flow ahead of the surface front tied to the upper trough as well as the upper trough itself) which has allowed Paulette to keep up with the upper southwesterly wind speed. It is also possible the divergence on the east side of the upper trough is beginning to aid the hurricane as well. Thus Paulette has yet to weaken from its category 2 105 mph maximum sustained wind peak. Although I have raised my intensify forecast due to Paulette's current strength...I forecast weakening by 24 hours as the hurricane reaches cooler waters. However I keep the weakening rate slow as it transitions into a strong non-tropical remnant cyclone supported by divergence on the east side of the incoming upper trough.


I expect Paulette to retain hurricane force winds as a non-tropical remnant cyclone through 48 hours while aligning with the robust upper divergence maximum of the incoming upper trough. After that time the upper trough should amplify into a cold core cut-off upper vortex due to the cold surface northerly flow on the west side of Paulette...and also due to amplification of adjacent upper ridging located upstream (to the west) in the warm sector of another frontal system developing over Canada. This will cause Paulette's remnant to whirl directly beneath the cut-off upper vortex center where there is a lack of divergence...thus where it begins to weaken as a classical post-mature non-tropical cyclone. During this weakening phase all models are in agreement that the remnant of Paulette and upper vortex will swing southward to the west of the Azores in the northerly flow to set up between the amplifying upper ridging to the west and northeast Atlantic upper trough to the east. This will take the remnant of Paulette back toward increasingly warmer waters...but at this time I do not anticipate regenesis into a subtropical cyclone through 96 hours as the remnant will still be over waters below 26 deg C and the upper vortex in the 0600Z GFS model run measures too warm (around 1215 to 1220 dekameters in height at 200 mb instead of a colder 1200) to aid in generation of instability of thunderstorms at those water temperatures. By 120 hours the southward track approaches the 26 deg C sea surface temperature isotherm...but I am not very confident at this time in calling for Paulette to regenerate as a subtropical cyclone as the forecast track may shift...and as the upper vortex could become stretched southwest-to-northeast by the upper ridging to the northwest such that there is a possiblity that Paulette's remnant gets caught in unfavorable upper convergence between the northwest side of the upper vortex and southeast of the upper ridging.


Given this outlook however...I have extended my forecast for Paulette through 5 days even though Paulette will not be tropical for much of that time. This is because I believe the odds that Paulette regenerates as a subtropical cyclone by day 5 are not zero either...so the forecast points after 24 hours for now are only serving as preparation for me to begin probability outlooks on the remnant of Paulette after it transitions into a non-tropical remnant gale.

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

0 Hr Position (1200Z Sep 15)...105 mph maximum sustained wind hurricane centered at 38.3N-57.9W

IOH 24 Hr Forecast (1200Z Sep 16)...85 mph maximum sustained wind hurricane transitioning to a non-tropical remnant gale centered at 43.5N-46W

IOH 48 Hr Forecast (1200Z Sep 17)...Hurricane force non-tropical remnant gale centered at 45N-35W

IOH 72 Hr Forecast (1200Z Sep 18)...Non-tropical remnant gale centered at 42N-34W

IOH 96 Hr Forecast (1200Z Sep 19)...Non-tropical remnant gale centered at 37.5N-35W

IOH 120 Hr Forecast (1200Z Sep 20)...Non-tropical remnant gale centered at 34N-35W


TROPICAL STORM TEDDY...Teddy continues to intensify while in a favorable low shear and upper outflow environment beneath a tropical upper ridge axis. The tropical storm is approaching hurricane strength as indicated by a banding type eye feature developing at the center...and my previous intensity forecast predicted that by 1800Z today that Teddy would become a hurricane. Therefore my updated intensity forecast below is a continuity of my previous one...but for the 1200Z cycle instead of 1800Z. My updated forecast track is nudged northward due to the current position of Teddy...and starting in the next 24 hours a northward bend in the track is expected to begin. This is in response to how strong the northwest Atlantic upper ridge will be as it moves into the north Atlantic...with the ridge sending a chunk of the upper trough in the northeast Atlantic southwestward to Teddy. Because Teddy will be a strong/tall hurricane...it will be bent northward by the approaching upper trough. I flatten the intensification between 24 and 48 hours as the approaching upper trough potentially blocks the western outflow of Teddy and maybe even shears Teddy...and then ramp up the intensity again after 48 hours as the upper trough dissipates...and as Teddy approaches the western Atlantic upper vorticity currently north of the Caribbean Islands which will also be gradually fading. I forecast category 4 intensity by 120 hours due to the unanimous model consensus that Teddy will be a powerful hurricane by that time...and as Teddy will be in a low shear and upper outflow environment to the northeast of the western Atlatnic upper vorticity. This upper vorticity will keep Teddy moving northwest through 120 hours...albeit I bend the track a little more westward around days 4 and 5 as Teddy rounds the northeast side of the upper vorticity. One concern with Teddy in the longer range is whether or not it will affect Bermuda not long after Paulette already struck the island. Because Teddy will likely be a powerful hurricane tall enough to be coupled to the upper-level steering flow...it is likely Teddy begins to bend northward in track just after 120 hours due to the approach of a large upper trough which will be a merger between an upper trough to move across Canada and the cut-off upper trough over the southern United States...so it is likely Teddy passes just east of Bermuda while generating coastal sea swells for the island...but interests here should pay attention to Teddy due to the usual longer term error in the forecast track. For the surface layer of the atmosphere...models vary in the strength of what will be the remnant of Hurricane Sally and a cold front entangled with and supported by the eastern divergence zone of this upper trough...but the surface layer will be inconsequential in the long-term fate of Teddy with the approach of such a large upper trough and Teddy being tall to be steered by it.

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

0 Hr Position (1200Z Sep 15)...65 mph maximum sustained wind tropical storm centered at 14N-47W

IOH 24 Hr Forecast (1200Z Sep 16)...75 mph maximum sustained wind hurricane centered at 15.5N-49.5W

IOH 48 Hr Forecast (1200Z Sep 17)...80 mph maximum sustained wind hurricane centered at 17.5N-52W

IOH 72 Hr Forecast (1200Z Sep 18)...100 mph maximum sustained wind hurricane centered at 20N-54W

IOH 96 Hr Forecast (1200Z Sep 19)...120 mph maximum sustained wind major hurricane centered at 23N-58W

IOH 120 Hr Forecast (1200Z Sep 20)...135 mph maximum sustained wind major hurricane centered at 27N-61.5W


TROPICAL STORM VICKY...Vicky continues northwestward over the open eastern tropical Atlantic as a sheared tropical storm...the westward component in track supported by the surface ridge in the north Atlantic...the northward component supported by the upper southwesterly flow on the south side of a northeastern Atlantic upper trough trying to pull Vicky...but instead pulling off (shearing) the thunderstorm clouds northeastward from the swirl center. Despite this pattern of shear Vicky slightly intensified to 50 mph maximum sustained winds instead of weakening to a remnant low pressure while exhibiting strong thunderstorm bursts...perhaps supported by a zone of divergence on the southeast side of the upper trough. Recently the burst has faded and Vicky looks a little more disheveled on colorized infrared satellite...and there is no telling if another burst of thunderstorms will redevelop and keep Vicky going in the short term or if this is the early ending of Vicky. Even though Vicky has hanged on as a tropical storm instead of dissipating as I previously forecasted...I still vote that Vicky dissipates in the next 24 hours once a chunk of vorticity from the northeastern Atlantic upper trough retrogrades southwestward around the northwest Atlantic upper vorticity and moves closer to Vicky and then Teddy...with the shear intensifying as the upper vorticity nears.

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

0 Hr Position (1200Z Sep 15)...50 mph maximum sustained wind tropical storm centered at 20.6N-31W

IOH 24 Hr Foreast (1200Z Sep 16)...Remnant low pressure centered at 22N-34W


HURRICANE SALLY...Sally has slowed to a very slow northward drift in the northeastern Gulf of Mexico just offshore of Alabama...and the hurricane has weakened to a category 1. Despite this...as Sally moves northward conditions are still expected to deteriorate across the Florida panhandle as well as coastal Alabama and Mississippi with increasing rainfall...gusty winds with damage potential...and ongoing coastal storm surge which may be causing beach erosion problems due to how long the surge event is lasting. Some storm surge potential is also possible for the southeastern Louisiana coastline. Wind damage may spread inland over southern Alabama and southeastern Mississippi if Sally retains its current strength at landfall as it continues to drift northward. The slow motion will also produce severe rainfall flooding across the Florida panhandle...Alabama and Mississippi...when encountering a flooded roadway remember to turn around instead of accidentally getting drowned should your car get stuck in flood waters.


Sally has probably weakened as its slow motion has upwelled cooler waters...and also due to light westerly shear ahead of a cut-off upper trough over the southeastern United States.The divergence zones of this cut-off upper trough and also another upper trough beginning to sweep across Canada are weakening the steering surface ridge to the north of Sally enough to cause a stall...and also are too far away to pick up Sally. However an eventual slow north then northeast motion is anticipated once the surface ridge weakens a little more and as the cut-off upper trough slowly approaches from the west and bends the track eastward with its eastern upper southwesterly flow. Once Sally weakens to a remnant low inland over the southeastern United States...it will become entangled with a surface frontal zone to be generated in the eastern divergence zone of the the merger between the Canadian upper trough and southern US cut-off upper trough. Models simply vary on whether or not Sally's remnant retains its identity along this front as it moves into the western Alantic.

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

0 Hr Position Forecast (1200Z Sep 15)...85 mph maximum sustained wind hurricane centered offshore of the Alabama coast at 29.1N-88.2W

IOH 24 Hr Forecast (1200Z Sep 16)...70 mph maximum sustained wind tropical storm centered just inland from the Alabama coast at 31N-88W

IOH 48 Hr Forecast (1200Z Sep 17)...Remnant low pressure centered over east-central Alabama at 32.5N-85.6W


AREA OF INTEREST #1...The surface trough of low pressure in the Gulf of Mexico has swung southwestward to a location near 22.5N-96W while pushed by a fujiwhara interaction with Hurricane Sally to the northeast. The surface trough has intensified into an organizing surface low pressure with thunderstorms in its northwest quadrant supported by upper outflow that has been able to build in the wake of upper vorticity that dissipated in the region. As Sally continues northward into the southeastern United States...the fujiwhara interaction should cause surface low pressure to swing east then northeastward. A surface ridge to then build under the western convergence zone of an upper trough swinging across Canada should then turn this system back westward by day 3. Given the improved upper winds and increase in organized thunderstorm activity...I have notably raised the peak 5-day odds of tropical cyclone formation from this system to 60%. I begin to trim odds downward from that peak after 48 hours as the cut-off upper trough over the southern US will slowly approach and potentially increase wind shear with time. Although the upper trough will pass which will reduce the shear by 120 hours...I drop the odds further to 0% due to potential land interaction with northeastern Mexico on my current forecast track. On a final note...should this system indeed become a tropical cyclone...it could track slower and further to the north later in the forecast period as it becomes a tall enough system to be dragged by the upper southwesterly flow ahead of the upper trough...and as the divergence zone potentially creates a pocket of low pressure to the northeast that slows the track of this system around the surface ridge.

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

IOH 24 Hr Outlook (1200Z Sep 16)...50% chance of tropical cyclone formation (southwestern Gulf of Mexico near 22.5N-93.5W)

IOH 48 Hr Outlook (1200Z Sep 17)...60% chance of tropical cyclone formation (western Gulf of Mexico near 24N-93W)

IOH 72 Hr Outlook (1200Z Sep 18)...50% chance of tropical cyclone formation (western Gulf of Mexico near 24N-96W)

IOH 96 Hr Outlook (1200Z Sep 19)...10% chance of tropical cyclone formation (just inland from the northeastern coast of Mexico near 24N-98.5W)

IOH 120 Hr Outlook (1200Z Sep 20)...0% chance of tropical cyclone formation (over northeastern Mexico near 24N-99.5W)


AREA OF INTEREST #2...The tropical wave of low pressure in the eastern tropical Atlantic has become a little better organized while in a low shear and upper outflow environment beneath a tropical upper ridge axis and to the south of the northeast Atlantic upper trough. However the organizational trend has recently stopped in the most recent satellite frames...therefore I have slightly trimmed down the odds of tropical cyclone formation in the short term. In the medium term I retain a high 70% peak chance of development...followed by tapering down of the odds by days 4 and 5 as some of the northeast Atlantic upper vorticity retrogrades southwest toward this tropical wave and potentially shears it. Also this upper vorticity by day 4 and 5 may bend the track of the wave north as shown in the outlook below...especially if it becomes a strong enough tropical cyclone that couples with upper level steering flow. For the short term...I show a slower forward speed due to the ridge weakness from Tropical Storm Vicky and northeast Atlantic frontal cyclone (area of interest #3)....with increasing speed as Vicky weakness and this system moves further away from the frontal cyclone. My forecast points are adjusted eastward as this system has not been moving as fast to the west thus far.

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

IOH 24 Hr Outlook (1200Z Sep 16)...40% chance of tropical cyclone formation (tropical Atlantic near 10N-24W)

IOH 48 Hr Outlook (1200Z Sep 17)...65% chance of tropical cyclone formation (tropical Atlantic near 10N-28W)

IOH 72 Hr Outlook (1200Z Sep 18)...70% chance of tropical cyclone formation (tropical Atlantic near 10N-33W)

IOH 96 Hr Outlook (1200Z Sep 19)...60% chance of tropical cyclone formation (tropical Atlantic near 11N-39W)

IOH 120 Hr Outlook (1200Z Sep 20)...40% chance of tropical cyclone formation (tropical Atlantic near 13N-42W)


AREA OF INTEREST #3...The northern portion of the upper trough in the northeastern Atlantic has amplified into a quiet cold cut-off upper vortex measuring in the 1180s in dekameters in height at 200 mb...courtesy of southward cold air tranpsort on the west side of the northeastern Atlantic surface frontal cyclone its supporting with its eastern divegence...and due to adjacent amplification of high latitude upper ridging in the warm sector of a strong frontal cyclone southwest of Greenland and supported by the current upper trough exiting eastern North America. Despite being centered at 44N-21W and over 18 deg C waters...pockets of showers and thunderstorms are developing around the frontal cyclone's center due to the destabilizing effect of the rather cold upper vortex. When seeing this evolving pattern and model projections that have this system moving southward toward warmer water temperatures yesterday...I had considered assessing whether or not to add it as an area of interest for subtropical development...but due to the high amounts of activity elsewhere I had chose to delay that assessment to today. But given that this system has already been introduced into the NHC tropical weather outlook...by default I have added it as an area of interest on this blog post.


Going forward the frontal cyclone should follow the path of the cold core upper vortex while it weakens as a classical post-mature non-tropical system as there is a lack of divergence beneath the upper vortex center. As such the upper vortex (and hence the surface frontal cyclone) should first be pushed south-southeastward by the expanding block of high latitude upper ridging that passes to the north...followed by an east-northeast drift toward the direction of Portugal as the upper trough from eastern North America tries to drag the upper vortex as it passes north of the vortex. This will position the frontal cyclone over warmer 20 deg C waters by 24 hours...and combined with the current pockets of showers and thunderstorms and rather cold upper vortex still expected to measure well below 1200 dekameters at 200 mb...I forecast a 50% chance of subtropical cyclone formation. After that time I gradually drop the odds as the upper vortex gradually warms to 1200 dekameters by 96 hours and as this system moves back toward the cooler 18 deg C sea surface temperature isotherm by 72+ hours (would like to see water temperatures of at least 20 deg C if the upper vortex warms to 1200 dekameters).

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

IOH 24 Hr Outlook (1200Z Sep 16)...50% chance of subtropical cyclone formation (northeastern Atlantic near 41N-19.5W)

IOH 48 Hr Outlook (1200Z Sep 17)...40% chance of subtropical cyclone formation (northeastern Atlantic near 39N-18W)

IOH 72 Hr Outlook (1200Z Sep 18)...10% chance of subtropical cyclone formation (west of Portugal near 41N-15W)

IOH 96 Hr Outlook (1200Z Sep 19)...0% chance of subtropical cyclone formation (west of Portugal near 41N-15W)


...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 Paulette...located at 37.5N-39W at 120 hours. For Hurricane Sally...center makes landfall on Mississippi coast at 36 hours...after landfall remnant low pressure loses identity at Georgia/South Carolina border just after 90 hours. For Tropical Storm Teddy...located at 26N-58W at 120 hours as a strong hurricane. For Tropical Storm Vicky...weakens to a remnant low pressure near 21.5N-36W at 54 hours. For area of interest #1...tropical cyclone formation suggested near 22.5N-95W at 90 hours..located at 25N-92.5W at 120 hours. For area of interest #2...tropical cyclone formation suggested at 10N-22.5W at 42 hours...located at 15N-37.5W at 120 hours. For area of interest #3...dives southward to 40N-19W by 42 hours...shifts eastward and gradually weakens to the west of Portugal by 120 hours.


0000Z ECMWF Model Run....For Hurricane Paulette...located at 40.5N-33W at 120 hours. For Hurricane Sally...center makes landfall on the Mississippi/Alabama border at 48 hours...after landfall remnant low pressure transitions to elongated frontal low that moves across southeastern United States and into the western Atlantic by 120 hours. For Tropical Storm Teddy...located at 25N-58W at 120 hours as a strong hurricane. For Tropical Storm Vicky...weakens to a remnant low pressure near 21N-40W at 72 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...no tropical cyclone formation shown. For area of interest #3...dives southward to 39.5N-19.5W by 48 hours...shifts eastward and gradually weakens to the west of Portugal by 120 hours. Elsewhere...strong tropical wave emerges from western Africa at 120 hours...tropical cyclone formation suggested just northeast of the Republic of Cabo Verde Islands at 144 hours.


0600Z GFS Model Run...For Hurricane Paulette...located at 35N-35W at 120 hours. For Hurricane Sally...center makes landfall on the Alabama coast at 30 hours...after landfall remnant low loses identity over South Carolina by 78 hours. For Tropical Storm Teddy...located at 27.5N-60W at 120 hours as a strong hurricane. For Tropical Storm Vicky...weakens to a remnant low pressure near 22.5N-36W at 42 hours. For area of interest #1...tropical cyclone formation suggested just offshore of Mexico near 22N-97W at 144 hours. For area of interest #2...no tropical cyclone formation shown. For area of interest #3...dives southward to 38N-19W by 48 hours...shifts eastward and gradually weakens to the west of Portugal by 120 hours.


0600Z NAVGEM Model Run...For Hurricane Paulette...located at 36N-31.5W at 120 hours. For Hurricane Sally...center makes landfall on the Mississippi coast at 36 hours...after landfall remnant low loses identity offshore of the eastern United States by 120 hours. For Tropical Storm Teddy...located at 26N-57.5W at 120 hours as a strong hurricane. For Tropical Storm Vicky...weakens to a remnant low pressure near 23N-35W at 48 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...no tropical cyclone formation shown. For area of interest #3...dives southward to 37.5N-18W by 48 hours...shifts eastward and gradually weakens to the west of Portugal by 102 hours.

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