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 #123

Updated: Sep 18

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


...THURSDAY SEPTEMBER 17 2020 5:09 PM EDT...

See remnants of Sally...Hurricane Teddy...and Tropical Depression Vicky sections below for an update on all current named systems 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. Elsewhere...the ECMWF model has insisted that the current tropical wave over interior western Africa may develop after it emerges into the eastern tropical Atlantic in 48 hours...therefore it may need to be added as another area of interest for possible tropical cyclone formation.


More recent satellite image of Hurricane Teddy (as of 2030Z):

MAJOR HURRICANE TEDDY...Teddy is defying expectations as its thunderstorm latent heat release has weakened the cold core upper vorticity that was approaching from the northeast...thus keeping wind shear low and allowing Teddy to intensify into a major category 3 hurricane this morning. This now positions Teddy to intensify further in a low shear environment with upper outflow channels extending eastward into the remainder of the upper vorticity which is toward Tropical Depression Vicky's location and westward into the western Atlantic upper vorticity that lies north of the Caribbean islands in the next 24 hours. Even by days 2 and 3 Teddy will find itself in a vast low shear and upper outflow environment to the northeast of the western Atlantic upper vorticity as it continues northwestward while steered by the northeast side of the western Atlantic upper vorticity. And with warm 28 to 29 deg C waters during this timeframe...I have no choice but to forecast Teddy to become a top-end category 4 hurricane in the next 48 hours...and it wouldn't surprise me if Teddy reaches category 5 status in that window. I forecast weakening toward a lower-end category 4 by day 3 as I assume an eye wall replacement cycle would have occurred by then...but it is impossible to actually know when such cycles will actually occur.


The biggest concern with Teddy is how it will affect Bermuda not long after Paulette already struck the island. As a powerful hurricane coupled to upper-level steerig...at some point Teddy will be recurved northward in track due to the approach of a large upper trough which will be a merger between an upper trough currently moving across Canada and the cut-off upper trough over the southern United States. The longer range model runs have shifted back eastward on a consensus showing a path just east of Bermuda as it shows the upper trough holding together instead of splitting into two halves like yesterday. So while my updated forecast track points are shifted northwestward due to Teddy's current position...my longer range forecast is shifted back eastward. If the latest model consensus is true...Bermuda will see coastal sea swells and storm surge along with damaging winds caused by the western rain bands of Teddy. I forecast further weakening to category 3 by 96 hours due to cooler waters that were upwelled by Paulette that Teddy would be passing over and increasing westerly shear as the large upper trough from the west approaches. Between 96 and 120 hours...the northerly surface flow on the west side of Teddy will likely amplify the 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 category 1 or 2 hurricane force just after 120 hours. With Teddy initially becoming a powerful 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 also reach the northeastern Caribbean Islands...the Bahamas...United States east coast...and Atlantic Canada coast over the next few days. In the very long range...it initially appears the non-tropical remnant cyclone of Teddy and amplified upper trough will be pushed eastward by another upper trough to sweep across Canada...which may allow the remnant cyclone to stay offshore of Atlantic Canada (Nova Scotia and Newfoundland) but still pass close enough to still bring high winds...stay tuned.


Update as of 5 PM EDT: Teddy is now a category 4 hurricane with 140 mph maximum sustained winds. Therefore no changes to my forecast shown below.

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

0 Hr Position (1200Z Sep 17)...120 mph maximum sustained wind major hurricane centered at 19.3N-53W

IOH 24 Hr Forecast (1200Z Sep 18)...155 mph maximum sustained wind major hurricane centered at 22N-56W

IOH 48 Hr Forecast (1200Z Sep 19)...155 mph maximum sustained wind major hurricane centered at 25N-59.5W

IOH 72 Hr Forecast (1200Z Sep 20)...135 mph maximum sustained wind major hurricane centered southeast of Bermuda at 29N-63W

IOH 96 Hr Forecast (1200Z Sep 21)...125 mph maximum sustained wind major hurricane centered just east of Bermuda at 31N-63W

IOH 120 Hr Forecast (1200Z Sep 22)...105 mph maximum sustained hurricane centered in the northwestern Atlantic at 36N-61W


TROPICAL DEPRESSION VICKY (RECENTLY DOWNGRADED TO A REMNANT LOW)...While a weak and shallow tropical cyclone...Vicky continues westward while pushed by the northeast Atlantic surface ridge. The track forecast below is based on the fact Vicky has had a slight southward angle in track and is moving a little faster than yesterday. This direction of travel remains opposed to the upper westerly shearing winds produced by cut-off upper vorticity to the northwest...thus keeping wind shear values high. The shear experienced by Vicky is increasing as the tropical cyclone moves closer to the upper vorticity on its westward heading...which has caused Vicky to weaken to a tropical depression. Upper divergence on the southeast side of this upper vorticity...as marked in the above birdseye view chart...may have been what kept Vicky's surface low pressure just strong enough in the face of the shear to hang on for a tropical cyclone for as long as it has been one. In 24 hours the forecast point takes Vicky below a less favorable upper convergence zone on the southwest side of the upper vorticity. Combined with the fact that Vicky's surface cloud swirl is now fully exposed with no new thunderstorm bursts firing near the center...I expect Vicky to be a remnant low pressure in 24 hours...this time for sure.


Update as of 5 PM EDT: The National Hurricane Center just downgraded Vicky to a remnant low pressure. Therefore this is my final statement on Vicky on this blog.

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

0 Hr Position (1200Z Sep 17)...35 mph maximum sustained wind tropical depression centered at 21.4N-38.2W

IOH 24 Forecast (1200Z Sep 17)...Remnant low pressure centered at 21.2N-42W


REMNANTS OF SALLY...The center of what was Hurricane Sally is moving into Georgia as it transitions into an elongated remnant frontal low pressure supported by the eastern divergence zone of the upper troughs approaching from Canada and the southern United States. The heaviest shower and thunderstorm activity containing the heaviest rainfall is sheared northeastward from the center by the upper southwesterly flow ahead of the upper troughs. Based on radar imagery...heavy rainfall with flash flooding potential is possible across the Carolinas...Virginia...eastern Maryland....Delaware...and possibly southern New Jersey over the next several hours. The wind threat with Sally is over as it has weakened below tropical storm force several hours ago. While models disagree on exactly how long Sally's remnant retains its identity along the front developing across Sally's circulation as it moves into the western Atlantic...the consensus is that Sally and the front will lose dominance to Teddy as Teddy transitions into the primary feature supported by the upper troughs...especially by day 5. This is my final statement on Sally on this blog as it is no longer a tropical cyclone.


AREA OF INTEREST #1...The surface low pressure spin in the southwestern Gulf of Mexico has been generally stationary near 22N-95W over the last 24 hours while continuing to become better organized in a low shear and upper outflow environment. The recent ramp up in organization maybe from Sally finally moving northward out of the Gulf of Mexico which has given room for this system to have more low-level inflow instead of competing with Sally. Based on the current organization featuring increasing spiral banding features in the thunderstorm clouds...I have begun a tropical cyclone formation forecast as outlined below.


My updated forecast points below are nudged southwestward as this system has yet to drift northeastward toward the low pressure field of Sally's remnant low pressure. For the next 24 hours my forecast assumes this system will still drift northeastward. After that time the current central United States surface ridge is expected to build under the western convergence zone of the upper trough currently swinging across Canada...which should begin to turn this system westward. Because this system is highly likely to become a tropical cyclone strong enough to be coupled to upper level steering...the westward motion is shown to be very slow through 120 hours while dragged by the upper westerly flow of the upper trough over the southern United States...espeically as that trough moves eastward and closer to this system. The western convergence zone of this upper trough will extend the central United States surface ridge southwestward...with the southwestern lobe of the ridge blocking west progress. Because of this forecast southwestern lobe...I forecast zero forward speed from 24 to 72 hours. This southwestern lobe finally may weaken by 96 to 120 hours...but I show only a very slow westward motion commencing as another upper trough to pivot across Canada and the United States may produce upper westerly flow that opposes this motion...and as the southwestern convergence zone of that trough may still somewhat re-enforce the stubborn blocking southwestern lobe of the surface ridge.


Regarding intensity...I forecast a quick ramp up to moderate tropical storm status in the next 24 hours due to the current organization and favorable upper winds. I pause the intensification through 72 hours as the southern US cut-off upper trough passes over and north of this system and delivers disrupting westerly shear. Once that trough passes I forecast another round of strengthening to strong tropical storm strength by 96 hours...followed by no strengthening at 120 hours once another upper trough pivoting across the United States and Canada potentially delivers another round of shear.

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

0 Hr Position (1200Z Sep 17)...Well organized surface low pressure centered in the southwestern Gulf of Meixco at 22.2N-95.5W

IOH 24 Hr Forecast (1200Z Sep 18)...50 mph maximum sustained wind tropical storm centered in the western Gulf of Mexico at 23.5N-95W

IOH 48 Hr Forecast (1200Z Sep 19)...50 mph maximum sustained wind tropical storm centered in the western Gulf of Mexico at 24N-95W

IOH 72 Hr Forecast (1200Z Sep 20)...50 mph maximum sustained wind tropical storm centered in the western Gulf of Mexico at 24N-95W

IOH 96 Hr Forecast (1200Z Sep 21)...65 mph maximum sustained wind tropical storm centered in the western Gulf of Mexico at 24N-96W

IOH 120 Hr Forecast (1200Z Sep 22)...65 mph maximum sustained wind tropical storm centered in the western Gulf of Mexico just offshore of northeastern Mexico at 24N-97W


AREA OF INTEREST #2...The tropical wave of low pressure in the eastern tropical Atlantic continues to exhibit a low pressure spin (currently near 11N-27.5W) with plenty of thunderstorm bands to the southwest but a lack of activity to the northeast. The lack of activity in one half of the circulation maybe due to some dry saharan air as seen by a beige tint in true color high resolution satellite imagery...and perhaps from some northeasterly shear as the tropical wave is under the south side of the tropical upper ridge axis in the region where the flow is predominately norhteasterly...instead of directly below the upper ridge axis where the upper flow would otherwise be more symmetric. Nonetheless given the amount of spin and thunderstorm bands on the southwest side....I still forecast a high 80% chance of tropical cyclone formation for the next five days. The high odds are for the short term...with odds tapering down by 2 to 5 days due to the cut-off upper vorticity currently shearing Vicky...which will get pushed southward toward the path of this tropical wave by expanding warm upper ridging in the central and north Atlantic becomes re-enforced by Teddy's thunderstorm latent heat release and also later on 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 trough associated with Paulette's remnant cyclone southward which will re-enforce the upper vorticity expected to later on shear this tropical wave. Forecast track in the outlook below also assumes this upper vorticity may bend the track of the wave north...especially if it becomes a strong enough tropical cyclone that couples with upper level steering flow.

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

IOH 24 Hr Outlook (1200Z Sep 18)...80% chance of tropical cyclone formation (tropical Atlantic near 11N-32.5W)

IOH 48 Hr Outlook (1200Z Sep 19)...60% chance of tropical cyclone formation (tropical Atlantic near 12N-38.5W)

IOH 72 Hr Outlook (1200Z Sep 20)...40% chance of tropical cyclone formation (tropical Atlantic near 14N-41.5W)

IOH 96 Hr Outlook (1200Z Sep 21)...20% chance of tropical cyclone formation (tropical Atlantic near 16N-44.5W)

IOH 120 Hr Outlook (1200Z Sep 22)...0% chance of tropical cyclone formation (tropical Atlantic near 18N-48W)


AREA OF INTEREST #3...A deep-layered cyclone in the northeastern Atlantic consisting of a cold core cut-off upper vortex and surface spin is the remnants of a classic frontal cyclone and upper trough that was in the region that has been cut-off from the mid-latitude westerlies by a northeastern Atlantic upper ridge supported by the warm sector of the frontal system that now contains the remnant circulation of Paulette. Despite being centered at 37.5N-17W and over 22 deg C waters...pockets of showers and thunderstorms continue around the surface spin's center due to the destabilizing effect of the rather cold upper vortex.


Going forward the deep-layered cyclone should be pushed on an east-northeast drift toward the direction of Portugal as a north fracture of the north Atlantic upper trough tied to Paulette's frontal zone tries to drag this system after the northeastern Atlantic upper ridge passes to the north. I have once again shifted my forecast points south and east due to the current position of the surface cyclone...followed by a northeastward swing by 48 hours as the current dominant surface spin is shown in nearly all models to become a secondary swirl orbiting northeastward around a mean broad surface center to be further to the west. I agree with the National Hurricane Center's 2 PM EDT outlook in keeping 30% odds for the next 24 hours for subtropical cyclone formation as there continues to be pockets and bands of showers and thunderstorms around the surface spin. It should be noted the surface low pressure spin is undergoing a continuing weakening phase as it remains trapped below the center of the upper vortex where there is no upper divergence...and by 48 hours all of the modeling shows the surface spin weakening into multiple swirls. Thus I drop odds of development to 0% by then...and also as the thermodynamic picture becomes less favorable as the track takes this system toward increasingly cooler waters and as the upper vortex also warms as it remains cut-off from higher latitude cold air.

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

IOH 24 Hr Outlook (1200Z Sep 18)...30% chance of subtropical cyclone formation (just west of Portugal near 39N-12.5W)

IOH 48 Hr Outlook (1200Z Sep 19)...0% chance of subtropical cyclone formation (just offshore of northwestern Spain near 44N-10W)


AREA OF INTEREST #4...A tropical wave of low pressure that has recently exited the western African coast is producing thunderstorm activity in the vicnity of 10N-18W. However the activity is less widespread and appears to be becoming increasingly entangled with the nearby wave to the west...area of interest #2. Therefore at this time I assume this tropical wave will not develop as the better organized tropical wave in area of interest #2 dominates the low-level inflow in the region. This is my planned final statement on this tropical wave on this blog unless this situation changes.

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

IOH 24 Hr Outlook (1200Z Sep 18)...0% chance of tropical cyclone formation (tropical Atlantic near 10N-23W)


AREA OF INTEREST #5 (REMNANTS OF PAULETTE)...What was Hurricane Paulette remains a strong surface frontal cyclone supported by the eastern divergence zone of the upper trough now moving across the north Atlantic. In the next 24 hours a portion of 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 the frontal system over eastern Canada and the northeastern United States. 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 deep-layered cyclone to the east (area of interest #3). The updated forecast track shown below is adjusted eastward to account for the fact the remnant of Paulette is east of my previous track. Paulette is also north of the previous track...but the forecast northerly flow is expected to be strong enough to push Paulette southward quickly...and so little to no north-south adjustment is made in the forecast track points.


The southward drive of the remnant of Paulette should take it back toward increasingly warmer waters. The upper vortex by late in the 5-day forecast period is forecast to become stretched southwest-to-northeast by the strength upstream upper ridging...leaving Paulette to stall beneath the stretched upper vorticity axis by days 3 to 5. The currently forecast stall location is just north of the 26 deg C sea surface temperature isotherm...so I only forecast 10% odds that Paulette regenerates as a subtropical cyclone as the upper vorticity is forecast to be on the warmer side (colder upper-level temperatures are needed for more instability and thunderstorms)...so it will take at least 26 deg C water temperatures for Paulette to regenerate.

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

IOH 24 Hr Outlook (1200Z Sep 18)...0% chance of subtropical cyclone formation (northeastern Atlantic near 43N-30W)

IOH 48 Hr Outlook (1200Z Sep 19)...0% chance of subtropical cyclone formation (northeastern Atlantic and just southwest of the Azores near 37.5N-30W)

IOH 72 Hr Outlook (1200Z Sep 20)...10% chance of subtropical cyclone formation (eastern Atlantic near 34N-30W)

IOH 96 Hr Outlook (1200Z Sep 21)...10% chance of subtropical cyclone formation (eastern Atlantic near 34N-30W)

IOH 120 Hr Outlook (1200Z Sep 22)...10% chance of subtropical cyclone formation (eastern Atlantic near 34N-30W)


...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 Major Hurricane Teddy...passes just east of Bermuda in 102 hours...located at 39N-61W at 120 hours. For Tropical Depression Vicky...circulation dissipates near 20N-41W at 36 hours. For area of interest #1...tropical cyclone formation suggested near 22.5N-95W at 72 hours..located just offshore of northeastern Mexico at 24N-97.5W at 120 hours as a compact and strong tropical cyclone. For area of interest #2...tropical cyclone formation suggested at 12.5N-32.5W at 42 hours...located at 17.5N-42W at 120 hours as a remnant low pressure. For area of interest #3...weakens into a low pressure with multiple swirls just west of Portugal by 48 hours. For area of interest #4...no tropical cyclone formation shown. For area of interest #5 (remnants of Paulette)...located at 33N-36W at 120 hours as a weakening low pressure.


0000Z ECMWF Model Run....For Major Hurricane Teddy...passes just east of Bermuda just after 96 hours...located at 37.5N-61.5W at 120 hours. For Tropical Depression Vicky...circulation dissipates near 20N-43W at 48 hours. For area of interest #1...tropical cyclone formation suggested near 22.5N-96W at 48 hours..located just offshore of the Texas/Mexico border at 120 hours as a compact and strengthening tropical cyclone...in long range shifts east-northeastward offshore of Texas. For area of interest #2...no tropical cyclone formation shown. For area of interest #3...weakens into a low pressure with multiple swirls just west of Portugal by 48 hours. For area of interest #4...no tropical cyclone formation shown. For area of interest #5 (remnants of Paulette)...located at 36N-32.5W at 120 hours as a stalled low pressure southwest of the Azores trapped beneath upper vorticity. Elsewhere...strong tropical wave emerges from western Africa in 48 hours...tropical cyclone formation suggested just north of the western Cabo Verde Islands in 96 hours...located at 21N-30W at 120 hours.


0600Z GFS Model Run...For Major Hurricane Teddy...passes just east of Bermuda in 108 hours...located at 36N-60.5W at 120 hours. For Tropical Depression Vicky...circulation dissipates near 20N-44W at 48 hours. For area of interest #1...shown to become a north-south elongated low pressure area by 60 hours...northern part becomes a weak tropical cyclone offshore of Louisiana and Texas from 66 to 120 hours...southern part becomes a compact tropical cyclone just offshore of the Mexico Bay of Campeche coast near 19N-95W at 126 hours. For area of interest #2...no tropical cyclone formation shown. For area of interest #3...weakens into a low pressure with multiple swirls just west of Portugal by 42 hours. For area of interest #4...no tropical cyclone formation shown. For area of interest #5 (remnants of Paulette)...located at 35N-27.5W at 120 hours as a stalled low pressure south of the Azores trapped beneath upper vorticity.


0600Z NAVGEM Model Run...For Major Hurricane Teddy...passes just east of Bermuda in 114 hours...located at 35N-62.5W at 120 hours. For Tropical Depression Vicky...circulation dissipates near 20N-45W at 54 hours. For area of interest #1...tropical cyclone formation suggested near 25N-96.5W at 78 hours...stalls at a location just offshore of the Texas/Mexico border as a strengthening tropical cyclone at 120 hours. For area of interest #2...no tropical cyclone formation shown. For area of interest #3...weakens into a low pressure with multiple swirls just west of Portugal by 36 hours. For area of interest #4...no tropical cyclone formation shown. For area of interest #5 (remnants of Paulette)...located at 32.5N-27.5W at 120 hours as a stalled low pressure south of the Azores trapped beneath upper vorticity.

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