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 #117

*******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 10 2020 4:13 PM EDT...

See Tropical Storm Paulette and Tropical Storm Rene sections below for the two currently active tropical cyclones in the Atlantic basin. See area of interest sections below for multiple disturbances being monitored for tropical cyclone formation.


TROPICAL STORM PAULETTE...Paulette has slightly weakened over the open central tropical Atlantic while moving into a belt of shearing upper southwesterly winds out ahead of upper vorticity that spans from the Caribbean Sea to the northeastern Atlantic. My updated forecast below is a continuity of my previous one as Paulette continues northwestward under the combined influences of the Atlantic surface subtropical ridge to the north trying to push the storm westward and the upper southwesterly shearing winds trying to pull the storm northward. A westward component is kept in the track through 96 hours as the surface ridge currently over the northern United States passes north of Paulette...with the tropical storm rounding the southwest side of that ridge. By 120 hours...the current western United States upper trough will have merged with another upper trough from western Canada...with the merger creating a frontal zone moving into the northwestern Atlantic. For now I currently forecast this frontal zone to sweep Paulette more northward and north-northeastward in track by the end of the 120-hour forecast period. However I only show a slow north-northeast motion as the frontal zone is forecast to be narrow...with another surface ridge to build behind the front. Some modeling suggests a further west position of Paulette directly over or west of Bermuda...suggesting that the aforementioned upper vorticity breaks up with the southwestern lobe coaxing Paulette more westward in the middle of the forecast...positioning Paulette to then be influenced even further westward by the surface ridge to build behind the front at 120 hours. However I am not yet convinced about the southwestern lobe of the upper vorticity having weight as the remaining northeastern lobe may (or may not) be near enough to negate the steering effects of the southwestern lobe during the middle of the forecast period...explaining my forecast remaining further east and leaning towards the front at 120 hours...albeit with a slow forward speed till we see how the upper vorticity...surface front...and surface ridge behind the front actually end up evolving.


Regarding intensity...more models seem to be in agreement that the cold core upper vorticity shearing Paulette will break into two halves while weakening...as the vorticity remains cut-off from higher latitude cold air and potentially from Paulette's thunderstorm latent heat release. This is indicated by more models showing Paulette become a strong hurricane by the end of the forecast period. Even though Paulette is currently weaker than my previous intensity forecast...I forecast re-strengthening to 60 mph max winds as the GFS shows the upper vorticity already beginning to weaken in the next 24 hours...with gradual strengthening into a hurricane shown in 48 to 96 hours when Paulette moves into the gap between the split halves of the upper vorticity. Paulette could strengthen more than I forecast depending on the size of the gap...with a smaller gap allowing the upper vorticity to interefere with Paulette's outflow and causing a weaker storm...and a larger gap allowing for enhanced outflow channels into both halves of the upper vorticity and thus a stronger storm. I pause the strengthening at 120 hours as Paulette may incur some southwesterly shear from the upper trough associated with a northwestern Atlantic frontal zone expected by that time.


While there remains some long term uncertainty in regards to the track and intensity of Paulette as it passes the vicinity of Bermuda...models are in better agreement on the storm passing either close to or directly over the island and possibly as a strong hurricane by early next week. Therefore interests here should carefully monitor the progress of Paulette.

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

0 Hr Position (1200Z Sep 10)...50 mph maximum sustained wind tropical storm centered at 21.5N-49.1W

IOH 24 Hr Forecast (1200Z Sep 11)...60 mph maximum sustained wind tropical storm centered at 23N-54W

IOH 48 Hr Forecast (1200Z Sep 12)...60 mph maximum sustained wind tropical storm centered at 25N-57W

IOH 72 Hr Forecast (1200Z Sep 13)...70 mph maximum sustained wind tropical storm centered at 28N-60W

IOH 96 Hr Forecast (1200Z Sep 14)...80 mph maximum sustained wind hurricane centered just east-southeast of Bermuda at 31N-63W

IOH 120 Hr Forecast (1200Z Sep 15)...80 mph maximum sustained wind hurricane cenered northeast of Bermuda at 34N-62W


TROPICAL STORM RENE...Despite being below a vast tropical upper ridge axis at the 200 mb upper layer of the atmosphere...curiously Rene has had the appearance of a sheared tropical storm during much of the last 24 hours with thunderstorm bursts tending to be west of the center instead of symmetrically distributed around the center...a pattern of light easterly shear that has only allowed Rene to strengthen to 50 mph maximum sustained winds and only very recently. I could understand if Rene was under easterly shear if the tropical storm was south of the 200 mb upper ridge axis instead of directly under it while also moving slower to the west than it currently has been...which would allow the easterly winds on the south side of the upper ridge axis to rake the thunderstorms westward from the center...but this is not the case. As the 11 PM EDT Rene discussion from the National Huricane Center stated last night...there is a mid-level easterly jet "undercutting an otherwise favorable outflow layer"...presuming that outflow layer refers to the outflow being generated by the 200 mb tropical upper ridge axis. Perhaps then the mid-level African Easterly Jet that generates surface African tropical waves of low pressure...located below 200 mb and above the surface...is what has been shearing Rene. The thunderstorms have only recently become more symmetric around Rene's center which has allowed for a little strengthening as of 11 AM EDT...perhaps as Rene moves furhter away from the African Easterly Jet...thus additional strengthening still appears to be in the cards for Rene.


My updated forecast track points are nudged northard due to the current position of the tropical storm. By 48 hours I forecast Rene to curve more northward in track in response to a surface ridge weakness to be induced by Paulette and also a piece of energy from the current eastern Canada upper trough that will generate a surface frontal cyclone in the north Atlantic. The steering picture gets a little murky by 72+ hours as the current surface ridge over the northern United States will be passing north of Rene which will try to push Rene more westward. At the same time the energy that ejects from the eastern Canada upper trough is forecast to amplify in the northeast Atlantic in response to the northwestern Atlantic upper ridge amplifying in the warm sector of a frontal zone arriving to eastern North America (to be driven by the currently amplified western United States upper trough and also an upper trough from western Canada merging with it). Since it is probable that Rene will be a strong/tall enough tropical cyclone to also be steered by upper-level winds...it is possible that the back western side of the northeast Atlantic upper trough tries to turn Rene more eastward. For now my solution is to have Rene continue its northwest direction from 72 to 96 hours but with a slower forward motion while the surface ridge and upper trough try to move Rene in opposite directions...an effect that will likely shear the storm as well. By 120 hours I vote Rene will continue northwestward toward the low pressure field of Paulette and around the southwest side of the surface ridge as the northeast Atlantic upper trough moves away. I will note that some models have shifted southwest of my 120-hour forecast point while positioning Paulette more westward...but for now I vote Paulette will be more toward the east...see Paulette section above for details.


Regarding intensity...given that the easterly shear that has plauged Rene appears to have reduced somewhat...I still forecast Rene to strengthen into a hurricane...but I have lowered my peak forecast intensity to a top-end category 1 at this point as Rene has failed to strengthen much thus far and the thunderstorms are not organizing into banding features on infrared satellite imagery. I flatten the intensification by day 3 and show weakening by day 4 due to possible northerly shear from the northeast Atlantic upper trough mentioend in the previous paragraph. Some re-intensification is possible by day 5 as the upper trough and its shear shifts eastward...allowing for the vast northwest Atlantic upper ridge to overspread Rene with lower shear and upper outflow...but I assume the pulse of shear from day 4 will be strong enough to disrupt Rene such that it would need time to re-organize...thus my intensification rate at day 5 is shown to be only slow.

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

0 Hr Position (1200Z Sep 10)...50 mph maximum sustained tropical storm centered at 18.6N-35.8W

IOH 24 Hr Forecast (1200Z Sep 11)...70 mph maximum sustained wind tropical storm centered at 19N-41W

IOH 48 Hr Forecast (1200Z Sep 12)...95 mph maximum sustained wind hurricane centered at 22N-43W

IOH 72 Hr Forecast (1200Z Sep 13)...95 mph maximum sustained wind hurricane centered at 27N-46W

IOH 96 Hr Forecast (1200Z Sep 14)...65 mph maximum sustained wind tropical storm centered at 29N-47W

IOH 120 Hr Forecast (1200Z Sep 15)...75 mph maximum sustained wind hurricane centered at 31N-49W


AREA OF INTEREST #1...The surface low pressure in the western Atlantic heading toward the Carolina coast has merged with a decaying frontal zone that was located just offshore...resulting in a surface trough of low pressure. There is a current lack of organized thunderstorm activity associated with this surface trough...perhaps as the inflow of the new disturbance in area of interest #4 to the southeast is beginning to dominate. In addition the cold front over the eastern United States is expected to absorb this system as the front shifts east in the next 24 hours. This is my final statement on this disturbance on this blog as it has been dropped from the 2 PM EDT National Hurricane Center tropical weather outlook.

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

IOH 24 Hr Outlook (1200Z Sep 11)...0% chance of tropical cyclone formation (absorbed by cold front while located on the North Carolina coast near 34.5N-76.5W)


AREA OF INTEREST #2...The tropical wave of low pressure behind Tropical Storm Rene has become better organized as it arrives onto the west African coast. A circular cluster of thunderstorms suggests a low pressure center emerging near 13N-20W...and bands on the south side of the tropical wave suggest another potential low pressure center near 11N-17.5W. For my current outlook below...I intialize this disturbance in between both possible low pressure centers in the vicinity of 12N-18W and begin forecasting forward from there. Although this current position is west of my previous outlook for this timeframe...I show a slightly slower westward track for the next 72 hours as the tropical wave mentioned in area of interest #3 appears to be undergoing a fujiwhara type of interaction with this wave as the two waves are close to each other...which may cause this wave to slow down its forward speed and potentially stay further south in track. I increase the foward speed of this wave after 72 hours as the wave to the east may be slowed by a surface ridge weakness to be created by an upper trough in the northeast Atlantic...increasing the seperation between the two. Computer models appear to have also shifted further south with this tropical wave perhaps while now picking up upon the potential fujiwhara interaction...and also as the surface ridge weakness from Paulette and Rene may start to fade as both storm lift northward by 120 hours. Likewise I have shifted my forecast points southward. Models have also trended with taking longer in showing this wave developing into a tropical cyclone...perhaps as the two waves compete with each other for low-level inflow and upper outflow. But given that this wave has become better organized...I still have a high 90% chance of tropical cyclone formation from this wave by day 5. I have also not yet gone with a tropical cyclone formation forecast however as the two waves may compete with each other in the short term.

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

IOH 24 Hr Outlook (1200Z Sep 11)...70% chance of tropical cyclone formation (southeast of the Republic of Cabo Verde Islands near 12N-22W)

IOH 48 Hr Outlook (1200Z Sep 12)...90% chance of tropical cyclone formation (southwest of the Republic of Cabo Verde Islands near 12N-26W)

IOH 72 Hr Outlook (1200Z Sep 13)...90% chance of tropical cyclone formation (tropical Atlantic near 12N-30W)

IOH 96 Hr Outlook (1200Z Sep 14)...90% chance of tropical cyclone formation (tropical Atlantic near 12N-35W)

IOH 120 Hr Outlook (1200Z Sep 15)...90% chance of tropical cyclone formation (tropical Atlantic near 12N-40W)


AREA OF INTEREST #3...A tropical wave of low pressure over interior western Africa in the vicinity of 12.5N-6W continues to produce strong thunderstorm activity...and computer models are more indicative today that this wave could eventually develop. Therefore the National Hurricane Center has added it into their tropical weather outlook. The wave is further north than yesterday as it appears to be undergoing a fujiwhara type of interaction with the wave mentioned in area of interest #2. Thus I have shifted my forecast points northward for this wave assuming this interaction continues...with the forward speed potentially slowing around 72 hours as the eastern divergence zone of a northeast Atlantic upper trough potentially weakens the east side of the steering surface subtropical ridge in the Atlantic (this upper trough is forecast to originate from energy to eject from the current eastern Canada upper trough...see Rene section above for details). As the upper trough shifts east...the Atlantic surface subtropical ridge is forecast to recover...so I bend adjust the track back up to a normal speed and with a more westward angle by 120 hours. I have only slightly raised 5-day peak odds of development to 40%...in agreement with the National Hurricane Center...as the tropical wave in area of interest #2 is the better organized in the region and will potentially dominate...or if the two waves stay close enough to each other...it could possibly absorb this wave. There is also some potential that the south side of the northeast Atlantic upper trough may impart some disrupting westerly shear in the later part of the forecast period...espeically if the wave tracks more northward. On the home page bulletins of this site...I have begun to mention this wave in regards to the Republic of Cabo Verde Islands as the northward adjusted track takes this wave toward the islands.

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

IOH 24 Hr Outlook (1200Z Sep 11)...0% chance of tropical cyclone formation (western Africa near 13N-11W)

IOH 48 Hr Outlook (1200Z Sep 12)...0% chance of tropical cyclone formation (west coast of Africa near 14N-16W)

IOH 72 Hr Outlook (1200Z Sep 13)...20% chance of tropical cyclone formation (east of the Republic of Cabo Verde Islands at 15N-21W)

IOH 96 Hr Outlook (1200Z Sep 14)...40% chance of tropical cyclone formation (over the Republic of Cabo Verde Islands near 16N-25W)

IOH 120 Hr Outlook (1200Z Sep 15)...40% chance of tropical cyclone formation (tropical Atlantic near 16.5N-30W)


AREA OF INTEREST #4...An area of showers and thunderstorms in the vicnity of 25N-73.5W has increased and become gradually better organized to the east-northeast of the Bahamas over the last day or so...initially triggered by split flow upper divergence between western Atlantic upper vorticity and the upper ridge currently in the western Atlantic...and now maintained by outflow on the southeastern quadrant of the upper ridge. This developing surface low pressure disturbance has been introduced into the National Hurricane Center tropical weather outlook as a result...and is forecast to head generally westward across the western Bahamas...south Florida peninsula...and Gulf of Mexico under the influence of the Atlantic subtropical ridge and then the surface ridge currently over the northern United States. For the next 72 hours I forecast a westward speed of about 4W longitude per day instead of the typical 5W for tropical disturbances due to the narrow ridge weakness being created by the current eastern United States front. A slight bend to the north is shown between 24 and 72 hours as the current upper trough over the western United States merges with a trough from western Canada...with another surface ridge weakness to be created by the divergence zone of the combined trough. A straight west track is again shown between 72 and 96 hours as this ridge weakness and combined upper trough move away...followed by another slight northward bend in track by 120 hours as a shortwave upper trough is currently forecast to produce a frontal system near the central US/Canada border region...potentially inducing yet another ridge weakness.


Given the current increasing organization of the thunderstorm activity...I already forecast 30% odds of tropical cyclone formation for the next 48 hours. I haven't gone higher than this for the short-term just yet as land interaction with the southern Florida peninsula and some potential northerly shear from a lobe of upper vorticity heading toward the Carolina coast (a lobe currently breaking off from the main vorticity axis in the western Atlantic and retrograding around the northwest Atlantic upper ridging) maybe some negatives working against this system. After 48 hours the upper-level wind outlook for this system improves as follows. The north-south axis of upper vorticity currently off to the west in the Gulf of Mexico is expected to tilt southwest to northeast...with the northeastern part shifting east toward the aforementioned vorticity at the Carolina coast...and the southwestern part retrograding southwestward and away under the influence of warm upper ridging that has built in the warm sector of the unusual snowstorm that affected Colorado and Wyoming a couple of days ago (snowstorm supported by the sharp upper trough currently over the western United States). As the Gulf upper vorticity tilts and then breaks into two parts that move away from each other...this will leave a favorable low shear and upper outflow environment in between and directly over this disturbancce as it traverses the Gulf...thus I give a high 70% chance of tropical cyclone formation in the longer range. On a final note...if current organizaitonal trends continue...I will consider a special update tonight where I notably raise the short term odds of development as well...so interests in south Florida and the western Bahamas should monitor this disturbance carefully for possible impacts over the next couple of days.

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

IOH 24 Hr Outlook (1200Z Sep 11)...30% chance of tropical cyclone formation (western Bahamas near 25N-77.5W)

IOH 48 Hr Outlook (1200Z Sep 12)...30% chance of tropical cyclone formation (just west of south Florida near 25.5N-81.5W)

IOH 72 Hr Outlook (1200Z Sep 13)...50% chance of tropical cyclone formation (Gulf of Mexico near 26N-85.5W)

IOH 96 Hr Outlook (1200Z Sep 14)...70% chance of tropical cyclone formation (Gulf of Mexico near 26N-90.5W)

IOH 120 Hr Outlook (1200Z Sep 15)...70% chance of tropical cyclone formation (northwestern Gulf of Mexico near 26.5N-95W)


AREA OF INTEREST #5...Upper divergence on the east side of cut-off upper vorticity that has been in the northwestern Caribbean and Gulf of Mexico region has produced a surface trough of low pressure now in the eastern Gulf of Mexico...in the vicinity of 27.5N-82.5W and just west of Tampa Bay Florida as of 1200Z earlier today. This surface trough may also have its origins from the tail end of a decaying frontal zone that was parked just offshore of the southeastern United States yesterday...and also maybe from the north fracture of a tropical wave currently moving through the western Caribbean Sea. I have included this surface trough as yet another area of interest for tropical developemnt due to its recent mentions in the National Hurricane Center tropical weather outlook. Due to the current organization of the disturbance to the east....area of interest #4... and the lack of thunderstorms with this surface trough...I forecast that disturbance to dominate over this surface trough terms of low-level inflow in the region. Instead of a typical 5W longitude per day westward track around the surface ridge over the northern United States...I forecast only an increasingly slowing west-southwest track while it undergoes a fujiwhara type interaction with area of interest #4 and gets pulled toward its increasing low-level inflow...followed by absoprtion into area of interest #4 in 48 hours. Therefore at this time...I am forecasting a 0% chance of tropical cyclone formation from this surface trough.

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

IOH 24 Hr Outlook (1200Z Sep 11)...0% chance of tropical cyclone formation (north-central Gulf of Mexico near 27.5N-87W)

IOH 48 Hr Outlook (1200Z Sep 12)...0% chance of tropical cyclone formation (absorbed by area of interest #4 while located in the northern Gulf of Mexico near 27N-89W)


...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 Tropical Storm Paulette...located east-southeast of Bermuda at 31.5N-61.5W at 120 hours as a hurricane. For Tropical Storm Rene...located at 28N-45W as a remnant low pressure at 120 hours. For area of interest #1...absorbed into eastern United States cold front at 24 hours while located over coastal North Carolina. For area of interest #2...located at 12.5N-47.5W at 120 hours as a weak tropical low pressure. For area of interest #3...organizes into a tropical low pressure over the Republic of Cabo Verde Islands at 78 hours...tropical low pressure located at 21N-27W at 120 hours. For areas of interest #4 and #5...no tropical cyclone formation shown.


0000Z ECMWF Model Run....For Tropical Storm Paulette...located just southwest of Bermuda at 31.5N-66.5W at 120 hours as a large strong hurricane. For Tropical Storm Rene...located at 30N-50W at 120 hours. For area of interest #1...absorbed into eastern United States cold front at 24 hours while located over coastal North Carolina. For area of interest #2...tropical cyclone formation suggested near 14N-50W at 120 hours. For area of interest #3...tropical cyclone formation suggested just west of the Republic of Cabo Verde Islands at 96 hours...located at 16N-32W at 120 hours. For areas of interest #4 and #5...no tropical cyclone formation shown.


0600Z GFS Model Run...For Tropical Storm Paulette...located west-southwest of Bermuda at 32N-68W at 120 hours as a large and intense hurricane. For Tropical Storm Rene...located at 27.5N-48.5W at 120 hours . For area of interest #1...absorbed into eastern United States cold front at 48 hours while located over coastal North Carolina. For area of interest #2...compact tropical cyclone formation suggested near 11N-49W at 120 hours. For area of interest #3...organizes into a tropical low pressure located just southeast of the Republic of Cabo Verde Islands at 60 hours...tropical low pressure located at 17.5N-34W at 120 hours. For area of interest #4...organized into a tropical low pressure south of southeastern Louisiana near 27.5N-90W at 120 hours. For area of interest #5...no tropical cyclone formation shown.


0000Z NAVGEM Model Run...For Tropical Storm Paulette...located southeast of Bermuda at 31N-62.5W at 120 hours as a large and intense hurricane. For Tropical Storm Rene...located at 27.5N-47W at 126 hours. For area of interest #1...absorbed into eastern United States cold front at 36 hours while located over coastal North Carolina. For area of interest #2...located at 16N-32.5W as a weak broad tropical low pressure at 120 hours. For areas of interest #3 and #4...no tropical cyclone formation shown. For area of interest #5...organizes into a tropical low pressure south of Louisiana near 27.5N-91W at 60 hours...moves west-southwest into the Texas/Mexico border region at 120 hours.

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