*******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 8 2020 11:57 AM 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 areas of interest being monitored for tropical cyclone formation.
Elsewhere...the eastern divergence zone of a cut-off upper vortex in the northeastern Atlantic is producing a surface low pressure south of the Azores that has seen some increase in shower and thunderstorm activity...thanks to the cold temperatures of the upper vortex despite the water temperatures only being a marginal 26 deg C for tropical development in the region. However computer models agree that the surface low pressure will soon whirl directly below the upper vortex center where there is a lack of divergence...thus causing the surface low to weaken. In addition surface pressures in the region are high thanks to the Atlantic surface subtropical ridge which will make the formation of a subtropical cyclone here difficult. Therefore I have not added this feature as an area of interest for subtropical cyclone formation.
TROPICAL STORM PAULETTE...Paulette continues to strengthen over the open central tropical Atlantic while taking advantage of upper outflow beneath the upper ridge axis in the region...with an outflow channel also streaming northeastward into the large upper vortex currently in the northeastern Atlantic. My updated forecast track below is nudged eastward as Paulette has been moving a bit slower to the west than I anticipated. The slow westward motion is being caused by low surface pressures that have weakened the south side of the steering Atlantic subtropical ridge...being created by divergence zones of cut-off upper upper vortex in the northeast Atlantic and also the upper vorticity in the western Atlantic. The slow forward speed is expected for 24 more hours...with some increase in forward speed thereafter as the south side of the Atlantic subtropical ridge recovers once the cut-off upper vorticity to the northeast and west begin to weaken. I have some northward angle in track as Paulette has been and will continue to be tall enough to be dragged by the upper southwesterly flow ahead of the western Atlantic upper vorticity. I do not show a complete turn to the north thru 120 hours as the surface ridge currently exiting the eastern United States and the surface ridge currently over the northwestern United States will pass north of Paulette and make it difficult for the tropcial storm to turn completely north.
In the short term...my intensity forecast is the same as the previous...showing Paulette reaching a strength just below hurricane force by 24 hours before it moves closer to the belt of southwesterly shearing winds being generated out ahead of the western Atlantic upper vorticity. It would not suprise me if Paulette became a hurricane within the next 48 hours before it reaches the worst of the shear. Each day the GFS model continues to show less separation between the northeast Atlantic upper vortex and western Atlantic upper vorticity...while showing a chunk of the northeast Atlantic upper vortex retrograding southwestward into the western Atlantic upper vorticity. Thus I am forced to lower the longer term intensity forecast as this upper air pattern will cause prolonged shear instead of allowing for a gap between both lobes of upper vorticity that would allow for less shear.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Sep 8)...65 mph maximum sustained wind tropical storm centered at 18.4N-43.3W
IOH 24 Hr Forecast (1200Z Sep 9)...70 mph maximum sustained wind tropical storm centered at 19.2N-46.5W
IOH 48 Hr Forecast (1200Z Sep 10)...70 mph maximum sustained wind tropical storm centered at 20N-50.5W
IOH 72 Hr Forecast (1200Z Sep 11)...60 mph maximum sustained wind tropical storm centered at 21.2N-54W
IOH 96 Hr Forecast (1200Z Sep 12)...60 mph maximum sustained wind tropical storm centered at 24N-57W
IOH 120 Hr Forecast (1200Z Sep 13)...60 mph maximum sustained wind tropical storm centered at 27.5N-60W
TROPICAL STORM RENE...Since yesterday afternoon...tropical depression eighteen took the prize of being the earliest seventeenth named storm on record in the Atlantic basin while strengthening to Tropical Storm Rene as it moved into the Republic of Cabo Verde Islands. Rene beats Rita of 2005 which was named on September 18. The tropical storm has not strengthened above 40 mph maximum sustained winds while featuring bands of thunderstorms broken up by dry saharan air that the circulation has ingested. Therefore outside of gusty winds...some heavy rain...and perhaps some rough waters along the shore...the impacts from Rene have likely been not substantial.
My updated forecast track is shifted westward as Rene has been moving a bit faster than I previously forecasted. As Rene continues to depart the islands...I expect the track to bend more west as the northeastern Atlantic surface low pressure responsible for the northward component in Rene's track will weaken as it whirls directly beneath its parent upper vortex where there is a lack of supportive divergence for it. I do forecast a slow forward motion for another 24 hours as both Paulette and Rene are experiencing a weakened steering Atlantic subtropical surface ridge...see Paulette section above for details on what is causing the weakened ridge. After 24 hours...I expect the forward motion of both storms to increase as the subtropical ridge recovers. With Paulette being further east and Rene being further west than my previous forecasts...the distance between the two tropical storms has decreased which increases the potential for interaction between them. Thus I forecast a sharper northwestward turn by 96+ hours than I previously showed...to be caused by a ridge weakness to be induced by Paulette and also a piece of energy from the current eastern Canada upper trough that generates a surface frontal cyclone in the north Atlantic by 72+ hours.
Regarding intensity...thru the next 5 days this system will remain in low shear and upper outflow environment beneath a tropical upper ridge axis. Therefore I still forecast major hurricane strength by the end of the forecast period...but I have delayed the timeframe of major hurricane status by 24 hours given that Rene has ingested dry sahran air and will need time to mix that out. This is much higher than my intensity forecast for Tropical Storm Paulette as I expect thru day 5 that this system will stay east of the shearing upper southwesterly winds that will affect Paulette. My intensity forecast does not go above category 3 for the next five days as this system will remain east of the very warm 28+ deg C waters.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Sep 8)....40 mph maximum sustained wind tropical storm centered just west of the Republic of Cabo Verde Islands at 16.5N-26.5W
IOH 24 Hr Forecast (1200Z Sep 9)....50 mph maximum sustained wind tropical storm centered at at 16.8N-29W
IOH 48 Hr Forecast (1200Z Sep 10)...75 mph maximum sustained wind hurricane centered at 17.3N-34W
IOH 72 Hr Forecast (1200Z Sep 11)...100 mph maximum sustained wind hurricane centered at 17.8N-39W
IOH 96 Hr Forecast (1200Z Sep 12)...115 mph maximum sustained wind major hurricane centered at 20N-42W
IOH 120 Hr Forecast (1200Z Sep 13)...125 mph maximum sustained wind major hurricane centered at 25N-45W
AREA OF INTEREST #1...The tropical wave of low pressure entering the western Caribbean Sea after passing over Jamaica has lost thunderstorm activity while moving directly below upper vorticity in the region that has constricted upper outflow. Therefore the chances of thunderstorm latent heat release defeating the cold core upper vorticity have diminished and I have dropped my odds of tropical cyclone formation from 10% yesterday to 0% today. This is my final statement on this tropical wave on this blog.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 9)...0% chance of tropical cyclone formation (western Caribbean Sea east of Belize and the Yucatan peninsula near 17.5N-87W)
AREA OF INTEREST #2...The surface low pressure in the western Atlantic...currently centered at 30N-69.5W...saw an increase in thunderstorm overnight that have since dwinlded this morning. The thunderstorm activity remains sheared southeastward from the center which is keeping this system disorganized...thanks to northwesterly upper winds between a western Atlantic upper ridge axis to the west and upper vorticity to the southeast. This system is expected to continue west-northwest toward the Carolina coast under the influence of the surface ridge currently exiting the eastern United States...and toward the low pressure field of the cold front over the eastern United States. This track will take this system beneath more favorable low shear and upper outflow beneath the western Atlantic upper ridge axis. However my peak odds of development remain only at 20%..lower than the National Hurricane Center's current outlook...as this system will only have a breif window of low shear before potentially dealing with southerly shear from upper vorticity that spans the western Caribbean and southeastern United States. It is also possible this upper vorticity stays weak enough to not really shear this system such that I may have to raise my odds of development later on. By 72 hours I drop the odds of development down to 0% as this system becomes absorbed by the aformentioned cold front.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 9)...20% chance of tropical cyclone formation (western Atlantic near 31N-74.5W)
IOH 48 Hr Outlook (1200Z Sep 10)...20% chance of tropical cyclone formation (just offshore of South Carolina near 32N-79.5W)
IOH 72 Hr Outlook (1200Z Sep 11)...0% chance of tropical cyclone formation (absorbed by cold front while just offshore of northeastern South Carolina near 33N-79.5W)
AREA OF INTEREST #3...Computer models insist that the next tropical wave to emerge from western Africa behind Tropical Storm Rene will have a high chance at tropical cyclone formation. Given that thunderstorm activity has increased with this tropical wave while showing banding features...and given that the favorable environment of low shear and upper outflow beneath an eastern tropical Atlantic upper ridge axis will persist (the same environment in which Rene and Paulette formed)...I have notably increased my odds of tropical cyclone formation to 90%. If current trends continue...I will consider a tropical cyclone formation forecast in my next update. Forecast track is steady to the west thru 120 hours as this system will stay east of the surface subtropical ridge weakness to be created by Rene and Paulette.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 9)...0% chance of tropical cyclone formation (western Africa near 12.5N-10W)
IOH 48 Hr Outlook (1200Z Sep 10)...0% chance of tropical cyclone formation (west coast of Africa near 12.5N-15W)
IOH 72 Hr Outlook (1200Z Sep 11)...60% chance of tropical cyclone formation (southeast of the Republic of Cabo Verde Islands near 12.5N-20W)
IOH 96 Hr Outlook (1200Z Sep 12)...70% chance of tropical cyclone formation (just south of the Republic of Cabo Verde Islands near 13N-25W)
IOH 120 Hr Outlook (1200Z Sep 13)...90% chance of tropical cyclone formation (tropical Atlantic near 13.5N-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 Tropical Storm Paulette...located at 22N-52.5W at 120 hours. For Tropical Storm Rene...circulation of Paulette causes northward turn...arriving to 26N-45W at 120 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...absorbed into eastern United States cold front at 72 hours while located over coastal North Carolina. For area of interest #3...emerges from western Africa near 12N-15W at 54 hours...tropical cyclone formation suggested near 11.5N-19W at 72 hours...located at 16N-32W at 120 hours.
0000Z ECMWF Model Run....For Tropical Storm Paulette...located at 25.5N-58.5W at 120 hours. For Tropical Storm Rene...large circulation of Paulette causes northward turn...arriving to 27.5N-47W at 120 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...merges with cold front from eastern United States at 96 hours while just offshore of South Carolina. For area of interest #3...emerges from western Africa at 48 hours...tropical cyclone formation suggested near 15N-37.5W at 120 hours.
0600Z GFS Model Run...For Tropical Storm Paulette...located at 22.5N-55W at 120 hours. For Tropical Storm Rene...circulation of Paulette causes northward turn...Rene shown to be a strong tropical cyclone from 36 to 102 hours over the open eastern Atlantic...located over east-central Atlantic as a weakening tropical cyclone near 30N-37.5W at 120 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...absorbed into eastern United States cold front at 72 hours while located over coastal North Carolina. For area of interest #3...emerges from western Africa at 48 hours...tropical cyclone formation suggested near 12.5N-26W at 102 hours...shown to be a strong tropical cyclone at 15N-34W at 132 hours.
0600Z NAVGEM Model Run...For Tropical Storm Paulette...located at 27.5N-60W at 120 hours as a large and intense hurricane. For Tropical Storm Rene...located at 22.5N-46W at 120 hours as a strong hurricane. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...For area of interest #2...absorbed into eastern United States cold front at 72 hours while located over coastal North Carolina. For area of interest #3...emerges from western Africa at 60 hours...located near 14N-29W at 120 hours as a weak and broad surface low.