*******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.**********
...WEDNESDAY SEPTEMBER 9 2020 1:09 PM EDT...
See Tropical Storm Paulette and Tropical Depression Rene sections below for the two currently active tropical cyclones in the Atlantic basin. See area of interest sections below for disturbances being monitored for tropical cyclone formation.
TROPICAL STORM PAULETTE...Paulette has stopped strengthening over the open central tropical Atlantic while moving closer to a belt of shearing upper southwesterly winds out ahead of upper vorticity that spans the western and northeastern Atlantic. My updated forecast track below is nudged northward over my previous due to Paulette's current position. The tropical storm has been moving slowly since its inception as the aforementioned upper vorticity's divergence zones have kept the south side of the steering Atlantic subtropical ridge weak...but the ridge is expected to soon recover as the cold core upper vorticity continues to gradually weaken during the forecast period while remaining cut-off from higher latitude cold air. Thus I anticipate an increase in forward speed...with a northward angle in track continuing courtesy of the upper southwesterly shearing winds. A westward component is kept in the track through 120 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. After the 120-hour forecast period...it is probable that the current western United States upper trough will have merged with another upper trough from western Canada...with the merger creating a frontal zone that would curve Paulette completely northward. But with a west component in track expected for the next 120 hours...Paulette could pass very close to or directly over Bermuda just after 5 days....therefore I have begun to mention potential impacts from Paulette to Bermuda on the home page bulletins of this site.
Using the latest GFS model upper level wind projections...it appears the upper vorticity may split in half in the vicinity of Paulette sooner than projected yesterday...potentially allowing the wind shear to be less than previously thought. Maybe the GFS may be picking up on the latent heat release of Paulette's thunderstorms as a catalyst for splitting the upper vorticity? Thus my updated intensity forecast shows Paulette hanging on to its current strength through 72 hours...followed by gradual intensification into a hurricane by 120 hours once the upper vorticity splits in half. My intensity forecast only shows gradual intensifcation at the end of the forecast period as the projections on the evolution of the upper vorticity have been changing day to day...so I am uncertain if it will change again.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Sep 9)...60 mph maximum sustained wind tropical storm centered at 20N-46.5W
IOH 24 Hr Forecast (1200Z Sep 10)...60 mph maximum sustained wind tropical storm centered at 21.5N-50.5W
IOH 48 Hr Forecast (1200Z Sep 11)...60 mph maximum sustained wind tropical storm centered at 23N-54W
IOH 72 Hr Forecast (1200Z Sep 12)...60 mph maximum sustained wind tropical storm centered at 25N-57W
IOH 96 Hr Forecast (1200Z Sep 13)...70 mph maximum sustained wind tropical storm centered at 28N-60W
IOH 120 Hr Forecast (1200Z Sep 14)...80 mph maximum sustained wind hurricane centered just east-southeast of Bermuda at 31N-63W
TROPICAL DEPRESSION RENE (RECENTLY UPGRADED TO TROPICAL STORM RENE)...While pulling westward and away from the Republic of Cabo Verde Islands...Rene weakened to a tropical depression last night as the thunderstorm activity remained broken up by dry saharan air. Then in the overnight strong thunderstorms began firing over and west of the center of circulation...allowing the tropical depression to re-strengthen into a tropical storm as of the recent 11 AM EDT National Hurricane Center advisory. Based on the latest satellite imagery...the beige tint of dry saharan air no longer appears within Rene's circulation like it did yesterday...instead only showing up as a band north of the tropical storm. Thus it appears Rene has mixed out the dry air while moistening the atmosphere with its thunderstorms.
My updated forecast track points are nudged northwestward due to the current position of the tropical storm. This indicates Rene is accelerating its forward speed as the steering Atlantic subtropical ridge has recovered while the northeastern Atlantic surface low pressure has continued to weaken below its parent upper vortex where there is a lack of divergence...thus Rene's forward motion will be faster than it has been in previous days. By 72+ 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 generates a surface frontal cyclone in the north Atlantic by 48+ hours. The steering picture gets murky by 96+ 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 western 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 thru 120 hours but just slow the track while the surface ridge and upper trough try to move Rene in opposite directions...an effect that will likely shear the storm as well.
Regarding intensity...given that Rene has mixed out the dry air it ingested and that in the next 3 days it will remain in low shear and upper outflow environment beneath a tropical upper ridge axis...I still forecast Rene to strengthen into a strong hurricane. I slow the intensification rate by day 4 due to possible northerly shear mentioend in the previous paragraph...but this is just enough for me to forecast Rene to peak out as a minimal category 3 hurricane. I then show weakening by day 5 as the shear potential increases.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Sep 9)....40 mph maximum sustained wind tropical storm centered at 17.6N-31.5W
IOH 24 Hr Forecast (1200Z Sep 10)...60 mph maximum sustained tropical storm centered at 18N-36.2W
IOH 48 Hr Forecast (1200Z Sep 11)...95 mph maximum sustained wind hurricane centered at 18.5N-41W
IOH 72 Hr Forecast (1200Z Sep 12)...110 mph maximum sustained wind hurricane centered at 21N-43W
IOH 96 Hr Forecast (1200Z Sep 13)...115 mph maximum sustained wind major hurricane centered at 26N-46W
IOH 120 Hr Forecast (1200Z Sep 14)...85 mph maximum sustained wind hurricane centered at 28.5N-47W
AREA OF INTEREST #1...The surface low pressure in the western Atlantic...currently centered at 31N-74.5W...remains disorganized while still experiencing northerly wind shear in between a western Atlantic upper ridge axis and upper vorticity to the southeast. This system is expected to continue west-northwest toward the Carolina coast under the influence of the Atlantic subtropical ridge...and toward the low pressure field of the cold front over the eastern United States. While this track takes this system beneath the upper ridge axis in 24 hours where wind shear may be less than current levels...the 0600Z GFS shows by 48 hours that a piece of the upper vorticity to the southeast will retrograde toward this system while moving around the western Atlantic upper ridge which may constrict upper outflow by that timeframe. Given that this system has not become better organized and only has a narrow window of favorable upper winds...I have dropped the odds of tropical cyclone formation to 10%. Although the National Hurricane Center (NHC) has also dropped their odds of this system developing...I remain below the latest NHC outlook. I drop my odds to 0% by 48 hours as this system merges with the aforementioned cold front currently over the eastern United States.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 10)...10% chance of tropical cyclone formation (just offshore of South Carolina near 32N-79.5W)
IOH 48 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 #2...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 not increased or become better organized with respect to yesterday...I have not done a tropical cyclone formation forecast for this feature at this time...but I still forecast a 90% chance of tropical cyclone formation by day 5 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). Forecast track is steady to the west thru 96 hours as this system will stay east of the surface subtropical ridge weakness to be created by Rene and Paulette. I bend the track slightly more northward by 120 hours as this system nears the ridge weakness.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 10)...0% chance of tropical cyclone formation (west coast of Africa near 12.5N-15W)
IOH 48 Hr Outlook (1200Z Sep 11)...50% chance of tropical cyclone formation (southeast of the Republic of Cabo Verde Islands near 12.5N-20W)
IOH 72 Hr Outlook (1200Z Sep 12)...60% chance of tropical cyclone formation (just south of the Republic of Cabo Verde Islands near 13N-25W)
IOH 96 Hr Outlook (1200Z Sep 13)...80% chance of tropical cyclone formation (tropical Atlantic near 13.5N-30W)
IOH 120 Hr Outlook (1200Z Sep 14)...90% chance of tropical cyclone formation (tropical Atlantic near 14.5N-35W)
AREA OF INTEREST #3...Another tropical wave of low pressure is located over interior western Africa in the vicinity of 10N-1W based on the above satellite image. Based on its current organization and the fact that the favorable low shear and upper outflow pattern over western Africa and eastern Atlantic is expected to continue over the next few days,..I have added it as another area of interest for tropical development. However my 5-day odds of development are only at a low 30% as the GFS model is currently the only model that develops this system...and also because this system will be in close proximity to the tropical wave in area of interest #2 that will likely develop first in which case the low-level inflow and upper outflow of that tropical wave may suppress this one. This could also be why most models do not currently develop this tropical wave. Therefore on the home page bulletins of this site...at this time I have not mentioned this wave in regards to the Republic of Cabo Verde Islands. This wave is also further south than the recent waves that have exited the African coast which also increases the chances this wave passes south of the islands rather than over them.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 10)...0% chance of tropical cyclone formation (western Africa near 10N-6W)
IOH 48 Hr Outlook (1200Z Sep 11)...0% chance of tropical cyclone formation (western Africa near 10N-11W)
IOH 72 Hr Outlook (1200Z Sep 12)...0% chance of tropical cyclone formation (west coast of Africa near 10N-16W)
IOH 96 Hr Outlook (1200Z Sep 13)...10% chance of tropical cyclone formation (west coast of Africa near 10.5N-21W)
IOH 120 Hr Outlook (1200Z Sep 14)...30% chance of tropical cyclone formation (south of the Republic of Cabo Verde Islands near 11N-26W)
...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 28N-59.5W at 120 hours as a large and strong hurricane. For Tropical Depression Rene...located at 28N-47W as a remnant low pressure 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...emerges from western Africa near at 24 hours...tropical cyclone formation suggested just southeast of the Republic of Cabo Verde Islands at 12.5N-21.5W at 66 hours...located at 17.5N-33W at 120 hours. For area of interest #3...no tropical cyclone formation shown.
0000Z ECMWF Model Run....For Tropical Storm Paulette...located just southeast of Bermuda at 30N-62.5W at 120 hours. For Tropical Depression Rene...located at 28N-47.5W as a remnant low pressure 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...emerges from western Africa at 24 hours...tropical cyclone formation suggested near 18N-34W at 144 hours. For area of interest #3...no tropical cyclone formation shown.
0600Z GFS Model Run...For Tropical Storm Paulette...located southeast of Bermuda at 29N-60.5W at 120 hours. For Tropical Depression Rene...becomes a strong compact tropical cyclone near 21.5N-40W at 60 hours...while remaining a strong compact tropical cyclone located at 29N-43W 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...emerges from western Africa at 24 hours...tropical cyclone formation suggested near 10.5N-20.5W at 48 hours...shown to be a large and intense ropical cyclone at 15N-38W at 120 hours. For area of interest #3...tropical wave emerges from western Africa at 84 hours...compact tropical cyclone formation suggested near 15N-20.5W at 102 hours...moves into the southern Republic of Cabo Verde Islands at 120 hours.
0600Z NAVGEM Model Run...For Tropical Storm Paulette...located at 30N-58W at 126 hours as a large and intense hurricane. For Tropical Depression 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...emerges from western Africa at 36 hours...located west of the Republic of Cabo Verde Islands as a weak and broad surface low at 120 hours. For area of interest #3...no tropical cyclone formation shown.