MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #120
*******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.**********
...MONDAY SEPTEMBER 14 2020 10:05 PM EDT...
See Hurricane Paulette...Tropical Depression Rene...Hurricane Sally...Tropical Storm Teddy...and Tropical Storm Vicky for the five currently active tropical cyclones in the Atlantic basin. See area of interest sections below for multiple disturbances being monitored for tropical cyclone formation.
HURRICANE PAULETTE...While remaining in a low shear environment to the north of western Atlantic upper vorticity and out ahead of an upper trough approaching from eastern North America...Paulette strengthened further into a category 2 hurricane as the eye passed over Bermuda. Going forward...Paulette will be a classic high latitude hurricane accelerating northeastward ahead of the upper trough and its surface front...thus I forecast gradual weakening as the trough potentially shears Paulette. I have nudged the intensity forecast upward as the hurricane is a little stronger than my previous forecast...and as Paulette is accelerating faster to the northeast than previously thought which may allow the hurricane to keep up with the shearing upper southwesterlies ahed of the upper trough and effectively reduce the shear potential. My updated track forecast is faster to the northeast....reaching cooler waters by 48 hours. At that time I forecast slow weakening as it transitions into a strong non-tropical remnant low pressure supported by divergence on the east side of the incoming upper trough.
Some of the latest modeling suggests upper ridging upstream (west) of the upper trough may amplify in the warm sector of another frontal system over central Canada after 48 hours....leaving the possibility the upper trough evolves into an upper vortex pushed southeastward toward the Azores by day 5 by the upper ridging. This may cause Paulette to potentially regenerate as a subtropical cyclone in the vicinity of the Azores...but for now my forecast only goes thru 48 hours to see if this model trend persists.
0 Hr Position (1800Z Sep 14)...105 mph maximum sustained wind hurricane centered just north of Bermuda at 33.9N-64.4W
IOH 24 Hr Forecast (1800Z Sep 15)...95 mph maximum sustained wind hurricane centered at 39N-58W
IOH 48 Hr Forecast (1800Z Sep 16)...80 mph maximum sustained wind non tropical remnant gale centered at 44N-45W
TROPICAL DEPRESSION RENE (RECENTLY DOWNGRADED TO REMNANT LOW)...As a shallow tropical cyclone...Rene turned westward under the influence of a surface ridge passing to the north. Meanwhile the upper wind direction has shifted in the opposite direction of Rene’s forward direction courtesy of a northeast Atlantic amplifying upper trough...which has recently caused the thunderstorms to be separated from Rene’s cloud swirl. Thus Rene should be downgraded to a remnant low pressure soon. Most models have some southward angle in Rene’s track...perhaps due to the pull of Teddy’s circulation to the southeast? My updated forecast track below is based on the 1200Z GFS but a little slower given that Rene stalled its forward progress recently. After 24 hours...as the upper trough shifts eastward and away the shear should relax. However it is doubtful Rene’s remnant survive beyond 24 hours to take advantage as it cold weaken further in the short term in a zone of upper convergence and sinking air between the upper trough and northwest Atlantic upper ridge.
Update as of 5 PM EDT: Rene was downgraded to a remnant low pressure by the National Hurricane Center as of 5 PM EDT. This is my planned final statement on Rene on this blog.
0 Hr Position (1800Z Sep 14)...30 mph maximum sustained wind tropical depression centered at 27.5N-48.3W
IOH 24 Hr Forecast (1800Z Sep 15)...Remnant low pressure centered at 26N-50W
TROPICAL STORM TEDDY...Over the last day tropical depression twenty has intensified into Tropical Storm Teddy while in a favorable low shear and upper outflow environment beneath a tropical upper ridge axis. Also the nearby tropical wave to the northeast intensified into Tropical Storm Vicky....coupling it to upper level winds associated with the northeast Atlantic upper trough which has kept Vicky held eastward away from Teddy. The increased separation between both storms may have reduced the competition between the two...thus allowing Teddy to strengthen. Also Teddy has moved faster to the west as the fujiwhara interaction with Vicky has ended as the two storms are further...thus my updated forecast track is nudged westward.
Later in the forecast period...Teddy is expected to bend northward in track. 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 tropical storm...it will be bent northward by the approaching upper trough. I have increased my intensity forecast as Teddy is ramping up a bit faster in intensity compared to my previous assessment. I flatten the intensity between 24 and 48 hours as the approaching upper trough potentially blocks the western outflow of 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 south of Paulette as that vorticity also weakens. This upper vorticity will keep Teddy moving northwest through 120 hours.
0 Hr Position (1800Z Sep 14)...50 mph maximum sustained wind tropical storm centered at 13N-44W
IOH 24 Hr Forecast (1800Z Sep 15)...75 mph maximum sustained wind hurricane centered at 13.5N-48W
IOH 48 Hr Forecast (1800Z Sep 16)...75 mph maximum sustained wind hurricane centered at 15.5N-50.5W
IOH 72 Hr Forecast (1800Z Sep 17)...85 mph maximum sustained wind hurricane centered at 17.5N-53W
IOH 96 Hr Forecast (1800Z Sep 18)...105 mph maximum sustained wind hurricane centered at 20N-55W
IOH 120 Hr Forecast (1800Z Sep 19)...125 mph maximum sustained wind major hurricane centered at 23N-59W
TROPICAL STORM VICKY...The tropical wave of low pressure that passed over the Republic of Cabo Verde Islands over the weekend has strengthened into tropical depression twenty-one and then Tropical Storm Vicky today at a location west-northwest of the Cabo Verde Islands. This intensification has allowed this system to become tall enough to be slowed and dragged more northward in track by upper southwesterly flow on the southeast side of the northeast Atlantic upper trough. This flow is also shearing Vicky which should keep the tropical storm weak...and with the upper trough amplifying I expect the shear to increase further such that I already forecast Vicky to weaken to a remnant low by 24 hours.
0 Hr Position (1800Z Sep 14)...45 mph maximum sustained wind tropical storm centered at 19.3N-29.5W
IOH 24 Hr Forecast (1800Z Sep 15)...Remnant low pressure centered at 21N-32W
HURRICANE SALLY...Sally has explosively intensified into a category 2 hurricane this afternoon while located offshore of the Florida panhandle and Alabama coasts...conditions deteriorating here as coastal storm surge flooding is already underway...with high damaging winds and heavy rainfall to increase in the next 24 hours as Sally begins to drift northward at a further east location than previously anticipated. Strong to severe impacts are also likely for the Mississippi coast...while the threat along the southeast Louisiana coast has greatly reduced with this forecast track shift (but some storm surge is still a possibility here). Wind damage will likely spread inland over southern Alabama and southeastern Mississippi as Sally drifts northward. The slow motion will also produce severe rainfall flooding across 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 achieved its intensification feat with warm Gulf of Mexico waters coupled with light shear and upper outflow between upper vorticity lobes to the southwest and northeast. I do not anticipate further intensification to category 3 as satellite shows part of the circulation is already over land and as the thunderstorm bands are more lopsided to the east in a regime of light westerly shear...courtesy of upper westerly flow ahead of a cut off upper trough fragment over the southern United States being left behind by the upper trough over eastern North America. This upper westerly flow is responsible for the east shift in track as Sally has become quiet a strong and tall tropical cyclone to moreso couple with the upper flow. The divergence zones of the southern US cut off upper trough and another upper trough to sweep across Canada will slowly weaken the surface ridge to the north to allow Sally to move north...but the motion of Sally will remain slow as the ridge weakness will be relatively weak.
0 Hr Position (1800Z Sep 14)...100 mph maximum sustained wind hurricane centered over southeastern Louisiana at 28.8N-87.4W
IOH 24 Hr Forecast (1800Z Sep 15)...90 mph maximum sustained wind hurricane centered just inland from the Alabama coast at 31N-88W
IOH 48 Hr Forecast (1800Z Sep 16)...Remnant low pressure centered over northern Alabama at 33.5N-86.5W
AREA OF INTEREST #1...The surface trough of low pressure in the Gulf of Mexico has swung southwestward to a location near 22.5N-95W while pushed by a fujiwhara interaction with Hurricane Sally to the northeast. As Sally continues northward into the southeastern US...the fujiwhara interaction should initially stall the surface trough and then swing it 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 days 4 and 5. I have low 10% odds of development as the upper vorticity over the western Gulf of Mexico should diminish by 24 hours...clearing the way for some upper outflow potential that could increase the thunderstorms of this disturbance. The odds are kept low as the upper trough fragment over the southern US will slowly approach and potentially increase wind shear with time. Odds are dropped back to 0% at day 5 (120 hours) as this system could be making landfall over northeastern Mexico.
This disturbance continues to be a feature on this blog from its continued mention in the NHC tropical weather outlook...and also as it has not been absorbed by Sally such that it now has a chance to develop.
IOH 24 Hr Outlook (1800Z Sep 14)...0% chance of tropical cyclone formation (southwestern Gulf of Mexico near 22.5N-95W)
IOH 48 Hr Outlook (1800Z Sep 15)...10% chance of tropical cyclone formation (southwestern Gulf of Mexico near 22.5N-92.5W)
IOH 72 Hr Outlook (1800Z Sep 16)...10% chance of tropical cyclone formation (southwestern Gulf of Mexico near 24N-92W)
IOH 96 Hr Outlook (1800Z Sep 18)...10% chance of tropical cyclone formation (southwestern Gulf of Mexico near 24N-95W)
IOH 120 Hr Outlook (1800Z Sep 19)...0% chance of tropical cyclone formation (northeastern coast of Mexico near 24N-98W)
AREA OF INTEREST #2..The next tropical wave of low pressure from Western Africa has made its way into the eastern tropical Atlantic near 10N-20W while showing a little organization in its thunderstorms. It is added as an area of interest in the NHC tropical weather outlook and here...especially as over the next 4 days it remains in a low shear and upper outflow environment beneath a tropical upper ridge axis and to the south of the northeast Atlantic upper trough. I have a high 70% peak chance of development in the next 5 days...with some tapering down from the peak by day 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....with increasing speed as Vicky weakness and this system moves further away from the frontal cyclone.
IOH 24 Hr Outlook (1800Z Sep 14)...20% chance of tropical cyclone formation (tropical Atlantic near 10N-23W)
IOH 48 Hr Outlook (1800Z Sep 15)...50% chance of tropical cyclone formation (tropical Atlantic near 10N-27W)
IOH 72 Hr Outlook (1800Z Sep 16)...70% chance of tropical cyclone formation (tropical Atlantic near 10N-32W)
IOH 96 Hr Outlook (1800Z Sep 18)...70% chance of tropical cyclone formation (tropical Atlantic near 11N-36.5W)
IOH 120 Hr Outlook (1800Z Sep 19)...60% chance of tropical cyclone formation (tropical Atlantic near 13N-39W)
...COMPUTER MODEL SUMMARY...
Due to the currently high amount of activity in the Atlantic basin...this section is temporarily halted to shorten the time needed to put this post together.