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 #119A (Special Update)

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


...SUNDAY SEPTEMBER 13 2020 10:15 PM EDT...

The following are special updates on Hurricane Paulette and Tropical Storm Sally as they both are threatening land areas.


0200Z Infrared Satellite Image of Paulette:


HURRICANE PAULETTE...Since last night...Paulette was able to reach hurricane strength while reaching a lower shear environment in a gap between weakening upper vorticity to the southwest and northeast. However on infrared satellite the intensity of the thunderstorms is somewhat lackluster around the eye...perhaps an indication that the upper outflow of the hurricane is being constricted with the gap between the two lobes of upper vorticity being a bit too narrow for Paulette. Thus my intensity forecast remains the same as my previous...forecasting a peak of 100 mph maximum sustained category 2 winds which is below the NHC forecast that now has Paulette becoming a minimal category 3.


Paulette did get coaxed more westward by the lobe of upper vorticity to the southwest...therefore my forecast track is nudged westward and now has the eye going directly over Bermuda just before 24 hours. After 24 hours...the current central North America upper trough will push a cold front into the northwestern Atlantic. I show a faster northeast acceleration after 24 hours under the influence of the upper trough and surface front compared to my previous forecast as the 1800Z GFS shows a south fracture of the incoming upper trough moving closer to Paulette which will increase the southwesterly upper steering flow. This upper flow may also begin to shear Paulette...so I forecast weakening to begin by 48 hours. By 96 hours Paulette should reach cooler waters...but slowly weaken as it transitions into a strong non-tropical remnant low pressure supported by divergence on the east side of the south fracture upper trough and northwest side of the northwest Atlantic upper ridge....which will have shifted east into the North Atlantic ahead of the upper trough. Interests in Bermuda should have finished preparations for Hurricane Paulette as storm surge...damaging winds...and heavy rain will increase through tonight and tomorrow.

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

0 Hr Position (1800Z Sep 13)...85 mph maximum sustained hurricane centered southeast of Bermuda at 30.9N-63.6W

IOH 24 Hr Forecast (1800Z Sep 14)...100 mph maximum sustained wind hurricane centered just northwest of Bermuda at 33N-65W

IOH 48 Hr Forecast (1800Z Sep 15)...85 mph maximum sustained wind hurricane centered at 37N-60W

IOH 72 Hr Forecast (1800Z Sep 16)...75 mph maximum sustained wind hurricane centered at 41N-50W

IOH 96 Hr Forecast (1800Z Sep 17)...70 mph maximum sustained wind non-tropical remnant gale centered at 45N-37.5W


0200Z Infrared Satellite Image of Sally:

TROPICAL STORM SALLY...A surface trough of low pressure to the west and a frontal zone to the north driven by an upper trough moving across central North America have moved Tropical Storm Sally northwestward across the eastern Gulf of Mexico. Soon the track should bend more westward toward southeastern Louisiana as a surface ridge enforced by the convergent back side of the aforementioned upper trough builds to the north. The troubling thing is a slowing westward track is expected...due to the south fracture of the upper trough expected to cut off while becoming stretched east to west across the southern US...with the divergence zone of this feature inducing a faint surface ridge weakness to the northeast that will slow the track. Sally will also be tall enough to also be slowed by the upper westerly winds of the cut off upper trough. A turn to the north is shown after 48 hours when a shortwave upper trough over southern Canada creates more of a surface ridge weakness and toward the US/Canada border region...but with this weakness will also be weak such that the track is expected to remain slow. The slow track could mean a significant rainfall flooding problem across southeastern Louisiana and southern Mississippi Monday through Wednesday. I have adjusted the slow track more eastward more in agreement with the NHC forecast and the latest model consensus. The models early on were further to the west likely from failing to predict the formation of Sally from the incipient surface low pressure...thus underplaying how tall the storm would be and it’s coupling to the upper westerly flow of the forecast southern US cut off upper trough that will keep the system pushed more to the east. As such the eastward adjusted track may involve the southern Alabama and western Florida panhandle region in the rainfall flood problem as well.


Sally has intensified into a strong tropical storm while moving away from upper vorticity to the northeast had been disrupting Sally with light westerly shear. The tropical storm has been on par with my previous forecasts and so I have left the intensity forecast unchanged. It is probable that Sally becomes a category 1 hurricane before my 24 hour forecast point which has Sally beginning to weaken from land interaction. My initial rate of weakening is kept slow with the center remaining at the coast rather than fully inland thru 48 hours on my forecast track...with some of the weakening also possibly being caused by some light westerly shear from the forecast southern US cut off upper trough mentioned in the previous paragraph. Remnant low pressure status is shown by 72 hours once the center of Sally moves more inland.


Interests across the coastal regions of the Florida panhandle... Alabama... Mississippi.... and southeastern Louisiana should have finished preparations for coastal storm surge....gusty tropical storm force winds with some damage possible...and heavy rain as weather conditions will deteriorate by tomorrow. Stronger hurricane conditions (more wind damage and coastal storm surge) are likely along coastal southeast Louisiana should Sally indeed become a category 1 hurricane.

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

0 Hr Position (1800Z Sep 13)...60 mph maximum sustained wind tropical storm centered offshore of the Florida panhandle at 27.9N-86.2W

IOH 24 Hr Forecast (1800Z Sep 14)...65 mph maximum sustained wind tropical storm centered over southeastern Louisiana at 28.5N-90W

IOH 48 Hr Forecast (1800Z Sep 15)...50 mph maximum sustained wind tropical storm centered over southern coastal Louisiana at 28.5N-91W

IOH 72 Hr Forecast (1800Z Sep 16)...Remnant low pressure centered over southwestern Mississippi at 31N-91W

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