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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 #139A (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.**********


...MONDAY OCTOBER 5 2020 12:55 AM EDT...

Satellite Image from 0440Z (G marking Tropical Storm Gamma...26 marking newly formed tropical depression 26):

Tropical Storm Gamma drifts northeastward in the southern Gulf of Mexico while the central Caribbean Sea tropical wave becomes a tropical depression poised to more strongly influence Gamma...the following are adjustments to my forecasts from full update #139.


TROPICAL STORM GAMMA...Slow-moving Tropical Storm Gamma has drifted northeastward offshore of the northern Yucatan peninsula under the influence of the upper southwesterly winds shearing the tropical storm. However as the central North America upper trough generating those winds fractures into a southwestern and northeastern half...with both halves moving away from the region....and as tropical depression 26 from the east nears...the track is expected to reverse to a southwest drift as it undergoes a fujiwhara interaction with the depression...with an east drift now possible by 120 hours as the depression passes north of Gamma. In this special update my updated forecast track points are adjusted eastward to reflect a stronger interaction as the depression is becoming organized and more likely to be stronger than I previously assessed when it passes near Gamma. I have also lowered the intensity forecast...keeping Gamma at its current strength and below hurricane force as it will have more competition for low-level inflow and upper outflow with the incoming depression.


Over the next few days we can expect slow-moving Tropical Storm Gamma to produce coastal sea swells for the shores of the Yucatan....Campeche....Tabasco...Veracruz... and Tamaulipas provinces of Mexico. The track forecast remains highly uncertain as the exact details of the impending fujiwhara interaction are unknown...but it appears for now the greatest potential for wind and rain by day 5 can be anywhere from southern Veracruz to the Campeche province coast on the west coast of the Yucatan peninsula. The government of Mexico has issued tropical storm advisories covering the north and west coast of the Yucatan in the outside chance that depression 26 strengthens enough to pull Gamma even further east back into the northern Yucatan region.

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

0 Hr Position (0000Z Oct 5)...60 mph maximum sustained wind tropical storm centered just offshore of the northern Yucatan peninsula at 22.8N-87.2W

IOH 24 Hr Forecast (0000Z Oct 6)...60 mph maximum sustained wind tropical storm centered over the southern Gulf of Mexico at 22.8N-88W

IOH 48 Hr Forecast (0000Z Oct 7)...60 mph maximum sustained wind tropical storm centered over the southern Gulf of Mexico offshore of the northwestern Yucatan peninsula at 22N-90.5W

IOH 72 Hr Forecast (0000Z Oct 8)...60 mph maximum sustained wind tropical storm centered over the Bay of Campeche and just west of the Yucatan peninsula at 20N-92W

IOH 96 Hr Forecast (0000Z Oct 9)...60 mph maximum sustained wind tropical storm centered over the Bay of Campeche and just west of the Yucatan peninsula at 20N-92W

IOH 120 Hr Forecast (0000Z Oct 9)...60 mph maximum sustained wind tropical storm centered over the Bay of Campeche and just west of the Yucatan peninsula at 20N-91W


TROPICAL DEPRESSION TWENTY-SIX...The vigorous tropical wave of low pressure crossing the central Caribbean Sea has organized further into a tropical depression while fighting cold core upper vorticity that has been retrograding southwestward around the western Atlantic upper ridge and toward the area. This is evidenced by ongoing strong thunderstorm activity initially triggered a few days ago by the upper divergence on the southeast side of the vorticity...with the thunderstorm latent heat release washing out the cold core upper vorticity. The north half of the depression is still absent of thunderstorms for now due to the dissipating upper vorticity...but will likely become active once the vorticity fully dissipates. However I am still hesitant to rapidly strengthen this system in my updated forecast below as it is unclear to me how much Gamma’s low level inflow and upper outflow could negatively affect this system...especially as the distance between Gamma and thus system is shrinking as Gamma has refused to turn west thus far. I have also adjusted the track more northward as the shrinking distance between both circulations should send this system more sharply northward as they undergo a fujiwhara interaction with each other. By 120 hours the southwest fracture of the current North America upper trough will swing back eastward from Mexico and (along with the northern outflow of Gamma) increase the southwesterly shear in the region...so I do not forecast hurricane strength from this system at this time. Also given that this system will likely be strong/tall enough to couple with upper winds...I have adjusted this part of the forecast track northward in response to the upper southwesterly shearing flow...in agreement with the NHC for a landfall in southeast Louisiana.


Jamaica will not experience much from this system given its north side is currently lacking in thunderstorms. But the Cayman Islands and western Cuba should be preparing for tropical storm conditions to occur within the next 48 hours. Quintana Roo will likely not experience weather from this system as the outflow of Gamma should keep the heaviest weather from this system pushed off to the east...but coastal sea swells are likely by 48 hours. Chances are increasing that the US Gulf coast will see sea swells from this system...with the southeast Louisiana and southern Mississippi region at greatest risk for seeing some gusty damaging winds and heavy rain by day 5.

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

0 Hr Position (0000Z Oct 5)...35 mph maximum sustained wind tropical depression centered just south of Jamaica at 17N-77.3W

IOH 24 Hr Forecast (0000Z Oct 6)...45 mph maximum sustained wind tropical storm centered just south of the Cayman Islands at 17.8N-82W

IOH 48 Hr Forecast (0000Z Oct 7)...45 mph maximum sustained wind tropical storm centered just south of the western tip of Cuba at 20.5N-85.2W

IOH 72 Hr Forecast (0000Z Oct 8)...50 mph maximum sustained wind tropical storm centered over the Gulf of Mexico at 23N-88W

IOH 96 Hr Forecast (0000Z Oct 9)...60 mph maximum sustained wind tropical storm centered in northern Gulf of Mexico at 27.5N-91W

IOH 120 Hr Forecast (0000Z Oct 10)...50 mph maximum sustained wind tropical storm centered over southeastern Louisiana at 30.2N-91W

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