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 #140

*******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 12:00 PM EDT...

See Tropical Storm Gamma and Tropical Storm Delta sections below for the two currently active tropical cyclone in the Atlantic basin. See area of interest sections below for additional areas being monitored for tropical cyclone formation.


TROPICAL STORM GAMMA...Slow-moving Tropical Storm Gamma in the far southern Gulf of Mexico has reversed from an eastward drift overnight to a southwestward drift back toward the Yucatan province shore as of this morning. This maybe the beginnings of a fujiwhara interaction with strengthening Tropical Storm Delta incoming from the east. This forward motion has pulled the swirl center of Gamma away from its sheared-off thunderstorms to the northeast as the upper southwesterly shearing flow from the eastern North America upper trough has not yet let up. My updated forecast track and intensity is a radical change from the previous ones given these current observations...taking Gamma southwestward back into the Yucatan province by 24 hours as it weakens to a remnant low under the southwesterly shear and land interaction. Even though the shear may let up once the eastern North America upper trough fractures into two halves that move away from the region...the chances of Gamma being able to hang on in the western Yucatan or eastern Bay of Campeche waters is now very low as Delta's low-level inflow will dominate the region and prevent Gamma from being able to accumulate low-level heat and moisture needed for thunderstorms. With this forecast...I now expect minimal impact from Gamma in the Yucatan peninsula region...with impacts in the Quintana Roo province being related to Delta...see Tropical Storm Delta section below for details.

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

0 Hr Position (1200Z Oct 5)...45 mph maximum sustained wind tropical storm centered over the southern Gulf of Mexico offshore of the northern Yucatan peninsula at 22.6N-87.5W

IOH 24 Hr Forecast (1200Z Oct 6)...Remnant low pressure centered over the northern Yucatan peninsula at 20.5N-88.5W


TROPICAL STORM DELTA...Tropical depression twenty-six in the central Caribbean Sea has been doing quiet well in its battle with 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 with time such that the shear induced by the vorticity reduces...and as such the thunderstorm activity has been able to become considerably better organized enough for the depression to become Tropical Storm Delta at a location southwest of Jamaica this morning. The new tropical storm is continuing on a strengthening trend as the 11 AM EDT advisory from the National Hurricane recently upped the maximum sustained winds to 45 mph. Thunderstorm activity has been limited on the north side thanks to the fading upper vorticity...with the center of Delta reforming a little further south and further away from Jamaica into its stronger southern thunderstorm activity. Water vapor satellite animation suggests another piece of upper voriticity sneaking by to the north of Detla while appearing as a curl of dry air moving westward across Cuba...but the 0600Z GFS model run from this morning suggests this upper vorticity is weak enough that it will dissipate in the next 24 hours. However this vorticity is enough for me to hold off on forecasting hurricane strength in the next 24 hours...after which time I expect Delta to become a strong hurricane (possbibly as strong as a category 3) by 48 to 72 hours. This is because Delta is clearly winning its battle against Tropical Storm Gamma such that it will no longer have to compete with Gamma for low-level inflow...and it will be over warm western Caribbean and southern Gulf of Mexico waters in that timeframe as it takes the prominent spot of low shear and upper outflow in the midst of the large upper ridge in the region. With Gamma staying further to the east...I expect the fujiwhara interaction with Gamma will take place further east such that I lean with a more east track that takes the center of Delta potentially over or very close to Grand Cayman Island...and then the western tip of Cuba...as it intensifies.


Once in the Gulf of Mexico...I forecast Delta's track to lean more west by 72 hours after the remnant low pressure of Gamma dissipates over the northern Yucatan which will end the fujiwhara interaction between Gamma and Delta...and as the central United States surface ridge recovers in the western convergence zone of another upper trough to dive into central North America during that timeframe. By 96 hours the southwest fracture of the current North America upper trough will swing back eastward from Mexico which will increase the upper southwesterly shearing flow over Delta. Delta will also be tall enough to couple with this upper flow such that the track is expected to bend northward...but I withold an eastward angle in the track during that time as the central United States surface ridge will still be in place. By 120 hours the surface ridge begins to shift eastward...which will allow Delta's track to bend more eastward in the upper southwesterly flow after making landfall in teh southeastern Louisiana and southern Missisippi region. Although Delta will be moving over cooler water temps in the northern Gulf of Mexico and be under southwesterly shear as it approaches landfall...the eastern divergence zone of the incoming upper trough fragment from Mexico may make the weakening rate of Delta slower. Transition into a remnant frontal low pressure inland over the southeastern United States...supported by the divergence of the upper trough fragment...will likely occur by 120 hours.


Outside of sea swells...Jamaica will not experience much tangible impact from Delta given that the tropical storm is consolidating to the southwest of the island. Intersts in the Cayman Islands and western Cuba should be preparing for strong tropical storm and possible hurricane force conditions to occur within the next 48 hours (as soon as 24 hours for the Cayman Islands)...which will include damaging winds...heavy rainfall...and coastal storm surge. The worst of the impacts in the Cayman Islands are expected over Grand Cayman Island. Given that Tropical Storm Gamma and its upper outflow are weakening....Quintana Roo province in the northeastern Yucatan peninsula may now not be as shielded from Delta's western rain bands and therefore in addition to coatal sea swells with possible storm surge...the province may experience tropical storm conditions in 48 hours. Given the likelihood of Delta becoming a strong hurricane in the Gulf of Mexico by Thursday...a dangerous coastal storm surge caused by the onshore push of winds on Delta's east side may occur for southeastern Louisiana...coastal Mississippi and Alabama...and the Florida panhandle on Friday even if Delta weakens from wind shear as it approaches landfall...as the water in the Gulf will be kicked up by Delta's potentially strong peak intensity on Thursday. Damaging winds across southeastern Louisiana and southern Mississippi are becoming increasingly likely by Friday and Saturday...gather storm preparation supplies early to avoid shopping in last-minute crowds amid the COVID-19 virus pandemic in the region...think of a hotel or family/friend residence you may have to relocate to in the event your current residence becomes at risk from impacts such as coastal storm surge...as a public storm shelter may not be as ideal for controlling your exposure to COVID-19.

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

0 Hr Position (1200Z Oct 5)...40 mph maximum sustained wind tropical storm centered just southwest of Jamaica at 16.4N-78.4W

IOH 24 Hr Forecast (1200Z Oct 6)...65 mph maximum sustained tropical storm centered just south of Grand Cayman Island at 18.5N-81W

IOH 48 Hr Forecast (1200Z Oct 7)...95 mph maximum sustained hurricane centered over the western tip of Cuba at 22N-85W

IOH 72 Hr Forecast (1200Z Oct 8)...115 mph maximum sustained wind major hurricane centered over the central Gulf of Mexico at 25N-90W

IOH 96 Hr Forecast (1200Z Oct 9)...95 mph maximum sustained wind hurricane centered over coastal southeastern Louisiana at 29.5N-90W

IOH 120 Hr Forecacst (1200Z Oct 10)...Remnant frontal low pressure centered over the Alabama/Mississippi border at 33N-88.8W


AREA OF INTEREST #1...A tropical wave of low pressure that has recently entered the the eastern tropical Atlantic from western Africa has lost thunderstorms...as the outflow in the north half had been choked off by upper vorticity from the east-central Atlantic being pushed southward toward the tropical wave by the current northeast Atlantic upper ridge. With these latest developments...it is probable the tropical wave has weakened enough such that it is unlikely to develop later on when it reaches the more favorable upper outflow environment of the eastern tropical Atlantic upper ridge. This is my planned 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 Oct 6)...0% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-29W)


AREA OF INTEREST #2...The tropical wave of low pressure in the open central Atlantic continues to produce limited and disroganized thunderstorm activity currently being disrupted by light southerly shear on the east side of a a chunk of central Atlantic upper vorticity retrograding southwestward around the west Atlantic upper ridge and into the Caribbean. However with the vorticity chunk expected to continuously retrograde westward ahead of the tropical wave thru 120 hours as it weakens while remaining cut-off from higher latitude cold air...the shear over the tropical wave could reduce enough to allow the wave to develop...espeically as it moves into the central Caribbean Sea. Forecast track in the outlook below is based on the tropical wave moving west-northwest in the east-southeasterly flow to setup between mid-latitude surface ridging and the east side of Tropical Storm Delta.

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

IOH 24 Hr Outlook (1200Z Oct 6)...0% chance of tropical cyclone formation (central tropical Atlantic east of the Lesser Antilles near 12N-56.5W)

IOH 48 Hr Outlook (1200Z Oct 7)...5% chance of tropical cyclone formation (just west of the Lesser Antilles near 12.5N-61.5W)

IOH 72 Hr Outlook (1200Z Oct 8)...10% chance of tropical cyclone formation (eastern Caribbean sea near 13N-66.5W)

IOH 96 Hr Outlook (1200Z Oct 9)...10% chance of tropical cyclone formation (central Caribbean sea near 13.5N-71W)

IOH 120 Hr Outlook (1200Z Oct 10)...20% chance of tropical cyclone formation (central Caribbean sea near 14N-75W)


AREA OF INTEREST #3...The surface trough of low pressure in the open central Atlantic will continue westward toward Bermuda while steered by the North Atlantic surface ridge. A large upper trough that will dive southeastward into central North America will create a surface ridge weakness in the northwestern Atlantic that should slow the track and then bend the track of the surface trough northward...which I estimate will keep the trough just east of Bermuda in the coming days. The surface trough is currently located beneath suppressing upper convergence between central Atlantic upper vorticity and western Atlantic upper ridge...and on its forecast track will briefly pass under low shear and upper outflow of the upper ridge before encountering less favorable westerly shear to be induced across the northwest Atlantic by the North American upper trough expected by 72+ hours. Given the loss of all thunderstorm activity with this surface trough...it appears the trough has become too weak to develop in the narrow window of favorable upper winds...therefore I have dropped the odds of tropical cyclone formation to 0%. This is my final statement on this feature on this blog.

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

IOH 24 Hr Outlook (1200Z Oct 6)...0% chance of tropical cyclone formation (western Atlantic to the east-southeast of Bermuda near 28N-61W)


...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 Gamma...gradually drifts southward into the northern Yucatan peninsula through 66 hours...loses identity to the south of Delta shortly thereafter. For Tropical Storm Delta...passes over the Cayman Islands as a strengthening compact tropical cyclone through 36 hours...passes over western Cuba without additional strengthening by 48 hours...becomes a larger and stronger tropical cyclone over the central Gulf of Mexico by 96 hours...makes landfall over southeastern Louisiana at 114 hours...makes second landfall over Mississippi/Alabama border at 120 hours. For areas of interest #1 to #3...no tropical cyclone formation shown. Elsewhere...a tropical wave of low pressrue to the east of area of interest #1 becomes better defined over the open central Atlantic in the long range.


0000Z ECMWF Model Run....For Tropical Storm Gamma...drifts southwestward into the northwestern Yucatan peninsula through 48 hours...loses identity to the south of Delta shortly thereafter. For Tropical Storm Delta...passes over the western Cayman Islands as a compact and strong tropical cyclone by 36 hours...passes over the western tip of Cuba at 48 hours...from the northwestern Gulf of Mexico moves northeastward into southern Louisiana and accelerates into southern Mississippi by 120 hours. For areas of interest #1 to #3...no tropical cyclone formation shown.


0600Z GFS Model Run...For Tropical Storm Gamma...drifts southwestward into the west coast of the Yucatan peninsula through 48 hours...loses identity to the south of Delta shortly thereafter. For Tropical Storm Delta...passes over the western Cayman Islands as a compact and strong tropical cyclone by 36 hours...passes between the western tip of Cuba and the Yucatan peninsula at 48 hours...makes landfall in south-central Louisiana at 108 hours...weakens to a remnant low pressure over central Mississippi by 126 hours. For areas of interest #1 to #3...no tropical cyclone formation shown.


0600Z NAVGEM Model Run...For Tropical Storm Gamma...drifts southwestward into the western Yucatan peninsula through 42 hours...loses identity to the south of Delta shortly thereafter. For Tropical Storm Delta...passes over the western Cayman Islands at 30 hours...passes between the western tip of Cuba and the Yucatan peninsula at 42 hours...becomes a large and strong tropical cyclone in the north-central Gulf of Mexico by 78 hours...makes landfall in south-central Louisiana at 90 hours...accelerates northeastward into the Ohio Valley region of the United States as a vigorous remnant low pressure by 120 hours. For areas of interest #1 to #3...no tropical cyclone formation shown.

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