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 #136

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


...THURSDAY OCTOBER 1 2020 12:35 PM EDT...

See area of interest #1 section below for an update on the western Caribbean tropical disturbance emerging from an active tropical wave that will soon merge with the tail end of a frontal zone. See area of interest #2 section below for the tropical wave approaching the Lesser Antilles which has been added into the National Hurricane Center tropical weather outlook.


Long range computer model runs showing a tropical wave of low pressure emerging from western Africa and developing in the eastern tropical Atlantic underneath a favorable upper ridge to persist over the region have recently ceased. Satellite imagery shows a pair of tropical waves southwest and southeast of the Repbulic of Cabo Verde Islands...but I have not added these tropical waves as areas of interest for further development as they are too close to each other such that they will likely compete for low-level inflow and upper outflow. However I have added another organized tropical wave over interior western Africa as an area of interest as their are no nearby tropical waves competing with it...see area of interest #3 section below for more details.


AREA OF INTEREST #1...High-amplified upper trough energy over central North America has driven a surface cold front into the western Atlantic...with the tail end of the front heading slowly southeastward into the western Caribbean Sea. Meanwhile upper-level winds over region have quickly become more favorable for tropical development as the central North America upper trough regime is relaxing...allowing for the expansion of a western Caribbean upper ridge (featuring low shear and upper outflow) in the trough regime's wake. A surface tropical wave of low pressure to the east...incoming from the central Caribbean Sea...continues to produce extensive and organizing thunderstorm activity now supported by the outflow the expanding western Caribbean upper ridge...therefore as the tropical wave and tail end of the front merge into a tropical disturbance it is more likely the center of lowest surface pressure will be further south toward the more extensive thunderstorm activity tied to the tropical wave...as this will be where the thunderstorm latent heat release will primarily drive warm core upper outflow and the resulting surface pressure falls. I have leaned toward a southern track solution that takes this disturbance more toward Belize...northern Guatemala...and southeastern Mexico as the more southern position of the disturbance makes it less likely that it will engage with upper southwesterly steering flow from a shortwave upper trough to pivot around the central North America longwave upper trough in the timeframe that is now 72 hours away...and also as the latest GFS model run depicts a weaker shortwave upper trough that fractures into two parts after 72 hours. Curiously the GFS and NAVGEM show this disturbance consolidating further north despite the more southern location of the current thunderstorm activity...with enough strengthening occuring such that this system becomes tall enough to in fact track more northward toward the northeastern Yucatan and western Cuba under the influence of the shortwave upper trough.


I have adjusted my outlook forecast points a little westward due to the current position of the tropical wave and strongest thunderstorm activity which will likely already be crossing 85W instead of 84W in the next 24 hours...and as it appears this disturbance may consolidate sooner to be steered westward around the central United States surface ridge earlier...due to the concentration of the tropical wave's thunderstorm activity over a smaller area as opposed to a situation where thunderstorms are widespread. I have a slight northward angle in the track for the next 48 hours as the tail end of the front to the north of the tropical wave may still play a role in shaping the low pressure field of the emerging disturbance. A slow track is shown however during the forecast period as the western convergence zone of the shortwave upper trough at 72+ hours will produce surface ridging over Mexico that blocks the westward progress of this system...with this ridging persisting once the southwest part of the shortwave upper trough breaks away from the northeastern part and persists over Mexico as a cut-off upper vortex. Due to the organization of the tropical wave's thunderstorm activity...I have raised odds of tropical cyclone formation to 75% by 48 hours...and if current trends continue I will begin a tropical cyclone formation forecast in my next update. After 48 hours odds are knocked down as the latest forecast track increases land interaction with the Yucatan peninsula and southeastern Mexico by that timeframe. Although my forecast positions by that time are also over land...in the event this system does become a large sprawling system it may still be able to become a weak tropical cyclone centered over land due to thunderstorms bands reaching offshore...and so my odds of development are higher than 0% for days 3 to 5...albeit they are also lower than in my previous outlook as this system is also less likely to become large and sprawling due to the concentration of the tropical wave's thunderstorms as noted above. However the low odds are steadily increased from day 3 to day 5 as my forecast track increasingly brings the center of circulation closer to the Bay of Campeche waters with time.


I have removed the Cayman Islands and added Honduras to the home page bulletins regarding this emerging disturbance due to the current positon of the concentrated thunderstorms. Western Cuba...the entire Yucatan peninsula...Guatemala...and southeastern Mexico are kept in the bulletins as the exact track of this system will depend on where the disturbance consolidates...with a southern consoldiation decreasing the chances of interaction with the shortwave upper trough expected at 72+ hours and hence a more southern track...and a more northern consolidation (coupled with rapid enough strengthening to make this system taller) increasing the coupling to the shortwave upper trough and hence allowing the trough to pull this system north.

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

IOH 24 Hr Outlook (1200Z Oct 2)...25% chance of tropical cyclone formation (western Caribbean Sea offshore of Honduras near 16.5N-85W)

IOH 48 Hr Outlook (1200Z Oct 3)...75% chance of tropical cyclone formation (east of the Belize/Mexico border near 17.5N-87W)

IOH 72 Hr Outlook (1200Z Oct 4)...10% chance of tropical cyclone formation (Guatemala/Mexico border near 17.5N-90W)

IOH 96 Hr Outlook (1200Z Oct 5)...20% chance of tropical cyclone formation (just inland from Mexico's Bay of Campeche coast near 18N-92W)

IOH 120 Hr Outlook (1200Z Oct 6)...30% chance of tropical cyclone formation (just inland from Mexico's Bay of Campeche coast near 18.5N-94W)


AREA OF INTEREST #2...The tropical wave of low pressure that has been approaching the Lesser Antilles islands from the open central Atlantic has been added into the National Hurricane Center tropical weather outlook...perhaps as the disturbance in the western Caribbean...area of interest #1...will consolidate sooner and around the active and organizing tropical wave in that region...decreasing the chances that this trpoical wave merges with that disturbance and instead becomes its own disturbance to the east of area of interest #1. Even though the tropical wave is currently producing active thunderstorm bands...this is with the support of upper divergence from upper vorticity diving southward toward the tropical wave...with this upper vorticity simulatenously shearing this tropical wave...therefore tropical cyclone formation is not expected in the short term. I keeps odds of development at 0% through 48 hours as the axis of upper vorticity where there is a lack of divergence will likely suppress this tropical wave. By 72 hours the tropical wave will likely reach a region of split flow upper divergence between the west side of upper vorticity and east side of the western Caribbean upper ridge...which should support redevelopment of this tropical wave's thunderstorms...this time in a lower shear environment as the upper flow will be northeasterly and more aligned with the tropical wave's westward track...so I begin to raise odds of tropical cyclone formation above 0% by 96+ hours. I agree with the NHC's peak 5-day low odds of development of 20% as it is possible that area of interest #1 dominates the low-level inflow and upper outflow in the region. Will only increase odds above this level should area of interest #1 stay weaker and/or this system becomes better organized in the forecast more favorable upper winds by 72+ hours.


Regarding track...I show a slight northward angle in the surface east-southeasterly steering flow to setup between the southwest side of the north Atlantic surface ridge and east side of area of interest #1. Should area of interest #1 track further north as the GFS and NAVGEM models currently depict...the surface steering flow would be more southerly and less easterly....also resulting in a more northward track of this tropical wave. Given the uncertainty in the longer range track forecast...I have mentioned Jamaica and the Cayman Islands in regards to this tropical wave on the home page bulletins of this site.

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

IOH 24 Hr Outlook (1200Z Oct 2)...0% chance of tropical cyclone formation (eastern Caribbean Sea near 12.5N-62.5W)

IOH 48 Hr Outlook (1200Z Oct 3)...0% chance of tropical cyclone formation (eastern Caribbean Sea near 14N-69W)

IOH 72 Hr Outlook (1200Z Oct 4)...0% chance of tropical cyclone formation (central Caribbean Sea near 15.5N-75W)

IOH 96 Hr Outlook (1200Z Oct 5)...10% chance of tropical cyclone formation (western Caribbean Sea near 16.5N-80W)

IOH 120 Hr Outlook (1200Z Oct 6)...20% chance of tropical cyclone formation (western Caribbean Sea near 17.5N-85W)


AREA OF INTEREST #3...A tropical wave of low pressure over interior western Africa is producing curved thunderstorm bands with some signs of organization near 11N-2.5W. Given that the tropical wave will move into a tropical upper ridge (with low shear and upper outflow) to persist over the eastern tropical Atlantic and that some model runs in previous days indicated development in this region...I have added this tropical wave as an area of interest for tropical development. At the present time I am keeping peak 5-day odds of development at a low 20% as the latest model suite does not show development...but will raise odds of development should the tropical wave maintain organization as it moves toward and into the eastern tropical Atlantic waters.

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

IOH 24 Hr Outlook (1200Z Oct 2)...0% chance of tropical cyclone formation (western Africa near 11N-7.5W)

IOH 48 Hr Outlook (1200Z Oct 3)...0% chance of tropical cyclone formation (western Africa near 11N-12.5W)

IOH 72 Hr Outlook (1200Z Oct 4)...0% chance of tropical cyclone formation (offshore of western Africa near 11N-17.5W)

IOH 96 Hr Outlook (1200Z Oct 5)...10% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-22.5W)

IOH 120 Hr Outlook (1200Z Oct 6)...20% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-27.5W)


...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 area of interest #1...large broad surface low pressure develops in western Caribbean Sea by 120 hours. For area of interest #2...merges with area of interest #1 by 120 hours while contributing to the formation of large broad surface low pressure.


0000Z ECMWF Model Run....For areas of interest #1 and #2...no tropical cyclone formation shown.


0600Z GFS Model Run...For area of interest #1...tropical cyclone formation suggested on northeast coast of the Yucatan peninsula at 48 hours...drifts slowly westward across the southern Gulf of Mexico through 120 hours. For area of interest #2...tropical wave organizes into a surface low pressure spin in the central Caribbean Sea near 15N-79.5W


0600Z NAVGEM Model Run...For area of interest #1...tropical cyclone formation suggested in the western Caribbean Sea near 18N-86W at 42 hours...crosses the northeastern corner of the Yucatan peninsula as a strengthening tropical cyclone at 66 hours...located in the central Gulf of Mexico as an intense tropical cyclone at 26.5N-90W at 120 hours. For area of interest #2...no tropical cyclone formation shown due to dominance of area of interest #1.

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