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 #137

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


...FRIDAY OCTOBER 2 2020 11:09 AM EDT...

See area of sections below for multiple areas being monitored for tropical cyclone formation. Note that area of interest #1 in the western Caribbean Sea was upgraded to tropical depression twenty-five as I was putting this post together.


AREA OF INTEREST #1 (RECENTLY UPGRADED TO TROPICAL DEPRESSION TWENTY-FIVE)...The tropical wave of low pressure moving across the western Caribbean Sea ahead of the cold front that spans the western Atlantic and southeastern Gulf of Mexico has continued to become organized...and it appears a tropical depression or tropical storm is already forming with satellite imagery showing spiral thunderstorm bands around a well-defined center...and upper-level winds are favorable for additional development as this system is underneath an upper ridge cell with low shear and upper outflow. At this point it is apparent the tropical wave is contributing to the latest developments while the front has played no role. I have begun a tropical cyclone formation forecast as outlined below.


My updated forecast track is adjusted northward for a landfall in the northern Yucatan peninsula just after 24 hours as I anticipate short-term brisk strengthening that will allow this system to become tall enough to couple to the upper southwesterly steering flow ahead of a shortwave upper trough to pivot around the central North America longwave trough. As the shortwave upper trough fractures into a southwestern and northeastern half...with both halves moving away from the region....I anticipate a more westward track as this system exits the northern Yucatan and moves into the southwestern Gulf of Mexico after 48 hours. At this time I do not anticipate a southward bend in track induced by the tropical wave to approach from the east...area of interest #2...as the chances for that tropical wave to develop are fairly low...see area of interest #2 section below for more details on that wave. A slow track is shown throughout the forecast period as the western convergence zone of the aformentioned shortwave upper trough will produce surface ridging over Mexico that blocks the westward progress of this system...with this ridging persisting through 72 hours 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. Even though by 96+ hours the Mexico surface ridging will likely weaken once the cut-off upper vortex continues retrograding westward and away...a slow forward speed is still expected as the eastern divergence zone of another longwave upper trough to dive into central North America weakens the central United States surface ridge trying to push this system westward. Regarding intensity...due to the current low shear...upper outflow...warm waters...and very well organized structure of the system...I anticipate brisk strengthening into strong tropical storm status in the next 24 hours...followed by weakening to tropical depression status by 48 hours from some southwesterly shear induced by the aforementioned shortwave upper trough and land interaction with the northern Yucatan peninsula. Once the shortwave upper trough fractures into two halves...the shear should relax and provide an opportunity for this system to strengthen once it arrives over the warm southwestern Gulf of Mexico waters. Therefore at this time I am forecasting hurricane strength by 120 hours.


I encourage interests along northern coastal Belize and coastal Quintana Roo province to quickly make preparations for possible strong tropical storm conditions to arrive by tomorrow morning (some damaging winds...coastal sea swells...and heavy flash flooding rains). Going into this weekend and early next week...the north shore of the Yucatan province may also deal with coastal sea swells and gusty winds depending on the exact track...with the center being further north and closer to the coast (or even over water) allowing for higher strength and stronger winds...and a more inland southern track of the center allowing for weaker strength with less wind. Regardless of intensity...expect a risk of signficant rainfall flooding across northern Belize...Quintana Roo...Campeche province...and Yucatan province as this system will be slow moving...resulting in long periods of heavy rain.


11 AM EDT update...the National Hurricane Center has just upgraded this area of interest to tropical depression twenty-five...centered at 18.1N-84.7W with 35 mph maximum sustained winds and 1005 mb central surface pressure. No changes to my track and intensity forecast below.

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

0 Hr Position (1200Z Oct 2)...Organized surface low pressure centered at 17.5N-84.5W

IOH 24 Hr Forecast (1200Z Oct 3)...60 mph maximum sustained wind tropical storm centered just offshore of the eastern Yucatan peninsula coast at 18.5N-87W

IOH 48 Hr Forecast (1200Z Oct 4)...35 mph maximum sustained wind tropical depression centered over the northern Yucatan peninsula at 20.5N-89W

IOH 72 Hr Forecast (1200Z Oct 5)...45 mph maximum sustained wind tropical storm centered over the northwest coast of the Yucatan peninsula at 21N-90W

IOH 96 Hr Forecast (1200Z Oct 6)...65 mph maximum sustained wind tropical storm centered over the southwestern Gulf of Mexico at 21N-92W

IOH 120 Hr Forecast (1200Z Oct 7)...85 mph maximum sustained wind hurricane centered over the southwestern Gulfo fo Mexico at 21N-94W


AREA OF INTEREST #2...The tropical wave of low pressure that has crossed the Lesser Antilles and entered the eastern Caribbean Sea continues to produce bands of thunderstorm activity with the support of upper divergence from upper vorticity diving southward toward the tropical wave...but this upper vorticity is simulatenously shearing this tropical wave...therefore tropical cyclone formation is not expected in the short term. I keeps odds of development at 0% through 24 as the tropical wave passes through the axis of upper vorticity where there is a lack of divergence...which will likely suppress this tropical wave. By 48 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 72+ hours. However I have lowered the odds of development to a very low peak of 10% as area of interest #1 is developing and will likely dominate the low-level inflow and upper outflow in the region as this system moves closer to the area of interest. Moreover the forecast evolution with the upper vorticity is uncertain as it changes day to day in the model runs...for example the 0600Z run of the GFS yesterday showed the upper vorticity staying off to the east of this tropical wave in the long range...and today shows a lobe of the upper vorticity breaking off and retrograding westward with the tropical wave while pushed around by the sprawling western Atlantic upper ridge. If indeed a chunk of upper vorticity does stay coupled with the tropical wave as today's 0600Z GFS run suggested...this could keep the thunderstorm activity of the tropical wave suppressed...or alternatively cause the lowest pressure and thunderstorm activity of the tropical wave to relocate should such a lobe of upper vorticity develop a peripherial upper divergence zone.


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...with a slow down in forward speed shown at 120 hours as the steering flow weakens once the central United States surface ridge weakens under the influence of a longwave upper trough forecast to dive into central North America. The track forecast could also be complicated in the longer range depending on how the upper vorticity in the region evolves as noted at the end of the previous paragraph. So given the uncertainty in the longer range track forecast...I mention 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 3)...0% chance of tropical cyclone formation (eastern Caribbean Sea near 14N-69W)

IOH 48 Hr Outlook (1200Z Oct 4)...0% chance of tropical cyclone formation (central Caribben Sea near 15.5N-75W)

IOH 72 Hr Outlook (1200Z Oct 5)...5% chance of tropical cyclone formation (western Caribben Sea near 16.5N-80W)

IOH 96 Hr Outlook (1200Z Oct 6)...10% chance of tropical cyclone formation (western Caribben Sea near 17.5N-85W)

IOH 120 Hr Outlook (1200Z Oct 7)...10% chance of tropical cyclone formation (east coast of the Yucatan peninsula near 18.5N-87.5W)


AREA OF INTEREST #3...A tropical wave of low pressure over interior western Africa has seen a reduction in thunderstorms over the last 24 hours while passing near 11N-8.5W...but so far has maintained curvature in its cloudiness. The reduction in the thunderstorm activity is likely due to suppressed poleward (northward) outflow beginning to take hold as upper vorticity from the east-central Atlantic and also from a trough that has recently moved into western Europe get pushed southward toward the tropical wave by the eastern tropical Atlantic upper ridge and also the expanding north Atlantic upper ridge. Today's 0600Z GFS model run shows this upper vorticity reaching further to the south than it did in yesterday's run...therefore I have lowered my odds of tropical cyclone formation from this tropical wave to 10% by day 5. Odds are kept at 0% in the short term until this tropical wave escapes the upper vorticity and potentially develops underneath the low shear and upper outflow of the eastern tropical Atlantic upper ridge.

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

IOH 24 Hr Outlook (1200Z Oct 3)...0% chance of tropical cyclone formation (just inland from the western Africa coast near 11N-14W)

IOH 48 Hr Outlook (1200Z Oct 4)...0% chance of tropical cyclone formation (offshore of western Africa near 11N-19W)

IOH 72 Hr Outlook (1200Z Oct 5)...0% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-24W)

IOH 96 Hr Outlook (1200Z Oct 6)...10% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-29W)

IOH 120 Hr Outlook (1200Z Oct 7)...10% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-34W)


...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 just east of the Yucatan peninsula 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. For area of interest #3...no tropical cyclone formation shown.


0000Z ECMWF Model Run....For area of interest #1...possible weak tropical cyclone formation just east of the Belize/Mexico border at 24 hours...landfall on the east coast of the Yucatan peninsula at 48 hours...while drifting southwestward under the influence of area of interest #2 approaching from the east it dissipates over the Yucatan peninsula by 120 hours. For area of interest #2...tropical wave organizes into broad surface low pressure just northeast of Honduras at 120 hours. For area of interest #3...no tropical cyclone formation shown.


0600Z GFS Model Run...For area of interest #1...tropical cyclone formation suggested just offshore of the eastern Yucatan peninsula coast at 24 hours...while strengthening briskly drifts more northward in track and reaches the northeast corner of the peninsula at 42 hours...drifting turns westward across southern Gulf of Mexico and reaches 22N-92.5W at 120 hours. For area of interest #2...no tropical cyclone formation shown due to dominance of area of interest #1. For area of interest #3...no tropical cyclone formation shown.


0600Z NAVGEM Model Run...For area of interest #1...tropical cyclone formation suggested offshore of the eastern Yucatan peinsula coast at 24 hours...passes over northeastern corner of the peninsula at 36 hours...while drifting southwestward under the influence of area of interest #2 approaching from the east...strengthening into a strong tropical cyclone suggested offshore of the northwestern coast of the peninsula by 120 hours. For area of interest #2...organizes into a surface low pressure centered between Jamaica and Haiti at 78 hours...after moving northwestward and crossing eastern Cuba tropical cyclone formation suggested between Florida and Cuba at 120 hours. For area of interest #3...no tropical cyclone formation shown.

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