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 #183

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


...TUESDAY NOVEMBER 17 2020 2:33 PM EDT...

See Hurricane Iota section below for the only currently active tropical cyclone in the Atlantic basin. See area of interest sections below for areas being monitored for tropical cyclone formation.


Elsewhere...a warm deep-layered ridge is expected to develop across the central Atlantic in the next 48 hours due to the warm sector of the strong frontal cyclone exiting eastern North America. This will cause the south part of the current northeast Atlantic upper trough to cut-off into an upper vortex located south of the Azores and west of the Canary Islands. Although this cut-off upper vortex is forecast to be cold enough to potentially produce thunderstorms with water temps in the low 20s of deg C...any surface low pressure to be generated by the eastern divergence zone of the upper vortex is forecast to quickly shift westward under the influence of the surface layer of the central Atlantic deep-layered ridge and away from the supportive divergence zone of the vortex. Therefore any surface low pressure that forms in the northeast Atlantic is unlikely to become a subtropical cyclone...and I have not introduced a new area of interest for subtropical development in the northeast Atlantic at this time.


HURRICANE IOTA (RECENTLY DOWNGRADED TO TROPICAL STORM IOTA)...Last night...Iota's sharply defined eye became cloud filled as it made landfall in northeastern Nicaragua...and the National Hurricane Center estimated that Iota made landfall as a top end category 4 with 155 mph maximum sustained winds. This slight weakening from category 5 does not make the situation any better as this is still a catastrophic landfall intensity. Iota has been able to spread damaging tropical storm and hurriacne force winds far inland into central Honduras and north-central Nicaragua as it is still a category 1 hurricane even as the center of circulation approaches the central Nicaragua/Honduras border. Iota will likely be downgraded to a tropical storm by 1 PM EDT...and as a tropical storm spread damaging gusty winds into northwestern Nicaragua and souhwestern Honduras. Further weakening to a remnant low pressure is expected in the next 24 hours. My updated forecast track points for Iota are shifted north and west given that Iota has been able to move a little faster and on a less southward angle as the steering southern US surface ridge apparently has not been far south enough to slow Iota's forward speed and bend the track as far southward as previously thought.


Even though Iota is moving a little faster as mentioned in the previous paragraph...the mudslide and flooding potential from heavy rain remains high as the forecast track has not sped up enough to drastically shortern the forecast heavy rainfall periods...and extends to El Salvador and Guatemala on the current forecast track. The upper anticyclone with low shear and upper outflow in the Caribbean Sea extends to the eastern Pacific...so should the remannt low pressure of Iota emerge into the eastern Pacific and redevelop as an eastern Pacific tropical cyclone...I will not be forcasting it on this blog but instead only mention potential impacts to land areas...if any...on the home page bulletins of this site.


Update as of 1 PM EDT...Iota has officially been downgraded to a tropical storm with 65 mph maximum sustained winds by the National Hurricane Center.

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

0 Hr Position (1200Z Nov 17)..75 mph maximum sustained wind hurricane centered over northern Nicaragua just south of the Honduras border at 13.7N-85.2W

IOH 24 Hr Forecast (1200Z Nov 18)...Remnant low pressure centered over eastern El Salvador at 13.5N-88.5W


AREA OF INTEREST #1...A surface trough of low pressure in the western Atlantic north of the Caribbean Islands is currently located at 22N-64W. It is possible this surface trough originated a couple of days ago from the eastern divergence zone of the cut-off upper vortex northeast of the Lesser Antilles islands...or alternatively is the north fracture of the tropical wave tied to area of interest #2. A west-southwest track of the surface trough is likely for the next 72 hours as the strong surface ridge over the southern US approaches. After that time the upper trough currently over eastern North America will have left behind a string of upper vorticity...forecast to evolve into a cut-off upper vortex over the western Bahamas in response to an adjacent amplified warm eastern US upper ridge ahead of a mid-latitude front. The surface trough should turn northeast from 72 to 120 hours as it transitions to a feature supported by the divergence zone of the western Bahamas upper vortex. The short-term track forecasts are shifted south and west due to the current position of the surface trough...but are kept the same in the long term as the forecast Bahamas upper vortex remains in the same position.


Tropical cyclone formation is unlikely for the next 3 days as the surface trough will be exposed to southwesterly shear generated by the eastern North America upper trough. I slowly raise the odds of development to a low 10% by day 5 in response to the increase in upper divergence and reduction in shear induced by the forecast western Bahamas upper vortex. The odds of development are kept low as the GFS...NAVGEM have reverted back to showing an amplified surface trough in the long range instead of a closed surface circulation...and the CMC continues to show a total lack of development (not even a surface trough shown in the long range).

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

IOH 24 Hr Outlook (1200Z Nov 18)...0% chance of tropical cyclone formation (western Atlantic near 22N-66W)

IOH 48 Hr Outlook (1200Z Nov 19)...0% chance of tropical cyclone formation (western Atlantic near 21.5N-68.5W)

IOH 72 Hr Outlook (1200Z Nov 20)...0% chance of tropical cyclone formation (just east of the eastern Bahamas near 21N-70W)

IOH 96 Hr Outlook (1200Z Nov 21)...5% chance of tropical cyclone formation (just east of the eastern Bahamas near 22N-70W)

IOH 120 Hr Outlook (1200Z Nov 22)...10% chance of tropical cyclone formation (western Atlantic near 25N-67.5W)


AREA OF INTEREST #2...The tropical wave of low pressure moving through the eastern Caribbean Sea has developed some arc clouds suggesting rotation just north of the island of Aruba (near 13N-70W) with some thunderstorm clusters to the south that extend into northwestern Colombia. Upper-level winds will become more conducive to possible developemnt as the wave continues into the core of the Caribbean upper ridge cell that produced the anticyclonic outflow and low shear that helped Iota strengthen over the last couple of days. I forecast 0% odds of development in the next 24 hours as the tropical wave currently lacks organized thunderstorms needed for short-term development...with my peak odds remaining at a low 20% despite the GFS model dropping development as of 0600Z this morning and the remaining models not showing development...because of the increased definition of the tropical wave in satellite animation and pictures. Some increase in forward speed and south angle is expected with the track as the strong surface ridge over the southern US approaches. The updated forecast track is shifted south due to the current position of the tropical wave's rotation...and brings this tropical wave across southern Nicaragua by 3 to 4 days. We must hope for this forecast track to hold as northern Nicaragua and Honduras have been battered by intense Hurricanes Eta and Iota. Given the increased definition of the tropical wave and favorable upper winds that lie ahead for the tropical wave...I have begun to mention the potential for heavy rainfall and possible gusty winds from this tropical wave in Costa Rica and southern Nicaragua 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 Nov 18)...0% chance of tropical cyclone formation (central Caribbean Sea near 13N-74W)

IOH 48 Hr Outlook (1200Z Nov 19)...10% chance of tropical cyclone formation (central Caribbean Sea near 12.5N-78W)

IOH 72 Hr Outlook (1200Z Nov 20)...20% chance of tropical cyclone formation (just offshore of southern Nicaragua near 12.2N-82W)

IOH 96 Hr Outlook (1200Z Nov 21)...0% chance of tropical cyclone formation (eastern Pacific coast of southwestern Nicaragua at 12N-86W)


...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 Hurricane Iota...weakens to a remnant low over the western Honduras/Nicaragua border at 24 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...no tropical cyclone formation.


0000Z ECMWF Model Run...For Hurricane Iota...weakens to a remnant low southern Honduras at 24 hours. For area of interest #1...evolves into an elongated suface low pressure in the vicinity of Bermuda at 168 hours. For area of interest #2...no tropical cyclone formation shown.


0600Z GFS Model Run...For Hurricane Iota...weakens to a remnant low over the western Honduras/Nicaragua border at 18 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...no tropical cyclone formation.


0600Z NAVGEM Model Run...For Hurricane Iota...weakens to a remnant low over the western Honduras/Nicaragua border at 18 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...no tropical cyclone formation.

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