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 #190

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


...WEDNESDAY NOVEMBER 25 2020 11:51 PM EDT...

Satellite Image as of 0400Z (red indicates an active tropical cyclone of remnants of a tropical cyclone...green indicates an area of interest currently in the NHC outlook...yellow indicates an area of interest currently in the NHC outlook):

NHC TAFB Surface Analysis 0000Z:

GFS Model Upper Level Winds 0000Z:

See area of interest sections below for areas being monitored for tropical development in the Atlantic basin.


AREA OF INTEREST #1...The meandering western to central Atlantic surface low pressure that we have been monitoring for several days for tropical development remains attached to the tail end of a cold front tied to a large western Atlantic upper trough. Based on tonight’s 0000Z NHC TAFB surface analysis...the surface low is now elongated with two centers...and for forecasting I have initialized the surface low at 27.5N-60W which is midway between the two centers. The base of the western Atlantic upper trough is in the process of becoming cut-off into a vortex in response to an upstream deep-layered ridge to the northwest...and the surface low pressure of interest is forecast to become a subtropical low pressure supported by the eastern divergence zone of the developing upper vortex. I have lowered peak odds of subtropical cyclone formation to 30% even though the surface low will be over warm 26 deg C water...as the surface low is currently disorganized with two centers and the model runs do not show much strengthening of the surface low. I have also delayed the timing of peak odds due to the current disorganization. In the next 24 hours I forecast an eastward drift of the surface low as the northeastern center will have the most upper air support beneath the eastern divergence zone of the developing upper vortex. After 24 hours the surface low is forecast to reverse to a west drift under the influence of the passing deep-layered ridge to the northwest...with the track stalling from 48 to 72 hours due to a blocking surface ridge to the west to be supported by the western convergence zone of the shortwave upper trough currently approaching from Illinois. The 1800Z GFS suggests that during this time the supportive divergence zone of the shortwave upper trough may overspread the surface low...thus I keep the peak 30% odds of subtropical cyclone formation through 0000Z November 29. The frontal low pressure associated with this shortwave upper trough will likely drag the surface low northeastward by 96 hours...and this is when I lower odds of subtropical cyclone formation to 0% while the surface low will likely exposed to the back west side of the shortwave upper trough where northwesterly shear and upper convergence would be present.

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

IOH 24 Hr Outlook (0000Z Nov 27)...10% chance of subtropical cyclone formation (central Atlantic near 27.5N-58W)

IOH 48 Hr Outlook (0000Z Nov 28)...30% chance of subtropical cyclone formation (central Atlantic near 27.5N-59W)

IOH 72 Hr Outlook (0000Z Nov 29)...30% chance of subtropical cyclone formation (central Atlantic near 27.5N-59W)

IOH 96 Hr Outlook (0000Z Nov 30)...0% chance of subtropical cyclone formation (central Atlantic near 30N-55W)


AREA OF INTEREST #2...Computer models remain in agreement that the north end of the western Atlantic upper trough currently interacting with area of interest #1 will become a cut-off upper vortex in the northeast Atlantic in the vicinity of Madeira Island in 3 to 5 days thanks to the strength of the deep-layered ridge currently west of the upper trough. Due to the tremendous amount of upper divergence to form on the east side of this strong and rather cold upper vortex (expected to measure 1160 dekameters in height at 200 mb)...the upper vortex will trigger a strong surface cyclone in the region. Even though water temps are currently running at 18 to 20 deg C...the rather cold temps of the upper vortex may aid in the generation of thunderstorms with the surface cyclone such that acquisition of tropical characteristics may have to be watched for. Given the model consensus of a strong surface cyclone which may also help in the generation of thunderstorms with surface convergence...the rather cold destabilizing temps of the forecast upper vortex...and the introduction of this system into the 5-day NHC tropical weather outlook...I have added a new area of interest in the northeast Atlantic with my peak odds of subtropical cyclone formation already up at 40%. Forecast positions in the outlook below are based on the divergence maximum of the current west Atlantic upper trough in the 1800Z GFS model run which transitions into the forecast upper vortex just after 48 hours...followed by forecasting the surface cyclone to whirl beneath the upper vortex by 72+ hours (and the 72+ hour upper vortex positions from the 1800Z GFS are used in my forecast). See home page bulletins of this site for expected impacts to the Canary Islands and Portugal in the coming days.

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

IOH 24 Hr Outlook (0000Z Nov 27)...0% chance of subtropical cyclone formation (northeast Atlantic near 50N-30W)

IOH 48 Hr Outlook (0000Z Nov 28)... 0% chance of subtropical cyclone formation (northeast Atlantic near 45N-20W)

IOH 72 Hr Outlook (0000Z Nov 29)...30% chance of subtropical cyclone formation (northeast Atlantic near 38N-18W)

IOH 96 Hr Outlook (0000Z Nov 30)...40% chance of subtropical cyclone formation (just west of Madeira Island near 33N-17.5W)

IOH 120 Hr Outlook (0000Z Dec 1)...40% chance of subtropical cyclone formation (just northeast of Madeira Island near 34N-15.5W)


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)


1200Z CMC Model Run... For area of interest #1...surface low consolidates near 28N-58.5W at 24 hours...degenerates to elongated circulation along 60W longitude at 66 hours. For area of interest #2...surface cyclone forms near 43N-16W at 66 hours...center of cyclone reaches location just west of Madeira Island by 120 hours.


1200Z ECMWF Model Run...For area of interest #1...surface low consolidates near 29.5N-58.5W at 24 hours...degenerates to elongated circulation near 30N-59W at 72 hours. For area of interest #2...surface cyclone forms near 42.5N-15.5W at 72 hours...center of cyclone reaches location northeast of Madeira Island by 120 hours.


1800Z GFS Model Run...For area of interest #1...surface low consolidates near 24.5N-60W at 48 hours...degenerates to elongated circulation along 60W longitude at 72 hours. For area of interest #2...surface cyclone forms near 41.5N-16W at 72 hours...center of cyclone passes just east of Madeira Island by 102 hours and reaches location midway between Madeira Island and Portugal by 120 hours.


1800Z NAVGEM Model Run...For area of interest #1...surface low consolidates near 26N-59W at 42 hours...degenerates to elongated circulation near 28N-59W at 66 hours. For area of interest #2...surface cyclone forms west of Portugal near 40.8N-13W at 78 hours...center of cyclone passes over Madeira Island by 108 hours and reaches location midway between Madeira Island and Portugal by 120 hours.

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