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 #26

*******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 JUNE 8 2020 11:56 AM EDT...

Tropical Storm Cristobal weakens to a tropical depression while moving further inland across the eastern Louisiana and southwestern Mississippi region...see Cristobal section below for details and an updated outlook on the storm. See area of interest section below on the potential for subtropical cyclone development east of Bermuda over the next few days.


TROPICAL DEPRESSION CRISTOBAL...Southerly surface flow out ahead of the broad frontal low pressure area moving into the central United States...supported by the upper divergence zone of the vigorous upper trough located over the western United States...continues to channel Cristobal northward across the eastern Louisiana/southwestern Mississippi region. A westward lean in track has occurred due to the steering influence of the surface ridge building over the northeastern United States as well as the longwave upper ridge passing to the north...which has caused the center of circulation to reach northeastern Louisiana. Due to the further inland position...Cristobal has weakened to a tropical depression. The structure of the storm remains tropical with a well-defined swirl of showers and thunderstorms near the center...in addition to warm core upper outflow supporting Cristobal supplied by the passing longwave upper ridge. This structure is expected to continue as the center moves through Arkansas and eastern Missouri over the next 24 hours...but further weakening over land should cause Cristobal to be downgraded to a remnant tropical low pressure during this time.

After 24 hours...computer models are in unanimous agreement that the remants of Cristobal will align with the eastern upper divergence maximum of the approaching western United States upper trough...resulting in the remnant circulation intensifying into a vigorous and possibly intense frontal cyclone that moves through the Great Lakes and into eastern Canada. Models also show that the remainder of the broad frontal low pressure area which is currently moving into the central United States will end up as a second lobe of low pressure orbiting eastward around the south side of Cristobal's remnant circulation duirng this time while also intensifying under the support of the upper trough....therefore on the home page of this site I have extended the wind impact in the Great Lakes region to include other states. Impacts to the Great Lakes region on the United States and Canada side is likely by Wednesday. For the shorter-term impacts going on due to the current rain bands of Cristobal...also see bulletins on home page of this site.

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

0 Hr Position (1200Z Jun 8)...35 mph maximum sustained wind tropical depression centered over northeastern Louisiana at 31.8N-91.6W

IOH 24 Hr Forecast (1200Z Jun 9)...Remnant frontal low pressure centered over northeastern Missouri at 38N-91W


AREA OF INTEREST #1...The National Hurricane Center in their 5-day tropical weather outlook continues to highlight the central tropical Atlantic to the east of Bermuda as an area of interest for subtropical development. This is response to continued computer model solutions that show a surface low pressure area developing in about 1 to 2 days in response to current upper trough over eastern Canada diving southward and amplifying into a cut-off upper vortex in the Atlantic along the east side of the upper ridge emerging from central North America...as the upper ridge later amplifies in the eastern warm air advection zone of what is expected to be the remnant frontal cyclone of Cristobal moving into the Great Lakes region and Ontario Canada. The cold temperatures of the forecast cut-off upper vortex may allow for subtropical development despite central Atlantic water temperatures of 22 deg C in the central Atlantic region. I have slightly raised the odds of subtropcal cyclone formation to 10% as the models taken together show a better defined surface low pressure area developing...especially the usually-conservative Euro (ECMWF) which has been the most gung-ho in developing a well-defined surface low pressure spin over the last couple of days. In addition the GFS model which previously trended with an elongated upper vortex now shows a more circular upper vortex...which increases the chances for a more consolidated surface circulation. The upper vortex is also shown to be cooler...measuring in the mid-1210s in dekameters at 200 mb...than in yesterday's GFS run...which would help with the instability needed for thunderstorms over 22 deg C waters. We know from the more recent subtropical disturbance in this region from May 30 that a mid-1210 upper vortex can help generate thunderstorms when water temps are just below 26 deg C...but I am keeping odds at a low 10% as I am less certain about the same kind of upper vortex with the cooler 22 deg C water temperatures. I drop odds of development back to 0% by 96 hours as the models all taken together suggest that the surface circulation will have weakened due to the lack of upper divergence at the core of the upper vortex. My forecast positions once again show a slower...now almost stalled...track with some southwest drifting by 96 hours based on the foercast postions of the upper vortex in the 0600Z GFS...which shows the upper vortex stalled for much of the forecast period with some southwest drifting at 96 hours. This steering will be caused by the upper ridge approaching from central North America as it enters the northwest Atlantic...during that time the ridge will have a southwest lobe directly west of this system such that the forward west/southwest progress of this system will be slow as the rest of the ridge to be located to the north tries to steer the system. Not mentioning any impacts to Bermuda on the home page bulletins of this site as the models taken together show this system either quickly becoming or staying weak during its lifecycle as it whirls into a position directly below the upper vortex where a lack of supportive divergence causes the weakening.

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

IOH 24 Hr Outlook (1200Z Jun 9)...0% chance of subtropical cyclone formation (east of Bermuda near 32.5N-55W)

IOH 48 Hr Outlook (1200Z Jun 10)...10% chance of subtropical cyclone formation (east of Bermuda near 32.5N-55W)

IOH 72 Hr Outlook (1200Z Jun 11)...10% chance of subtropical cyclone formation (east of Bermuda near 32.5N-55W)

IOH 96 Hr Outlook (1200Z Jun 12)...0% chance of subtropical cyclone formation (southeast of Bermuda near 30.5N-57.5W)


...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 Tropical Depression Cristobal...has remnant circulation crossing western Great Lakes region and entering eastern Canada as a large intensifying frontal cyclone at 60 hours. For area of interest #1...develops weak and broad central Atlantic surface low at 30.5N-58.5W at 30 hours in response to current eastern Canada upper trough diving south and amplifying into the Atlantic...has surface low consolidate further north at 35N-57.5W by 54 hours...keeps feature stationary through 78 hours at which time the surface low is weakened to a surface trough.


0000Z ECMWF Model Run...For Tropical Depression Cristobal...has remnant circulation crossing western Great Lakes region and entering eastern Canada as a large intensifying frontal cyclone between 48 and 72 hours. For area of interest #1...develops well-defined surface low at 31N-55W at 48 hours in response to current eastern Canada upper trough diving south and amplifying into the Atlantic. Suggests maximum strength of surface low at 72 hours. Shows surface low in much weaker state at a location just northeast of Bermuda at 120 hours.


0600Z GFS Model Run...For Tropical Depression Cristobal...has remnant circulation crossing western Great Lakes region and entering eastern Canada as a large intensifying frontal cyclone at 48 hours. For area of interest #1...develops weak and broad central Atlantic surface low at 32.5N-55W at 48 hours in response to current eastern Canada upper trough diving south and amplifying into the Atlantic...keeps feature stationary through 78 hours at which time the surface low is weakened to a surface trough.


0600Z NAVGEM Model Run...For Tropical Depression Cristobal...has remnant circulation crossing western Great Lakes region and entering eastern Canada as a large intensifying frontal cyclone at 48 hours. For area of interest #1...in 24 hours develops weak and broad surface low pressure at 34N-56W in response to current eastern Canada upper trough diving south and amplifying into the Atlantic...suggests maximum strength of surface low around 36 hours...keeps feature stationary through 96 hours at which time the surface low is weakened to a surface trough.

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