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 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #1

*******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 MAY 19 2021 11:30 AM EDT...

Resuming daily birdseye view posts on the Atlantic tropics as chances are increasing for subtropical cyclone formation in the waters east of Bermuda over the next few days. See area of interest #1 section below for additional details.


AREA OF INTEREST #1...Over the last few days models have generally agreed that the current broad western Atlantic upper trough would amplify and trigger a surface frontal low east of Bermuda with its increasing eastern upper divergence zone. The upper trough is expected to amplify due to adjacent amplification of a warm upper ridge over eastern North America bolstered by warm surface southerly flow between the current eastern US surface ridge and a series of frontal systems to pivot across western and northern North America. Since 0000Z this morning the GFS model has suggested the western Atlantic upper trough will now amplify into a cut-off upper vortex with temperatures cold enough to aid in the generation of thunderstorms...suggesting strengthening as a possible subtropical cyclone. The ECMWF with each model run has trended in a similar fashion...while the CMC briefly suggested this in its 1200Z model run yesterday. The National Hurricane Center has probably started issuing a 5-day outlook on this system...beginning 2 AM EDT today...due to the recent trends with the more reliable GFS and ECMWF models.


As the upper trough in the western Atlantic amplifies into a cold-core upper vortex over the next 48 to 72 hours...increasing divergence on the east side of the upper trough/vortex will cause the current western Atlantic surface trough to intensify into the dominant surface frontal low in the region and absorb the frontal low currently diving southward from southeastern Canada (the Canadian frontal low is diving southward due to steering from the amplifying eastern US surface ridge and eastern North America upper ridge). The cold air brought southward by the Canadian frontal low will ensure upper air temperatures are cold enough for thunderstorm activity despite the current 22 to 24 deg C water temperatures in the region...as verified by the GFS forecast of an 1190 dekameter 200 mb height for the forecast upper vortex. The upper vortex will cause the forecast surface frontal low to whirl westward towards the waters east of Bermuda through 72 hours...followed by the surface frontal low ejecting northeastward across the northwest Atlantic through 120 hours under the steering influence of another upper trough/surface frontal system expected to approach from eastern Canada. Forecast track in the outlook below is a compromise between the more west GFS/CMC model solutions and more east NAVGEM/ECMWF solutions.


I have 60% odds of subtropical cyclone formation...notably higher than the NHC outlook as of this writing...due to suggestion of an intensifying...circular...and compact surface frontal low stacked below the upper vortex (suggestive of a surface frontal low strenghtening with the aid of a tropical thunderstorm core) at some point in the latest GFS...ECMWF...and NAVGEM solutions. I have odds of 40% as soon as 48 hours when the ECMWF and NAVGEM suggest possible tropical development...with odds of 60% by 72 hours when the GFS suggests possible tropical development. My odds are kept at 60% at 96 hours depsite a northward track...as this track will take this system into the south edge of the Gulf stream where water temps are still 22 deg C and the upper vortex will still be a rather cold 1192 dekameters in height at 200 mb according to the GFS...still providing instability needed for thunderstorms. By 120 hours odds of development are sharply dropped to 0% as the next frontal system/upper trough to approach from eastern Canada will likely have absorbed this system.

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

IOH 24 Hr Outlook (1200Z May 20)...0% chance of subtropical cyclone formation (western Atlantic near 32.5N-54W)

IOH 48 Hr Outlook (1200Z May 21)...40% chance of subtropical cyclone formation (western Atlantic near 33N-58W)

IOH 72 Hr Outlook (1200Z May 22)...60% chance of subtropical cyclone formation (western Atlantic near 33N-60W)

IOH 96 Hr Outlook (1200Z May 23)...60% chance of subtropical cyclone formation (western Atlantic near 35N-60W)

IOH 120 Hr Outlook (1200Z May 24)...0% chance of subtropical cyclone formation (absorbed by front moving into the northwest Atlantic near 41N-56W)


...COMPUTER MODEL SUMMARY...

Source...Tropical Tidbits (https://www.tropicaltidbits.com/analysis/models/)


0000Z CMC Model Run...For area of interest #1...western Atlantic surface trough intensifies to frontal low near 33N-55W at 36 hours and absorbs frontal low to the west diving southward from SE Canada...dominant frontal low whirls westward towards Bermuda through 72 hours...accelerates northeastward across the open northwest Atlantic through 120 hours as an amplifying surface frontal system and upper trough appoaches from eastern Canada (area of interest absorbed by approaching surface front around this time).


0000Z ECMWF Model Run...For area of interest #1...between 24 and 48 hours shows western Atlantic surface trough intensifying to frontal low near 30N-56.5W while absorbing frontal low to the west diving southward from SE Canada...dominant frontal low whirls westward and strengthens to a possible subtropical cyclone near 35N-58.5W at 48 hours...stalls well east of Bermuda through 72 hours...accelerates northward into the open northwest Atlantic through 120 hours as an amplifying surface frontal system and upper trough appoaches from eastern Canada (area of interest absorbed by approaching surface front around this time).


0600Z GFS Model Run...For area of interest #1...western Atlantic surface trough intensifies to frontal low near 31N-53.5W at 30 hours and absorbs frontal low to the west diving southward from SE Canada...dominant frontal low whirls westward towards Bermuda through 60 hours...possible intensification as a subtropical cyclone while stalled just east of Bermuda and beneath upper vortex through 78 hours...accelerates northestward across the open northwest Atlantic through 120 hours as an amplifying surface frontal system and upper trough appoaches from eastern Canada (area of interest absorbed by approaching surface front around this time).


0600Z NAVGEM Model Run...For area of interest #1...model data limited to 42 hours....suggests more early and more eastward possible subtropical cyclone formation similar to the 0000Z ECMWF.

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