MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #159
*******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 9 2021 8:27 PM EDT...
The NHC has recently re-introduced the current west Atlantic surface cyclone into its tropical weather outlook as showers and thunderstorms have increased in the northwestern quadrant of its circulation...increasing its potential to become a subtropical cyclone in the short term. See area of interest #1 section below for more information.
Elsewhere... the current central Canada upper trough by next week is forecast to be in the northeast Atlantic while a warm deep-layer ridge amplifies to its west in the warm sector of another strong frontal system to be located over eastern North America. The deep-layer ridge may cut-off the southern part of the upper trough into a cold core upper vortex that glides south into mild eastern Atlantic water temps... potentially resulting in enough instability to allow acquisition of tropical characteristics for any surface cyclone to be generated by the vortex. Therefore the east Atlantic region may require monitoring for signs of subtropical development by next week.
AREA OF INTEREST #1...A surface frontal cyclone continues in the western Atlantic with the support of the eastern divergence zone of its parent upper trough. As the upper trough continues to move briskly eastward... the surface cyclone has followed suit and as of 0000Z the center was passing 35.5N-60.5W. The instability for tropical development is currently lackluster as the upper air temps are not very cold (200 mb heights above 1200 dekameters) and the water temps in the region currently in the mid to low 20s of deg C. However the surface cyclone has seen bands of showers and weak thunderstorms increase in the northwestern quadrant and near the center...courtesy of the aid of the upper divergence zone associated with its parent upper trough. Although the upper trough is also not having much amplitude... which is keeping the upper westerly flow over the surface cyclone linear and thus shearing in nature... the fast eastward pace of the surface cyclone is helping it keep up with the upper westerly wind speed and thus reducing the effect of the shear. Given the combo of the reduced shear and upper divergence helping to produce the bands of activity near the center of the surface cyclone... and some suggestion of cirrus outflow clouds located on the edge of the activity reminiscent of warm core upper outflow seen in tropical systems...I have raised my odds of subtropical cyclone formation from 20% in the previous update to 50% in this update. It is also worth noting that as of 8 PM EDT... the NHC has re-introduced this system into their tropical weather outlook while issuing 30% odds of subtropical cyclone formation.
After 24 hours... the models continue to trend with a more amplified central Canada upper trough once that trough ejects from southeast Canada... which scoops the surface cyclone more northward toward cooler waters sooner and causes it to become more quickly absorbed by a much larger cyclone to the north to be tied to the trough from Canada. Therefore by 48 hours I forecast 0% odds of subtropical development from this system.
With these forecast updates:
**Coastal sea swells on the shores of Bermuda generated by the surface cyclone are declining as the cyclone continues to pull eastward and away.
**The surface cyclone is no longer expected to approach the Azores while at 48 hours becoming absorbed by the forecast larger cyclone in the north Atlantic as discussed above.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Nov 11)... 50% chance of subtropical cyclone formation (central Atlantic near 36N-53.5W)
IOH 48 Hr Outlook (0000Z Nov 12)... 0% chance of subtropical cyclone formation (north Atlantic near 41N-39.5W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Nov 9) CMC Model Run...
**For Area of Interest #1...located at 35N-58W at 24 hours as a potential subtropical storm...at 60+ hours becomes absorbed by much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada.
1200Z (Nov 9) ECMWF Model Run...
**For Area of Interest #1... located at 35N-57W at 24 hours as a potential subtropical storm...in between 48 and 72 hours becomes absorbed by much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada.
1800Z (Nov 9) GFS Model Run...
** For Area of Interest #1... located at 35N-56W at 24 hours as a potential subtropical storm...at 57+ hours becomes absorbed by much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada.
1200Z (Nov 9) NAVGEM Model Run...
**For Area of Interest #1... located at 35N-57W at 24 hours as a potential subtropical storm... at 54+ hours begins merging with much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada...in the process becoming the dominant of the two in the merger...the remnant frontal cyclone shifts north-northeast toward the waters between Greenland and Iceland by 120 hours.