MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #158
*******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 6:30 AM EDT...
Satellite image as of 1020Z. Areas of interest circled in yellow are not mentioned in the NHC tropical weather outlook. Areas circled in a green dashed line are in the NHC 5-day tropical weather outlook. Areas circled in a solid green are in the NHC 2-day tropical weather outlook:
NHC TAFB Surface Analysis 1800Z (Nov 8):
GFS Model Upper-Level Winds 0000Z:
The NHC has recently removed the current west Atlantic surface cyclone from its tropical weather outlook as it is forecast to be absorbed sooner by a larger North Atlantic cyclone to be generated by the current west Canada upper trough… once that trough moves into the Atlantic at 48+ hours. However I continue to monitor the cyclone for acquisition of tropical characteristics before it’s forecast absorption time… see area of interest #1 section below for more information.
In regards to the current western Canada upper trough… by next week the trough 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 be monitored for signs of subtropical development 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 which has recently entered the western Atlantic from the eastern United States. Because the upper trough has begun to accelerate east… the surface cyclone has followed suit and as of 0600Z this morning was passing just north of Bermuda while centered at 35N-65W. The upper trough is undergoing a southwest-to-northeast elongation… with the northeast part of the elongated upper trough now generating an adjacent surface cyclone to the northeast. However it is the older surface cyclone now passing north of Bermuda that remains the focus for possible tropical development instead of the newer adjacent cyclone.
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 for much of the last several hours is producing a clump of showers and weak thunderstorms just northwest of center with the aid of the upper divergence of its supporting 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 eastward acceleration 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 some activity near the center of the surface cyclone… and some model runs which show a more circular and potentially tropical structure to the surface cyclone developing in the short-term… I am continuing to monitor the cyclone for acquisition of tropical characteristics even though the NHC has recently dropped this feature from its tropical weather outlook. Albeit the amount of time this feature has to acquire tropical characteristics has reduced as the models have trended with a more amplified western Canada upper trough once that trough ejects from southeast Canada at 48+ hours… which scoops this 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 I have lowered my peak subtropical development odds for this surface cyclone from 30% in the previous update to now 20%.
With these forecast updates:
**Coastal sea swells for the United States east coast have dropped from the surface cyclone as it accelerate eastward and away.
**Bermuda may see coastal sea swells and gusty winds from the outer southern circulation of the surface cyclone this morning.
**The potential for the surface cyclone to bring impacts to the Azores later this week has greatly reduced as the long range forecast track has shifted north as discussed above
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Nov 10)… 20% chance of subtropical cyclone formation (central Atlantic near 35N-55W)
IOH 48 Hr Outlook (0600Z Nov 11)… 20% chance of subtropical cyclone formation (central Atlantic near 36N-50W)
IOH 72 Hr Outlook (0600Z Nov 12)… 0% chance of subtropical cyclone formation (north Atlantic near 42N-39W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Nov 8) CMC Model Run...
**For Area of Interest #1… Passes just north of Bermuda at 24 hours… at 78+ hours becomes absorbed by much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada.
1200Z (Nov 8) ECMWF Model Run...
**For Area of Interest #1… Passes just north of Bermuda at 24 hours…potentially acquires tropical characteristics near 35N-56W at 48 hours…at 72+ hours becomes absorbed by much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada.
1800Z (Nov 8) GFS Model Run...
** For Area of Interest #1… Passes just north of Bermuda at 18 hours while potentially acquiring tropical characteristics… at 81+ hours becomes absorbed by much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada.
1800Z (Nov 8) NAVGEM Model Run...
**For Area of Interest #1... Passes just north of Bermuda at 12 hours… potentially acquires tropical characteristics near 36.5N-53W at 54 hours… at 78+ hours becomes absorbed by much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada.