MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #157
*******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 NOVEMBER 8 2021 1:10 AM EDT...
Satellite image as of 0540Z. 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 7):
GFS Model Upper-Level Winds 1800Z (Nov 7):
See Wanda section below for a final statement on the former tropical storm which has become absorbed by a cold front in the open North Atlantic. Elsewhere… the surface cyclone currently offshore of the southeastern US coast is now being monitored for acquisition for tropical characteristics. The cyclone is forecast to move toward Bermuda in the short-term and possibly the Azores by the end of this week. See area of interest section below for more information.
REMNANTS OF WANDA…The cold front of the approaching North Atlantic surface frontal cyclone has overspread the circulation of what has been a tenacious Tropical Storm Wanda. As a result Wanda quickly lost tropical characteristics while accelerating northeast in the waters northwest of the Azores. On satellite pictures what is left of Wanda is hard to identify within the thunderstorm cloud band of the cold front… and Wanda will soon lose its identity within the front’s low pressure field. This is my final statement on Wanda on this blog as it is no longer a tropical feature.
AREA OF INTEREST #1…A surface frontal cyclone continues offshore of the southeastern United States with the support of the eastern divergence zone of its parent upper trough which remains located inland over the eastern United States. As of 0000Z the swirl center of the cyclone was located at 32.5N-74W. In the short-term… the upper trough is forecast to undergo a southwest-to-northeast elongation as it enters the western Atlantic. The northeast part of the elongated upper trough will generate an adjacent surface cyclone to the northeast… however the latest model guidance has converged on the current surface cyclone being the dominant instead of the adjacent one… with the current surface cyclone potentially gaining tropical characteristics in the days ahead.
Over the next 48 hours the surface cyclone is expected to shift east with its parent upper trough toward Bermuda… where sea surface temps are in the mid-20s of deg C and upper air temps are not that cold (200 mb heights above 1200 dekameters)… resulting in an environment that may lack instability. In addition the upper trough is forecast to not have much amplitude… which will keep the upper westerly flow over the surface cyclone linear and thus shearing in nature. However I assign low 10% odds of subtropical development in case the divergence zone of the upper trough does aid in the generation of thunderstorms. By 72 hours the upper trough and surface cyclone’s eastward speed picks up which is the same direction which may allow the surface cyclone to catch up to the upper westerly wind speed and thus reduce the effects of the westerly shear. As a result I slightly raise subtropical development odds to 15%. By 96+ hours… even though the surface cyclone moves into slightly cooler waters in the low 20s of deg C… the upper divergence is forecast to increase over the surface cyclone and the upper air temps are forecast to drop (200 mb heights dropping to 1200 dekameters)… due to the approach of an amplifying cold upper trough ejecting from southeast Canada. The increased divergence and increased instability brought on by the cooler upper air could increase the thunderstorm activity and tropical characteristics… and I raise subtropical development odds to 30% for this timeframe. As of this writing… the NHC’s development odds by day 5 are at 20%… however I have slightly higher odds of 30% as the models have markedly converged on possible subtropical development. If this convergence persists… I plan to raise subtropical development odds further in future updates.
With these forecast updates… expect the following impacts from the surface cyclone regardless of whether or not it acquires tropical characteristics:
**Coastal sea swells for the United States east coast and Bermuda in the next 48 hours. Bermuda may see gusty winds as the cyclone center passes nearby.
**The Azores may see coastal sea swells and gusty winds by late this week. The impacts to the Azores are uncertain due to the divergence in the models in regards to the long-range track. Some models swing the surface cyclone north away from the Azores while having a larger North Atlantic cyclone (supported by the upper trough to exit southeast Canada) whirl in this system… while others have a strong surface ridge (supported by the western convergence zone of the upper trough to exit southeast Canada) keeping the surface cyclone on a more south track toward the Azores.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Nov 9)… 10% chance of subtropical cyclone formation (west of Bermuda near 32.5N-70W)
IOH 48 Hr Outlook (0000Z Nov 10)… 10% chance of subtropical cyclone formation (just east of Bermuda near 32.5N-62W)
IOH 72 Hr Outlook (0000Z Nov 11)… 15% chance of subtropical cyclone formation (central Atlantic near 35N-51W)
IOH 96 Hr Outlook (0000Z Nov 12)… 30% chance of subtropical cyclone formation (central Atlantic near 37N-45W)
IOH 120 Hr Outlook (0000Z Nov 13)… 30% chance of subtropical cyclone formation (west of the Azores near 38.5N-35W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Nov 7) CMC Model Run...
**For Area of Interest #1… Passes just north of Bermuda at 48 hours… potentially acquires tropical characteristics near 35N-59.5W at 66 hours… through 120 hours loses any tropical characteristics and identity while absorbed by much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada.
1200Z (Nov 7) ECMWF Model Run...
**For Area of Interest #1… Passes just north of Bermuda at 48 hours…potentially acquires tropical characteristics near 34.5N-57.5W at 72 hours… while passing north Azores between 120 and 144 hours becomes absorbed by much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada.
1800Z (Nov 7) GFS Model Run...
** For Area of Interest #1… Passes just north of Bermuda at 39 hours while potentially acquiring tropical characteristics… by 144 hours passes just south of the Azores while continuing east.
1800Z (Nov 7) NAVGEM Model Run...
**For Area of Interest #1... Passes just north of Bermuda at 42 hours… potentially acquires tropical characteristics near 34.8N-59.5W at 60 hours…by 120 hours loses tropical character while transitioning into a powerful frontal cyclone accelerating into the far northeast Atlantic near 49.5N-30W (transition and intensification into a powerful frontal cyclone aided by amplifying upper trough that ejects from southeastern Canada)