MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #156
*******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.**********
...SUNDAY NOVEMBER 7 2021 1:45 AM EDT...
Satellite image as of 0420Z. 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 6):
GFS Model Upper-Level Winds 1800Z (Nov 6):
See Wanda section below for an update on the tropical storm located in the open north-central Atlantic. Elsewhere… a surface frontal cyclone has developed offshore of the southeastern US coast with the support of an amplified upper trough. Expect coastal sea swells to affect the US east coast over the next couple of days. During this time… the upper trough is now forecast by the GFS and ECMWF to undergo a southwest-to-northeast elongation as it enters the western Atlantic. This could result in the surface cyclone splitting into a pair of cyclones… one to the southwest and another to the northeast. The GFS favors the northeastern cyclone… while the ECMWF favors the southwestern cyclone (see computer model summary section for details)… and both models suggest possible tropical characteristics with their favored cyclone in the days ahead.
Interests in Bermuda and the Azores may see coastal sea swells and possibly gusty winds from either cyclone regardless of acquisition of tropical characteristics or not after this weekend… with impacts to Bermuda possible early in the week and impacts to the Azores possible later in the week. I will declare an area of interest for tropical development if models converge on the same solution (right now there is model divergence with the GFS and ECMWF favoring different cyclones)… or if current observations warrant in the days ahead.
TROPICAL STORM WANDA…As expected… the approaching northwest Atlantic upper trough and surface frontal cyclone has eroded the surface ridge that was previously pushing Wanda south. The result is Wanda has begun to accelerate northeast in the deep-layer southwesterly flow ahead of the approaching frontal system. Wanda’s ongoing tropical character is occurring over water temps in the low 20s of deg C and under upper-level air that is not very cold (200 mb heights above 1200 dekameters). Whatever thunderstorm activity… low surface pressures… and resulting wind speed that Wanda has had is therefore attributed to the upper divergence zone of the central Atlantic upper trough rather than the instability caused by upper-level or sea surface temps. In the last 24 hours… Wanda’s thunderstorms became limited and pushed to the east of its surface swirl from northwesterly shear induced by the outflow of the incoming frontal system’s thunderstorms… and Wanda has weakened to a minimal tropical storm of 40 mph max sustained winds. However in recent hours the small area of thunderstorms has intensified. It is possible that Wanda strengthens in the next 12 hours as the upper trough of the approaching frontal system will retain cold upper air temps and it’s amplified structure… which will increase the instability and upper divergence over Wanda while it remains over low-20 deg C waters. As a result my intensity forecast shows some strengthening… but is lowered compared to the previous forecast to acknowledge Wanda’s recent weakening. By 24 hours… Wanda will have crossed the 20 deg C isotherm and reaches cooler waters in the teens of deg C… and I anticipate Wanda will finally begin losing its tropical characteristics.
It is possible in the next 24 hours that the Azores will receive coastal sea swells from Wanda as the storm track passes just to the northwest of the islands.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Nov 7)… 40 mph maximum sustained wind tropical storm centered at 37.8N-36.8W
IOH 24 Hr Forecast (0000Z Nov 8)… 50 mph maximum sustained wind tropical storm transitioning into a non-tropical frontal cyclone… centered at 43N-31W
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Nov 6) CMC Model Run...
**For Tropical Storm Wanda...accelerates northeast and by 42 hours loses identity along cold front of the currently approaching northwest Atlantic frontal cyclone.
1200Z (Nov 6) ECMWF Model Run...
**For Tropical Storm Wanda... accelerates northeast and between 24 and 48 hours loses identity along cold front of the currently approaching northwest Atlantic frontal cyclone.
**Currently developing western Atlantic frontal cyclone reaches 32N-72W at 48 hours while potentially gaining tropical characteristics… while the frontal cyclone continues east the northeast part of its parent upper trough splits off and develops an adjacent northeastern frontal low… however the frontal cyclone remains the dominant of the two… in between 72 and 96 hours the frontal cyclone passes just north of Bermuda with possible tropical characteristics… by 144 hours the frontal cyclone (while still possibly having tropical character) begins to approach the Azores while orbiting a much larger and rapidly intensifying frontal cyclone and its amplifying upper trough that ejects from southeastern Canada.
1800Z (Nov 6) GFS Model Run...
**For Tropical Storm Wanda... accelerates northeast and by 51 hours while nearing the British Isles loses identity along cold front of the currently approaching northwest Atlantic frontal cyclone.
**Currently developing western Atlantic frontal cyclone evolves into a pair of circulations through 54 hours while the parent upper trough stretches into a southwest-northeast elongation (southwest circulation at 32N-72.5W and northeast circulation at 37N-52.5W)…through 96 hours the southwestern frontal low nears Bermuda while in a weaker state while the northeastern frontal low strengthens into a frontal cyclone nearing the Azores as the cyclone is able to pull cold air southward and amplify its upper trough fragment… as the upper trough fragment amplifies further into an upper vortex the surface cyclone near the Azores potentially acquires tropical characteristics near 36.5N-32W at 120 hours
1800Z (Nov 6) NAVGEM Model Run...
**For Tropical Storm Wanda... accelerates northeast and by 42 hours loses identity along cold front of the currently approaching northwest Atlantic frontal cyclone.