MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #152
*******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 2 2021 4:30 PM EDT...
See Wanda section below for an update on the tropical storm in the open central Atlantic. Elsewhere... in the wake the current southern Caribbean surface low exiting the region through Central America... upper-level winds in the southern Caribbean Sea will remain divergent in the split flow between the south side of the western Caribbean upper ridge and eastern Caribbean upper vorticity. And in a few days as the upper vorticity dissipates while remaining cut-off from high-latitude cold air... the upper ridge in the Caribbean is forecast to expand which will provide an area of low shear and upper outflow. Will watch to see if another southern Caribbean surface low forms with the support of the split flow upper divergence and/or with the support of the expanding Caribbean upper ridge in the days ahead.
And finally in approximately five days...the currently amplified upper trough over southern California is forecast to be heading into the western Atlantic and drive the formation of a rapidly intensifying surface frontal cyclone offshore of the United States east coast with its eastern divergence zone. If the upper trough amplifies into a sufficiently cold upper vortex that keeps the surface cyclone on a more south track over mild/warmer waters as hinted by the 0000Z CMC model run from earlier today...there may be enough instability to allow the surface cyclone to acquire tropical characteristics in approximately one week from today. If model trends move toward a more amplified upper trough/vortex...will consider adding an area of interest for tropical development in regards to this situation. Regardless...another round of coastal sea swells for the east coast of North America is possible by next week...similar to what was seen with the precursor surface cyclone that eventually became Wanda.
TROPICAL STORM WANDA...While continuing to meander in the open central Atlantic...Wanda has begun to turn north in response to a solid wall of surface ridging to the east and approaching upper trough to the west. Even though the east side of the upper trough is supporting Wanda with its eastern divergence zone...Wanda is barely tropical as it has lost thunderstorm intensity over the last several hours. This is due to a lack of instability caused by water temps in the low 20s of deg C combined with upper air temperatures that are not very cold (200 mb heights above 1200 dekameters). I forecast Wanda to weaken in the next 24 hours due to the lack of thunderstorms...and by 48 hours when it reaches even cooler water temps at or below 20 deg C I forecast Wanda to transition into a remnant non-tropical surface cyclone supported by the upper trough.
It was previously forecast by multiple model runs that an impulse ejecting from the current North American upper vortex would scoop Wanda northeast into the far northeast Atlantic. Models today have trended slower with this impulse...allowing the expanding surface ridge from North America (currently over the central US) to reverse the track of Wanda southward. The initial southward acceleration causes Wanda to then miss the later-arriving impulse...which causes Wanda to drift south for an even longer period of time. Because Wanda misses the surface cold front to be driven by this impulse...I now do not expect Wanda's remnants to be frontal in nature...which is I have removed the "frontal" designation at the 48-hour forecast point. Eventually by day 5 the latest models have Wanda turn northeast from a northwestern Atlantic frontal low/cyclone to be generated by the divergence zone of the current North America upper vortex...when that vortex finally swings toward the Atlantic as a strong upper trough. My 48-hour forecast point is only adjusted a margin southward while waiting to see if current model trends hold or break. I also end my forecast for Wanda at the 48-hour mark as this is when I expect Wanda to lose tropical character as mentioned in the prior paragraph... therefore the southward turn and subsequent northeast acceleration after 48 hours is not shown in the forecast below. The initial south turn could now bring Wanda closer to the Azores in the days ahead...and depending on the exact details of the south turn Wanda could remain in the supportive eastern divergence zone of the current upper trough in the region such that it remains a strong non-tropical remnant low. This could result in coastal sea swells for the Azores.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Nov 2)...50 mph maximum sustained wind tropical storm centered at 36N-40.6W
IOH 24 Hr Forecast (1800Z Nov 3)...45 mph maximum sustained wind tropical storm centered at 40N-40W
IOH 48 Hr Forecast (1800Z Nov 4)...Remnant non-tropical surface cyclone centered at 44N-40W
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z CMC Model Run...
**For Tropical Storm Wanda...moves north-northeast and reaches 42.2N-39W at 66 hours as a potentially stronger tropical storm...turns east and transitions into a weakening remnant non-tropical frontal low that reaches the waters just northwest of the Azores near 41.5N-31.5W at 102 hours...performs a small anti-cyclonic loop in this region through 120 hours while passing around the south side of a surface ridge cell that ejects from North America.
**Surface frontal low forms in the southeastern Gulf of Mexico at 84 hours with the support of amplifying upper trough that approaches from its current position over southern California...crosses the Florida peninsula through 102 hours...rapidly intensifies into a frontal cyclone just offshore of the North Carolina coast at 126 hours...potentially acquires tropical characteristics near 35.5N-66W at 168 hours.
0000Z ECMWF Model Run...
**For Tropical Storm Wanda...moves northeast to 42.5N-39.5W at 72 hours as a potentially stronger tropical storm...afterwards drifts east-southeast and transitions to a less tropical remnant low as the cold front from a northwestern Atlantic frontal low overspreads the region (the frontal low is supported by the current North America upper vortex as that vortex later shifts toward the Atlantic as a strong upper trough)
**Rapidly intensifying surface frontal cyclone forms offshore of the southeastern US at 120 hours with the support of amplifying upper trough that approaches from its current position over southern California... moves quickly north to cooler waters and before it can acquire tropical characteristics and approaches Nova Scotia by 168 hours.
1200Z GFS Model Run...
** For Tropical Storm Wanda...moves north to 41.5N-40.2W at 54 hours as a potentially stronger tropical storm...afterwards turns south in response to a surface ridge cell that ejects from North America and reaches 36.5N-39W at 87 hours...afterwards turns east-northeast in the flow ahead of a northwestern Atlantic frontal cyclone (the frontal cyclone is supported by the current North America upper vortex as that vortex later shifts toward the Atlantic as a strong upper trough)...reaches waters just northwest of the Azores near 40.5N-31W at 120 hours.
**Rapidly intensifying surface frontal cyclone forms offshore of the southeastern US at 96 hours with the support of amplifying upper trough that approaches from its current position over southern California...moves quickly north to cooler waters and before it can acquire tropical characteristics and passes just east of Newfoundland by 168 hours.
1200Z NAVGEM Model Run...
**For Tropical Storm Wanda...moves north to 40.5N-39.5W at 42 hours...turns east-southeast toward the waters just northwest of the Azores through 90 hours in response to a surface ridge cell that ejects from North America and weakens to a tropical depression during this time...becomes absorbed by approaching northwestern Atlantic frontal cyclone by 108 hours (the frontal cyclone is supported by the current North America upper vortex as that vortex later shifts toward the Atlantic as a strong upper trough)
**Rapidly intensifying surface frontal cyclone develops offshore of the mid-Atlantic US at 120 hours with the support of amplifying upper trough that approaches from its current position over southern California...moves quickly north to cooler waters and before it can acquire tropical characteristics and is located at 41N-52.5W at 168 hours.