Atlantic Hurricane Feed

Tropical Storm Wanda Forecast Discussion

WTNT41 KNHC 012049

Tropical Storm Wanda Discussion Number   8
NWS National Hurricane Center Miami FL       AL212021
900 PM GMT Mon Nov 01 2021

Wanda is now moving east-northeastward and, as a result, has moved 
to the east of the upper-level trough axis, while the parent 
upper-low has detached and pulled out to the north. As a result, 
Wanda has now made the transition from a subtropical cyclone to a 
tropical cyclone. This meteorological metamorphosis has been 
confirmed by ASCAT data from 1200-1300 UTC that showed Wanda now has 
a small radius of maximum winds (RMW) of 30-35 nmi, and that the 
outer wind field has weakened and also contracted in size. The 
intensity is being held at 40 kt based on the earlier ASCAT data 
showing winds of 33-34 kt, and assuming that there is undersampling 
owing to the relatively large footprint/resolution of the 
scatterometer instrument.

The initial motion estimate is 070/06 kt. A complex steering flow 
pattern is forecast to evolve across the northern Atlantic during 
the next several days as a series of troughs and ridges in the 
mid-latitude westerlies pass over and to the north of Wanda. This 
will cause Wanda to make a zig-zag track across the north-central 
Atlantic, moving poleward ahead of the troughs and equatorward ahead 
of the ridges, resulting in a net eastward propagation toward the 
western Azores. The latest NHC model guidance is in fairly good 
agreement on the forecast track through day 3, but then diverge on 
days 4 and 5, with the GFS and ECMWF taking the cyclone more 
southward closer to the Azores and the remaining dynamical models 
lifting out Wanda to the north of the Azores. The new NHC official 
track forecast is similar to the previous advisory track, and 
follows a blend of the GFEX (GFS-ECMWF) and TVCA simple-consensus 

Some slight restrengthening will be possible during the next 48 h 
or so due to a significant decrease in the deep-layer vertical wind 
shear while Wanda moves over slightly warmer sea-surface 
temperatures (SST) near 24 deg C. By 96-120 h, Wanda is forecast to 
devolve into a post-tropical cyclone due to the unfavorable 
combination of sub-20-deg-C SSTs, a significantly drier air mass, 
and strong southerly wind shear in excess of 30 kt. The new NHC 
intensity forecast remains unchanged from the previous advisory and 
is basically in the middle of the tightly packed intensity guidance 


INIT  01/2100Z 34.2N  42.2W   40 KT  45 MPH
 12H  02/0600Z 34.7N  41.3W   45 KT  50 MPH
 24H  02/1800Z 36.0N  40.4W   45 KT  50 MPH
 36H  03/0600Z 37.8N  40.0W   45 KT  50 MPH
 48H  03/1800Z 39.9N  39.7W   45 KT  50 MPH
 60H  04/0600Z 41.7N  39.4W   45 KT  50 MPH
 72H  04/1800Z 42.8N  38.3W   45 KT  50 MPH
 96H  05/1800Z 43.4N  33.3W   45 KT  50 MPH...POST-TROPICAL
120H  06/1800Z 42.5N  31.0W   40 KT  45 MPH...POST-TROPICAL

Forecaster Stewart

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