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| #1068137 (Received by flhurricane at: 4:59 PM 01.Nov.2021) TCDAT1 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 models. 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 suite. FORECAST POSITIONS AND MAX WINDS 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 |
