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| #1068104 (Received by flhurricane at: 10:56 AM 01.Nov.2021) TCDAT1 Subtropical Storm Wanda Discussion Number 7 NWS National Hurricane Center Miami FL AL212021 300 PM GMT Mon Nov 01 2021 Wanda has been moving southeastward since the previous advisory and has now moved back underneath the axis of the upper-level trough that the cyclone is embedded in. However, strong northwesterly vertical wind shear of 30-35 kt has persisted and has displaced the deep convection into the southeastern quadrant. The initial intensity has been lowered to 40 kt based on a blend of satellite intensity estimates of 35 kt from TAFB, and 39 kt and 41 kt from UW-CIMSS ADT and SATCON, respectively. Although Wanda had been moving southeastward at 10-11 kt as of 1200 UTC, the most recent motion vector appears to be slowly eastward or 090/05 kt. Wanda and the parent upper-level trough should move eastward this late morning and early afternoon, and then turn northeastward by this evening, followed by a northward motion by late Tuesday as southerly steering flow gradually develops between a larger mid-latitude trough to the west and a ridge to the east. By day 3, another mid-latitude ridge is forecast to build between Wanda and the aforementioned larger trough, causing the cyclone to turn eastward and then southward toward the westernmost Azores. The latest NHC track guidance has shifted sharply to the east of the previous forecast track through 72 hours, and the new official track forecast has followed suit. However, the new advisory track lies along the western edge of the guidance through day 3, and then lies in the middle of the track guidance envelope on days 4 and 5. Although Wanda has weakened slightly, some slight restrengthening will be possible in the 24-60-h period when the shear is forecast to decrease sharply down to around 10 kt while the cyclone remains over 23.5-24-deg-C sea-surface temperatures. The weaker shear conditions should also help Wanda transition to a tropical cyclone. By 96 h, however, Wanda is forecast to devolve into a post-tropical low due to the cyclone moving over sub-20-deg-C water temperatures, into a significantly drier air mass, and into strong southerly vertical wind shear -- a detrimental combination that should cause the convection to erode near the center. The new NHC intensity forecast is essentially unchanged from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 34.0N 43.0W 40 KT 45 MPH 12H 02/0000Z 34.1N 42.0W 40 KT 45 MPH 24H 02/1200Z 35.0N 41.1W 45 KT 50 MPH...TROPICAL CYCLONE 36H 03/0000Z 36.8N 40.2W 45 KT 50 MPH 48H 03/1200Z 39.0N 40.0W 45 KT 50 MPH 60H 04/0000Z 40.8N 39.7W 45 KT 50 MPH 72H 04/1200Z 42.3N 39.0W 45 KT 50 MPH 96H 05/1200Z 43.6N 34.0W 45 KT 50 MPH...POST-TROPICAL 120H 06/1200Z 42.9N 31.5W 40 KT 45 MPH...POST-TROPICAL $$ Forecaster Stewart |
