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Tropical Storm Rose Forecast Discussion Number 4
2021-09-20 04:50:08| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Sep 19 2021 000 WTNT42 KNHC 200250 TCDAT2 Tropical Storm Rose Discussion Number 4 NWS National Hurricane Center Miami FL AL172021 1100 PM AST Sun Sep 19 2021 The center of Rose has been very difficult to locate in infrared satellite imagery this evening. However, an earlier ASCAT-A overpass as well as an SSMIS microwave image from around of the time of the previous advisory were both helpful in establishing the initial position, motion, and intensity of the tropical cyclone. Rose's center is located on the eastern edge of the main convective mass due to some southeasterly shear. The ASCAT ambiguity data revealed an area of 30-35 kt winds around the southeastern portion of the circulation, so the wind speed remains 35 kt for this advisory. This is also in agreement with subjective Dvorak T-numbers of T2.5 form both SAB and TAFB. The ASCAT data indicated that Rose is located slightly west of the earlier estimates, and the initial motion estimate is now northwestward or 320/14 kt. The cyclone is forecast to move generally northwestward during the next several days around the southwestern and western portions of a subtropical ridge located over the far eastern Atlantic. After day 4, a strong mid- to upper-level trough over the north-central Atlantic should cause Rose to turn northward. The dynamical models are in reasonably good agreement through about 60-72 hours, but there is growing east-to-west (cross-track) spread after that time. The NHC track forecast is not too different from the previous advisory, and lies close to the various consensus models in deference to the increasing model spread late in the period. Rose has about 24 hours over warm waters and in low vertical wind shear conditions in which to strengthen, and the new NHC intensity forecast for that time is unchanged from before. After 24 hours, increasing westerly shear is likely to result in some gradual weakening. A further increase in shear is anticipated by day 3 as Rose approaches the aforementioned trough. This is likely to result in additional weakening, and Rose is forecast to weaken to a tropical depression by day 4. Some of the global model guidance suggests that weakening could occur faster than indicated below, and it is possible that Rose will degenerate into a remnant low by the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 15.3N 31.1W 35 KT 40 MPH 12H 20/1200Z 16.9N 32.6W 40 KT 45 MPH 24H 21/0000Z 18.9N 34.2W 45 KT 50 MPH 36H 21/1200Z 20.9N 35.5W 40 KT 45 MPH 48H 22/0000Z 22.6N 36.6W 40 KT 45 MPH 60H 22/1200Z 23.9N 37.5W 40 KT 45 MPH 72H 23/0000Z 25.0N 38.7W 35 KT 40 MPH 96H 24/0000Z 27.1N 40.8W 30 KT 35 MPH 120H 25/0000Z 29.0N 40.5W 30 KT 35 MPH $$ Forecaster Brown
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