Tropical Storm Rose Forecast Discussion Number 5
ActuCyclone
20 septembre 2021
000 WTNT42 KNHC 200859 TCDAT2 Tropical Storm Rose Discussion Number 5 NWS National Hurricane Center Miami FL AL172021 500 AM AST Mon Sep 20 2021 Rose remains a sheared tropical storm with the low-level center located near the eastern edge of the convective cloud mass based on an earlier 0359Z AMSR2 microwave overpass. These same data also revealed that a well-defined mid-level circulation center was located about 80-90 nmi west of the low-level center, an indication of the magnitude and effect of the mid-level shear impinging on the cyclone. The intensity of 35 kt is being maintained for this advisory based on subjective Dvorak satellite intensity estimates of 35 from both TAFB and SAB. Objective estimates from UW-CIMSS are higher at 45-55 kt, which are considered to be unrepresentative due to the severe westward tilt of Rose's vortex column. The initial motion estimate is northwestward or 315/13 kt. Rose is expected to move generally northwestward around the southwestern and western periphery of a strong subtropical ridge during the next few days. By day 4 and beyond, a mid- to upper-level trough over the north-central Atlantic is forecast to dig southeastward, causing the cyclone to turn northward. The latest NHC model guidance remains in excellent agreement on this track scenario through 72 hours, but then diverge significantly thereafter owing to whether Rose weakens to shallow system or remains a little stringer and deeper. The weaker solutions go more toward the northwest and the stronger solutions take Rose northeastward. The NHC forecast track on days 4 and 5 is a blend of these two extremes. Rose only has about 24 hours over warm waters and in a weak vertical wind shear regime that will allow for some addition strengthening to occur. On days 2-5, however, increasing westerly shear is expected to induce some gradual weakening. Rose is forecast to weaken to a tropical depression by 96 hours, although some of the models suggest that weakening could occur faster than indicated below, and that Rose could degenerate into a remnant low by the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 15.9N 32.6W 35 KT 40 MPH 12H 20/1800Z 17.5N 33.8W 40 KT 45 MPH 24H 21/0600Z 19.8N 35.5W 40 KT 45 MPH 36H 21/1800Z 21.7N 36.7W 35 KT 40 MPH 48H 22/0600Z 23.0N 37.7W 35 KT 40 MPH 60H 22/1800Z 24.2N 38.7W 35 KT 40 MPH 72H 23/0600Z 25.2N 39.8W 30 KT 35 MPH 96H 24/0600Z 27.3N 41.3W 25 KT 30 MPH 120H 25/0600Z 29.2N 40.6W 25 KT 30 MPH $$ Forecaster Stewart