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Tropical Storm Rose Forecast Discussion Number 8
2021-09-21 04:45:43| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Mon Sep 20 2021 000 WTNT42 KNHC 210245 TCDAT2 Tropical Storm Rose Discussion Number 8 NWS National Hurricane Center Miami FL AL172021 1100 PM AST Mon Sep 20 2021 Although Rose's convective pattern does not appear to be as organized as it was earlier today, a couple of ASCAT overpasses this evening indicated that the tropical cyclone has strengthened since this morning. Both ASCAT-A and -B instruments detected 40-45 kt winds around the southeastern portion of the circulation, and the initial intensity was raised to 45 kt around 0000 UTC with the issuance of a Tropical Cyclone Update. That intensity is maintained for this advisory, and it is also in agreement with subjective Dvorak data T-numbers of 3.0 from TAFB and SAB. The ASCAT data also indicated that the center of Rose is located to the west of the previous estimates, near the northwestern edge of the convective mass noted in satellite imagery. As a result of the center re-location, the initial motion is a somewhat uncertain 320/13 kt. Although the short-term portion of the track forecast has been adjusted westward due to the more westward initial position, there has been no overall change in forecast track reasoning for this advisory. Rose should continue northwestward around the western portion of a strong subtropical ridge during the next couple of days. Beyond that time, a mid- to upper-level trough over the north-central Atlantic should cause Rose to recurve northward, then northeastward, and finally east-northeastward by the end of the forecast period. The dynamical models are in general agreement on this scenario but there are some differences in how sharp Rose will turn, and how fast it will move northeastward late in the period. The new NHC track forecast shows a somewhat sharper turn than the previous advisory to be closer to the latest consensus aids. Rose has likely reached its peak intensity as increasing shear and the entrainment of drier mid-level air are likely to cause weakening by this time tomorrow. Additional weakening is expected after that time as a further increase in shear is anticipated when Rose nears the aforementioned trough in 2 to 3 days. The updated NHC wind speed forecast is slightly stronger at 12 and 24 hours due to the higher initial intensity, but is unchanged after that time. Given the expected hostile environmental conditions, it would not be surprising to see Rose wither more quickly and degenerate into a remnant low sooner than indicated below. That is indicated by at least some of the global model guidance. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 18.9N 35.4W 45 KT 50 MPH 12H 21/1200Z 20.5N 36.5W 45 KT 50 MPH 24H 22/0000Z 22.2N 37.6W 40 KT 45 MPH 36H 22/1200Z 23.5N 38.7W 35 KT 40 MPH 48H 23/0000Z 24.8N 39.9W 30 KT 35 MPH 60H 23/1200Z 26.1N 40.7W 30 KT 35 MPH 72H 24/0000Z 27.3N 40.8W 30 KT 35 MPH 96H 25/0000Z 29.0N 38.2W 25 KT 30 MPH 120H 26/0000Z 30.5N 33.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown
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