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Tropical Storm Rose Forecast Discussion Number 3
2021-09-19 22:39:36| National Hurricane Center (Atlantic)
Issued at 800 PM CVT Sun Sep 19 2021 000 WTNT42 KNHC 192039 TCDAT2 Tropical Storm Rose Discussion Number 3 NWS National Hurricane Center Miami FL AL172021 800 PM CVT Sun Sep 19 2021 Satellite images show that deep convection has increased in coverage near the low-level center during the last 6 hours, while the overall structure of the tropical cyclone has also improved. Based on the improved organization and consensus T-2.5 numbers from TAFB and SAB, the initial intensity is set to 35 kt, making Rose the seventeenth named storm of the busy 2021 Atlantic hurricane season. Only 2005 and 2020 have had the seventeenth named storm on an earlier date. The 12-hour motion is north-northwest, or 330/14. However, Rose appears to be moving more in a northwest direction during the past few hours. This is probably the start of a northwest motion that should continue through day 4 as the system moves along the southwestern and western periphery of a subtropical ridge that extends from Africa across the Cabo Verde Islands. A turn to the north is predicted in about 5 days, as Rose comes under the influence of a strong mid-level trough approaching from the northwest. No significant changes were made to the previous track forecast. Environmental conditions are conducive for strengthening during the next day or so, with low wind shear, SSTs near 27C, and sufficient mid-level atmospheric moisture. Therefore, a little more strengthening is shown compared to the previous NHC forecast. The new NHC forecast is in agreement with the various consensus aids, but slightly below the SHIPS model, in deference to the global models which show a weaker cyclone. Westerly wind shear will likely increase in about 36 hours as a strong upper-level trough approaches from the northwest. Given that the cyclone is forecast to remain rather small, it will likely be vulnerable to the higher shear so weakening is forecast in the 36-72 h time period. Beyond day 3, a further increase in wind shear is expected to cause Rose to weaken to a tropical depression. Although not explicitly forecast, it is possible that the cyclone could become a remnant low in 4-5 days if the shear is too much for the system to handle. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 14.3N 29.9W 35 KT 40 MPH 12H 20/0600Z 15.9N 31.4W 40 KT 45 MPH 24H 20/1800Z 17.9N 33.3W 45 KT 50 MPH 36H 21/0600Z 20.0N 34.8W 45 KT 50 MPH 48H 21/1800Z 22.0N 36.0W 40 KT 45 MPH 60H 22/0600Z 23.5N 37.0W 40 KT 45 MPH 72H 22/1800Z 24.7N 38.0W 35 KT 40 MPH 96H 23/1800Z 26.7N 40.6W 30 KT 35 MPH 120H 24/1800Z 28.7N 41.2W 30 KT 35 MPH $$ Forecaster Hagen/Blake
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