588 WTNT41 KNHC 210835 TCDAT1 Tropical Storm Peter Discussion Number 11 NWS National Hurricane Center Miami FL AL162021 500 AM AST Tue Sep 21 2021 Peter is a ragged and strongly sheared tropical storm. Satellite images and surface observations indicate that the low-level center is fully exposed and located about 100 miles west-southwest of the edge of the main area of deep convection. This very asymmetric structure is due to strong west-southwesterly shear associated with an upper-level low to the northwest of Peter. The initial intensity is held at 45 kt based on the Dvorak CI-numbers from TAFB and SAB, but this could be a little generous. An Air Force Hurricane Hunter aircraft is scheduled to investigate the storm later this morning. Since the storm has decoupled, the low-level center has been moving just south of due west at 265/10 kt. This motion has brought the storm to the southwest of the previous track. The models insist that Peter will turn back to the west-northwest soon and continue moving in that direction during the next couple of days as the storm moves in the flow on the southwest side of a mid-level ridge. After that time, a turn to the north and then northeast is expected as Peter moves toward broad troughing over the north Atlantic. The latest run of the ECMWF has come into line with the remainder of the guidance, and the new forecast is to the west of, and slower than, the previous one. This prediction lies on the south side of the guidance envelope during the first 24 hours of the forecast. Peter is expected to remain in fairly hostile conditions during the next few days with strong westerly shear continuing and dry air likely entraining into the circulation. These negative factors for the storm should cause a slow decay, and that is reflected in the NHC forecast. In fact, some of the guidance suggests that Peter could succumb to the hostile conditions and open into a trough later this week. The NHC intensity forecast is the same as the previous one and in line with the majority of the guidance. Key Messages: 1. Rainfall around the southern periphery of Tropical Storm Peter could lead to areas of urban and small stream flooding through Tuesday across northern Hispaniola, Puerto Rico, portions of the Virgin Islands, and the Northern Leeward Islands. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 19.6N 63.8W 45 KT 50 MPH 12H 21/1800Z 20.3N 65.3W 40 KT 45 MPH 24H 22/0600Z 21.2N 66.9W 40 KT 45 MPH 36H 22/1800Z 22.2N 67.9W 35 KT 40 MPH 48H 23/0600Z 23.2N 68.2W 35 KT 40 MPH 60H 23/1800Z 24.0N 68.0W 30 KT 35 MPH 72H 24/0600Z 25.2N 67.2W 30 KT 35 MPH 96H 25/0600Z 27.2N 65.8W 30 KT 35 MPH 120H 26/0600Z 29.2N 64.2W 30 KT 35 MPH $$ Forecaster Cangialosi