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| #1063366 (Received by flhurricane at: 11:00 AM 26.Sep.2021) TCDAT3 Hurricane Sam Discussion Number 16 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Sun Sep 26 2021 The satellite presentation of Hurricane Sam has been quite steady over the past 6 hours. Sam continues to have a well-defined, 12 n mi wide eye on visible and infrared satellite imagery this morning, with cloud tops colder than -70C completely surrounding the center. The latest subjective satellite intensity estimates from TAFB and SAB were both T-6.5/127 kt, while the objective estimate from ADT is near 122 kt. Based on these data, there is no reason to change the 125-kt initial intensity at this time, especially given that a NOAA Hurricane Hunter aircraft is scheduled for a late afternoon/early evening mission into Sam today. Sam is moving toward the west-northwest, or 290/7 kt. A deep-layer subtropical ridge to the north and northeast of Sam should generally steer the hurricane west-northwestward to northwestward for the next several days. By midweek, an amplifying upper-level trough will move off the east coast of the U.S. and dig southward over the western Atlantic, which will erode the western extent of the steering ridge. The deep-layer southerly flow ahead of the trough should cause Sam to begin recurving, with a somewhat faster north-northwestward motion forecast by day 5. The latest NHC track forecast was adjusted a little to the left, or southwest of the previous official forecast, mainly at days 4 and 5, but not quite as far southwest as the model consensus aids. The hurricane will likely experience some fluctuations in intensity during the next few days. Guidance, however, indicates that the chance of an eyewall replacement cycle during the next 36 hours is below climatology. Sam will remain over warm sea-surface temperatures and in a low wind shear environment for the next 3 days, with less than 10 kt of shear diagnosed by the SHIPS guidance. It is possible that Sam`s slow forward motion during the next 2 to 3 days could cause some upwelling of cooler water, but this will probably not result in significant weakening. The official NHC intensity forecast lies on the high end of the guidance for the first 36-48 h of the forecast period. Thereafter, the NHC forecast is closer to the middle of the guidance envelope. Some gradual weakening is forecast later in the period as southwesterly vertical wind shear begins to increase, but Sam is still forecast to remain a major hurricane through the 5-day period. The radii were expanded slightly by 5-10 n mi in the western semicircle from the previous advisory based on a 1155 UTC ASCAT-A pass. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 13.9N 50.2W 125 KT 145 MPH 12H 27/0000Z 14.4N 51.2W 125 KT 145 MPH 24H 27/1200Z 15.2N 52.4W 120 KT 140 MPH 36H 28/0000Z 16.0N 53.5W 120 KT 140 MPH 48H 28/1200Z 16.8N 54.6W 115 KT 130 MPH 60H 29/0000Z 17.7N 55.7W 115 KT 130 MPH 72H 29/1200Z 18.6N 57.1W 115 KT 130 MPH 96H 30/1200Z 21.4N 60.3W 110 KT 125 MPH 120H 01/1200Z 25.6N 63.1W 110 KT 125 MPH $$ Forecaster Hagen/Pasch |
