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Hurricane Sam Forecast Discussion Number 28
2021-09-29 16:42:08| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Wed Sep 29 2021 000 WTNT43 KNHC 291441 TCDAT3 Hurricane Sam Discussion Number 28 NWS National Hurricane Center Miami FL AL182021 1100 AM AST Wed Sep 29 2021 Sam has a well-organized cloud pattern on satellite imagery, with a 90 n mi-wide Central Dense Overcast surrounded by numerous convective banding features. Upper-level outflow has now become better established to the southeast of the hurricane. A NOAA Hurricane Hunter mission from a couple of hours ago reported a 20 n mi-wide diameter circular eye. The current intensity is held at 115 kt for this advisory, which is a little higher than the maximum winds observed in the earlier aircraft mission. However, since the estimated minimum central pressure of 949 is a little lower than it was earlier this morning and Sam's intensity has been fluctuating, it is considered prudent not to lower the winds at this time. An Air Force Hurricane Hunter aircraft is scheduled to investigate the hurricane soon and will provide another intensity estimate. Sam continues its slow northwestward trek with the current motion remaining near 310/8 kt. Sam should move northwestward and then northward around the western portion of the subtropical ridge over the eastern Atlantic during the next few days, and turn toward the north-northeast and northeast later in the forecast period. The track guidance models are in very good agreement through 72 hours or so, with some increase in model spread thereafter. This increase in spread is largely due to how Sam will interact with a strong mid-latitude trough moving through Atlantic Canada. Some of the guidance suggests that this trough could partially bypass the hurricane around the end of the period and beyond, but this is not yet clear. The current NHC forecast track is not much different from the previous one and is in good agreement with the dynamical model consensus, TVCA. The hurricane will continue to move over warm waters and in an environment of low vertical shear and diffluent upper-level flow for the next 1-2 days. Thus, it would not be surprising to soon see some restrengthening. The official intensity forecast is essentially a blend of the latest Decay-SHIPS and LGEM predictions, and is very similar to the previous NHC forecast. Sam is likely to remain a major hurricane into this weekend. Key Messages: 1. Large swells generated by Sam are affecting the Leeward Islands and will spread to portions of the Virgin Islands, Puerto Rico, Hispaniola, the Bahamas, and Bermuda by Thursday or Friday. Significant swells will likely reach the east coast of the United States and Atlantic Canada by the weekend. These swells will likely cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the advice of lifeguards and local officials through the upcoming weekend. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 19.4N 57.0W 115 KT 130 MPH 12H 30/0000Z 20.3N 58.1W 120 KT 140 MPH 24H 30/1200Z 21.8N 59.6W 120 KT 140 MPH 36H 01/0000Z 23.9N 61.0W 120 KT 140 MPH 48H 01/1200Z 26.6N 61.8W 115 KT 130 MPH 60H 02/0000Z 29.4N 61.8W 110 KT 125 MPH 72H 02/1200Z 32.0N 60.9W 105 KT 120 MPH 96H 03/1200Z 36.2N 57.3W 90 KT 105 MPH 120H 04/1200Z 39.5N 53.0W 75 KT 85 MPH $$ Forecaster Pasch
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