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| #1158488 (Received by flhurricane at: 10:38 PM 22.Oct.2023) TCDAT5 Hurricane Tammy Discussion Number 19 NWS National Hurricane Center Miami FL AL202023 1100 PM AST Sun Oct 22 2023 Satellite images show that Tammy has not become better organized over the past several hours. In fact, the Central Dense Overcast (CDO) has become more fragmented in appearance and the center appears to be near the southern portion of the CDO. There are however a couple of prominent convective bands over the eastern portion of the circulation. Upper-level outflow is restricted over the southern semicircle of the system, suggesting the influence of southerly vertical wind shear. SFMR-observed surface winds from a NOAA Hurricane Hunter aircraft conducting a research mission into Tammy support a current intensity of 70-75 kt, so the advisory intensity estimate is unchanged. A center position estimate from the aircraft indicates that the motion remains northwestward, or 325/8 kt at this time. The cyclone should turn northward to northeastward over the next 72 hours or so while moving around the western side of a mid-level subtropical high. Later in the forecast period, Tammy should begin to interact with a cyclonic circulation that cuts off from an eastward-moving mid-latitude trough over the western Atlantic. This should cause the system to turn westward around the northern side of the larger circulation in 3-5 days. There continues to be a fairly large spread in the track guidance in this time frame, however. The dynamical guidance indicates that Tammy will be in an environment of significant south-southwesterly vertical wind shear for the next few days. This negative influence could be counteracted somewhat by the presence of a moist and unstable air mass along with warm ocean waters. Therefore some slight strengthening is still predicted, along the lines of the Decay-SHIPS model. This is also similar to the previous official intensity forecast. By day 4, Tammy should begin to merge with a baroclinic zone and simulated satellite imagery from the GFS and ECMWF models depict a frontal appearance. Therefore the system is forecast to have become extratropical by 96 hours. KEY MESSAGES: 1. Heavy rain from Tammy will remain possible over the British Virgin Islands, Leeward Islands, and northern Windward Islands into Monday morning. This rainfall may produce isolated flash and urban flooding, along with isolated mudslides in areas of higher terrain. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 20.8N 64.0W 75 KT 85 MPH 12H 23/1200Z 21.5N 63.9W 75 KT 85 MPH 24H 24/0000Z 22.5N 63.4W 80 KT 90 MPH 36H 24/1200Z 23.2N 62.6W 80 KT 90 MPH 48H 25/0000Z 24.0N 61.6W 80 KT 90 MPH 60H 25/1200Z 25.3N 60.4W 80 KT 90 MPH 72H 26/0000Z 26.6N 59.5W 75 KT 85 MPH 96H 27/0000Z 29.6N 60.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 28/0000Z 30.5N 64.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch |
