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Tropical Storm IAN Forecast Discussion Number 11
2016-09-15 04:56:57| National Hurricane Center (Atlantic)
Issued at 1100 PM AST WED SEP 14 2016 000 WTNT45 KNHC 150256 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 1100 PM AST WED SEP 14 2016 Water vapor imagery indicates that an upper-level low has moved over and has become superimposed with Ian's low-level center. Broken convective banding features, along with an abundance of lightning, have developed northwest through northeast of the center. Drifting buoy 41506, located about 20 nmi north of the center reported 1001.5 mb pressure at 0100Z. Another drifting buoy located about 150 nmi east of the center reported a pressure of around 1015 mb, and the pressure difference between Ian and that buoy supports a gradient wind of 50-52 kt. For now, the initial intensity of Ian will remain at 45 kt since another scatterometer pass over the cyclone is due shortly. Ship BATFR13 has been reporting winds of 30 kt about 250 nmi north-northeast of the center, which supports the previous and current 34-kt wind radius of 200 nmi in that quadrant. Ian has made the much anticipated turn toward the north-northeast, and the cyclone is now moving 015/12 kt. Ian should gradually turn more toward the northeast during the next 24 hours and accelerate as the storm moves around the western portion of Bermuda-Azores High, and ahead of an advancing strong shortwave trough. The new forecast track is essentially just an extension of the previous advisory track and lies down the middle of the tightly packed NHC track model guidance. Ian is looking more like a subtropical cyclone on conventional satellite. However, the recent increase in deep convection near and within 75 nmi of the center, along with recent AMSU data indicating that the system still has a mid- to upper-level warm-core structure, support maintaining Ian as a tropical cyclone. Ian has about 24 hours or so remaining to intensify as a tropical cyclone while it is located south of the Gulf Stream and over warm waters. By 36 hours, Ian will lose its tropical characteristics over cooler water, but some baroclinic forcing is expected to help strengthen the cyclone. By 72 hours, Ian is expected to be absorbed by a larger extratropical low. The intensity forecast remains unchanged from the previous advisory and follows the trend of global models. FORECAST POSITIONS AND MAX WINDS INIT 15/0300Z 33.9N 53.4W 45 KT 50 MPH 12H 15/1200Z 36.3N 51.6W 50 KT 60 MPH 24H 16/0000Z 40.3N 47.0W 50 KT 60 MPH 36H 16/1200Z 45.8N 39.7W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 17/0000Z 51.7N 32.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 18/0000Z...ABSORBED $$ Forecaster Stewart
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