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| #874944 (Received by flhurricane at: 4:52 AM 15.Sep.2016) TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 500 AM AST THU SEP 15 2016 Ian continues to have a structure somewhat resembling a subtropical cyclone, with the low-level center situated beneath an upper-level low and a cloud pattern featuring a broken band of convection. However, there is still some moderate to deep convection not too far from the center, and the most recent AMSU pass still showed a deep warm core structure. The initial intensity remains 45 kt in agreement with the latest satellite classification of ST3.5 from TAFB. Ian is running out of time to strengthen via diabatic processes, and most of the strengthening shown here is expected to be due to baroclinic effects, especially given the current convective structure. By 24 hours, strong shear and cool SSTs should result in Ian being post-tropical, and the cyclone should be fully extratropical by 36 hours. The intensity forecast is based mainly on the global models and guidance from the Ocean Prediction Center, and shows the post-tropical cyclone intensifying to near hurricane strength before it`s absorbed by a larger extratropical low in 48 hours. The initial motion estimate is 025/17. Ian should accelerate northeastward ahead of a large upper-level trough moving eastward across the northwestern Atlantic during the next 36 hours before being absorbed. The new NHC track forecast is similar to the previous one and near the middle of the guidance envelope. The initial 34-kt wind radii were adjusted based on a partial ASCAT pass from around 0100 UTC. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 35.5N 52.4W 45 KT 50 MPH 12H 15/1800Z 38.3N 49.8W 50 KT 60 MPH 24H 16/0600Z 43.0N 43.7W 55 KT 65 MPH...POST-TROPICAL 36H 16/1800Z 49.1N 35.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 17/0600Z...ABSORBED BY ANOTHER EXTRATROPICAL LOW $$ Forecaster Brennan |
