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| #874799 (Received by flhurricane at: 5:24 PM 13.Sep.2016) TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 500 PM AST TUE SEP 13 2016 Ian continues to be sheared, and the low-level center is estimated to be near the southern edge of a ragged-looking area of deep convection. Since there has been no appreciable increase in the organization of the tropical cyclone, the advisory intensity is held at 40 kt, which is the mean of Dvorak intensity estimates from TAFB and SAB. Given that the shear is forecast to remain strong enough to inhibit strengthening for the next 24 hours or so, with some relaxation thereafter, the official intensity forecast shows some slow strengthening beginning tomorrow night. The official forecast is in good agreement with the latest LGEM guidance. In 72 hours, the global models predict the cyclone to have a frontal structure over the north Atlantic, so the official forecast shows Ian as extratropical by that time. The storm has sped up a bit, and the initial motion is now near 340/14 kt. Over the next day or so, Ian will continue to move through a weakness in the mid-level subtropical ridge. Later, when the cyclone moves into the mid-latitude westerlies, a shortwave trough approaching from the west should cause Ian to accelerate north-northeastward to northeastward. The official track forecast is faster than the previous one, but not quite as fast as the latest ECMWF and GFS solutions. This is close to the multi-model consensus and the FSU Superensemble. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 27.0N 52.7W 40 KT 45 MPH 12H 14/0600Z 29.1N 53.3W 40 KT 45 MPH 24H 14/1800Z 31.8N 53.6W 40 KT 45 MPH 36H 15/0600Z 34.5N 53.0W 45 KT 50 MPH 48H 15/1800Z 37.5N 50.5W 50 KT 60 MPH 72H 16/1800Z 48.5N 37.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 17/1800Z 58.0N 22.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 18/1800Z 64.5N 8.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch |
