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Tropical Storm IAN Forecast Discussion Number 9
2016-09-14 16:50:56| National Hurricane Center (Atlantic)
Issued at 1100 AM AST WED SEP 14 2016 000 WTNT45 KNHC 141450 TCDAT5 TROPICAL STORM IAN DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102016 1100 AM AST WED SEP 14 2016 Ian's center has lost some definition and appears to have re-formed north of the feature we had been tracking. The center remains exposed to the south and southeast of the deep convection due to almost 30 kt of vertical shear. Based on the Dvorak Current Intensity number from TAFB, the estimated maximum winds remain 45 kt. Due to the center's re-formation, the initial motion is a faster 355/17 kt. However, unless the center jumps again, this motion is expected to stabilize back to around 14 kt in the next 12 hours. A mid-/upper-level low to the west of Ian and a mid-tropospheric high to the east should steer the cyclone northward and north- northeastward during the next day or so. After that time, Ian is expected to accelerate toward the northeast as it gets picked up by a progressive mid-latitude trough moving eastward from Atlantic Canada. The new track guidance agrees on this scenario, although a slight westward shift in the official track forecast was required, probably due to the updated initial position. The new NHC forecast is very close to the TVCN multi-model consensus. Although the vertical shear is expected to decrease only slightly, marginally warm waters and Ian's baroclinic interaction with the mid-/upper-level low to its west are expected to foster some strengthening during the next 36 hours. Ian is then expected to lose the last of its tropical characteristics and become extratropical by 48 hours and then be absorbed by another extratropical low by 72 hours. This forecast follows guidance provided by the Ocean Prediction Center and is closest to the scenario shown by the ECMWF model. There is still some uncertainty in this thinking, however, since the GFS, UKMET, and Canadian models make Ian the dominant extratropical low over the far northern Atlantic. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 31.4N 53.0W 45 KT 50 MPH 12H 15/0000Z 33.7N 52.8W 50 KT 60 MPH 24H 15/1200Z 36.7N 51.1W 50 KT 60 MPH 36H 16/0000Z 40.2N 46.9W 55 KT 65 MPH 48H 16/1200Z 45.4N 39.8W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 17/1200Z...DISSIPATED $$ Forecaster Berg
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