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Tropical Storm KARL Forecast Discussion Number 12
2016-09-17 10:33:11| National Hurricane Center (Atlantic)
Issued at 500 AM AST SAT SEP 17 2016 000 WTNT42 KNHC 170833 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 500 AM AST SAT SEP 17 2016 Karl is maintaining the status quo with its center at least 120 n mi to the southwest of the deep convection. Since the ASCAT pass from last evening showed a sizable area of 35-40 kt winds, and the Dvorak estimates have been steady, the initial intensity remains 40 kt. Karl is located just to the south of an upper-level low, and the resultant westerly shear should gradually relax and change direction during the next few days once Karl moves away from this feature. Sea surface temperatures will be steadily increasing along Karl's forecast path, and mid-tropospheric moisture may begin to increase after 48 hours. Therefore, the NHC intensity forecast continues to call for little change in intensity during the next 48 hours, followed by steady strengthening from day 3 to day 5. This forecast closely follows an average of the SHIPS and LGEM models and still allows for the possibility of Karl becoming a hurricane by day 5. There is no doubt that the center of Karl has been losing latitude during the past 6-12 hours, and the initial motion estimate is 265/12 kt. A strengthening low- to mid-level ridge over the central Atlantic is expected to continue pushing Karl south of due west during the next 36 hours. After that time, Karl will begin to approach a weakness in the ridge located over the western Atlantic, and the tropical cyclone is forecast to move west-northwestward on days 3-5 well to the northeast of the Leeward Islands. Although there is some uncertainty on how far south Karl will get before it turns west-northwestward, the spread among the track models is actually quite small. The updated NHC track forecast essentially lies along the TVCN multi-model consensus line, which ends up being a little south and west of the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 18.2N 38.2W 40 KT 45 MPH 12H 17/1800Z 18.1N 40.1W 35 KT 40 MPH 24H 18/0600Z 17.9N 42.8W 35 KT 40 MPH 36H 18/1800Z 17.6N 45.4W 40 KT 45 MPH 48H 19/0600Z 17.8N 47.9W 40 KT 45 MPH 72H 20/0600Z 19.4N 53.1W 50 KT 60 MPH 96H 21/0600Z 22.0N 58.5W 60 KT 70 MPH 120H 22/0600Z 24.5N 63.0W 70 KT 80 MPH $$ Forecaster Berg
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