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Tropical Storm KARL
ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM KARL DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 500 PM AST FRI SEP 16 2016 Convection is quite strong in the northeastward quadrant of Karl, although the center has recently become exposed due to moderate-to-strong westerly shear. There has been little change to the overall satellite presentation in the past several hours, and the initial wind speed is kept at 40 kt. A continuation of the shear is forecast to keep Karl from strengthening much over the next day or two. This shear is forecast to relax by all of the models by early next week, and some strengthening should then take place while Karl moves over warmer waters. The amount of intensification is a big question mark, with the GFS/ECMWF now showing only a weaker tropical storm, while the rest of the standard intensity guidance (HWRF, GFDL, SHIPS and LGEM models) have Karl as a hurricane by the end of the period. Because of the uncertainty, the intensity forecast is kept the same as the previous one, not too far from the model consensus. The initial motion estimate is about the same as before, 280/12. Model guidance has made a large northward shift today due to the forecasted interaction of a mid/upper-level trough with Karl over the next few days. Initially, the tropical cyclone was expected to be on the western side of the trough, which would have helped steer the cyclone more to the west-southwest over the next couple of days. However, almost all of the guidance now show the trough staying to the west of Karl, which would impart a west or west-northwest motion during that time. The lack of a west-southwest track has large implications down the line, with the cyclone gaining a lot more latitude since Karl is closer to a weakness in the subtropical ridge. Continuity dictates that the NHC forecast not be shifted as much as the guidance suggests for this package, since the guidance could still shift back to the south. A large northward adjustment is made to the NHC forecast at all times, but it remains south of the model consensus and the ECMWF solutions. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 18.8N 35.6W 40 KT 45 MPH 12H 17/0600Z 19.0N 37.3W 40 KT 45 MPH 24H 17/1800Z 19.0N 39.7W 40 KT 45 MPH 36H 18/0600Z 19.0N 42.5W 40 KT 45 MPH 48H 18/1800Z 19.0N 45.3W 45 KT 50 MPH 72H 19/1800Z 20.0N 50.5W 50 KT 60 MPH 96H 20/1800Z 22.0N 55.5W 60 KT 70 MPH 120H 21/1800Z 25.0N 60.5W 70 KT 80 MPH $$ Forecaster Blake NNNN