ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM KARL DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 PM AST FRI SEP 16 2016 The deep convection with Karl is limited to the northeastern quadrant because of the 20 kt westerly vertical shear currently afflicting the tropical storm. Despite this, a 0007 UTC ASCAT scatterometer pass indicated maximum winds of about 40 kt, which is the initial intensity. Karl should continue to struggle for the next day or so due to the hostile vertical shear. The shear should relax as Karl reaches the west side of an upper-level trough in about 36 to 48 hours. From that point in time onward, Karl should be experiencing more conducive conditions: gradually warming SSTs, a moist low to middle troposphere, and low vertical shear. The NHC intensity forecast is for Karl to weaken slightly within the next day and then steadily strengthen starting in about two days onward. This is quite similar to the previous advisory and is based upon the IVCN multi-model consensus. However, confidence in Karl actually becoming a hurricane in five days is low because of the spread in the guidance. Karl is moving toward the west at 13 kt. The Bermuda-Azores high will be building in north of the tropical storm, helping to propel Karl on a general westward track for the next couple of days. Beginning in about three days, Karl will reach the western periphery of the Bermuda-Azores high and bend toward the west-northwest. The reliable track models have substantial spread - especially during days one to three - with some solutions showing a west-southwesterly track, which is rarely seen in this part of the Atlantic basin. The NHC track forecast is slightly south of the previous advisory, and is based upon the TVCN multi-model consensus. The initial size of Karl is determined by the recent scatterometer pass, which showed a large area of tropical-storm-force winds in the northern semicircle, but none to the south. The NHC wind radii forecast is based upon the RVCN consensus technique. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 18.5N 37.0W 40 KT 45 MPH 12H 17/1200Z 18.5N 38.8W 35 KT 40 MPH 24H 18/0000Z 18.5N 41.5W 35 KT 40 MPH 36H 18/1200Z 18.5N 44.1W 35 KT 40 MPH 48H 19/0000Z 18.5N 46.8W 40 KT 45 MPH 72H 20/0000Z 20.0N 52.0W 50 KT 60 MPH 96H 21/0000Z 22.0N 57.0W 60 KT 70 MPH 120H 22/0000Z 25.0N 61.5W 70 KT 80 MPH $$ Forecaster Landsea NNNN
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