000 WTNT42 KNHC 191448 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1100 AM AST MON SEP 19 2016 Visible satellite imagery shows Karl consists of a swirl of low clouds with nearly all of the associated deep convection located to the northeast of the exposed low-level center. The structure has changed relatively little from six hours ago, and the initial wind speed remains 35 kt based on the Dvorak Current Intensity estimate from TAFB. Karl is still being affected by 10-15 kt of southwesterly vertical shear, and with the mid-level relative humidity in the surrounding environment only 40-50 percent, the cyclone continues to struggle to produce deep convection near its center and over the western part of the circulation. However, the SHIPS guidance indicates that the shear should continue to decrease during the next few days, and mid-level moisture is likely to increase over 60 percent by day 3. Therefore, only slight strengthening is anticipated during the next 48 hours, but that should be followed by quicker intensification on days 3-5, with Karl still expected to reach hurricane intensity by the end of the forecast period. The updated official intensity forecast is very close to the SHIPS guidance for the entire forecast period, and it is just slightly below the previous forecast after 24 hours. The initial motion is just a little slower at 275/11 kt. Karl's westward motion is the result of it being positioned south of the Bermuda-Azores high. However, the cyclone is expected to reach a break in the ridge located over the western Atlantic in a few days, which will cause it to turn northwestward by day 3 and then northward by day 5. The track models are tightly clustered through day 3 before Karl makes its turn, but there is more spread on days 4 and 5 regarding where the turn will occur. The GFS and GFS ensemble mean both take Karl farther west before it turns toward the north, while the bulk of the other models make the turn east of the previous forecast track. For the sake of continuity, the updated official track forecast is very similar to the previous forecast, and it lies relatively close to a consensus of the GFS and ECMWF models. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 18.6N 48.3W 35 KT 40 MPH 12H 20/0000Z 18.9N 50.3W 35 KT 40 MPH 24H 20/1200Z 19.5N 52.8W 40 KT 45 MPH 36H 21/0000Z 20.4N 55.2W 40 KT 45 MPH 48H 21/1200Z 21.6N 57.7W 45 KT 50 MPH 72H 22/1200Z 24.5N 62.3W 55 KT 65 MPH 96H 23/1200Z 27.5N 65.5W 70 KT 80 MPH 120H 24/1200Z 29.5N 65.0W 80 KT 90 MPH $$ Forecaster Berg