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Tropical Depression KARL Forecast Discussion Number 31
2016-09-22 04:40:17| National Hurricane Center (Atlantic)
Issued at 1100 PM AST WED SEP 21 2016 000 WTNT42 KNHC 220240 TCDAT2 TROPICAL DEPRESSION KARL DISCUSSION NUMBER 31 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 PM AST WED SEP 21 2016 While the convection associated with Karl has become more concentrated to the northwest of the center during the past several hours, dropsonde data from the NOAA G-IV jet indicates that the cyclone's circulation is at least somewhat disorganized. A closed circulation exists from the surface to 700 mb. Above that, there is a poorly defined trough at 500 and 400 mb with southwesterly winds of 10-15 kt above the low level center. Finally, the flow at 300 and 200 mb is from the east and southeast. The maximum surface winds in the dropsonde data were 25 kt, and recent ASCAT data implies maximum winds near 30 kt. Thus, the initial intensity remains 30 kt. The initial motion is 315/13 as Karl continues to move between the southwestern periphery of subtropical ridge and a upper- to mid-level low located north of Puerto Rico. This northwestward track should continue for another 24 hours or so. Beyond that time, Karl should turn northward, move through a break in the ridge, and then accelerate northeastward as it becomes embedded in the westerlies. Since the last advisory, the track guidance has shifted a little to the east during the first 72 hours, and the new forecast track for that period lies between the model consensus and the previous forecast. After recurvature, there remain some differences in the guidance regarding the forward speed of Karl, and the forecast track is in best agreement with a blend of the GFS and HWRF models. While the vertical shear is forecast to gradually decrease over Karl, mid-level moisture values to the southwest of the cyclone remain marginal according to the NOAA jet data. In addition, the disorganized circulation argues against any rapid strengthening. The intensity forecast calls for slow intensification for the next 36 hours, followed by faster strengthening until the 72 hour point when the cyclone is forecast to be a hurricane. Karl should weaken as it begins extratropical transition between 72-96 hours, with the transition to a storm-force extratropical low being complete by 120 hours. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 22.9N 59.6W 30 KT 35 MPH 12H 22/1200Z 24.2N 61.3W 35 KT 40 MPH 24H 23/0000Z 25.9N 63.4W 40 KT 45 MPH 36H 23/1200Z 27.6N 64.3W 45 KT 50 MPH 48H 24/0000Z 29.7N 64.1W 55 KT 65 MPH 72H 25/0000Z 33.5N 58.5W 70 KT 80 MPH 96H 26/0000Z 40.0N 47.0W 70 KT 80 MPH 120H 27/0000Z 47.5N 33.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven
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