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Tropical Storm KARL Forecast Discussion Number 7
2016-09-16 04:56:34| National Hurricane Center (Atlantic)
Issued at 1100 PM AST THU SEP 15 2016 000 WTNT42 KNHC 160256 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 PM AST THU SEP 15 2016 During the past six hours, a significant increase in the amount and the organization of the deep convection has occurred near and over the well-defined low-level circulation center. The southwestern edge of the cold cloud canopy, characterized by tops as cold as -89C, has continued to expand southwestward over the center despite southwesterly vertical wind shear of 20-25 kt. The initial intensity has been increased to 40 kt based on a constrained Dvorak satellite estimate of 35 kt form TAFB, but with a data T-number of T3.0/45 kt using a shear pattern. A 15/2247Z partial ASCAT-B pass indicated several 35-36 kt surface wind vectors in the northeastern quadrant more than 60 nmi from the center. Based on continued improvement in the satellite presentation since the ASCAT pass, the initial intensity is set at 40 kt, making Karl the eleventh named storm of the season. Karl is moving westward or 275/11 kt. The cyclone is expected to move westward and then west-southwestward around a strengthening Atlantic subtropical ridge for the next 48-72 hours. After that time, the ridge is forecast to weaken some, allowing Karl to turn back toward the west and then west-northwest by day 5. The new NHC forecast is essentially on top of the previous advisory track, and lies close to the multi-model consensus TVCX and the Florida State Superensemble model. Karl is expected to remain in a moderate to strong vertical wind shear environment for the next 36 hours or so, which should inhibit significant intensification. After that time, however, the shear is forecast to decrease to around 5 kt for the remainder of the 120-h period. That would normally result in more robust strengthening while the cyclone is moving over 28-29C SSTs. However, Karl will also be moving through a very dry mid-level moisture regime during that time, so the intensification trend is forecast to be much slower than the climatological rate of 20 kt per day, and lies close to the SHIPS intensity forecast. The large 34-kt wind radius in the northeastern quadrant is based on the aforementioned ASCAT wind data. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 17.9N 32.5W 40 KT 45 MPH 12H 16/1200Z 18.0N 34.5W 40 KT 45 MPH 24H 17/0000Z 18.0N 37.1W 40 KT 45 MPH 36H 17/1200Z 17.8N 39.7W 40 KT 45 MPH 48H 18/0000Z 17.5N 42.4W 45 KT 50 MPH 72H 19/0000Z 17.1N 47.8W 50 KT 60 MPH 96H 20/0000Z 17.8N 52.7W 55 KT 65 MPH 120H 21/0000Z 19.0N 57.0W 60 KT 70 MPH $$ Forecaster Stewart
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