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Tropical Storm KARL Forecast Discussion Number 17
2016-09-18 16:54:20| National Hurricane Center (Atlantic)
Issued at 1100 AM AST SUN SEP 18 2016 000 WTNT42 KNHC 181454 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 AM AST SUN SEP 18 2016 The overall appearance of Karl has changed little in satellite imagery since the previous advisory. However, recent water vapor imagery suggest that the strong southwesterly shear that has been plaguing the cyclone for the past few days is beginning to relax. The initial wind speed is held at 35 kt based on a TAFB satellite estimate of T2.5/35 kt. Ship BATFR18, which has been skirting the eastern portion of Karl's circulation the past 12 hours, has reported winds as high as 32 kt. That data has been helpful in determining the extent of the 34-kt wind radius in the northeastern quadrant. Karl has trended westward and the initial motion estimate is now 270/11 kt. A deep-layer subtropical ridge over the central Atlantic to the north of Karl is expected to keep the cyclone moving in a general westward direction for the next 48 hours or so, followed by west-northwestward motion during the remainder of the forecast period. The new NHC track forecast is similar to the previous advisory, and lies close to the various consensus model solutions. Although Karl's convective pattern is currently somewhat disheveled due to the hostile shear and dry mid-level conditions that the cyclone has been encountering the past several days, the surface wind field has remained remarkably robust, including a tight inner-core. The GFS and ECMWF models are forecasting the vertical wind shear to decrease to less than 5 kt from 24-120 hours, which favors a strengthening trend, especially since Karl will be moving 29-30C SSTs during that time. However, only a marginally moist mid-level environment is expected, a condition that could slow down the intensification process. The official intensity forecast follows the trend of the previous advisory, showing gradual strengthening throughout the forecast period, and remains on the conservative side close to the intensity consensus model IVCN. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 18.0N 43.4W 35 KT 40 MPH 12H 19/0000Z 18.2N 45.5W 35 KT 40 MPH 24H 19/1200Z 18.6N 48.2W 40 KT 45 MPH 36H 20/0000Z 19.3N 50.9W 45 KT 50 MPH 48H 20/1200Z 20.2N 53.3W 50 KT 60 MPH 72H 21/1200Z 22.3N 58.4W 55 KT 65 MPH 96H 22/1200Z 24.7N 63.2W 65 KT 75 MPH 120H 23/1200Z 27.3N 66.7W 75 KT 85 MPH $$ Forecaster Stewart
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