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Tropical Storm KARL Forecast Discussion Number 15
2016-09-18 04:31:46| National Hurricane Center (Atlantic)
Issued at 1100 PM AST SAT SEP 17 2016 000 WTNT42 KNHC 180231 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 PM AST SAT SEP 17 2016 Karl continues to struggle. The tropical storm is producing a few patches of deep convection to the north and east of the exposed center, but the cyclone lacks banding features. An ASCAT-B pass just prior to 0000Z captured a portion of the circulation and showed that the winds were lower there than they were in the previous pass. Based on that data and the Dvorak classifications, the initial wind speed is lowered a little to 35 kt. The poor structure of Karl is likely due to the combined effects of southwesterly shear and dry mid-level air. These unfavorable atmospheric conditions and marginally warm sea surface temperatures should keep Karl relatively steady state for the next day or so. After that time, lower shear, slightly more moisture, and warmer sea surface temperatures should allow the cyclone to strengthen. The intensity models are a bit higher this cycle at the longer range, and the NHC forecast has been nudged upward. This prediction lies near the lower end of the guidance, in best agreement with the SHIPS model. The center of Karl is moving south of due west at about 10 kt. A general westward motion at a slightly faster pace is expected during the next day or two while Karl is steered by the flow on the south side of a subtropical ridge. A turn to the west-northwest is predicted beyond a couple of days as Karl moves on the southwestern periphery of the ridge and toward a weakness. There is not a significant amount of spread in the models, or the ensemble members of the GFS and ECMWF, and the official forecast is largely an update of the previous one. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 17.8N 41.3W 35 KT 40 MPH 12H 18/1200Z 17.9N 43.3W 35 KT 40 MPH 24H 19/0000Z 18.1N 46.0W 40 KT 45 MPH 36H 19/1200Z 18.6N 48.6W 45 KT 50 MPH 48H 20/0000Z 19.4N 51.1W 50 KT 60 MPH 72H 21/0000Z 21.2N 56.1W 55 KT 65 MPH 96H 22/0000Z 23.7N 61.4W 65 KT 75 MPH 120H 23/0000Z 25.8N 65.2W 75 KT 85 MPH $$ Forecaster Cangialosi
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