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Tropical Storm ISELLE Forecast Discussion Number 2
2014-08-01 04:26:38| National Hurricane Center (East Pacific)
Issued at 800 PM PDT THU JUL 31 2014 000 WTPZ44 KNHC 010226 TCDEP4 TROPICAL STORM ISELLE DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 PM PDT THU JUL 31 2014 The satellite presentation of Iselle features an area of cold convective tops mainly to the north and east of the estimated center position, and the poleward outflow has been enhanced somewhat due to an upper-level trough to the northwest. The initial intensity has been raised to 40 kt based on a blend of the TAFB Dvorak estimate and the latest ADT from UW-CIMSS. Conditions appear favorable for steady intensification during the next couple of days. In fact, rapid strengthening is a possibility during the next 24 hours with the SHIPS RI index showing a 40 percent chance of a 25-kt increase in the next 24 hours. After 72 hours SSTs cool somewhat along the forecast track, which should result in gradual weakening. The NHC intensity forecast has been adjusted upward a little from the previous advisory and is close to or just below the SHIPS model through the period and above the intensity consensus. The initial motion estimate is a somewhat uncertain 290/10 given the recent formation of the cyclone, and the initial position is a little to the south and west of previous estimates. Overall the track forecast reasoning has not changed, as Iselle will be steered generally west-northwestward south of the subtropical ridge for the next 72 hours or so. After that time, the ridge weakens as a mid/upper-level trough digs equatorward along 135W, which should result is a slower westward motion late in the period. The track guidance envelope remains tightly clustered for the first 48 hours and the only change to the NHC track during that time is a westward adjustment due to the initial position and motion. Late in the period the spread of the guidance increases a little, and the envelope has shifted northward this cycle. At days 3 through 5 the NHC track has been adjusted northward and westward, but still lies south of the TVCE multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 13.2N 123.9W 40 KT 45 MPH 12H 01/1200Z 13.8N 125.1W 50 KT 60 MPH 24H 02/0000Z 14.6N 126.7W 60 KT 70 MPH 36H 02/1200Z 15.2N 128.3W 65 KT 75 MPH 48H 03/0000Z 15.6N 130.1W 70 KT 80 MPH 72H 04/0000Z 16.5N 134.0W 70 KT 80 MPH 96H 05/0000Z 16.5N 136.5W 60 KT 70 MPH 120H 06/0000Z 16.5N 140.0W 55 KT 65 MPH $$ Forecaster Brennan
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