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Hurricane ISELLE Forecast Discussion Number 17
2014-08-04 16:37:04| National Hurricane Center (East Pacific)
Issued at 800 AM PDT MON AUG 04 2014 000 WTPZ44 KNHC 041436 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 AM PDT MON AUG 04 2014 Iselle continues to intensify and has reached category 4 strength. Convective cloud tops as cold as -75C surround the eye, which has grown to a diameter of 25-30 n mi. Dvorak estimates were a consensus T6.0/115 kt from TAFB and SAB at 1200 UTC, and the objective UW-CIMSS ADT has crept up to T6.3/122 kt since that time. Based on these estimates, the initial intensity is raised to 120 kt. Vertical shear is expected to remain light for the next 24 hours or so while Iselle moves over gradually cooler SSTs. Since Iselle has some characteristics of an annular hurricane, it is likely to change little in intensity during the next day or so, and even when it begins to weaken, the trend should be gradual. On day 3, Iselle will be moving over the coldest water (between 25 and 26C) along its forecast track, and vertical shear is expected to increase to about 15-20 kt. Both factors should induce quicker weakening at that time. The NHC intensity forecast remains above all of the typically used intensity models during the first 24 hours, is very close to the consensus on days 2-3, and then more closely follows the decay shown by the LGEM model toward the latter part of the forecast period. Iselle's initial motion is 275/9 kt. A mid- to upper-level shortwave trough is swinging by to the north of the hurricane and eroding the subtropical ridge, which should cause Iselle to slow down a bit during the next 24 hours. After that time, a mid-level high is forecast to develop and strengthen between Hawaii and California, forcing Iselle to turn west-northwestward and accelerate as it approaches and moves near the Hawaiian Islands. The track guidance has been stable and tightly clustered for a few cycles now, and no significant changes were required to the NHC track forecast. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 16.2N 136.5W 120 KT 140 MPH 12H 05/0000Z 16.2N 137.7W 115 KT 135 MPH 24H 05/1200Z 16.3N 139.2W 110 KT 125 MPH 36H 06/0000Z 16.8N 141.4W 95 KT 110 MPH 48H 06/1200Z 17.4N 144.2W 80 KT 90 MPH 72H 07/1200Z 19.0N 150.5W 60 KT 70 MPH...EAST OF HAWAII 96H 08/1200Z 21.0N 157.0W 50 KT 60 MPH...NEAR HAWAII 120H 09/1200Z 22.5N 162.0W 45 KT 50 MPH...WEST OF HAWAII $$ Forecaster Berg
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