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Hurricane ISELLE Forecast Discussion Number 18
2014-08-04 22:42:38| National Hurricane Center (East Pacific)
Issued at 200 PM PDT MON AUG 04 2014 000 WTPZ44 KNHC 042042 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 18...CORRECTED NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 200 PM PDT MON AUG 04 2014 Corrected quasi-annual to quasi-annular Iselle has an impressive signature on visible satellite imagery with a solid central dense overcast surrounding a 25 n mi wide eye. Final-T estimates from the UW-CIMSS ADT have fallen slightly, but the CI number remains 6.3/122 kt. Along with steady T6.0/115 kt estimates from TAFB and SAB, the initial intensity is held at 120 kt. There is not much change to the intensity forecast. Due to its quasi-annual structure, Iselle should only gradually weaken in the short term while it moves over marginal sea surface temperatures and in a relatively light-shear environment. For that reason, the NHC intensity forecast remains above the intensity guidance for the first 24 hours. Faster weakening is expected thereafter while the cyclone spends about 24 hours over sub-26C water. However, the ocean warms again just to the east of Hawaii, which could allow Iselle to maintain some intensity. After 24 hours, the NHC intensity forecast more closely follows the intensity consensus ICON and the statistical LGEM, which tends to do a good job at the end of the forecast period. Iselle has been moving due westward, or possibly even wobbled just south of due west, during the past few hours. The initial motion estimate is 270/9 kt, but Iselle's forward speed should begin to decrease soon since the ridge to its north has weakened. A mid-level anticyclone is expected to develop and strengthen between California and Hawaii in a day or two, forcing Iselle to turn west-northwestward and accelerate starting in 36 hours. The track guidance has change very little on this cycle, and the updated NHC forecast continues to bring the center of Iselle across the main Hawaiian Islands between 72 and 120 hours. Based on this forecast, Iselle should be crossing 140W just before 1800 UTC on Tuesday. If this forecast holds, then the Central Pacific Hurricane Center in Honolulu, Hawaii, would assume responsibility for Iselle and begin issuing advisories at 2100 UTC, or 11 AM HST on Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 16.1N 137.4W 120 KT 140 MPH 12H 05/0600Z 16.2N 138.5W 115 KT 135 MPH 24H 05/1800Z 16.5N 140.3W 105 KT 120 MPH 36H 06/0600Z 17.1N 142.9W 85 KT 100 MPH 48H 06/1800Z 17.8N 146.1W 70 KT 80 MPH 72H 07/1800Z 19.5N 153.0W 60 KT 70 MPH...NEAR HAWAII 96H 08/1800Z 21.0N 159.0W 55 KT 65 MPH...NEAR HAWAII 120H 09/1800Z 22.5N 164.5W 45 KT 50 MPH...WEST OF HAWAII $$ Forecaster Berg
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