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Hurricane ISELLE Forecast Discussion Number 12
2014-08-03 16:34:40| National Hurricane Center (East Pacific)
Issued at 800 AM PDT SUN AUG 03 2014 000 WTPZ44 KNHC 031434 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 AM PDT SUN AUG 03 2014 It hasn't been particularly steady, but Iselle continues on a gradual strengthening trend. The eye has cleared out in infrared satellite imagery, and the overall presentation has become a little more symmetric. Dvorak estimates are now T5.5/102 kt from SAB, T5.0/90 kt from TAFB, and near 110 kt from the UW-CIMSS ADT. Therefore, the maximum winds are set at 100 kt as a blend of these numbers, making Iselle a major hurricane. The intensity forecast has been complicated. Iselle continues to push through the peak intensities shown in previous model cycles, so apparently the environment has been a little more favorable than expected. Vertical shear has decreased since yesterday, but still the latest model runs do not show any additional intensification, presumably because the thermodynamic environment is becoming more marginal. The NHC forecast maintains Iselle at 100 kt for the next 12 hours and then only gradually weakens it through 48 hours, but given the hurricane's history, I can't rule out some additional strengthening in the short term. Interestingly, the statistical models are stronger than the dynamical models during the first 48 hours, but the scenario flip-flops on days 3 through 5 with the dynamical models maintaining a stronger cyclone as Iselle approaches the Hawaiian Islands. For now, the NHC forecast closely follows the intensity consensus ICON and is unchanged from the previous advisory beyond 48 hours. The initial motion is 280/9 kt. Ridging to the north of Iselle is expected to maintain a westward heading for the next 3 days, but the forward motion will decrease in about 36 hours as that ridge weakens. After day 3, Iselle is forecast to turn west- northwestward and accelerate when a mid-level high develops halfway between Hawaii and California. The track models are in good agreement for the entire forecast period, but as mentioned in the previous advisory, a slight northward adjustment was needed in the official forecast on days 4 and 5 to account for recent model trends. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 15.5N 132.8W 100 KT 115 MPH 12H 04/0000Z 15.6N 134.3W 100 KT 115 MPH 24H 04/1200Z 15.7N 136.1W 95 KT 110 MPH 36H 05/0000Z 15.7N 137.6W 90 KT 105 MPH 48H 05/1200Z 15.8N 139.1W 80 KT 90 MPH 72H 06/1200Z 16.5N 143.5W 65 KT 75 MPH 96H 07/1200Z 18.0N 149.5W 55 KT 65 MPH 120H 08/1200Z 20.0N 156.0W 45 KT 50 MPH $$ Forecaster Berg
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