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Hurricane ISELLE Forecast Discussion Number 13
2014-08-03 22:39:29| National Hurricane Center (East Pacific)
Issued at 200 PM PDT SUN AUG 03 2014 000 WTPZ44 KNHC 032039 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 200 PM PDT SUN AUG 03 2014 The cold cloud tops of Iselle's convection have suddenly begun to expand during the past few hours, suggesting that vertical shear is relaxing. The eye has become a little more distinct, and the hurricane appears to be taking on a more circular, compact shape. Current intensity estimates remain unchanged from earlier this morning, so the initial intensity is held at 100 kt. Regarding the compact shape of the hurricane, conventional and microwave images seem to suggest that Iselle is losing its convective banding features. And, for the first time, the Annular Hurricane Index is indicating that Iselle has a marginal annular structure. If it does in fact become annular, then the hurricane is likely to only gradually weaken during the next couple of days in an environment of light easterly shear and slowly decreasing sea surface temperatures. Increasing vertical shear and even colder waters should induce a faster weakening trend after 48 hours, but most of the guidance still suggests that Iselle will maintain tropical storm status as it moves near the Hawaiian Islands on days 4 and 5. The NHC intensity forecast is essentially unchanged from the previous one and lies very close to the LGEM and intensity consensus ICON for the entire forecast period. The latest center fixes suggest that Iselle jogged west- northwestward earlier today, but the estimated initial motion is now westward, or 280/9 kt. The hurricane is expected to slow down a little during the next 36 hours coincident with a developing break in the subtropical ridge. A mid-level high is then forecast to develop between Hawaii and California by day 3, which should steer Iselle at a faster rate toward the west-northwest through the end of the forecast period. There is very little spread among the track models, but the entire envelope has shifted northward on days 3 through 5. Further shifts could be required if the models continue their recent trends, but at this point Iselle is still a potential threat to the Hawaiian Islands later this week. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 15.7N 133.7W 100 KT 115 MPH 12H 04/0600Z 15.8N 135.1W 95 KT 110 MPH 24H 04/1800Z 15.8N 136.8W 90 KT 105 MPH 36H 05/0600Z 15.8N 138.3W 85 KT 100 MPH 48H 05/1800Z 16.0N 140.0W 75 KT 85 MPH 72H 06/1800Z 17.5N 145.0W 60 KT 70 MPH 96H 07/1800Z 19.5N 151.5W 50 KT 60 MPH 120H 08/1800Z 21.5N 157.5W 45 KT 50 MPH $$ Forecaster Berg
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