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Hurricane ISELLE Forecast Discussion Number 8
2014-08-02 16:51:35| National Hurricane Center (East Pacific)
Issued at 800 AM PDT SAT AUG 02 2014 000 WTPZ44 KNHC 021451 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 AM PDT SAT AUG 02 2014 Iselle has maintained an eye during the past several hours, but the deepest convection has been unable to persist within the western eyewall. According to UW-CIMSS shear analyses, about 15 kt of north-northeasterly shear is affecting the hurricane, and a recent TRMM pass indicated that the mid-level center is displaced about 10-15 n mi south of the low-level center. The maximum winds are still estimated to be 70 kt based on Dvorak estimates of T4.5/77 kt from SAB and T4.0/65 kt from TAFB. Moderate vertical shear is expected to persist for another 12 hours or so and then become negligible between 24-72 hours. Even though sea surface temperatures are expected to stay near or just above 26C through the next 5 days, oceanic heat content is forecast to drop significantly in about 24-36 hours. Therefore, mixing and upwelling of colder water is likely to limit significant additional strengthening. The intensity models are in good agreement in showing Iselle leveling off around 75 kt during the next couple of days, and the official forecast maintains that scenario. Cooler ocean water and increased shear are expected to cause weakening beyond day 3. Iselle is located to the south of a mid-level ridge, which is steering the hurricane westward with an initial motion of 280/9 kt. A mid-level shortwave trough is still expected to develop to the north of Iselle in about 48 hours, but its only real effect will be to weaken the steering flow for a day or two. After day 3, mid-level ridging is forecast to restrengthen to the north and northeast of Iselle, causing the cyclone to accelerate westward by the end of the forecast period. There continues to be some latitudinal spread in the track guidance, especially on days 4 and 5. The updated NHC track forecast is very near the previous forecast and the model consensus TVCE for the sake of continuity. FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 15.0N 129.2W 70 KT 80 MPH 12H 03/0000Z 15.2N 130.5W 75 KT 85 MPH 24H 03/1200Z 15.6N 132.4W 75 KT 85 MPH 36H 04/0000Z 15.9N 134.2W 75 KT 85 MPH 48H 04/1200Z 16.0N 135.9W 75 KT 85 MPH 72H 05/1200Z 16.0N 139.0W 70 KT 80 MPH 96H 06/1200Z 16.0N 143.0W 60 KT 70 MPH 120H 07/1200Z 16.5N 148.5W 45 KT 50 MPH $$ Forecaster Berg
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