ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM HURRICANE ISELLE DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 PM PDT MON AUG 04 2014 Iselle's cloud pattern has been in a remarkably steady state since the last advisory. The hurricane continues to maintain a classic annular structure, with a large circular eye surrounded by a nearly uniform ring of convection. Satellite intensity estimates were T6.0/115 kt at 0000 UTC from TAFB and SAB and UW-CIMSS ADT values have also decreased to 6.0. Based on these data and minor warming of the cloud tops since that time, the initial intensity estimate is lowered to 115 kt. Iselle has jogged a little south of due west and slowed down during the past six hours, and the initial motion estimate is 265/07. The cyclone is forecast to continue on a slow westward course for the next 12 hours or so in response to a mid-latitude trough briefly weakening the subtropical ridge to the north of the cyclone. After that, Iselle should get caught under a building central Pacific ridge with a slightly different orientation, which should result in the cyclone's acceleration toward the west-northwest. On the forecast track, the center of Iselle should move near or over portions of the Hawaiian Islands in 72-96 hours. A slight southward adjustment was made to the previous forecast track in the direction of the multi-model consensus. Iselle should retain its current annular characteristics during the next 12 hour or so, and thus only slow weakening is likely. After that time, enough of an increase in southwesterly vertical shear and the ingestion of drier and more stable air should disrupt the status quo and result in steadier weakening. Even further weakening should occur by the time the center of Iselle approaches the Hawaiian Islands in 48-72 hours, mostly as a result of a very dry air mass in which the storm will be moving. By 96-120 hours, the GFS/ECMWF solutions show vertical shear increasing to nearly 30 kt which results in a decoupling of the cyclone. The NHC intensity forecast is lower than the previous one but above the multi-model consensus through 48 hours and is a blend of the multi-model consensus and LGEM output after that time. Remannt low status is now indicated on day 5. Interests in the Hawaiian Islands should closely monitor the progress of Iselle. However, it is important not to focus too closely on the exact track and intensity forecasts because the average track error 72 hours out is about 100 miles, the average intensity error is about 15 kt, and because the hazards of a tropical cyclone can extend over a broad area often well away from the center. Iselle is expected to cross into the Central Pacific Hurricane Center's area of responsiblity around 1800 UTC on Tuesday. Once this occurs, the Central Pacific Hurricane Center in Honolulu, Hawaii, will begin issuing advisories on Iselle. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 16.0N 138.0W 115 KT 135 MPH 12H 05/1200Z 16.1N 139.2W 110 KT 125 MPH 24H 06/0000Z 16.5N 141.4W 95 KT 110 MPH 36H 06/1200Z 17.2N 144.3W 80 KT 90 MPH 48H 07/0000Z 17.9N 147.7W 70 KT 80 MPH 72H 08/0000Z 19.5N 154.3W 55 KT 65 MPH 96H 09/0000Z 21.0N 160.2W 45 KT 50 MPH 120H 10/0000Z 22.0N 165.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Kimberlain NNNN