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Hurricane ISELLE Forecast Discussion Number 21
2014-08-05 16:53:40| National Hurricane Center (East Pacific)
Issued at 800 AM PDT TUE AUG 05 2014 000 WTPZ44 KNHC 051453 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 AM PDT TUE AUG 05 2014 Iselle has changed little in organization during the past six hours. The eye remains well defined, with cloud tops to -70C occurring in the eyewall. Analyses from the SHIPS model and from CIMSS at the University of Wisconsin indicate 15-20 kt of southwesterly vertical wind shear over the system. However, this has not yet disrupted the inner core. The initial intensity remains 110 kt based on a combination of subjective and objective satellite intensity estimates. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate Iselle near 06/0600Z, which will provide ground truth for the intensity. The initial motion estimate is 270/8 kt. The subtropical ridge to the north of Iselle should strengthen during the next several days, which should steer the cyclone generally west-northwestward with an increase in forward speed. The track model guidance remains tightly clustered and forecasts Iselle to pass near or over the Hawaiian Islands in 72-84 hours. Based on this, the new forecast track is again just an update of the previous track, and it lies in the center of the track guidance envelope. The analyzed and 24-hour forecast shear have both increased since the previous advisory, and it is likely that Iselle will lose its annular structure later today or tonight. This should result in weakening along the lines of the previous forecast since a significant part of the circulation is over sea surface temperatures of less than 26C. The intensity forecast becomes more uncertain after 36 hours. The cyclone will be moving over increasing sea surface temperatures west of 152W. The dynamical models are in poor agreement on how much shear the Iselle will experience, with the UKMET forecasting strong shear while the GFS/ECMWF forecast less shear. One last factor is that the cyclone is likely to encounter a very dry air mass as it approaches Hawaii. The intensity guidance responds to these factors by diverging. The SHIPS and Florida State Superensemble forecast an intensity near 40 kt when Iselle gets near Hawaii, while the GFDL and HWRF forecast it to be a hurricane. The intensity forecast from 48-120 hours has been nudged upward in agreement with the LGEM model and the intensity consensus, and it calls for Iselle to be just below hurricane strength near Hawaii. 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. In addition, the hazards of a tropical cyclone can extend over a broad area well away from the center. This is the last advisory issued by the National Hurricane Center on Iselle. Future Public Advisories will be issued by the Central Pacific Hurricane Center under AWIPS header HFOTCPCP3 and WMO header WTPA33 PHFO, while Forecast/Advisories will be issued under AWIPS header HFOTCMCP3 and WMO header WTPA23 PHFO. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 16.0N 139.5W 110 KT 125 MPH 12H 06/0000Z 16.3N 141.1W 100 KT 115 MPH 24H 06/1200Z 16.9N 143.9W 85 KT 100 MPH 36H 07/0000Z 17.6N 147.2W 70 KT 80 MPH 48H 07/1200Z 18.3N 150.4W 65 KT 75 MPH 72H 08/1200Z 20.0N 156.5W 55 KT 65 MPH...NEAR HAWAII 96H 09/1200Z 21.0N 162.0W 45 KT 50 MPH 120H 10/1200Z 21.5N 166.5W 35 KT 40 MPH $$ Forecaster Beven
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