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Hurricane GUILLERMO Forecast Discussion Number 9
2015-08-01 04:58:20| National Hurricane Center (East Pacific)
Issued at 800 PM PDT FRI JUL 31 2015 000 WTPZ44 KNHC 010258 TCDEP4 HURRICANE GUILLERMO DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092015 800 PM PDT FRI JUL 31 2015 Both microwave and conventional satellite imagery indicate that Guillermo has not become any better organized during the past several hours. In fact, the satellite presentation appears to have deteriorated since earlier today with microwave data showing the northwestern portion of the eyewall eroding. Satellite intensity estimates from TAFB and SAB and the latest objective intensity estimate from UW-CIMSS ADT suggest that initial intensity remains 90 kt. Guillermo continues to move rapidly to the west-northwest, with an initial motion estimate of 285/18 kt. Little change to this motion is expected for the next 24 hours, with the cyclone remaining to the south of a mid-level subtropical ridge. Beyond 24 hours to around 72 hours, a deepening mid- to upper-level trough over the central Pacific is forecast to create a break in the subtropical ridge, which should cause the tropical cyclone to slow down and turn more toward the northwest. The spread in the guidance suite increases beyond 72 hours, but most of the models maintain a general west-northwestward motion. The new forecast track is basically an update of the previous track through 72 hours, and is then nudged slightly to the right or north of the previous track toward the multi-model consensus thereafter. The intensity forecast has become somewhat problematic. The reason for the recent arrested development is unclear, although it might be related to dry air entrainment into the northwestern quadrant of the cyclone. However, there is still the opportunity for Guillermo to strengthen a bit more during the next 12 to 24 hours, while the system remains within a low-shear environment and over warm sea surface temperatures. The new intensity forecast is adjusted slightly downward to 95 kt at the 12- and 24-hour forecast times. Thereafter, the cyclone is forecast to move into an upper-level deformation zone between subtropical ridges to the east and west, which is a less favorable environment. Also, sea surface temperatures gradually cool along the forecast track. We have followed the previous forecast trend of gradual weakening, which is in good agreement with the latest SHIPS/LGEM and IVCN consensus guidance. When Guillermo approaches the Hawaiian Islands, it is expected to encounter increasing westerly shear, and the new intensity forecast follows the previous forecast in weakening Guillermo to tropical storm strength. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 13.2N 136.1W 90 KT 105 MPH 12H 01/1200Z 13.7N 138.5W 95 KT 110 MPH 24H 02/0000Z 14.3N 141.1W 95 KT 110 MPH 36H 02/1200Z 15.0N 143.2W 90 KT 105 MPH 48H 03/0000Z 15.8N 145.0W 80 KT 90 MPH 72H 04/0000Z 17.0N 147.5W 65 KT 75 MPH 96H 05/0000Z 19.0N 150.5W 60 KT 70 MPH 120H 06/0000Z 20.5N 153.5W 50 KT 60 MPH $$ Forecaster Beven/Jacobson
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