ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM HURRICANE NORBERT DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 PM PDT FRI SEP 05 2014 The satellite presentation of Norbert has improved dramatically since the last advisory. A ragged eye is apparent in infrared imagery surrounded by a ring of cloud tops colder than -70C. Dvorak estimates from TAFB and SAB at 00Z were T5.5/102 kt, and the initial intensity is set a bit below that value at 95 kt for this advisory given the very rapid change in the satellite appearance and the earlier recon data. This recent intensification occurred as Norbert moved over waters warmer than 29C, and some additional strengthening is still possible in the next few hours. However, SSTs steadily decrease along the track going forward, which should result in gradual weakening beginning by 12 hours. Steadier weakening is expected beyond 24 hours as SSTs fall below 26C and the cyclone moves into a drier and more stable airmass. By 72 hours Norbert is expected to become post-tropical and then weaken to a remnant low around day 4. The new NHC intensity forecast has been adjusted upward by 10-15 kt through 24 hours to account for the current intensity trend, and is about 5 kt higher than the previous advisory after that time. This forecast is a little above the intensity consensus through 36 hours and close to the consensus afterward. Smoothing through some short-term wobbles, the initial motion estimate is 320/08. The track forecast reasoning remains unchanged, as Norbert will be steered around the western periphery of a mid- level ridge centered over the southern United States through 48 hours. After that time, the ridge weakens as a mid-latitude trough moves into the U.S. West Coast. This should result in a weakening of the steering currents, leaving the low-level center of Norbert to drift slowly northward or move erratically at the end of the forecast period. The new NHC track forecast is similar to the previous one, but has been adjusted a little to the east to account for the initial position and motion. This track is close to the TVCE multi-model consensus through 72 hours, and shows little net motion after that time. Moisture from the remnants of Dolly and the Pacific ITCZ is being advected northward by the outer circulation of Norbert across northern Mexico and into the southwestern United States. This could result in heavy rains and life-threatening flash flooding in these areas during the next few days. Please see information from your local weather office for more details. FORECAST POSITIONS AND MAX WINDS INIT 06/0300Z 24.2N 112.8W 95 KT 110 MPH 12H 06/1200Z 24.9N 113.8W 90 KT 105 MPH 24H 07/0000Z 25.6N 114.9W 80 KT 90 MPH 36H 07/1200Z 26.5N 116.1W 65 KT 75 MPH 48H 08/0000Z 27.3N 117.0W 50 KT 60 MPH 72H 09/0000Z 29.0N 117.5W 35 KT 40 MPH...POST-TROPICAL 96H 10/0000Z 29.5N 117.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 11/0000Z 29.5N 117.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brennan NNNN