579 WTPZ42 KNHC 061437 TCDEP2 Hurricane Olivia Discussion Number 24 NWS National Hurricane Center Miami FL EP172018 800 AM PDT Thu Sep 06 2018 Satellite imagery indicates that Olivia has a well-defined 20 n mi wide eye, although the eye is not quite as distinct as it was at the time of the previous special advisory. The eye is inside of a central dense overcast with eyewall cloud tops as cold as -80C. Satellite intensity estimates are currently in the 100-115 kt range. Based on these, the initial intensity is set at 105 kt, and it is possible that this is a little conservative. The hurricane is now in a light vertical shear environment and is showing good cirrus outflow in the southwestern semicircle. The intensity guidance has been consistent in saying that Olivia should weaken due to a combination of decreasing sea surface temperatures along the forecast track and entrainment of dry air. The hurricane has not yet followed the guidance, and the current structure and convective trends suggest that this round of intensification may not be finished. After 12 h, Olivia should move north of the 26C isotherm, and the cyclone should mostly traverse sea-surface temperatures of 25-26C for the remainder of the forecast period. This development should start a weakening trend. The new intensity forecast allows for 12 h of additional strengthening, followed by a gradual weakening that follows the overall trend of the intensity guidance. However, the new forecast lies at the upper edge of the guidance, and thus most of the forecast intensities are higher than those in both the previous special and regular advisories. Water vapor imagery shows a large deep-layer ridge to the north of Olivia, and the large-scale models forecast the western end of the ridge to build westward during the next several days. This pattern should steer the cyclone west-northwestward for the next 48 h or so, followed by a westward motion from 72-120 h. The track guidance is in good agreement with this scenario, and the guidance is more tightly clustered than it was 24 h ago. The new forecast track is similar to the previous track through 48 h, then it is nudged a little to the south of the previous track from 72-120 h. The new track lies close to the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 18.4N 127.2W 105 KT 120 MPH 12H 07/0000Z 18.9N 129.2W 110 KT 125 MPH 24H 07/1200Z 19.8N 131.8W 100 KT 115 MPH 36H 08/0000Z 20.5N 134.4W 90 KT 105 MPH 48H 08/1200Z 21.2N 137.0W 80 KT 90 MPH 72H 09/1200Z 21.5N 142.0W 70 KT 80 MPH 96H 10/1200Z 21.5N 146.5W 65 KT 75 MPH 120H 11/1200Z 21.5N 150.5W 60 KT 70 MPH $$ Forecaster Beven