864 WTPZ42 KNHC 080852 TCDEP2 Hurricane Olivia Discussion Number 31 NWS National Hurricane Center Miami FL EP172018 200 AM PDT Sat Sep 08 2018 The satellite presentation of Olivia has continued to degrade overnight with the surrounding ring of deep convection warming and the eye becoming less distinct. Dvorak T-numbers have decreased and a blend of current intensity (CI) numbers from TAFB and SAB, and ADT and SATCON estimates from UW/CIMSS yields an initial wind speed of 80 kt. Although the vertical wind shear is expected to remain low over Olivia, the hurricane will be moving over marginal sea surface temperatures of 25-26C, and into a dry mid-level environment. These factors are expected to cause gradual weakening over the next 24 hours. After that time, slightly warmer SSTs along the forecast track should slow or halt the weakening process, and little change in strength is expected between 24 and 72 hours. Increasing southwesterly shear by day 3 is likely to result in additional weakening later in the forecast period. The NHC intensity forecast is similar to the previous advisory and is between the HFIP corrected consensus model and the IVCN consensus aid. Olivia is moving west-northwestward or 285/13 kt. A strong deep-layer ridge that is building westward across the central Pacific should steer Olivia generally westward over the next 2-3 days. After that time, most of the track guidance takes Olivia west-southwestward as it comes under the influence of the northeasterly trade wind flow. Although the track models are fairly unanimous in taking Olivia west-southwestward, there is large cross-track spread in the guidance at 72 hours and beyond. The HWRF and ECMWF are along the northern side of the guidance envelope while the GFS and UKMET bracket the southern side. Given the large amount of spread, the official forecast is again near the TVCN and HFIP consensus models at 72-120 h. On the forecast track, Olivia is expected to cross into the central Pacific basin later today and approach the Hawaiian Islands early next week. KEY MESSAGES 1. Olivia is forecast to approach the main Hawaiian Islands from the east early next week, but it is too soon to determine the exact location and magnitude of any impacts. Interests in Hawaii should monitor the progress of Olivia this weekend and use this time to enact your hurricane action plan. 2. Do not focus on the exact track or intensity forecast, or any specific landfall location, as errors can be large at extended time ranges. Tropical storm or hurricane conditions could be felt anywhere in the islands as significant impacts could extend well away from the center. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 21.2N 136.6W 80 KT 90 MPH 12H 08/1800Z 21.5N 138.7W 70 KT 80 MPH 24H 09/0600Z 21.7N 141.5W 65 KT 75 MPH 36H 09/1800Z 21.8N 144.0W 65 KT 75 MPH 48H 10/0600Z 21.8N 146.2W 65 KT 75 MPH 72H 11/0600Z 21.5N 150.0W 65 KT 75 MPH 96H 12/0600Z 20.5N 154.0W 55 KT 65 MPH 120H 13/0600Z 19.2N 159.0W 45 KT 50 MPH $$ Forecaster Brown