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ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM CCA Hurricane Olivia Discussion Number 27...Corrected NWS National Hurricane Center Miami FL EP172018 200 AM PDT Fri Sep 07 2018 Corrected second paragraph about previous category-4 strength Olivia's overall cloud structure in infrared and passive microwave satellite imagery has changed little since the previous advisory, except that the cloud tops have warmed significantly around the well-defined, 20-nmi-diameter eye. As a result, both subjective and objective intensity estimates have decreased markedly since Olivia briefly gained category-4 strength on the previous advisory. However, microwave imagery indicates that Olivia has evolved into an annular hurricane, with only inner-core convection present and no banding features. As a result, the initial intensity only been decreased to 110 kt, which is a typical slower rate of weakening for annular hurricanes. The initial motion estimate is 290/13 kt. There is no significant change to the previous forecast track or reasoning. Olivia is expected to continue moving west-northwestward for the next 24-36 hours, followed by a westward motion as the hurricane nudges up against a strong deep-layer subtropical ridge that stretches from Mexico and the southwestern U.S. westward into the central Pacific. The new NHC forecast track is essentially just an extension of the previous advisory track and is down the middle of the very tightly packed model guidance, closest to the speed of the TVCN consensus track model. As mentioned in the previous advisory discussion, the current annular pattern indicates that Hurricane Olivia should weaken more slowly than indicated by guidance, even though the cyclone will be moving over slightly cooler SSTS of about 25.5 deg C by 36 h. The low shear environment that the cyclone will be embedded in should help to offset some of the negative effects of the cooler waters. After that time, Olivia will move back over slightly warmer waters and remain in a low shear environment, so a little leveling off in the weakening process is forecast until 96 hours. On day 5, however, southwesterly vertical wind shear of 15-20 kt is expected to induce more significant weakening at that time. The official intensity forecast is similar to, but higher than, the consensus models, and more closely follows a blend of the dynamical models HWRF and HMON. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 19.6N 131.2W 110 KT 125 MPH 12H 07/1800Z 20.2N 133.1W 100 KT 115 MPH 24H 08/0600Z 20.9N 135.7W 90 KT 105 MPH 36H 08/1800Z 21.4N 138.3W 80 KT 90 MPH 48H 09/0600Z 21.7N 140.9W 75 KT 85 MPH 72H 10/0600Z 22.0N 145.6W 70 KT 80 MPH 96H 11/0600Z 21.9N 149.6W 65 KT 75 MPH 120H 12/0600Z 21.0N 153.5W 55 KT 65 MPH $$ Forecaster Stewart NNNN