000 WTPZ44 KNHC 200259 TCDEP4 HURRICANE OLAF DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192015 800 PM PDT MON OCT 19 2015 Olaf has maintained a small pinhole eye with a diameter of no more than 10 n mi. Satellite intensity estimates were a consensus T6.0/115 kt from TAFB, UW-CIMSS ADT, and the NHC AODT algorithm at 20/0000Z. However, since that time the eye has warmed a little and a ring of cloud tops colder than -75C has developed around the eye, so the intensity has been nudged slightly higher to 120 kt. The initial motion estimate is 275/09 kt. Olaf is expected to continue moving westward to west-northwestward along the southern periphery of a deep-layer ridge for the next 24 hours or so, and then turn northwestward toward a developing weakness in the ridge on days 2 and 3. By 96 and 120 hours, a series of fast-moving shortwave troughs embedded in the mid-latitude westerlies is expected to gradually create a break in the mid-level ridge between 145W-150W longitude, allowing Olaf to move northward and remain well east of the Hawaiian Islands. The latest NHC model guidance is in much better agreement on this developing scenario compared to 24 hours ago, and even the UKMET model has shifted eastward and is now on the east side of the guidance envelope at 96 and 120 hours. The official forecast track lies a little to the left of the previous advisory track, and follows the consensus models TVCE and GFEX. There has been slight flattening of the CDO in the northwestern quadrant caused by some light to moderate northwesterly mid-level shear as noted in recent UW-CIMSS shear analyses, which could inhibit intensification some in the short term. However, some additional strengthening is still likely over the next day or so since Olaf will be affected by deep-layer shear of 5 kt or less and be over 29C SSTs. As mentioned in the previous advisory, there could be fluctuations in intensity due to eyewall replacement cycles that can not be forecast more than a few hours in advance. The NHC intensity forecast continues to indicate a peak of 125 kt at 12-36 hours, followed by a slow decay by 48-72 as Olaf begins to move slowly over slightly cooler SSTs and into a moderate southwesterly vertical wind shear regime. The official intensity forecast remains above the intensity consensus, but below the LGEM and SHIPS forecasts, which bring Olaf to just below category 5 strength in 36-48 hours. With Olaf moving into the central North Pacific basin within the next six hours or so, this will be the last advisory from NHC. Future information on Olaf can be found in advisories issued by the Central Pacific Hurricane Center beginning at 1100 PM HST (0900Z). FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 10.1N 139.5W 120 KT 140 MPH 12H 20/1200Z 10.4N 140.8W 125 KT 145 MPH 24H 21/0000Z 11.1N 142.4W 125 KT 145 MPH 36H 21/1200Z 12.0N 143.8W 125 KT 145 MPH 48H 22/0000Z 13.0N 145.0W 120 KT 140 MPH 72H 23/0000Z 15.4N 146.6W 105 KT 120 MPH 96H 24/0000Z 18.3N 146.9W 95 KT 110 MPH 120H 25/0000Z 20.9N 146.4W 80 KT 90 MPH $$ Forecaster Stewart