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Hurricane OLAF Forecast Discussion Number 17
2015-10-19 04:42:29| National Hurricane Center (East Pacific)
Issued at 800 PM PDT SUN OCT 18 2015 000 WTPZ44 KNHC 190242 TCDEP4 HURRICANE OLAF DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192015 800 PM PDT SUN OCT 18 2015 Olaf's inner-core convective pattern has improved significantly since the previous advisory. A cloud-filled eye about 15 n mi in diameter has become apparent in visible, infrared, and passive microwave satellite data since around 18/2300Z, and cloud tops have cooled to below -80C almost encircling the eye during the past hour. The initial intensity has been increased to 85 kt based on a blend of Dvorak satellite intensity estimates of T5.0/90 kt from TAFB and T4.5/77 kt from SAB. This intensity is supported by NHC AODT satellite intensity estimates of T4.8/85 kt and T5.2/95 kt using embedded-center and obscured-eye patterns, respectively. The initial motion estimate is 275/10 kt based on microwave and visible eye fixes. Other than a slight southward adjustment due to the recent eye positions, the previous forecast track and reasoning essentially remain unchanged. Olaf is expected to gradually round the southwestern and western portion of a deep-layer subtropical ridge, turning northward and slowing down considerably on days 4 and 5 as the hurricane moves into a weakness in the ridge. The westward shift in the guidance as mentioned in the previous discussion appears to have settled down on this latest cycle with the UKMET and the other models now having moved closer together. The new NHC track forecast has been adjusted slightly to the left of the previous advisory track due to the more southward initial position, and lies between the consensus models and the more westward UKMET solution. Although Olaf has made a sharp intensity comeback, the proximity of a pronounced dry slot that has worked its way completely around the small inner-core convective region of the hurricane precludes forecasting rapid intensification at this time. However, with the vertical shear expected to be near or below 5 kt for the next 72 hours while Olaf remains over 29C or greater SSTs, at least steady strengthening appears to be in order for the next 36 hours or so. Although the LGEM intensity guidance brings Olaf to category 4 strength (115-120 kt) in the 36-72 h period, the official forecast levels off the intensity at 110 kt due to the likelihood of one or more eyewall replacement cycles occurring during that time. By days 4 and 5, a gradual weakening trend is forecast to occur as Olaf moves into a region of much drier mid-level air with humidity values less than 50 percent, along with cold upwelling occurring beneath the cyclone due to the hurricane's expected slower forward speed of around 5 kt. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 9.7N 135.4W 85 KT 100 MPH 12H 19/1200Z 9.9N 136.8W 95 KT 110 MPH 24H 20/0000Z 10.3N 138.6W 105 KT 120 MPH 36H 20/1200Z 11.0N 140.2W 110 KT 125 MPH 48H 21/0000Z 11.9N 141.6W 110 KT 125 MPH 72H 22/0000Z 13.7N 144.1W 110 KT 125 MPH 96H 23/0000Z 16.1N 145.4W 100 KT 115 MPH 120H 24/0000Z 18.2N 145.4W 90 KT 105 MPH $$ Forecaster Stewart
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