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Hurricane OLAF Forecast Discussion Number 14
2015-10-18 10:51:47| National Hurricane Center (East Pacific)
Issued at 200 AM PDT SUN OCT 18 2015 000 WTPZ44 KNHC 180851 TCDEP4 HURRICANE OLAF DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192015 200 AM PDT SUN OCT 18 2015 Olaf has intensified overnight. Satellite images show that convection has deepened with a sizable area of -90C cloud tops near the center, along with an eye occasionally appearing on the night-visible channel. Microwave data also show that the eye has become better defined, and the feature has even become more distinct in the lower resolution AMSU data. With the appearance of the eye in conventional satellite data and the increase in convection near the center, the initial wind speed is set to 65 kt, near the Dvorak estimate from SAB. It is also worth noting that ASCAT data show that Olaf has also grown in size significantly from yesterday, and this is reflected in the larger initial and forecast wind radii. Olaf should continue to intensify during the next couple of days with favorable environmental conditions of low shear, warm water and high mid-level moisture in the forecast. Rapid intensification is a distinct possibility, with the SHIPS-RI index showing about a 40 percent chance of a 30-kt increase in the next 24 hours. The intensity forecast will bring Olaf up to major hurricane strength in 36 hours, in line with the highest guidance from the LGEM model and the Florida State Superensemble. In a few days, some southerly shear and dry air entrainment is possible, which could lead to Olaf beginning a weakening trend. Little change was made to the long range intensity forecast, close to a blend of the previous NHC prediction and the intensity consensus. ASCAT and satellite data were very helpful in determining an initial motion of 275/8. A motion to the west and then west- northwest is expected for the next two days or so while the cyclone moves on the south side of the subtropical ridge. After that time, a mid- to upper-level trough passing north of the Hawaiian Islands is forecast to cause a break in the ridge, allowing Olaf to turn northwestward by 96 hours and northward by 120 hours. Although guidance is in general agreement on the large-scale pattern, the timing of the northward turn is in some question, especially since Olaf has been struggling to gain latitude. Overall, the guidance has generally been showing a later turn, with the ECMWF/UKMET models having a weaker trough and less of a ridge breakdown. The NHC track forecast is shifted west toward the latest consensus aids, although it still lies east of the model consensus. At 9.4N, Olaf is the lowest-latitude hurricane formation in the eastern Pacific dataset. Reliable records in the basin go back to about 1971. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 9.4N 131.9W 65 KT 75 MPH 12H 18/1800Z 9.6N 133.2W 75 KT 85 MPH 24H 19/0600Z 10.0N 135.1W 90 KT 105 MPH 36H 19/1800Z 10.6N 136.9W 100 KT 115 MPH 48H 20/0600Z 11.3N 138.6W 110 KT 125 MPH 72H 21/0600Z 13.3N 141.7W 105 KT 120 MPH 96H 22/0600Z 15.0N 143.5W 95 KT 110 MPH 120H 23/0600Z 17.5N 143.5W 80 KT 90 MPH $$ Forecaster Blake
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