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Hurricane Sergio Forecast Discussion Number 20
2018-10-04 10:51:09| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Thu Oct 04 2018 230 WTPZ41 KNHC 040851 TCDEP1 Hurricane Sergio Discussion Number 20 NWS National Hurricane Center Miami FL EP212018 200 AM PDT Thu Oct 04 2018 Sergio's intensity is estimated to have increased just a little more this morning, and it remains a powerful category 4 hurricane. Subjective Dvorak estimates are T6.5/127 kt from TAFB and T6.0/115 kt from SAB, and the initial intensity is raised to 120 kt, which is a blend of these numbers and very close to the latest objective ADT estimate. Sergio's maximum winds are expected to change little over the next 12-24 hours, and the hurricane's intensity could very well be modulated by difficult-to-forecast internal processes such as eyewall replacement cycles. After 48 hours, an increase in shear and gradually cooling sea surface temperatures should result in some weakening, especially when Sergio moves more slowly at the end of the forecast period and possibly upwells some cooler water from below. The updated NHC intensity forecast is nudged downward during the first 48 hours to follow the latest consensus aids, but no changes were made to the previous forecast beyond 48 hours. The hurricane's initial motion is northwestward, or 320/7 kt, with Sergio located along the southwestern periphery of a mid-level ridge extending westward from Mexico. This ridge is expected to build westward and connect to another mid-level ridge located near the central Pacific Ocean, forcing Sergio to turn westward, or even south of due west, between 36-72 hours. By days 4 and 5, a large trough near the west coast of the United States should have greater influence, causing Sergio to slow down and turn northward by the end of the forecast period. The track guidance is tightly clustered for much of the forecast period, although a notable southward shift among the guidance, especially from the ECMWF, required a bit of a southward shift in the official forecast as well. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 14.4N 118.8W 120 KT 140 MPH 12H 04/1800Z 15.1N 119.7W 120 KT 140 MPH 24H 05/0600Z 15.8N 121.0W 115 KT 130 MPH 36H 05/1800Z 16.0N 122.2W 105 KT 120 MPH 48H 06/0600Z 15.8N 123.5W 95 KT 110 MPH 72H 07/0600Z 15.5N 126.2W 90 KT 105 MPH 96H 08/0600Z 16.0N 128.5W 80 KT 90 MPH 120H 09/0600Z 17.5N 128.5W 75 KT 85 MPH $$ Forecaster Berg
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