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Hurricane Fernanda Forecast Discussion Number 18
2017-07-16 10:46:27| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Sun Jul 16 2017 000 WTPZ41 KNHC 160846 TCDEP1 Hurricane Fernanda Discussion Number 18 NWS National Hurricane Center Miami FL EP062017 200 AM PDT Sun Jul 16 2017 A 0235Z SSMI/S microwave overpass indicated that Fernanda was still undergoing an eyewall replacement cycle (ERC), with concentric eyewalls remaining at about 20 and 45 n mi diameters. Although the eye has once again cleared out and become warmer, the convective cloud tops surrounding the eye have not cooled much. However, the overall convective cloud pattern has improved and become more symmetric, and outer banding features have developed in the southeastern semicircle. Satellite intensity estimates are a consensus T6.0/115 kt from TAFB and SAB, and T6.2/122 kt from UW-CIMSS ADT. Therefore, the intensity has been increased slightly to 115 kt, making Fernanda once again a category 4 hurricane. The initial motion estimate is 285/10 kt. There is no significant change to the previous track forecast reasonings. Fernanda is forecast to be steered generally west-northwestward for the next 72 h by a large low-/mid-level ridge that spans the central and eastern Pacific Ocean, extending from north of the Hawaiian Islands eastward to the U.S. west coast. After that time, a broad upper-level trough currently located north of Hawaii is expected to weaken and lift out to the northeast, causing the ridge to build slightly southward and forcing Fernanda on a more westward track. The new NHC track forecast is similar to the previous advisory track, and lies close to the consensus model TVCN. Although Fernanda has about 24 hours or so remaining over warm-water and within a low vertical wind shear environment, there are already indications in SST data from Remote Sensing Systems that upwelling beneath the hurricane has begun. This cooler water, coupled with the ongoing ERC, makes the intensity forecast difficult in the near term. As a result, little change from the current intensity is forecast for the next 24 hours, although some intensity fluctuations could easily occur during that time. By 36 hours and beyond, steady weakening is forecast as Fernanda moves over sub-26C SSTs, and enters a hostile westerly wind shear regime by 96-120 hours. The official intensity forecast is similar to the previous one, and closely follows the consensus models ICON and IVCN. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 12.1N 126.2W 115 KT 130 MPH 12H 16/1800Z 12.6N 127.9W 115 KT 130 MPH 24H 17/0600Z 13.4N 130.1W 115 KT 130 MPH 36H 17/1800Z 14.2N 132.0W 105 KT 120 MPH 48H 18/0600Z 15.1N 133.5W 95 KT 110 MPH 72H 19/0600Z 16.6N 136.2W 70 KT 80 MPH 96H 20/0600Z 17.3N 139.4W 50 KT 60 MPH 120H 21/0600Z 17.6N 142.7W 35 KT 40 MPH $$ Forecaster Stewart
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