Summer is the best time for transit of the
West Coast. It's the sail down from
Seattle to Cape Mendocino that is the controlling factor.
Winter storm lows blow through on a 4-10 day spacing and you don't want to get caught out by the leading edge where winds are southerly. Actually you just don't want to get caught out in one of those lows anywhere. If you need to go in the
winter, pick your window carefully and be prepared to duck into any harbor well before the front arrival if need be. The harbor entrances are mostly river bars and close out in storm conditions.
Course depends on position of the high. If it's north, you can turn west about SF and rhumb line to Hilo. If the high is south, may have to go as far south as San Diego's latitude before heading straight for the islands. You don't need to head due south but more south than west until you get around the bottom of the high. IIRC, the high is more north in the winter and south in the summer so you can make your turn sooner in the winter than summer. Have sailed in the summer and did a rhumbline from SF DDW for most of the sail so position of the high varies a lot.
There are hurricanes to watch out for in the summer but they are easily avoided. Storms almost always stay between 10 and 20 degrees north until nearing Hawaii. If there is a storm passing through, hang out well north till it's passed. Seems in El Nino years, like this past summer, the storms take a more northerly course above the Big Island and below in La Nina years. Usually there is longish spacing between the storms and not all that many of them but, once again, in El Nino years things may not be so settled. Last summer had a couple of storms that were only days apart. Usually the storms are greatly diminished by the time they reach the islands. The really destructive storms seem to pass south of the islands building strength in the warmer waters and then right turning to nail
Kauai.