We did the Empress in October 2016...no real problems and overall pretty nice. Mostly pleasant sunny days with several showery days. Astoria had to be cancelled due to gale force winds and rain. Would have preferred June/July for longer days but, weren't able to travel until October.
Yes, there are times when fires and other events are more likely but, even in likely times, nothing can happen. Summer/fall tends to be "fire season" on the west coast but exactly when a fire starts can't be predicted. Like hurricanes and other natural events you just don't know at the time you book. This weeks weather can be dramatically different than next. Personally, I don't spend a lot of time trying to dodge future weather events.
Last August, we missed Hurricane Ida (Cat 4) in New Orleans by just a week. We were at the end of the "Mighty MIssissippi" on the Duchess and spending a couple of days in NOLA. Just the luck of the draw as the cruise was booked and paid for a year ahead of time.
You never know.