Checking out two cruises ..one from L.A. the other from S.F. mid to end of September..both go along the Mexican coast as far as Cabo amd then thourh the Panama Canal... What would the seas be like... rough and is it their stormy and rainy season?
The waters off the Pacific Coast between either Los Angeles or San Francisco and the Panama Canal obviously are much more open than the Caribbean. Nonetheless, the new cruise ships are big enough so normal waves don't bother them. If there are swells (very long waves that are less obvious, but possible at any time of year), the swells may produce motion that's noticeable but not objectionable for most people. A hurricane in the vicinity obviously would make the ocean very rough, but hurricanes visit that area much less frequently than the Caribbean. Also, you can be sure that a cruise ship will do whatever it can to avoid a hurricane.
The full transit of the Panama Canal is a nice itinerary, in either direction. Have a great cruise!