The traditional cruising season in
Central America (either coast) is approximately November to approximately June. The summer/fall is
hurricane season, although close to the Equator is generally considered safe (with the demarcation being somewhere between 5 and 10 degrees of latitude depending on location and who you ask).
So, if you have to do it in one season you leave the
PNW late summer/early fall (before
winter weather sets in) to arrive Socal late October. November to ??? down the coast to
Panama. Then it depends on how/when you want to be in the
Caribbean.
Christmas winds on the
Caribbean side of
Panama can be quite nasty. Later in the season is easier but allows less time before hurricanes.
That's the synopsis, lots of variables in actual preferred destinations and activities.