Just returned from a Panama Canal cruise on the Summit. The weather was perfect and HOT. In the 90's in Aruba, Costa Rica and Panama. The seas were very calm, but if you were going to do a full transit and then go on to Los Angeles, I would warn you of the very rough seas for the last two days of the cruise. But, I think the Galaxy only does a pass through the canal and then returns to the Caribbean.
Bring clothes for very HOT and HUMID weather.