We weren't sure about taking a snorkel/catamaran tour in the "winter"--but let me say this now--don't hesitate. Do it!!
While in Kauai, the mornings were typically calmer, so we decided to do the morning Catamaran/Snorkel tour on the Lucky Lady. Captain Greg, and the whole crew (CJ, Nate and Kai) were AMAZING! They were all very knowledgeable about the island, wildlife, the sea...we couldn't come up with a question to stump them. What's more, they were all super attentive and working hard to make sure everyone had a good trip. They helped us spot wildlife (of which there was a TON!), made sure everyone had snacks/drinks, tended to the seasick passengers. They were also genuinely fun and pleasant people to be around for the day. I can't say enough good things about them all. Without a doubt, take a trip with this outfit, you won't regret it!
P.S. We booked on the Northside (Hanalei) through their "info booth", though in the winter, the trip runs out of the south side (Port Allen). The gal at the info booth was great. She helped us find a tour (even though we booked kind of last minute) and helped us figure out which day was best to sail. That said, you can also book direct through Kauai Sea Tours website for $10 cheaper. I didn't mind paying the extra bit for the help though.