From our cruise Log...
Day 1 in Los Angeles 62.6F at noon, partly cloudy, moderate breeze
Day 2 at sea 63.5F at noon, partly cloudy, gentle breeze
Day 3 at sea 73.4F at noon, partly cloudy, gentle breeze
Day 4 Puerto Vallarta 80.6F at noon, mostly cloudy, moderate breeze
Day 5 Mazatlan 80.6F at noon, sunny with some cloud, variable breeze
Day 6 Cabo 73.4F at noon, sunny with some cloud, light breeze
Day 7 at sea 64.4F at noon, partly cloudy, fresh breeze
At sea days were chilly on deck with many folks trying to sun but actually huddling under towels. The trick is to get out of the wind! It was too cold to get much use out of the balcony on sea days unless you wore a sweater or light jacket...I did
!! I don't know about snorkelling but my guess is that it would have been be pretty chilly. The temperatures for touring in and around town were perfect!