Can I Swim in the Monterey Bay, Santa Cruz in the Winter?
The reality is the Monterey Bay is cold all year round. I can't recall a time I've been comfortable ever swimming there without a wetsuit. Of course, people do but it would never be warm enough to be "wetsuit illegal" for a triathlon (76°F). But the other truth is, unlike many lakes around the country, is that the temperature of the water doesn't change THAT much between seasons. It's just always cold.
From surf-forcast.com "Santa Cruz Harbour water temperatures peak in the range 14 to 17°C (57 to 63°F) on around the 23rd of September and are at their lowest on about the 7th of April, in the range 10 to 14°C (50 to 57°F)." But as you can see on the chart the average only oscillates between 54-59°F, a pretty narrow range. So if you swim there in the summer months you should be fine in the winter.
How to be comfortable at any time of year swimming in Santa Cruz? Cover up with a wetsuit! People experience the cold differently, largely I've observed, from differences in body composition but there's undoubtably a mental aspect in play too. Some people are just more motivated not to wear a wetsuit. I'm not one of them. I also think it can be dangerous, especially with prolonged efforts and exposures, to swim without protection from the cold.
Blue70 make a great thermal wetsuit that has a furry, wool-like zirconium liner. It's rated to a minimum temperature of 48°F, not sure exactly how they came up with that rating, but the coldest the Monterey Bay gets is 50°F. I have tested the Thermal Reaction and anecdotally feel like it is warmer, and still just as flexible, as the other wetsuits in their range.
But perhaps even more important than the style of wetsuit, is a thermal (neoprene) cap which you wear under your regular latex or silicon cap. Pull it right down to the tops of your eyes for max protection. Add some swim socks and gloves and you've maximized your protection and will still not be too weighed down to get a good swim in. You'll still likely have face freeze for the first 5-10 mins but once your warmed up inside your suit this should dissipate and you'll be able to enjoy your Santa Cruz swim at any time of year.