In reality, you can catch a norovirus any time of the year because when it's summer here it's winter in Australia and somebody can hop on a plane and spread it just about anywhere when they arrive. But since it's spread primarily from hand-to-mouth it can tend to hang around more when people spend a lot of time inside. That's why you hear about noroviruses in nursing homes, schools and cruise ships. These are places that a lot of people gather inside - all touching surfaces that can be contaminated.
Out in the general population if you don't have kids and don't go to schools and nursing homes without washing your hands after you've been there then it's almost impossible to catch a norovirus. If you do have kids and you're in the room nearby them when they vomit then you're at risk. But if you're not, then all you have to do is wash your hands before putting your fingers in your mouth and you'll be fine.
So what about cruise ships? Emetophobics are notoriously terrified of them because on slow news days reporters tell stories about norovirus on a ship. Here's the thing: cruise ships have 3,000+ people on them. That's more people than the entire population of my small town growing up. Every winter somebody got an illness in my town. And every winter somebody gets an illness on a cruise ship too. But that doesn't mean everyone on the ship catches it. My sister works as a theatre production manager aboard Royal Caribbean's Brilliance of the Seas. According to her the cruiseline is super-paranoid about noroviruses. So much so that every crew member, no matter what their job, is called out to bleach the hell out of every surface if ever someone on the ship gets sick. And they're confined to their rooms for 72 hours.
So cruise away! Cruises offer great fun, great food, and a wonderful and inexpensive way to see the world.