Yep, that’s certainly the case on the north side in the winter (to the point where it’s not safe to swim in many places due to the high surf, and/or the low visibility in the ocean there due to more rain in the rivers and the amount of churn coming from on shore winds there on the coast. The south side of Kauai has far, far less rain in the winter than the north and many more options for good swimming and snorkeling then.
My family’s been going to Kauai for close to 50 years (since I was a toddler), and we always stay around Poipu when we’re there in the winter months.
The north side is where all the stunning Jurassic Park coastal landscapes are, but you can always do a great day trip up there if you’re staying on the south side, by picking your weather window for it on a day by day basis while you’re there.