I've cruised there many times in different months. The first 2 to 3 days are a little wavy, as well at the end of the cruise on the way home.
Weather is a crapshoot. You really never know. I've had seas smooth as silk and some seas that nearly tossed me from my bed. Same months different weather.
Had a great cruise either way because I loved being rocked to sleep at night.
That being said, the weather varies from day to day usually, so you won't have bad weather the entire cruise. (Of course, this can't be said as an absolute)