Weather is unpreditictable. There's average temps, but that in no way can tell you what you can expect.
I remember my first transatlantic cruise (also in Apr.), and in my mind I expected some nice weather to begin, with more spotty weather and seas as we got further into the Altantic.
What we got the entire way across was temps in the 70s, and seas as calm as a bathtub, every day for 5 days crossing.
I hope you're as lucky, but there's no way to tell.