Which way? UK/US or US/UK?
Generally if your starting from the UK then if its March/April time it can be a little rough/chilly till you hit the Canaries then from there on should get warmer everyday! all depends on where you are starting from and going to!!
Remember on the UK>US route you gain an hour every day, whereas you lose an hour on the US>UK route.
And remember to get a balcony on starboard side of the ship for an US>UK crossing, and port side for a UK>US crossing to maximise the sunshine.
The weather in the Atlantic is in "the lap of the gods" had some wonderful and some horrendous crossings the best being on the QN2. The worst on the Artemis last year, when the bulk head was damaged in a storm and the seas were raging above A deck.... adds to the adventure