Unless the new ice-age has begun in the Americas without us noticing such, it is fairly warm off of the North American eastern coast in late-April and early-May as you travel the north Atlantic crossing route. To make it even warmer, your route is nearly a southern crossing, as it heard towards Gibraltar. No one on board will have a parka or thermal underwear. Take a jumper/sweater for early mornings, and some light rain gear (not a brolly). This is not a cold-weather crossing: it is a mild-weather to hot-weather crossing. My wife wears a sports coat for deck outings and has never needed more on trans-Atlantic northern corssings at this time of year.