We went in mid July 2005 and encountered high temps in the 70s on a couple of days, highs in the 50s a few days, a fair amount of wind, and sprinkles periodically. If you like to be out on the deck while the ship is moving, take a warm jacket; consider the ship is moving at 17 to 22 knots, which produces a 17 to 22 knot wind. Also factor in some natural wind combined with cool temps and it can be downright cold. Definitely pack a rain poncho; you may or may not use it.
All in all, Jim C. is right on the money when he calls it a crap shoot!