We have done several transatlantics (have 2 more booked) in various months and love the sea days. There is simply no predicting the weather on the Atlantic and it really does not matter what month you cross. We have had crossing that were as smooth as glass the entire way, and than this past April we had a major storm follow us across and give us 30 foot + seas for 3 straight days. The Captain finally changed course and managed to get out of a very major storm. In August, you run the risk of huricanes (the ones that come up from the Caribbean eventually make their way into the Atlantic, but keep in mind that when you are traveling west you are running into the weather which means you will generally get through any bad weather faster than the east bound crossings. Bottom line is that its like playing craps.