The safest approach right now is averaging. Each month buy some of your $'s and average it out. If the rate goes up, you buy as much as you can, if the rate goes down, buy the same set amount. It will average out in the end.
It is very hard to say what will happen and there are a number of factors that will affect it. All the major currencies are on a race to the bottom to improve their trading power and there is no way to predict it. If I had a gun to my head and had to say what I thought would happen, I'd say it's going to be between $1.45 and $1.55 for the rest of the year and when you think about the difference that actually makes, it's fairly negligible.