text: There are a broad number of things which could happen when a thunderstorm crosses water. If the water is cool, yes it could weaken a thunderstorm.\n\nBut more often than not, if it reaches a body of warm water it will strengthen. If you've ever been in Florida in the summer, you know about "pop-up" thunderstorms which form in the Gulf and Atlantic.  And if the conditions are right in tropical or semi-tropical waters, a thunderstorm could turn into a hurricane(which technically isn't a thunderstorm since it draws its energy from the heat of condensation and not from two layers of contrasting temperature air.