It just occurred to me that an iceberg placed in front of a hurricane could take the energy out of it. I just did a quick google, and came up with this guy, who thought it up ten years ago, but it’s not quantified in any way.

I don’t know how sensitive storms are to ocean surface temps, so you’d have to figure out how much you needed to lower the temperature, and over how wide an area, to see if it was in any way feasible. But I’d have to think that an iceberg in the tropics could do some pretty good cooling over a pretty broad area. Of course, getting it into position quickly could be a challenge. And around here, and in the Bahamas, the water is so shallow it would probably run aground.