They'd probably last longer and get more powerful without landmasses to get in the way but they won't be permanent features. On an Earth-type planet tropical storms are a seasonal event and come local winter the energy to sustain those sort of storms is going to fade away.
And what do you mean by all ocean? Does that mean nothing above sea level at all, or just no continental landmasses but there are still islands of varying size? Because if there are islands, their size and placement is going to have effects on the wind patterns and currents which will probably be important.
It might not matter much to the people living in this world. Storms form around the tropics and go toward the poles, so whatever weather there is in the northern hemisphere will stay in the northern hemisphere. And if there is no landmass here, there is no reason to cross that ocean (following the equator will be just as fast, even if you're going to the other side of the world). Unless there is an expedition to find out whether there is something at the pole, or similar.
Worldbuilding is fun, writing is a chore
@Knightof Lsama Possibly a sizable island under the ice cap. Might have small islands in other areas, but nothing that would be more than a dot on a map.
There would likely be submarine features that would affect currents, though.
@Aetol It wouldn't have much effect on most of the inhabitants, but a vast, dangerous ocean might be a good place to hide something or someone.
I'm also not sure what kind of weather would exist apart from the tropical systems. I'm less familiar with winter weather at sea than on land.
Well, the lack of a continent creates a lower albedo (also because water surfaces do not create icecaps as readily as a continent), so your ocean would be warmer than, say, the Antarctic ocean. Ceteris paribus of course.
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman
I've been thinking about a new world where the northern hemisphere is all ocean, and trying to figure out what the weather would be like. In particular, what would tropical storm systems do. Would they form some sort of permanent super-storm, run their course and fade away, or something else?