A typhoon has come up unexpectedly. Ships of the targeted fleet received a random amount of damage between 10-30%.

This card is way too powerful, especially considering that there is a rare card like it that already exist called Fire Ship. You sink one of your own ships causing 50% damage to a random ship in target fleet.

Aye, I have my doubts on this one too, though the idea is good : even a 10% damage over a fleet will reduce its fighting strength by considerably more than 10%, 30% would reduce it to a miserable level with average sotls now vulnerable to a decent frigate. So, as Roi says, its far to powerful for such a 'single cast' card : that's maybe the issue, we already have Kraken, Fireships and Worms : fitting this new card in and keeping its effect and cost proportionate doesnt seem to be practical.

If its uber powerful, make it cost a stupid amount of turns.... for example 100 turns per card, making the target fleet invulnerable to Call the Kraken, Fireship, and Swarm of Worms