Tris's Book by Tamora Pierce

Earthquake damage leaves Winding Circle vulnerable to pirate attack, so everyone - including the young mages-in-training Tris, Briar, Daja, and Sandry - is working to strengthen the community's defenses. When Tris's cousin Aymery comes to visit, he advises the "weather witch" to return to the family that exiled her, but she doesn't wish to leave her friends to the treat without her.

As the onslaught begins. two things become terribly clear: The pirates have a powerful new weapon, and they have an accomplice within Winding Circle. But the attackers have failed to reckon with the fury of a young mage betrayed once too often and her very stubborn, very loyal friends...

This second book in the Circle of Magic series by Tamora Pierce picks up, literally, right where the first left off, and it keeps building momentum. Unlike the first in the series this one focuses on Tris, a 'weather witch'.

After the earthquake hit Winding Circle our four young Mages find themselves strangely connected, and it's through this connection that they must explore their powers to save their only true home from Pirates.