User blog comment:SayuriDarling/The Mark of Athena Official Discussion/@comment-4902593-20121210091237/@comment-3146930-20121210105730

When it comes to storms with Zeus and Poseidon, it very much depends on the type of storm. Poseidon for example is known for creating storms at sea, which of course includes hurricanes, explaining why Percy himself has the ability to make small ones. Zeus on the other hand is known for making thunderstorms, as in lightning and rain. When they made the storm, they were on the edge of the ocean, meaning they were both within their father's territories and because both of their fathers can make storms, the one they made together was especially powerful.