Nope. The storm in the IC was just another one of his spells. It has something to do with what Kristia said in conjunction with the standard vampire weakness of water.
EDIT: Also I could utilize the Grima Aspect of Robin again to really make this strategy work.
Why bring the ocean to her... ...when you can bring her to the ocean?
Gensokyo is back in Japan now right?
And remember the part where I said there was a map in Fire Emblem Awakening where the team in the game is up against something way to powerful for them and the strategy was to run like hell and then turn around and take care of the enemy after a certain event happens?