You think moving a city is expensive? Try replacing the whole damn thing after a Category 6 hurricane wipes it off the beach.
But actually, it's not that expensive if you simply encourage people to leave naturally. Start soon enough and you can clear out the vast majority before disaster strikes. They might move far away, but often, they'll just settle a bit farther away from whatever's bothering them. The easiest way to move a city is just to stop developing on the danger side (mostly seaward in this case) and build up the safer side (inland in this case). If your problem is that the area closest to the water keeps getting drowned by sunny day floods, all you have to do is scooch high enough to get above the new waterline.
Wait for a direct hit, though, and then you're really fucked.