The last boy and girl in the world / Siobhan Vivian.

Enhanced descriptions from Syndetics:

From the critically acclaimed author of The List comes a stunning new novel about a girl who must say goodbye to everything she knows after a storm wreaks havoc on her hometown.

What if your town was sliding underwater and everyone was ordered to pack up and leave? How would you and your friends spend your last days together?

While the adults plan for the future, box up their possessions, and find new places to live, Keeley Hewitt and her friends decide to go out with a bang. There are parties in abandoned houses. Canoe races down Main Street. The goal is to make the most of every minute they still have together.

And for Keeley, that means taking one last shot at the boy she's loved forever.

There's a weird sort of bravery that comes from knowing there's nothing left to lose. You might do things you normally wouldn't. Or say things you shouldn't. The reward almost always outweighs the risk.

Almost.

It's the end of Aberdeen, but the beginning of Keeley's first love story. It just might not turn out the way she thought. Because it's not always clear what's worth fighting for and what you should let become a memory.