Earthworm Gods II: Deluge by Brian Keene

In Brian Keene's cult-classic, Earthworm Gods, global super-storms decimated the planet, eradicating most of mankind. In the midst of this ecological nightmare, the remnants of humanity fought against a supernatural menace in a war that ranged from the rooftops of submerged cities to the mountaintop islands jutting from the sea.

Now, the battle continues. As the last of the mountains sink beneath the waves, the survivors make a desperate final stand. But the worms aren't the only enemy they face. The world-wide ocean is host to a legion of monsters, each more terrifying than the last, and mankind is vastly outnumbered by these new horrors. Adrift at sea and struggling to stay alive, the surviving members of the human race cling to a thin strand of hope. But their possible salvation may be worse than their looming extinction...

Earthworm Gods II: Deluge - This is how the world ends.