This is "The Edge of the Sea" by Algis Budrys
Overseas Highway, two narrow white lanes on yellowed old-concrete piers, lay close to the shallow water, passed over the little
key, and went on.
All afternoon, the sea had been rising. Long, greasy-faced green sweDs
came in from the Atlantic Ocean and broke on the sharp rocks with a
sudden upsurge of surf. At mid-day, the water had been far down among
the coral heads. But now it was in the tumbled limestone blocks and
concrete prisms that had been dumped there to build up the key. In a
little while it would be washing its spume over the highway itself, and it
might well go farther, with increasing wind.
It was dark with twilight, and darker with clouds thick as oil smoke
covering the sun over the Gulf of Mexico. The Gulf was stirring, too,
and bayous were flooding in Louisiana. But it was over the Atlantic that
the hurricane was spinning. It was the broad, deep, deadly ocean that the
tide and wind were pushing down through the gloom onto the side of the
key where Dan Henry was struggling grimly, his massive back and shoulders naked and running with spray.
So your memory of both the title and the protagonist's name seem to be pretty intact! In the future, if you do know the title, The Internet Speculative Fiction Database is a great resource to find the author of a science fiction story when you know the title, just search on what you know and, in the case of duplicates, try to narrow down by year.