Even if by definition it’s an island.
That, and its position so far south, impart Key West with a uniquely warm maritime climate, even by Florida standards.
The waters that surround it blunt it from diurnal heating and cooling of the peninsula and shield it from the continental creep of cold air from the north.
The result is as “evenly a warm climate” you’ll find in the Lower 48.
Key West escapes the brunt of those arctic blasts.
About as chilly as it gets in Key West is “cool,”
Which isn’t even as cold as its famous pie served up “chilled.”