Key West water temperature by month

Swimmable year-round.

Month by month

Month Typical Feels
January 72° perfect
February 75° perfect
March 78° perfect
April 80° bath-warm
May 85° bath-warm
June 87° bath-warm
July 89° bath-warm
August 89° bath-warm
September 88° bath-warm
October 83° bath-warm
November 78° perfect
December 74° perfect

The year at a glance

swimmable 60° 70° 80° 90° 100° 89° 72° JFMAMJJASOND January: typically 72° — perfect February: typically 75° — perfect March: typically 78° — perfect April: typically 80° — bath-warm May: typically 85° — bath-warm June: typically 87° — bath-warm July: typically 89° — bath-warm August: typically 89° — bath-warm September: typically 88° — bath-warm October: typically 83° — bath-warm November: typically 78° — perfect December: typically 74° — perfect

The water right now

Typically about 83° in October — bath-warm.

from the Key West harbor station, about 3 miles away

bath-warm

bath-warm 80° and up perfect 72–79° refreshing 65–71° brisk below 65° 83° typical for October

Smathers Beach water rarely leaves the swimmable range — the question is bath-warm or merely perfect.

Seaweed season

On Florida's southeast coast and the Keys, sargassum season runs from April through August, heaviest from June through July.

USF's bulletins treat the Keys and the southeast coast together, and in an ordinary year report them largely clear until late April or May. North of Cape Canaveral the bulletins say nothing either way, so neither do we.

  1. January: rare
  2. February: rare
  3. March: rare
  4. April: some seaweed
  5. May: some seaweed
  6. June: peak season
  7. July: peak season
  8. August: some seaweed
  9. September: rare
  10. October: rare
  11. November: rare
  12. December: rare

This is a pattern, not a forecast. The lab that watches this says plainly that predicting seaweed on an individual beach is difficult or impossible — whether it comes ashore depends on winds, tides and currents nobody can call ahead. The bulletins track how much is out there and look about a month on.

From the Sargassum Watch System, the Optical Oceanography Lab at the USF College of Marine Science. Read the current bulletin for this month's outlook.

About this reading

The Key West harbor station sits in the harbor; open-water surf can read a few degrees different.

Reading from the Key West harbor station, about 3 miles away.

Warm water says nothing about surf, rip currents, or bacteria — check local lifeguard flags and advisories.