Key West Weather Guide: Year-Round Tropical Climate Explained

Key West is defined by a tropical savanna climate, a rare classification in the United States that keeps the island warm year-round with distinct wet and dry cycles. Located closer to the equator than any other city in the contiguous U.S., its weather is heavily moderated by the surrounding waters of the Gulf of Mexico and the Atlantic Ocean, resulting in a "maritime" effect where temperatures rarely fluctuate more than 10-15 degrees between seasons.

The Daily Rhythm

In Key West, the weather follows a predictable diurnal pattern. Mornings are often clear and "saturated" with high relative humidity, which begins to dip as the sun climbs. The cooling sea breeze is the island’s natural air conditioner; as the land heats up, air rises and pulls in cooler air from the surrounding ocean. This breeze is most prominent in the early afternoon, offering relief even on the hottest days. Locals often time their outdoor activity for these breezy windows or late afternoons when the angle of the sun softens.

Seasonal Trends

Rather than four traditional seasons, Key West experiences two primary phases: the Dry Season and the Wet Season.

• The Dry Season (November – April): This is characterized by nearly constant sunshine and low humidity. Cold fronts from the north occasionally reach the island, but they are significantly modified by the warm Florida Straits. By the time they reach Key West, they typically manifest as crisp, 70-degree days and "chilly" 60-degree nights.
• The Wet Season (May – October): Humidity levels soar, and the atmosphere becomes "heavier." This season is defined by afternoon thunderstorms. Unlike the mainland, where rain can linger, Key West’s showers are often intense but brief, frequently lasting less than 30 minutes before the sky returns to a brilliant blue.

Unique Weather Phenomena

• Waterspouts: These spinning columns of air and mist are common in the summer months. While they look like tornadoes over water, they are usually less intense and are a fascination for storm-watchers.
• Trade Winds: Historically, the "Easterlies" or trade winds guided sailors and continue to provide a steady breeze that keeps the island from feeling as stifling as the Florida mainland.
• Hurricane Context: While hurricane season runs from June to November, direct hits on Key West are statistically infrequent due to its small footprint. However, the island's low elevation makes it sensitive to storm surge, where even distant storms can push ocean water into the streets of Old Town.

Microclimates and Variations

Despite being only four miles long, Key West has subtle microclimates. The interior of the island (Old Town) can feel several degrees warmer than the Atlantic-facing beaches (like Smathers Beach), where the onshore wind provides constant circulation. Furthermore, Key West is often significantly drier than the Upper Keys or Miami; it is common for a storm to drench the mainland while Key West remains completely dry, a phenomenon locals call the "island effect."

What the Weather "Feels Like"

In Key West, the temperature on the thermometer is only half the story. The Dew Point is the ultimate measure of comfort.

• Winter: Dew points in the 50s or low 60s feel "crisp" and energetic.
• Summer: Dew points hitting 75°F or higher create an "oppressive" feel where the air feels thick. During these times, the weather is more about the "Heat Index" than the actual temperature. Even at 88°F, the high humidity can make it feel like 100°F.

Historical Context

Key West holds a remarkable meteorological record: it is the only city in the lower 48 states to never have recorded a frost or freeze. Since record-keeping began in 1871, the temperature has never officially dropped to 32°F. This consistent warmth has allowed tropical flora like the Royal Poinciana and Coconut Palm to thrive for generations, shaping the lush, jungle-like aesthetic of the island's residential lanes.