textproduct: Key West

KEY MESSAGES

- Moderate southerly breezes are expected across Florida Keys coastal waters.

- Heat indices may approach 108 to 110 degrees each afternoon for some Florida Keys island communities.

- Saharan Air Layer plumes will transit the area over the next several days, limiting rain and thunder chances.

DISCUSSION

Issued at 1124 AM EDT Sat Jul 18 2026 An upper-level composite analysis this morning reveals two deep layer mean anticyclones over the subtropics, one centered over the Atlantic south of Bermuda, and the other smaller system centered over the northwestern Gulf of America. A deepening cyclonic vortex was centered over the eastern Gulf of Mexico. This system was best defined in the middle and upper troposphere, with a weak trough at the surface. Geostationary satellite visible channel animations show numerous clusters and bands of deep cumulus convection rotating cyclonically about an ill-defined center. One persistent corridor of showers and thunderstorms along the southeastern periphery of this disorganized system was present over the western portions of the service area, extending roughly from 60 n mi south of Dry Tortugas National Park to near Marco Island. Much drier air was present to the east and southeast of this band of moisture convergence.

Data from the Key West morning radiosonde balloon indicated a moist and unstably stratified atmosphere with little convective inhibition. However, satellite products indicate a significant gradient of both total precipitable water and potential buoyancy across the service area from east to west, with richer moisture and greater instability to the west and drier, more stable conditions to the east and south.

Current air temperatures in most Keys island communities are in the upper 80s, with dewpoint temperatures in the mid 70s. Heat indices are generally 95-100F, with prevailing southerly breezes. It rained earlier in Marathon, and portions of North Key Largo are seeing rain at present.

FORECAST

The complex pattern remains in place across Florida and the eastern Gulf for the next few days. An upper level low will continue to slowly meander about the eastern Gulf sparking additional showers and thunderstorm coverage around it as it does so. The upper low has deepened with now closed off low pressure showing up at 850 mb and 700 mb. However, there is still no surface reflection. The National Hurricane Center (NHC) gives this system a 10% percent chance for tropical cyclone development over the next 48 hours and a 30% chance of tropical cyclone development over the next 7 days. Therefore, since the SE Gulf waters are the closest to the circulation, there remains a chance of showers and thunderstorms with a slight chance for the remainder of the Florida Keys and surrounding coastal waters. This upper level low is expected to lift northward as we head into early next week being replaced with ridging. Even with the ridging moving into place, moisture undulations will continue to propagate through the Keys resulting in slight chance of showers and thunderstorms. Outside of the rain chances, the dog days of summer are here with highs near 90 degrees and overnight lows in the lower 80s. Dew points are expected to remain in the mid to upper 70s resulting in heat values of 105 to 110 degrees. Therefore, make sure to take breaks and stay hydrated in the heat!

The Atlantic ridge will slowly gain more influence over the Keys over the coming days resulting in mainly southeast breezes. These breezes will largely peak in the evening and overnights and lull during the daytime hours.

MARINE

Issued at 1124 AM EDT Sat Jul 18 2026 No watches, warnings, or advisories are in effect for Florida Keys coastal waters. A trough of low pressure over the eastern Gulf of America will shift northward from this afternoon through Monday, with prevailing gentle to moderate south to southeasterly breezes across Florida Keys coastal waters. An Atlantic high pressure ridge will extend to the Florida Peninsula for the next several days. Gentle southeasterly breezes are expected to prevail across Keys coastal waters Monday night through Wednesday, with overnight surges and afternoon lulls.

AVIATION

Issued at 1124 AM EDT Sat Jul 10 2026 Through 19/12Z, prevailing VFR conditions are expected at both EYW and MTH. Although a sub-VFR episode from a transient rain shower is a possibility, probabilities are too low for inclusion in the TAFS.

KEY WATCHES/WARNINGS/ADVISORIES

FL...None. GM...None.