FXUS62 KKEY 181525 AFDKEY Area Forecast Discussion National Weather Service Key West FL 1125 AM EDT Sat Jul 18 2026 ...New DISCUSSION, MARINE, AVIATION, PREV DISCUSSION... .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. && .PREV DISCUSSION... Issued at 443 AM EDT Sat Jul 18 2026 CIMSS products shows a complex pattern across the Keys and much of Florida. The Keys remain in between two ridges with one over the Atlantic and the other one over the western Gulf. In between these is a trough that will continue to only slowly meander northward across the eastern Gulf and Florida over the coming days. At the surface, the ridge over the Atlantic is extending a little further west than in previous days, hence, increasing its influence across the area. Marine observation platforms surrounding the Island Chain are recording southeast to south breezes of near 10 knots as a result. KBYX radar is active tonight with isolated showers and thunderstorms throughout the Florida Keys coastal waters. The strongest activity has been across the SE Gulf waters to the east of L Tower. KBYX also continues to show a cyclonic spin to the reflectivity just off the Southwest Florida coastline or Sanibel Island area. Temperatures along the Island chain are in the lower to mid 80s and dew points are in the mid 70s. The cool spot this morning is Big Pine Key where the RAWS is recording a temperature of 76 degrees as of 238 am. .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. && $$ Public/Marine/Fire...Kasper Aviation/Nowcasts....Kasper Data Acquisition.....MJV Visit us on the web at weather.gov/key Follow us on Facebook and X at: www.facebook.com/nwskeywest www.x.com/nwskeywest