textproduct: Key West

KEY MESSAGES

- Very warm and humid conditions will continue across the Florida Keys, raising the risk for heat-related illnesses through the weekend. - Rain and thunder chances will be increasing starting tonight and peaking Sunday through Monday.

- Breezy conditions are possible by early next week.

DISCUSSION

Issued at 245 PM EDT Sat May 16 2026

It is sunny afternoon throughout the Keys with temperatures in the upper 80s to around 90, dewpoints in the lower to mid 70s and heat indices in the mid to upper 90s. East winds were steady 8 to 12 mph, and 8 to 13 knots along the reef and Gulfside. Interesting a persistent northeast component has maintained over the upper Keys and adjacent waters, not sure if there are relatively cooler waters near the reef vs. Florida Bay. It is taking longer for the seabreeze circulation to set the southeast winds for the time being. Otherwise cumulus has mixed out except for a couple lee convergence streets over the nearshore Gulf. Earlier mainly shallow convection in the distant Straits has also dissipated with the unfavorable flow in the lee of Cuba. GOES precipitable water estimates show a plume near 1.8 inches over our offshore Upper/Middle Straits near the Cay Sal Bank, which will available to tap tonight.

Guidance shows the possibility of a narrow stable layer above 700 mb mixing out with 700-500 mb lapse rates closer to the deep 850-700 mb rate of 5.8C/km - and while not stellar, noting steady >1K mixed CAPE and >2K over the (water) surface, increased shower and thunderstorm coverage with resultant outflow boundaries as a later focusing mechanism shows scattered/chance probability will be realized before sunrise Sunday. The initial veering through 10K feet is likely to become more uniform east-southeast in the lower troposphere after 12Z Sunday, and with flow under 15 knots, it seems the downdraft gusts supported by the remaining mid-level dry air will probably be localized. Still, whatever gets going before dawn will likely be advected west-northwest throughout the morning and midday in various Keys spots and the coastal waters, and receiving a few tenths of an inch on rain would be welcome.

MARINE

Issued at 245 PM EDT Sat May 16 2026 Currently, mainly east (northeast along the Upper Keys) winds were steady around 9 to 14 knots, with significant wave height now nearing 1.5 feet and 3 seconds at Satan Shoal. High pressure developing over the Southeast will take root across the western North Atlantic over the weekend. As a result, easterly winds will becoming moderate to fresh later tonight and Sunday, with peaks and lulls across the Florida Keys Sunday through at least Wednesday.

AVIATION

(18Z TAFS) Issued at 245 PM EDT Sat May 16 2026

VFR conditions are expected to prevail at EYW and MTH through tonight, with coverage of showers and a few thunderstorms increasing during the early morning hours Sunday. Vicinity showers were already added to the forecasts starting 17/08Z, with the possibilty of a TEMPO needed at either terminal later tonight. Surface winds are expected to remain east to east southeast, with speeds increasing slightly to a steadier 10-12 knots tonight, and closer to 15 knots Sunday evening.

PREVIOUS DISCUSSION

Issued at 446 AM EDT Sat May 16 2026

A high pressure cell moving into the Atlantic off the Carolinas is beginning to exert it's presence across the Florida Keys. This has resulted in winds clock around from the east and southeast and gradually increasing through the overnight. Meanwhile, moisture is slowly pushing back this morning in thanks to a southeast to south mean flow in the boundary layer. This has begun interacting with a lingering boundary out across the Straits of Florida where isolated showers and thunderstorms have developed over the past couple of hours.

As the high continues to build across the Atlantic, we expect winds to continue to strengthen through the day. Meanwhile, the low-level steering flow will initially becoming increasingly southerly. This flow is not a favorable wind direction for all day shower potential. We will see some showers this morning with the initial surge of moisture and instability but then quiet by the late morning and afternoon. The exception will be the Upper Keys, where winds will be more southeasterly and more favorable to keep scattered showers and isolated thunderstorms going at times.

As the high slides further east, the steering flow will become southeast allowing for better moisture transport and increase our rain chances overnight through Sunday. The high's position by Sunday night through Monday night will allow breezes to peak and we can expect a brief period of breezy conditions. This will also aid in mass/moisture convergence and rain chances look to peak Sunday night into Monday. Thereafter, the high will continue to slide further east out across the Atlantic and the pressure gradient will relax some. In addition, pockets of drier air will pivot through at times, leading to a generally drying trend for the second half of next week.

No air mass changes expected. Daily high temperatures will range from 85 to 90 degrees and could be a couple degrees warmer late in the week. Dew points will hold in the mid 70s, the combination of which will result in heat index values hovering around 100 degrees during the peak daytime heating.

PRELIMINARY POINT TEMPS/POPS

Key West 80 91 81 91 / 40 40 40 30 Marathon 80 87 81 87 / 40 50 40 40

KEY WATCHES/WARNINGS/ADVISORIES

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