textproduct: Key West

KEY MESSAGES

- Light to gentle variable breezes will assume a southeasterly direction overnight.

- Heat will be the primary weather concern through the rest of the week as indices may approach 108 to 110 degrees in the afternoon for portions of the island chain.

- Rounds of Saharan Air Layer will continue to stream across our area this week into next week, keeping rain and thunder chances slight at best.

DISCUSSION

Issued at 903 PM EDT Fri Jul 17 2026 While we typically address our local weather conditions in the evening update, we can't look past the elephant in the room. The low spinning over the southeastern Gulf sticks out like a sore thumb on virtually all forms of data ingestion this evening. Some of the tallest showers are being detected on our KBYX radar as satellite imagery shows the low sloppily spinning outside of our marine zones. CIMSS mean layer imagery shows the heart of the low is mostly "stacked", meaning we can see it reflected in both the upper, middle, and lower levels, and seems to slowly be tracking deeper into the southeastern Gulf. Closer to home, a col region has set up, and has helped to provide a few boundaries for showers and thunderstorms. We don't have many in situ surface observations to clearly define the wind field, but lower level tropospheric maps via SPC from this evening seem to reflect the light and variable wind pattern associated with the center of a col across our area. Convergence along the southwest to northeast axis of the col has resulted in some showers and thunderstorms this evening.

The 00Z KKEY sounding from this evening wasn't impressive with respect to supporting active weather. While there was 1700 J/kg of ML CAPE calculated, there was also a modest amount of inhibition around 850 mb. The moisture profile also isn't overtly impressive with 1.48" of PWAT calculated, just one hundredth of an inch higher than the tenth percentile. All of this is to say that a few showers and thunderstorms could occur overnight, particularly over our western marine zones where we can still see some convergence boundaries. The inherited slight chance of showers and thunderstorms seems justified. As the troughing is expected to dig just a little deeper, we may lose our col feature and our surface winds will resume a southeasterly direction.

Temperatures along the island communities are currently in the mid 80s. With just a little bit of mid to higher cloud cover filling in, some of the "trapped" heat will keep overnight lows from cooling down much more. No adjustments are needed to the inherited forecast package.

MARINE

Issued at 903 PM EDT Fri Jul 17 2026 A weak surface trough near the northeastern Gulf and northern Florida will maintain a split ridge pattern across Florida for the next several days. The Keys will either be within a col region south of the broad surface trough, or within the southern quadrant of the trough. Thus, breezes across the Florida Keys will be variable at times, or take on a southerly component. Our forecast takes the middle ground and is an average of the two scenarios.

AVIATION

(00Z TAFS) Issued at 903 PM EDT Fri Jul 17 2026 Both island terminals will see VFR conditions prevail through the TAF period, but isolated pockets of showers near EYW may lead to occasional MVFR CIGs as this activity breaks up. No long standing impacts are expected from any categorical changes. Initially light and variable surface winds will eventually become southeasterly near 5 knots. Both air fields should stay dry with anticipated activity well to the north and west of the Keys.

PRELIMINARY POINT TEMPS/POPS

Key West 84 91 83 91 / 20 20 20 20 Marathon 83 92 83 92 / 20 20 20 20

KEY WATCHES/WARNINGS/ADVISORIES

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