textproduct: Key West

KEY MESSAGES

- A Coastal Flood Statement remains in effect for the Lower and Middle Keys, with minor saltwater flooding possible, especially around the time of high tide in the late Thursday morning and afternoon hours.

- Rain and thunder chances through Thursday will generally be limited to any island cloud line formation or storms pushing off the South Florida Mainland.

- The best chances for measurable rainfall will be Friday through Saturday evening, before a swath of dry air progresses towards the Keys for late weekend and early next week.

DISCUSSION

Issued at 400 AM EDT Thu Aug 13 2026 As hypothesized when writing this discussion last evening, despite substantial dry air above 850 mb throughout the day today, it is always humbling to remember it is mid-August in the Florida Keys. Light winds supported broken island cloud line formation across the Lower and Middle Keys, although the aforementioned dry air largely stinted associated shower activity. Scattered strong convection developed across the South Florida Mainland, then propagated southwestward in the late evening hours towards the Florida Keys marine zones, before later interacting with a residual lurking ghost boundary north of the Lower and Middle Keys. Since then, the isolated to scattered activity has waned, leaving the entire CWA free of meteorological echo returns. Outside of briefly rain- cooled locations between Big Pine and Marathon, temperatures are generally in the lower to mid 80s at this early morning hour for all land- based surface observation locations.

For today, KBYX radar continues to detect residual ghost boundaries lurking throughout the marine zones. Forecast soundings indicate very little change to the synoptic setup, with weak mean northeasterly steering flow likely supporting of additional cloud line formation this afternoon. There is at least some convective allowing model (CAM) support for convective development over South Florida progressing southwestward tomorrow evening. Given the aforementioned lurking boundaries and the convective evolution on Wednesday (a persistence forecast), elected to nudge PoPs upward a bit (around 20%) for both this afternoon and tonight.

Beyond today, high pressure will once again strengthen in the North Atlantic over the next several days, supporting modestly freshening easterly breezes. A tropical wave in the vicinity of Puerto Rico will propagate westward towards the Straits of Florida over the next several days, supplying associated boundary layer moistening and cyclonic vorticity support for convection. A late season undulation of Saharan dust will trail the wave. As these two features interact, there will be an elevated chance for rain and thunder, first as the wave approaches the Keys, then again as the Saharan dust takes dominance over the Keys. Timing these windows of elevated rain and thunder chances will be left to the next several forecast cycles, lying somewhere between Friday afternoon and Saturday evening.

Global deterministic and ensemble numerical weather prediction guidance diverges a bit for late weekend through early next week. Although the Saharan, dry environment looks to stay for quite some time, a weak frontal boundary may stall somewhere to the north of the Keys. For now, will yield to slightly below normal rain chances, although this will be monitored, depending on the stalling frontal evolution.

In terms of the tropics, although the National Hurricane Center is monitoring two possible areas in the Main Development Region of the Tropical Atlantic, neither system is expected to provide impacts to the Keys at this time.

MARINE

Issued at 400 AM EDT Thu Aug 13 2026 A Coastal Flood Statement remains in effect for the Lower and Middle Keys, with minor saltwater flooding possible around the time of high tide late this morning through the early afternoon hours. Boaters can expect less clearance under fixed bridges, especially around the time of the high tide. From synopsis, a high pressure system in the central North Atlantic will continue to slide eastward and weaken today. Gentle east to southeast breezes will slacken, becoming light and variable this afternoon. As the high restrengthens and builds westward, breezes will somewhat freshen for Friday through the weekend. A weak frontal boundary will approach the Florida Peninsula early next week, allowing breezes to slacken once again, becoming light and variable at times.

AVIATION

(00Z TAFS) Issued at 400 AM EDT Thu Aug 13 2026 VFR conditions will prevail at both EYW and MTH through 14/06z. Light to gentle E to SE breezes will become variable at times by the early afternoon hours. This will tend to support possible island cloud line development. Northeasterly steering flow will also support any afternoon storms over the South Florida Mainland pushing southwestward towards the terminals after 00z. Due to low- level dry air, will keep explicit inclusion of impacts to the terminals of the TAFs for now.

PRELIMINARY POINT TEMPS/POPS

Key West 92 83 92 81 / 20 20 30 40 Marathon 90 83 90 82 / 20 20 30 40

KEY WATCHES/WARNINGS/ADVISORIES

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