textproduct: Key West

KEY MESSAGES

- A broken cloud line will continue to percolate along portions of the Island Chain through the early evening.

- Rain chances will slowly increase into the weekend as dust concentrations decrease.

- Warm and muggy conditions will continue throughout the work week, with light and often variable breezes.

AVIATION

(18Z TAFS) Issued at 159 PM EDT Thu Aug 20 2026 An island cloud line will continue to wane over the next several hours. Will leave mention of VCSH in the TAFs for a few more hours to account for this, although chances for sub-VFR CIGs and VISs is beginning to wane. VFR conditions will prevail thereafter through 18z Friday. Surface winds light and variable will gradually shift to the southeast overnight through Friday. Winds may go light and variable after 12z again Friday, and we will monitor possible additional cloud line development at that time.

PREV DISCUSSION

Issued at 230 AM EDT Thu Aug 20 2026 After the past 3 consecutive KEY soundings in recent days sampled PWAT values less than an inch, a rather remarkable feat considering the daily mean values this time of the year are closer to the 1.8- 1.9 inch range, there are finally some signs that atmospheric moisture is starting to recover. While the 20/00Z RAOB still only measured a PWAT value of 1.21 inches, it is a notable improvement compared to the stretch of record dry sounding data in recent days. Latest SPC mesoanalysis data shows a rather substantial moisture gradient is in place across the region with maximum PWAT values around 2.4 inches in central FL and values ranging from 1.2-1.6 inches across the Florida Keys. The higher moisture values to the north of the area are associated with a weak upper low in the vicinity of the northeast Gulf and some of this moisture will gradually advect southward across the Florida Keys throughout the day, which will help to scour out any last remnants of the most recent SAL event. Given a light and variable col flow pattern today with a split ridge setup and the uptick in moisture, there will finally be an introduction of PoPs back to the forecast once again with higher rain chances generally north of the Island Chain in closer proximity to the upper low and any outflow boundaries that push into the area from seabreeze convection over south FL. In addition, some activity could also form via cloud line development but forecast soundings still show some inhibition to contend with so would expect overall coverage to be on the limited side. Friday may also feature another opportunity for cloud line development, but the col region will be a bit displaced to the west as low-level flow becomes more out of the SE so precipitation chances will be a bit lower despite a continued moistening trend.

The aforementioned upper low will gradually weaken and become absorbed into an eastern US trough over the weekend. This trough gradually amplifies across the eastern CONUS throughout the weekend with its axis pushing across portions of the peninsula on Sunday. The trough will also drop a cold front across the northern Gulf Coast and Southeast US as it swings through with moisture pooling occurring in these areas ahead of the associated frontal boundary. As this occurs, surface high pressure in the central Gulf weakens and retreats westward, which will bring a more familiar summertime pattern back to the Florida Keys by late weekend and early next week with a more dominant southeasterly flow regime developing. As a result, atmospheric moisture values are anticipated to return to more typical values for this time of the year with daily Chance PoPs returning as well, especially from Monday onwards through the remainder of the forecast period. In addition, there might be another wave of Saharan dust that spreads across the region late in the weekend, but early indications are that dust concentrations will decrease as it moves across Cuba and The Bahamas.

MARINE

Issued at 1136 AM EDT Thu Aug 20 2026 Conditions will be favorable for waterspout formation through the early afternoon hours. Mariners are reminded a waterspout would most likely appear beneath a dark, flat bottom of a building cumulus line, just at the hint of rain. From synopsis, a split ridge across our waters with a nearby col will result in light and variable winds this afternoon. The split ridge pattern will remain in place through the end of the week and early in the weekend with a mostly light to gentle variable wind pattern. Winds will then increase and become more southeasterly for late weekend and into the new work week, with daily gentle to moderate breezes expected.

PRELIMINARY POINT TEMPS/POPS

Key West 92 82 91 83 / 20 10 10 10 Marathon 90 83 90 83 / 30 10 10 10

KEY WATCHES/WARNINGS/ADVISORIES

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