textproduct: Key West

KEY MESSAGES

- Conditions remain somewhat favorable for an island cloud line and associated waterspouts this afternoon.

- Rain and thunder chances will gradually return to near normal by early to middle of next week.

- Highs near 90 and dewpoints in the mid to upper 70s suggest afternoon heat indices will peak at 105 to 108 degrees.

DISCUSSION

Issued at 1040 AM EDT Sat Aug 22 2026

Surface ridging remains in the western north Atlantic with an axis extending into South Florida and the Southeast Gulf. Light southeast to south winds were noted around 5 mph over the island chain. The morning sounding added about three tenths of an inch in precipitable water and notably below 900 mb and a 1.5C decrease in 500 mb temperature. These two changes along made it not surprising several hundred J/kg of CAPE was added among the calcuation methods including mixed-layer. A deeper plume of moisture evident on GOES estimates near 2.0 inches of precipitable water was aligned from Andros Island southward with a westward drift.

Convection-allowing guidance responds in kind with a potential for isolated showers near the larger islands of the Lower Keys and Florida Bay developing around noon, with the potential for a few to become thunderstorms by mid afternoon. The light south to southwest steering flow, while mainly 10 knots or less, appears sufficiently deep to shift the convection northward into the Gulf and Bayside. The current slight rain chances with inclusion of thunder remains on the mark for this afternoon. The deeper moisture lurking to our southeast is likely to stretch northwest and northward with the westward component of drift slow enough to only make it into the easternmost Straits Sunday morning. Thus, no significant uptick in rain chances is seen for tonight with the slight chances continuing.

PREVIOUS DISCUSSION

Issued at 431 AM EDT Sat Aug 22 2026

A weak frontal boundary will stall along the Gulf Coast region today. It appears that deeper moisture content will remain focused just to our north/northwest closer to the convergent axis while latest forecast soundings and short term guidance suggests our PWATs will remain near the 10th to 25th percentiles for today, ranging from 1.4-1.6". This localized pocket of drier air is currently viewable on the GOES-E Split Window product and will likely be the primary limiting factor for our rain chances today. Our winds will remain on the weaker side with a general southeasterly component due to being within influence of the western periphery of the North Atlantic ridge, but winds may become variable at times this afternoon in which case conditions could become somewhat conducive for waterspouts if cloud line formation is able to occur. Otherwise, there is a slight chance of thunderstorms across the Upper Keys due to weak low-level speed convergence over the Bahamas which may support isolated thunderstorm develop west of Andros Island this afternoon. Any development that occurs may drift into the eastern Straits of Florida and towards the Upper Keys.

This setup will remain largely unchanged through Sunday and into next week due to the stagnant upper-level pattern. With mostly sunny skies and rain chances below-normal, afternoon heat indices along the island chain should easily reach the 105-108 degree range with highs in the lower 90s and dewpoints in the mid to upper 70s. Moisture advection early next week should bring the return of near- normal, to perhaps above-normal, rain chances, particularly as southeasterly flow becomes better established and the forecast area becomes better aligned with the zone of weak low-level speed convergence.

MARINE

Issued at 1040 AM EDT Sat Aug 22 2026

No watches, warnings, or advisories are currently in effect for the Florida Keys coastal waters.

From synopsis, a split ridge pattern remains in place across the Florida Keys coastal waters. This will promote generally light to gentle southeast to south breezes through Sunday, becoming variable at times during the afternoon hours. While North Atlantic ridging builds westward, southeasterly to easterly breezes will become more established for Sunday night through the middle of next week, becoming gentle and at times moderate during the overnight hours.

AVIATION

(15Z TAFS) Issued at 1040 AM EDT Sat Aug 22 2026

VFR conditions are expected to prevail at KEYW and KMTH through the TAF period. Light southeast to south winds 4 to 7 knots are expected to continue through Sunday morning. There is low confidence that a cloud line will be able to effectively form along the larger islands of the Lower Keys, but isolated showers or even a thunderstorm could form along the Gulf side given the weak southeast to south winds. At this time the probability for even a vicinity impact remains too low to include in the TAFs.

KEY WATCHES/WARNINGS/ADVISORIES

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