Marine Weather and Tide Forecast for Key West, FL

DISCUSSION
Issued at 1124 AM EDT Tue Apr 21 2026 Scattered showers can be seen lingering in the Straits of Florida as the previously mentioned frontal boundary continues to drift south of the island chain. Besides the Straits, convection has become limited as dry air makes its way in. While showers have waned, cloudy conditions remain across the area seen on GOES-19 Satelitte. Temperatures across the island chain are in the mid to upper 70s. Along the Reef, strong winds of near 25 knots are currently being observed. As high pressure builds in post-front, winds will continue to be fresh to strong due to the tightening pressure gradient. A Small Craft Advisory is in place for all coastal waters through the next few periods as a result. No changes were needed to this update.

PREVIOUS DISCUSSION
Issued at 500 AM EDT Tue Apr 21 2026 CIMSS MIMIC total precipitable water continues to show a tight pressure gradient across the Florida Keys with a frontal boundary continuing to drift southeastward. High pressure is slowly building in behind the front resulting in a tightened pressure gradient across the area. Marine observation platforms surrounding the Island Chain are recording northeast breezes of 20 to 25 knots as a result. KBYX radar has remained active all night with scattered showers. These showers have been affecting the nearshore and offshore waters, mainly surrounding the Middle and Upper Keys. Some of the showers occasionally brought some light rainfall to Island Chain communities. A few showers have moved across the Lower Keys as well but most activity has remained near the Middle Keys overnight. MRMS data shows estimated hourly rainfall amounts of a tenth to up to a quarter of an inch overnight. GOES 19 Nighttime Microphysics imagery shows decent cloud cover across the Keys in association with the showers leading to partly to mostly cloudy skies. Temperatures along the Island Chain are in the mid 70s and dew points are near 70 degrees.

FORECAST
The aforementioned frontal boundary that is draped across the area early this morning will continue to move slowly southward through the day. Surface high pressure is expected to build in behind it which will then dominate the Keys weather for the next several days. This will continue to promote windy conditions through at least Wednesday before breezes slowly diminish as the high slowly shifts out into the western North Atlantic. Moisture will remain plentiful this morning before some drier air moves in during the afternoon and evening. Chances of rain are expected today as a result with a dry forecast for tonight and Wednesday.

The Keys remain in general zonal flow in the mid to upper levels through the week. However, an upper level shortwave is expected to traverse eastward towards the latter half of the week. This may instigate more widespread showers and thunderstorms during this timeframe. Therefore, rain chances increase again for Thursday to Friday. There are also some indications on this period potentially being quite wet. However, uncertainty remains. Instability will also be across the area leading to the potential for thunderstorms.

Upper level ridging builds back into the region for the weekend with warming temperatures, decreasing rain chances, and increasing humidity along with east to southeast flow.

MARINE
Issued at 1124 AM EDT Tue Apr 21 2026 A Small Craft Advisory is in effect for all coastal waters. From synopsis, fresh to strong northeast to east breezes will continue through Wednesday as high pressure builds across the Eastern Seaboard in the wake of last evenings front. This high will continue to slowly migrate into the western North Atlantic over the next several days. As the high slowly weakens, breezes will begin to slacken by Thursday. Gentle to moderate breezes are expected for Friday and Saturday.

AVIATION
(15Z TAFS)
Issued at 1124 AM EDT Tue Apr 21 2026 VFR conditions will prevail at both EYW and MTH through the TAF period. Shower activity associated with the front that moved through our waters have moved south of the island chain and no longer pose a threat. Winds are expected to remain elevated with gusts of near 25 knots throughout the afternoon.

KEY WATCHES/WARNINGS/ADVISORIES
FL...None.
GM...Small Craft Advisory until 6 AM EDT Wednesday for GMZ031>035- 042>044-052>055-072>075.