Marine Weather and Tide Forecast for Marathon, FL

DISCUSSION
Issued at 430 AM EDT Sat Oct 10 2026 Post-Tropical Cyclone Isaias made landfall as a Category 2 Hurricane last evening near Destin, FL. The storm has completed its extra-tropical transition and continues to rapidly move northward through Alabama while weakening. To its south, ridging remains in place across the western North Atlantic with the center of this ridge to the north of Puerto Rico. The western periphery of this ridge extends westward influencing the Keys. Marine platforms surrounding the Island Chain are recording mainly south breezes of 10 to 15 knots with Smith Shoal and Sand Key recording 15 to 20 knots. KBYX radar was active earlier in the evening with showers and a couple thunderstorms across the offshore and nearshore waters of the Middle and Upper Keys which weakened on approach to the Chain. A few stronger cells then developed over Florida Bay which then moved quickly onshore South Florida and dissipated. Temperatures along the Island Chain are still very warm for this time of the night in the lower to mid 80s and dew points are in the upper 70s.

FORECAST
Taking a birds eye view of the weather across the Southeast U.S., Gulf, and Florida, we now have Post-Tropical Cyclone Isaias over southern Alabama. Post-Tropical Cyclone Isaias will continue to result in enhanced W swell across our western waters and SE Gulf today before subsiding tonight. We also continue to have the aforementioned ridge above in the western North Atlantic along with a stationary front draped across northern Florida. These features continue to work together to keep breezes elevated out of the southeast to south. Therefore, expect moderate to fresh breezes to continue today, especially across the SE Gulf and western Straits before modestly slackening late today.

We continue to watch a weak upper level feature with increased moisture moving northwestward as it rides the western periphery of the ridge. Latest guidance suggests the morning remaining dry across much of the Keys. However, as we get daytime heating and due to the south to southeasterly flow, any showers and thunderstorms that develop over Cuba this afternoon and evening are anticipated to move northward, potentially sparking new convection across the Keys. It appears on the latest guidance that the Lower Keys westward have the best chance to see something tonight, though, that is not to say some showers or storms cannot occur further east. The PoP chance is very low confidence with 40% in the Upper Keys to 50% for the Middle Keys, and 60% for the Lower Keys. We will see how this unfolds late today and tonight.

Ridging is expected to dominate for the second half of the holiday weekend including the holiday itself. One ridge will be over the North Atlantic while another ridge builds in across the Southeast U.S. Both of these acting together will help to keep breezes elevated through the period. Therefore, expect east to southeast gentle to moderate breezes to continue through this period. Drier air will also filter into the area leading to decreased rain chances. Expect daytime highs to remain quite warm in the upper 80s and overnight lows in the lower 80s with dew points potentially hovering near 80 degrees through this period.
Very warm and tropical for considering we are approaching mid- October at this point.

Numerical and global model guidance continues to show a front pressing through the Keys sometime Tuesday/Tuesday night.
Confidence continues to grow for a potential dip in dew points towards mid week and slightly cooler temperatures. Dew points potentially down to the lower 70s, or 70 degrees? It also appears like this front will press through which may result in near nil rain chances for a few forecast periods before lifting back north as a warm front later in the week with a return to muggier and potentially wetter conditions.

MARINE
Issued at 430 AM EDT Sat Oct 10 2026 Small Craft Should Exercise Caution (SCEC) until winds decrease and seas subside are headlined for today across the SE Gulf waters and the westernmost FL Straits. For the nearshore waters surrounding the Lower Keys, Small Craft Should Exercise Caution until winds decrease is headlined. Boaters should be aware of less clearance under fixed bridges around times of high tide as a Coastal Flood Statement is in effect for the Florida Keys. From synopsis, Post-Tropical Cyclone Isaias made landfall last evening near Destin, FL. The storm continues to move rapidly northward while weakening. Moderate to fresh southeast to south breezes are expected to continue throughout the Florida Keys coastal waters, especially the SE Gulf, western Strait, and the nearshore waters surrounding the Lower Keys today. Elevated swells will persist through the western FL Straits today and the SE Gulf waters today.
Breezes will only modestly slacken to gentle to moderate as the cyclone continues to move away and ridging builds in behind it.
Meanwhile, a plume of moisture will move through the Keys today through tonight with an increase in shower and thunderstorm coverage, especially tonight. Thereafter, a frontal boundary may push through the region early next week promoting northeast breezes.

AVIATION
(06Z TAFS)
Issued at 430 AM EDT Sat Oct 10 2026 VFR conditions are expected to persist at both EYW and MTH terminals through the TAF period. Near surface winds will remain mainly southerly this morning into the afternoon before shifting to the southeast for the evening and overnight hours. In addition, while most of the morning looks to remain dry, convection is anticipated to develop near Cuba and then move northward towards the Island Chain sometime this afternoon with the threat continuing through the overnight. The best chance time for this appears to be after 11/00z, though, we can't rule out activity before this time that may impact the terminals. Due to average confidence on timing and placement, VCSH was placed into the TAF for this evening.

CLIMATE
On this day on 2009, the daily record warm low temperature of 84F was recorded in Key West. Temperature records for Key West date back to 1872. Also, on this day in 1975, the daily record warm low temperature of 83F was recorded in Marathon. Temperature records for Marathon date back to 1951.

PRELIMINARY POINT TEMPS/POPS
Key West 89 83 89 83 / 10 60 20 10 Marathon 89 81 89 81 / 10 50 20 10

KEY WATCHES/WARNINGS/ADVISORIES
FL...None.
GM...None.