textproduct: Key West

KEY MESSAGES

- Moisture will linger across the region through the weekend, supporting slightly above normal rain and thunderstorm chances.

- The primary threat for any stronger thunderstorms will be lightning strikes. When thunder roars, go indoors. If on a boat, stay low, or go below.

- Heat index values will range from 100-108 degrees daily with little relief from the muggy conditions overnight. Know the signs of heat stress, take frequent breaks, and stay hydrated.

DISCUSSION

Issued at 1140 AM EDT Sat Sep 12 2026 Unsettled weather that had lingered into the early morning has already tapered off! Around sunrise, a localized cluster of showers was sitting over Key West, stretched to the northwest. Loud cracks of thunder from a cell approximately 2 to 4 miles offshore of the island prevented us from launching our upper air balloon. At the Key West International Airport, a total of 0.13" of rain was recorded by the ASOS station when these showers moved through. One, brief gust of 26 mph was also recorded by the station at the time of the heaviest rain (around 7:30 AM). With the moist air mass across the area, this activity likely spawned from lingering ghost boundaries as there doesn't appear to be a source of lift on any greater scale at this time. Visible satellite shows the mid level cloud deck gradually diminishing across our western marine zones, revealing some lower level cumulus clouds. Our eastern marine zones are seeing a greater area of coverage with respect to the cumulus field as this is where our greatest moisture is currently situated. THere doesn't appear to be enough cloud cover to keep the sunshine at bay today, so our current temperatures in the upper 80s may be able to come up a few more degrees by the time we reach peak heating later this afternoon. Dew points in the mid to upper 80s will result in heat index values in the mid 100s, so it'll be important to be aware of any signs of heat illness, especially if not acclimated to these conditions.

Even though we are currently advertising 50% PoPs, current conditions don't necessarily align with that. However, the combination of a moist air mass and a small area of vorticity gradually nudging in to the area could lead to another round of showers and thunderstorms during the later afternoon and evening hours. Both our KBYX and our neighboring KAMX radars are showing development approximately halfway between Florida and Andros, indicating the environment can support activity. For this reason, we will maintain the 50% PoPs rather than adjusting to account for the lack of activity currently occurring.

PREV DISCUSSION

Issued at 400 AM EDT Sat Sep 12 2026

Over the next few days, the surface through lower level ridge will retreat into the Atlantic as a mid latitude trough takes shape and pushes off the Atlantic Coast. The remaining ridge to our north will weaken and mainland day time heating will effectively batter the surface ridge. As a result, east to southeasterly breezes should trend downwards with bouts of variability. A moisture rich swath across the Central Bahamas and eastern Cuba is expected to spread westward across our area through the weekend and should help to keep rain chances above normal through at least today. The weakening steering flow with no support aloft may counter this some. For now will maintain the already advertised 50% PoPs for today, which is below global models and above the NBM. No trend in temperatures or moisture is expected. Highs will remain near 90, lows in the lower 80s and dew points in the upper 70s.

Through the first half of the weak, sharp deep layered ridging will build over the eastern United States as the mid latitude trough moves out to sea. This will setup robust surface ridging stretching along the Atlantic through Gulf coast states while an unusually amplified surface through lower level trough off the Atlantic Coast. A band of stronger northeasterly breezes will develop off the Southeast Atlantic Coast, Florida, and the Gulf. While there is uncertainty with how this unfolds, there is the added uncertainty as to how far south this band will reach. For now guidance shows breezes firming up slightly out of the northeast to the east for the Keys. Surface dew points may actually slip into the mid 70s for a change. Rain chances may be near to slightly However, for now, rain chances are expected to be near normal early in the week due to some drying and stabilization coming with the northern fringes of a Saharan layer. However, chances should return to slightly above normal heading into mid week as as band of lower level moisture pushes southwestward into our area.

MARINE

Issued at 1011 AM EDT Sat Sep 12 2026

Ridging across the southeastern United States and Florida will maintain light to gentle east to southeasterly breezes over the next few days, becoming variable at times. Low level moisture will remain abundant and keep convective potential slightly above normal today, but fall back to near normal early in the week as drier lower levels filter in. The ridge will be reinforced late in the forecast and may drive freshening northeast to easterly breezes.

AVIATION

(15Z TAFS) Issued at 1011 AM EDT Sat Sep 12 2026

VFR conditions will prevail at both island terminals through the TAF period with dry conditions in place. Showers and thunderstorms will develop to the west of the island chain, and approach the area around 22Z to 00Z. There is low confidence related to if and when any individual shower or thunderstorm will cross either air field, so we will keep the TAFs dry for now, and make amendments as needed. Surface winds will be light and variable initially before becoming east to southeast at 5 to 10 knots over the second half of the TAF period.

CLIMATE

ON this day in 2020, the daily record rainfall of 9.37" was recorded in Key West. This high daily rainfall value was attributed to Tropical Storm Sally passing by to the north of the Keys earlier in the day and then Cuban thunderstorm outflow surging northward across the Straits of Florida that evening. During the late evening hours a thunderstorm over the Lower Keys produced 3.98" of rainfall at KEYW in 1 hour. The second highest hourly rainfall rate recorded by the EYW ASOS, behind November 11, 1980. This led to numerous reports of flooded streets and stalled cars in Key West, with flooding lasting several hours. Additionally, 11.36" of rainfall was recorded at the WFO. This is also the wettest day ever recorded during the month of September, toppling 1919's record of 7.47" on September 10th, by almost 2 whole inches. Rainfall records for Key West date back to 1871.

PRELIMINARY POINT TEMPS/POPS

Key West 92 82 92 81 / 50 30 40 30 Marathon 90 82 90 82 / 50 30 40 30

KEY WATCHES/WARNINGS/ADVISORIES

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