textproduct: Key West

KEY MESSAGES

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

- 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.

- Winds are expected to trend upwards over the several days, likely peaking in the moderate to fresh range around mid week.

DISCUSSION

Issued at 400 AM EDT Sun Sep 13 2026

The weak western flank of an Atlantic surface ridge stretches westward into South Florida. This along with diurnal effects has resulted in light and variable breezes across the area. The environment is seasonably unstable and uncapped. Very moist lower levels along with the weak flow had the area primed for a considerable amount of very active boundary interactions through the day and evening. The area is now worked over and no showers are currently in the forecast area. Sultry conditions are in place with temperatures in the lower to mid 80s and dew points well up in the upper 70s.

The pressure field around the Keys and South Florida will remain rather flat over the next couple of days with diurnal heating disrupting the western end of the Atlantic ridge on a daily basis. As a result, surface winds will remain light and variable. Convective forcing will be weak due to no features aloft or at the surface. However, lower level moisture is expected to remain very moist today, and slightly less tomorrow. The environment is expected to remain uncapped with seasonable instability. As a result, high chance of precipitation will be retained today. The weak flow and humid air wafting in from very warm waters may allow for another slightly hotter than normal day. Dew points will remain in the upper 70s.

A mid latitude trough will swing off the Atlantic coast on Monday and hold the Atlantic ridge off to the east. The gradient will remain weak, however, guidance suggests a more prevailing easterly steering flow will take shape. This along with a bit less low level moisture should help to pair back rain chances some. Island cloud line and mainland outflow boundaries will remain a concern and will keep PoPs slightly above normal. Expect near normal temperatures with dew points ind the mid to upper 70s.

Our area will begin feeling the effects of a robust high pressure system expanding south southeastward out of Canada through the southeastern United States. Expect breezes to gradually firm up out of the northeast to east through the first half of the week. Breezes are expected to peak in the late Tuesday through late Wednesday time frame, becoming moderate. The more backed streamlines will help to keep dew points down in the mid 70s and shave a degree or two off our highs. Rain chances will be highly uncertain. This is due to a swath of increased low level moisture accompanying the freshening breezes. In addition, guidance shows a broad inverted trough setting up over the Bahamas and eastern Cuba. These factors may contribute to higher rain chances. For now will hold mid week rain probabilities at high chance.

MARINE

Issued at 400 AM EDT Sun Sep 13 2026

Weak ridging across South Florida and diurnal effects will keep breezes light and variable today, with a hint of easterlies showing up tomorrow. Through the first half of the week a continental high will expand southward down the Atlantic Coast and reinforce the pressure gradient across the Florida region. As a result, expect winds to gradually trend upwards while backing northeast to east. A couple of periods of cautions may be required for portions of Keys waters, most likely in the late Tuesday to late Wednesday time period.

AVIATION

(00Z TAFS) Issued at 400 AM EDT Sun Sep 13 2026

VFR conditions will prevail at the island terminals. With that said, shower and thunderstorm chances will be above normal today. There is a high chance for bouts of sub VFR conditions with considerable uncertainty in timing. Surface winds will be light and variable.

PRELIMINARY POINT TEMPS/POPS

Key West 92 81 92 82 / 50 40 20 30 Marathon 90 82 90 82 / 40 30 20 30

KEY WATCHES/WARNINGS/ADVISORIES

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