textproduct: Key West

KEY MESSAGES

- A Coastal Flood Statement remains in effect, and particularly low lying areas will see some saltwater ponding around the times of high tide.

- Westerly swell generated by Post-Tropical Cyclone Isaias will gradually subside across the western half of the coastal waters this evening.

- Elevated rain chances are expected tonight. Shower chances will decrease during the remainder of the holiday weekend.

UPDATE

Issued at 752 PM EDT Sat Oct 10 2026 Despite deep moisture in place with PWATs in excess of 2 inches area-wide, recent KBYX radar imagery just shows scattered showers and a few embedded storms moving to the NNW across the Straits this evening. The tropical moisture continues to feed into the region between the remnant circulation of Isaias in the TN Valley and mid/upper level ridging centered to the SW of Bermuda. Latest hi-res guidance continues to suggest that precipitation coverage will increase later this evening and overnight with scattered to occasional numerous showers and occasional storms drifting northwestward across the region. With the Atlantic ridge building in from the west overnight and heights aloft slightly increasing, overall forcing for ascent aloft will be lacking. However, the ridge building in from the west will also bring a much drier air mass into the region with PWATs possibly falling as low as 1.5 inches into Sunday. As the leading edge of this drier air mass approaches the region overnight into Sunday morning, the low-level flow will become increasingly more southeasterly and this should favor speed convergence precipitation development, which will be further enhanced along and ahead of the boundary of the dry air mass. Thus, despite the lack of any meaningful forcing aloft, there should still be enough lifting mechanisms in place to keep Chance/Likely PoPs for the overnight period so will maintain inherited forecast reasoning from earlier in the day. Otherwise, expect another warm and humid Saturday night across the Florida Keys with lows in the lower 80s and dewpoints in the upper 70s.

DISCUSSION

Issued at 225 PM EDT Sat Oct 10 2026 Weather across the Florida Keys turned out to be surprisingly uneventful this Saturday. Shower development was limited to the Outer Gulf waters and the western waters of the Florida Straits. Meanwhile, the morning sounding sampled a daily record PWAT value above 2.3 inches. Satellite observations from CIMSS-MIMIC estimated moisture totals closer to 2.1 to 2.2 inches this morning. However, if one looks outdoors the atmosphere does not appear very saturated. Clouds are struggling to form across the eastern waters surrounding the Keys, and the KBYX radar detected sparse shower activity, if any, east of the Lower Keys earlier today. Dew points in the upper 70s indicate more than enough moisture is present for widespread showers. Why has shower coverage been so sparse?

Low level winds are likely the reason we have seen a lack of shower activity. Moderate to fresh southerly breezes were present across the western Straits this morning while gentle to moderate southeasterly to south breezes were observed along the reef. This resulted in a region of low level divergence across the Keys, except for where winds were accelerating over the Outer Gulf. However, as what used to be Hurricane Isaias moves further north into the southeastern United States, breezes are on track to slacken and back southeasterly. Even though more than enough moisture is present, it is likely showers will struggle to form until winds shift further to the southeast. The most recent statistical guidance suggests the wind shift will occur after sunset. Tonight, we are forecasting that shower coverage will increase while winds slacken and back to gentle to moderate southeasterly breezes.

Looking ahead, there are a few features of interest. A tropical upper tropospheric trough is still spinning south of Cuba. Post- tropical cyclone Isaias is being absorbed into the mid-latitude flow field over the southeastern US. There are also two regions of high pressure; one is located over southeastern Texas, while the other is beginning to move into the North Atlantic from New England. Over the remainder of the weekend, Isaias is on track to fully transition into a mid-latitude system with a front extending south towards South Florida. The high over Texas will be sufficient to push the front over the Gulf and towards the Keys. Meanwhile, the Atlantic high will be able to build and maintain southeasterly breezes through tomorrow. The main source of uncertainty stems from what happens to the aforementioned front. Statistical models suggest it will pass across the Florida Keys by mid-week. The challenge stems from what happens to the winds and the dew points. Will dew points be able to decrease to near 70, or even the upper 60s? If so, how long will that last? Will there be a distinct wind shift and surge in wind speed? These questions will become more clear by the end of the holiday weekend. At the very least, the next couple of days will be free of nearby tropical cyclones.

MARINE

Issued at 225 PM EDT Sat Oct 10 2026 No watches, warnings, or advisories are in effect for the nearshore or offshore waters of the Florida Keys.

From synopsis: Enhanced swells generated by Post-Tropial Cyclone Isaias are steadily subsiding across the western waters of the Florida Keys. Breezes are slowly slackening to gentle to moderate breezes this weekend. Shower coverage will start to increase tonight as breezes back southeasterly to easterly. During the second half of the weekend, breezes are on track to back further northeasterly. Drier air will start to filter in on Sunday, and shower chances will drop below normal by the start of the work week. A frontal boundary associated with Post-Tropical Cyclone Isaias may push through the Florida Keys mid-week.

AVIATION

(18Z TAFS) Issued at 650 PM EDT Sat Oct 10 2026 Scattered SHRA and embedded TSRA are expected to push northward across the region later this evening and into the overnight hours, but overall confidence in coverage and timing is low at this time. Thus, have added VCSH to both KEYW and KMTH through around 10Z Sunday with mainly dry conditions then expected throughout the day tomorrow. Other than some possible brief VSBY restrictions during the precipitation activity, VFR conditions will primarily prevail with SE winds overnight and gradually becoming more easterly by Sunday evening with wind speeds around 10 kts and occasional higher gusts.

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.

KEY WATCHES/WARNINGS/ADVISORIES

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