Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
038 FXUS62 KKEY 281612 AFDKEY Area Forecast Discussion National Weather Service Key West FL 1212 PM EDT Mon Sep 28 2026 ...New UPDATE, AVIATION... .KEY MESSAGES... - Minor to moderate saltwater flooding of low elevation streets and lots is likely to continue through this week due to King Tide. Don`t drive through flooded roadways. Boaters can expect less clearance under fixed bridges. - A Coastal Flood Advisory is in effect for all of the Florida Keys through Tuesday morning. - Moisture will begin filtering into the area starting today and continuing through the end of the week. This will promote above normal rain and thunder chances, especially Tuesday and onward && .UPDATE... Issued at 1144 AM EDT Mon Sep 28 2026 The 12Z KEY RAOB shows a very dry atmospheric profile, especially in the mid levels with a mid level RH value of just 21% and a substantial dry layer in the 850-350 mb layer. Additionally, a PWAT value of 1.13 was sampled and this value is below the 10th percentile for late September. However, today is the final day of the brief reprieve from the extreme summer-time humidity for the FLorida Keys as deeper moisture comes surging back later today into tonight ahead of a sharpening trough axis positioned in the eastern Gulf and extending into the Yucatan region. Latest satellite imagery shows a large cluster of convection in the southern Gulf waters around the base of this feature and in the vicinity of a remnant frontal boundary. This activity combined with convection that fires along Cuba later today should generally advance towards the Florida Keys by tonight along the leading edge of deeper moisture advection, though this should primarily be in a weakening fashion as some stabilization occurs this evening. However, given plenty of forcing for ascent, enhanced divergence aloft, and the return of tropical moisture, additional activity should be able to develop late evening and overnight, which could make for wet and stormy conditions at times tonight into Tuesday. Otherwise, before the deeper moisture arrives, it should be a dry ahead with highs in the mid/upper 80s and one final day of sub-70 dewpoints before dewpoints quickly surge to the mid to upper 70s through mid week. The only other item of note from the morning update was canceling the Coastal Flood Warning in the Upper Keys in favor of a Coastal Flood Advisory for the entire Island Chain through Tuesday morning based on recent observations showing minor to moderate saltwater flooding in the region. && .DISCUSSION... Issued at 320 AM EDT Mon Sep 28 2026 It has been a quiet overnight across the Keys and surrounding coastal waters. However, not too far away we have been observing showers and thunderstorms developing from around the Isle of Youth (south of Cuba), northwest towards Andros Island. This activity is developing and moving northeast thanks to a rather deep early season trough that is digging across the Gulf waters and into the Yucatan Channel. At the surface we continue to see west to northwest winds at nearly all of our observation platforms. A weak frontal boundary can barely be made out on radar as it lies across the distant Straits of Florida. This frontal boundary and the aforementioned trough is causing quite the headache this morning with the going forecast. Satellite derived vorticity analysis shows no real indications of a shortwave present except at the 850 mb level. This vort max is developing at the base of the trough and we can see that it`s been enough to fire off the showers and thunderstorms as previously described. However, models are not enthusiastic of additional shortwaves developing and ejecting out of this trough today. Meanwhile, the frontal boundary noted across the Straits will slowly lift northward today. This would put the Keys in a southwest flow by the afternoon. This wind direction would tend to favor a reverse cloudline potentially developing. It will come down to how much overhead cirrus we get today. We could have enough of a cirrus shield from the nearby trough to inhibit much growth if a cloudline tries to develop. As such, made the difficult decision to lower PoPs slightly for today. Time will tell if the right decision was made. Regardless, as we go into tonight and into Tuesday, moisture will only be increasing while the trough begins sharpening across the Gulf basin. This will lead to much better convergence and confluence of both moisture and mass for much of this week. Therefore, still feel fairly confident at above normal rain/thunder chances for the remainder of the period. This active, wet period may also be problematic as a Nor`Easter has been parked north of the Gulfstream and the swells generated by this system is going to back up the Gulfstream over the coming days. Moderate to major saltwater flooding is likely to continue. && .MARINE... Issued at 320 AM EDT Mon Sep 28 2026 A Nor`easter in the New England States will continue to maintain a lingering northerly swell in our far eastern waters before subsiding throughout the day. A weak frontal boundary will lift northward across the Keys today. This will allow west to northwest winds to back to the south and southwest and eventually to the southeast to south this evening. Winds then become more easterly by Tuesday as a high pressure moves into the eastern U.S. Thereafter, this high will merge with an existing high pressure across the Atlantic and subsequently will build. This will promote freshening breezes, with an increasing likelihood of moderate to fresh breezes for the latter half of the week. && .AVIATION... (15Z TAFS) Issued at 1144 AM EDT Mon Sep 28 2026 VFR conditions will prevail throughout the remainder of the day with SSW winds around 5 kts. Winds shift to more southeasterly tonight and increase with winds around 5-10 kts and increasing moisture will also yield higher rain chances. As a result, VCTS was included after 08Z/Tuesday through the remainder of the period as some brief flight restrictions could occur, particularly during heavier downpours in the vicinity of either of the terminals. && .KEY WATCHES/WARNINGS/ADVISORIES... FL...Coastal Flood Advisory until 5 AM EDT Tuesday for FLZ076>078. GM...None. && $$ Public/Marine/Fire...RG Aviation/Nowcasts....RG Data Acquisition.....JY Visit us on the web at weather.gov/key Follow us on Facebook and X at: www.facebook.com/nwskeywest www.x.com/nwskeywest