Thunderstorms developed during the early morning hours of May 10, 2020, near and just north of a stationary front extending west-to-east across the Straits of Florida. Heavy rainfall produced widespread flooding on Long Key including the City of Layton.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS KEY wrote it up.
Thunderstorms developed during the early morning hours of May 10, 2020, near and just north of a stationary front extending west-to-east across the Straits of Florida. Heavy rainfall produced widespread flooding on Long Key including the City of Layton.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Key West, FL wrote its last area forecast discussion before the first event at May 9, 9:41 PM EST, 5 hours 19 minutes earlier.
Area Forecast Discussion National Weather Service Key West FL 1041 PM EDT Sat May 9 2020 .UPDATE... The whites of the eyes are coming into better focus for the heavy rain event and marginal severe event for the Keys over the next 24 hours. SPC currently has the Keys under a Marginal Risk for severe thunderstorms late tonight and Sunday. Satellite imagery shows a well-defined southern stream shortwave crossing over and just north of the Yucatan Peninsula. Meanwhile, MIMIC PW imagery shows a well-defined moisture and frontal boundary extending east from there through the Straits. For example, PW values north of Grand Cayman are a richly moist and tropical 2.25", while the 00z KEY sounding observed 1.28". So as the shortwave near the Yucatan moves east overnight, and interacts with the east-west frontal boundary that is already in place, further blossoming of rain, showers, and thunderstorms will take place. Already, radar has shown the gathering of an east-west area of showers and embedded thunderstorms this evening over the Straits between the Keys and Cuba. Meanwhile, GOES-16 1-minute imagery shows thunderstorm coverage north of far western Cuba blossoming recently, likely due to large-scale lift increasing along that portion of the east-west boundary. So as large-scale lift spreads east overnight, the frontal boundary to our south will light up further, with the focus of shower and thunderstorms coverage lifting north toward the Keys overnight. Due to the potential for some cells to be slow movers, there could be some particularly heavy rainfall amounts in localized spots. While our WPC-based QPF is already about 3" through Sunday evening, any slow-moving cells might exceed that amount by a couple more inches. Of course, that would be a localized as opposed to a widespread event. Besides heavy rainfall, storms will be capable of producing strong and possibly damaging wind gusts. There is plenty of wind shear to organize storms in multi-cell clusters, plus our location at the interface with drier air to the north could support some dry air entrainment into downdrafts. So the next 24 hours will be interesting to say the least. Was already interested with the stationary supercell that formed near the southwest corner of our forecast domain last hour. && .MARINE... A frontal boundary will settle near or just south of the Keys overnight, maintaining moderate easterly breezes. Low pressure will ripple east along the front on Sunday, causing widespread showers and numerous thunderstorms capable of heavy rainfall and gusty winds. A large surface high will strengthen over the Tennessee Valley on Monday and Tuesday, moving eastward into the Atlantic Wednesday through Thursday. && .AVIATION... A quick deterioration in aviation conditions is expected overnight, thanks to the arrival of showers and thunderstorms. The unsettled weather will continue through Sunday. These thunderstorms have the potential to dump particularly intense rainfall, bringing wet runways and reducing visibility temporarily into IFR ranges. Some of the thunderstorms could be slow movers, so duration of any one storm over a terminal could be lengthy. As showers and storms linger through Sunday and the air mass continues to moisten, the potential for reduced cigs and vsbys outside storms will increase through the day on Sunday. Eventually cigs under 010 will prevail. In addition, a marginal case for mentioning non-convective wind shear in the TAFs is possible on Sunday afternoon, as surface winds remain out of the E-NE, but winds near FL020 become southerly for a time. && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...None. && Public/Marine/Fire...Haner Aviation/Nowcasts....Haner Data Collection......DR Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest
Hazardous Weather Outlook National Weather Service Key West FL 535 AM EDT Sat May 9 2020 FLZ076>078-GMZ031>035-042>044-052>055-072>075-100945- Monroe Upper Keys-Monroe Middle Keys-Monroe Lower Keys- Florida Bay including Barnes Sound, Blackwater Sound, and Buttonwood Sound- Bayside and Gulf side from Craig Key to west end of Seven Mile Bridge- Gulf waters from East Cape Sable to Chokoloskee 20 to 60 NM out and beyond 5 fathoms- Gulf of Mexico including Dry Tortugas and Rebecca Shoal Channel- Gulf of Mexico from west end of Seven Mile Bridge to Halfmoon Shoal out to 5 Fathoms- Hawk Channel from Ocean Reef to Craig Key out to the reef- Hawk Channel from Craig Key to west end of Seven Mile Bridge out to the reef- Hawk Channel from west end of Seven Mile Bridge to Halfmoon Shoal out to the reef- Straits of Florida from Ocean Reef to Craig Key out 20 NM- Straits of Florida from Craig Key to west end of Seven Mile Bridge out 20 NM- Straits of Florida from west end of Seven Mile Bridge to south of Halfmoon Shoal out 20 NM- Straits of Florida from Halfmoon Shoal to 20 NM west of Dry Tortugas out 20 NM- Straits of Florida from Ocean Reef to Craig Key 20 to 60 NM out- Straits of Florida from Craig Key to west end of Seven Mile Bridge 20 to 60 NM out- Straits of Florida from west end of Seven Mile Bridge to south of Halfmoon Shoal 20 to 60 NM out- Straits of Florida from Halfmoon Shoal to 20 NM west of Dry Tortugas 20 to 60 NM out- 535 AM EDT Sat May 9 2020 This Hazardous Weather Outlook is for the Florida Keys and adjacent coastal waters. .DAY ONE...TODAY AND TONIGHT Scattered thunderstorms are expected to develop late this afternoon across the distant Straits of Florida, expanding northward and proliferating overnight. The primary hazards will be heavy downpours resulting in flooding of low-lying areas, frequent deadly cloud to surface lightning strikes, and localized gusty to strong winds. Most thunderstorms will move towards the north at 10 to 20 knots, but deviate storm motion towards the east to southeast at around 10 knots is also possible. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY Scattered to numerous thunderstorms are expected to continue into Sunday with the same primary hazards and storm motion. Eventually widespread moderate to heavy rainfall is expected to develop around the time of higher high tide on Sunday, exacerbating any flooding of low-lying areas. Heavy rainfall will begin to taper off significantly Sunday evening into Sunday night. In addition, a Small Craft Advisory may be required for portions of the coastal waters beginning as early as Monday night and continuing through much of next week. Forecast confidence is increasing in this scenario. Otherwise no hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated. WLC
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Secondary roads and parking lots were flooded through most portions of the City of Layton. Rainfall in excess of 4 inches was estimated by radar.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Florida in 2020Every state in 2020This day in weather historyWarnings in Florida, May 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 897085.