Numerous thunderstorms developing in advance of a slowly-approaching cold front trained over Vaca Key, producing extensive street flooding in the city of Marathon, Florida.
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The episode as NWS KEY wrote it up.
Numerous thunderstorms developing in advance of a slowly-approaching cold front trained over Vaca Key, producing extensive street flooding in the city of Marathon, Florida.
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 20, 3:51 AM EST, 2 hours 39 minutes earlier.
Area Forecast Discussion National Weather Service Key West FL 451 AM EDT Mon May 20 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 451 AM EDT Mon May 20 2024 This morning has felt like summertime in terms of convection across the Florida Keys. Mesoscale boundaries have been the main trigger mechanism for convection, with multiple outflow boundaries still present on radar. KBYX is currently detecting scattered convection within the forecast area, with most of the storms aligning with or being adjacent to the island chain. The strongest activity is currently located near the Upper and Middle Keys. Good upper- level support has been very evident across most of the region, with radar derived hail hedging close to 2" inches in the waters across the Bahamas and even in a storm that plowed through the distant Straits earlier. The activity closer to home has not been able to fire up as well until just recently, which may be due in part to drier air in the mid- levels sampled by last night's 00Z sounding. The storms that have been able to overcome this drier air have been able to tap into the fat CAPE profiles and have gone nuts. Panning out from the Keys, a trough is extending across the western North Atlantic, dragging a frontal boundary in its wake. This front has made it almost to Central Florida. A good environment will remain in place for scattered showers and isolated thunderstorms today. Winds will continue to shift to the north ahead of the aforementioned frontal boundary, which will continue to usher in lower dew points. Dew points have already dropped roughly 3-5 degrees over the past few hours, which has made quite an impressive difference in the level of comfort when walking outdoors. These lowered dew points and temperatures will keep the Keys below the threshold for Heat Advisories through the remainder of the week. Winds will remain generally from the northwest to north through Tuesday night, briefing becoming variable on Tuesday. Decent moisture will remain in place through Wednesday, which could help spur on mesoscale processes such as cloud lines during this timeframe. Guidance has trended downwards on the higher rain chances through Wednesday, so have capped PoPs at 30%. Forecast rain chances may continue to decrease, depending on how much dry air can invade into the mid-levels. Easterly flow will return by mid-week as high pressure really builds back in, which will allow for dew points to gradually rise back into the mid 70s. As of now, MOS guidance does not hint at any of the oppressive dew points we have been tormented with over the past few days returning through the extended forecast luckily. && .MARINE... Issued at 451 AM EDT Mon May 20 2024 There are no watches, warnings, or advisories in effect for the Florida Keys coastal waters. From synopsis, a frontal boundary currently draped across north Central Florida has helped the wind field across the Florida Keys become somewhat nebulous this morning. Breezes have begun to shift to the west to northwest in the western waters. By this afternoon, breezes will veer to the northwest and increase. Tuesday through Wednesday, breezes will gradually shift to the east as high pressure in the western North Atlantic builds back in across the region. && .AVIATION... (06Z TAFS) Issued at 451 AM EDT Mon May 20 2024 Widely scattered showers with a few isolated thunderstorms will wax and wane in the vicinity of the island chain early this morning. After sunrise, this activity will diminish with slight rain chances persisting throughout the rest of the day. VCTS is included at both terminals until we expect this activity to die down, though any shower passing over a terminal may result in MVFR CIGs or VIS and will be TEMPO'ed as needed. Near surface winds will start out light of the southwest, becoming northwest at 5 to 10 knots this afternoon. && .CLIMATE... On this day in 1932, the daily record rainfall of 3.83" was recorded in Key West. Rainfall records date back to 1871. && .PRELIMINARY POINT TEMPS/POPS... Key West 90 79 89 79 / 20 30 30 30 Marathon 89 80 89 80 / 30 30 30 30 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...None. && Public/Marine/Fire...NB Aviation/Nowcasts....JAM Data Acquisition.....JAM 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 356 AM EDT Mon May 20 2024 FLZ076>078-GMZ031>035-042>044-052>055-072>075-210800- 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- 356 AM EDT Mon May 20 2024 This Hazardous Weather Outlook is for the Florida Keys and adjacent coastal waters. .DAY ONE...Today and tonight. Isolated thunderstorms will be possible tonight. The primary hazards will be lightning strikes and locally gusty winds. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Isolated thunderstorms will be possible Tuesday through Sunday. The primary hazards will be lightning strikes and locally gusty winds. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. NB
Special Weather Statement
National Weather Service Key West FL
645 AM EDT Mon May 20 2024
FLZ076-201115-
Monroe Upper Keys FL-
645 AM EDT Mon May 20 2024
...A STRONG THUNDERSTORM WILL IMPACT UPPER KEYS IN MONROE COUNTY
THROUGH 715 AM EDT...
At 644 AM EDT, Doppler radar was tracking a strong thunderstorm over
Teatable Key, or 8 miles northeast of East End Of Channel 5 Bridge,
moving east at 25 mph.
HAZARD...Wind gusts up to 40 mph and pea size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor hail damage to vegetation is
possible.
Locations impacted include...
Key Largo, Plantation, Teatable Key, Lower Matecumbe Key, Upper
Matecumbe Key, Windley Key, and Islamorada.
This includes US 1 between mile markers 75 and 96.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 2503 8044 2493 8055 2486 8066 2485 8073
2490 8075 2493 8071 2494 8066 2504 8054
2507 8044
TIME...MOT...LOC 1044Z 253DEG 20KT 2492 8067
MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH
JAMThe national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Extensive street flooding with a few streets impassable to smaller vehicles was observed in Marathon due to several training thunderstorm cells passing over Vaca Key.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Florida in 2024Every state in 2024This day in weather historyWarnings in Florida, May 2024
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: 1171091.