Moist SE wind flow at the surface, along with instability provided by an upper level low pressure area just south of South Florida, helped to trigger scattered showers and thunderstorms, some with heavy rainfall.
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The episode as NWS MFL wrote it up.
Moist SE wind flow at the surface, along with instability provided by an upper level low pressure area just south of South Florida, helped to trigger scattered showers and thunderstorms, some with heavy rainfall.
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 Miami, FL wrote its last area forecast discussion before the first event at Oct 12, 2:30 AM EST, 3 hours earlier.
Area Forecast Discussion National Weather Service Miami FL 330 AM EDT Tue Oct 12 2021 .SHORT TERM... Today (through Wednesday) An upper level low has gradually drifted south, with convection developing on the eastern periphery of this feature, while dry air advects over South Florida. This is evidenced in the latest GOES water vapor imagery, which reveals dry slotting on the western periphery of the aforementioned upper low. Within the boundary layer, winds remain out of the east/southeast with a somewhat well mixed moisture profile (dewpoints around 22C). This advection of modest moisture and sufficient destabilization (roughly 2000-2500 J/Kg of surface-based CAPE) should allow for scattered showers and thunderstorms to develop today. Development should be favored over east coast locations mid-morning/early afternoon, with a graduation westwards propagation towards the interior by late afternoon. While the nature of convection should remain sub-severe today, cool temperatures aloft (roughly -8C at 500 hPa) and steepened mid-level lapse rates may allow for a few overachieving thunderstorms today, capable of producing wind gusts up to around 45 mph. Wednesday A broad, 500 hPa ridge of around 590 decameters is forecast to encompass portions of the southeastern United States, allowing a weakening and regressing of the aforementioned upper low and warming temperatures aloft. Additionally, the upper geopotential height gradient increases and allows a jet streak to become entrenched over the region, which may act to enhance upper level convergence. This environment will bode less favorable for potent storms. Nevertheless, the continuation of onshore moisture advection out of the ESE should allow for scattered shower and thunderstorm development during this day as well, with a similar east to west progression. Temperatures will remain seasonable today, perhaps a degree or two below climatological normals along the east coast. Wednesday will feature slightly warmer temperatures owing to increasing geopotential heights aloft as the upper ridge builds in. .LONG TERM (Wednesday night through Monday)... Synoptic Overview: The stubborn cut-off low will finally begin to retrograde southwestward Thursday into Friday as an increasingly- elongated SW-NE oriented ridge positions itself just north of South Florida. This ridge will then flatten into the weekend as a progressive shortwave trough pushes through the eastern CONUS. The system's surface low and attendant fronts should push into Florida over the weekend, but the front will likely stall just north of the area. Heading into early next week, predictability begins to wane as split flow looks to develop over the CONUS with generally low amplitude features present in the southern stream. Dailies... Thursday: Moist easterly flow will remain in place over the area resulting in another warm day (Highs in the upper 80s) with scattered convection progressing westward through the afternoon. Friday: A transition day as the low-lvl flow begins to back more northeasterly and the mid-lvls begin to dry as the ridge axis shifts closer. Still think there is enough moisture/instability for isolated convection to develop but coverage (both of precip and thunder) should be less than Thursday. Saturday/Sunday: The weekend largely looks dry as the front/associated precipitation remain north of the area. It is possible some frontal precipitation makes it to portions of our area on Sunday, but don't have much confidence it makes it this far south. Highs remain in the upper 80s with dewpoints in the low 70s, quite the contrast with postfrontal portions of Northern Florida where dewpoints could be in the low 40s. Monday: Uncertainty increases to start next week, as easterly flow begins to increase and moisture begins to return northward. The aforementioned stalled boundary could also serve as a focus but it's position is nebulous. Regardless, it looks like we will have to continue to wait for the true start of the dry season. && .AVIATION(06Z TAFS)... && .MARINE... An upper level disturbance will tap into remnant moisture, allowing for scattered shower and thunderstorm develop. The greatest coverage is anticipated over the Atlantic waters. Outside of locally gusty winds with showers and storms, light to moderate winds and small waves should retain generally benign marine conditions as high pressure builds into the region. A 1 to 2 ft long period swell will gradually move into the Atlantic waters off South Florida from an area of low pressure off the Carolina coast. && .BEACHES... Minor coastal flooding is possible along the coast of Palm Beach County today during high tide, though impacts should be isolated/minimal. The rip current risk will gradually increase for the east coast beaches this week, especially for beaches associated with Palm Beach County where a small long period swell will be present. && .PRELIMINARY POINT TEMPS/POPS... Miami 87 75 88 76 / 50 30 40 30 West Kendall 88 73 89 75 / 50 30 40 30 Opa-Locka 87 75 89 75 / 50 30 40 30 Homestead 86 73 87 75 / 50 30 40 40 Fort Lauderdale 86 75 87 77 / 40 30 40 30 N Ft Lauderdale 87 76 87 77 / 40 30 40 30 Pembroke Pines 86 74 87 75 / 40 30 40 30 West Palm Beach 87 75 87 75 / 40 30 40 30 Boca Raton 87 75 87 76 / 50 30 40 30 Naples 88 73 89 74 / 40 30 40 20 && .MFL WATCHES/WARNINGS/ADVISORIES... FL...None. AM...None. GM...None. && Today through Wednesday and Aviation/Marine...Bhatti Wednesday Night through Monday...Carr Visit us at weather.gov/miami Follow us on Facebook and Twitter at: www.facebook.com/nwsmiami www.twitter.com/nwsmiami
Hazardous Weather Outlook for South Florida...UPDATED National Weather Service Miami FL 1226 PM EDT Mon Oct 11 2021 AMZ610-630-650-651-670-671-FLZ063-066>075-168-172>174-GMZ656-657-676- 121030- Lake Okeechobee-Biscayne Bay- Coastal waters from Jupiter Inlet to Deerfield Beach FL out 20 NM- Coastal waters from Deerfield Beach to Ocean Reef FL out 20 NM- Waters from Jupiter Inlet to Deerfield Beach FL from 20 to 60 NM- Waters from Deerfield Beach to Ocean Reef FL from 20 to 60 NM excluding the territorial waters of Bahamas-Glades-Hendry- Inland Palm Beach-Metro Palm Beach-Coastal Collier-Inland Collier- Inland Broward-Metro Broward-Inland Miami-Dade-Metro Miami-Dade- Mainland Monroe-Coastal Palm Beach-Coastal Broward-Coastal Miami- Dade-Far South Miami-Dade- Coastal waters from Chokoloskee to Bonita Beach FL out 20 NM- Coastal waters from East Cape Sable to Chokoloskee FL out 20 NM- Waters from Chokoloskee to Bonita Beach FL from 20 to 60 NM- 1226 PM EDT Mon Oct 11 2021 ...ISOLATED TO SCATTERED STORMS POSSIBLE TODAY... ...MINOR COASTAL FLOODING POSSIBLE AROUND HIGH TIDE EAST COAST... This hazardous weather outlook is for South Florida. .DAY ONE...THIS AFTERNOON AND TONIGHT Thunderstorms: Isolated to scattered thunderstorms are possible today, with a focus over the east coast and interior this afternoon. Locally strong wind gusts and brief heavy downpours could accompany the stronger storms. Waterspouts: Conditions are favorable for waterspouts today, particularly over the Atlantic waters. Flooding: Isolated flooding will be possible with slow-moving showers and thunderstorms, especially over the east coast metro areas. Coastal Flooding: Minor tidal flooding of vulnerable low-lying areas along the Atlantic coast is possible during times of high tide. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY The rip current risk will gradually increase once again for the east coast beaches of South Florida this week. Isolated to scattered showers and thunderstorms are possible through much of the week. Main impacts will be lightning, locally gusty winds, and heavy rainfall/isolated flooding. .SPOTTER INFORMATION STATEMENT... Widespread spotter activation is not anticipated, however individual spotters are encouraged to report high wind, hail and flooding to the National Weather Service forecast office in Miami. For more information...visit the National Weather Service in Miami website at www.weather.gov/miami. Weinman
The national radar mosaic for the moment the first event began.
2 flood. Local standard time, as filed.
Reports of street flooding received via social media along portions of Hood Road in Palm Beach Gardens. Measured rainfall rates in the area were about 1-2 inches per hour.
Street flooding was reported via social media at the intersection of North Flagler Drive and 10th Street in West Palm Beach, with waters of about 2-3 inches deep covering the roadway.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Florida in 2021Every state in 2021This day in weather historyWarnings in Florida, October 2021
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: 988762, 988768.