A surface trough with an upper level short wave was moving across South Florida. This allowed mid level 500mb temps to cool and convective instability to increase over the region.
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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 MFL wrote it up.
A surface trough with an upper level short wave was moving across South Florida. This allowed mid level 500mb temps to cool and convective instability to increase over the region. Scattered showers and thunderstorms developed producing gusty winds and hail in Broward County.
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 Sep 20, 12:30 PM EST, 1 hour 30 minutes earlier.
Area Forecast Discussion National Weather Service Miami FL 130 PM EDT Thu Sep 20 2018 .AVIATION... Sea breeze has slowly developed this afternoon. Most of thunderstorm activity will be developing in the western suburbs and across the interior. VCTS for all terminals except TMB, where higher chances of convection moving over the terminal. Convection will diminish after sunset with light and variable winds across the region tonight. Tomorrow easterly flow will be more persistent with a chance of storms once again around 18-19Z. && .PREV DISCUSSION... /issued 951 AM EDT Thu Sep 20 2018/ UPDATE... Scattered to numerous thunderstorms across South Florida will favor the western east coast metro suburbs as well as interior and Gulf coast region this afternoon and evening. The 12Z MFL sounding shows very light steering flow leading to very slow storm motion and a precipitable water value of 1.92 inches, right around normal for this time of year. With the light storm motion there is the potential for some urban flooding in poor drainage areas with any storms capable of producing 1 to 2 inches of rain sitting stagnant over the same area. Other then introducing the chance for urban flooding no major changes to the current forecast as convective initiation looks to be this afternoon and continuing through the evening for the interior and west coast. PREV DISCUSSION... /issued 300 AM EDT Thu Sep 20 2018/ DISCUSSION... TODAY AND TONIGHT... Mid-level ridging will Begin breaking down today as troughing shifts equatorward from coastal Georgia and the western Atlantic into northern Florida. A diffuse frontal zone/surface trough associated with the upper wave will slowly advance south- southwestward into northeast Florida as its western extent hangs up across the lower Gulf Coast states. Moisture pooling will occur ahead of the frontal zone, with northeast steering flow maintaining better moisture over Southern Florida today. The 20.00z MIA sounding observed a precipitable water value of 2.09 inches, with upstream analysis suggesting a similar amount of deep layer moisture should be present today. Given decreased subsidence from the weakening ridge and cooling mid-level temperatures, expect better shower and thunderstorm coverage for today. The northeasterly flow suggests western interior areas will likely see the most numerous activity this afternoon with enhanced convergence from the colliding Atlantic and Gulf coast sea breezes. Thereafter Atlantic showers may affect the east coast metro areas late tonight towards Friday morning. High temperatures today will be in the upper 80s to the lower 90s. FRIDAY AND SATURDAY... A closed mid/upper low will evolve over the Bahamas Thursday night, before moving west across southern Florida on Friday and Friday night. This will bring an increase in moisture and upper level winds, along with cooling mid-level temperatures to around -10 Celsius. Better shower and thunderstorm coverage is expected during this period, with the potential for a few stronger thunderstorms producing gusty winds and heavy rainfall. While the best thunderstorm coverage should be focused towards the interior and west coast given the easterly wind regime, this pattern increases the possibility that Atlantic coastal showers and storms may impact the eastern metro areas during the morning to early afternoon hours before convection pushes inland. Temperatures should remain near to perhaps slightly below normal for this period. SUNDAY THROUGH WEDNESDAY... The upper low will shift into the central Gulf of Mexico on Sunday, bringing southeast flow at the surface and aloft. A few ribbons of vorticity will pass through South Florida, suggesting better thunderstorm coverage will continue into Sunday. While mid-level temperatures will have warmed some, they remain cool enough for a strong storm or two to be possible. Interior and west coast locations once again stand to see the best thunderstorm coverage in this flow regime. Slightly drier air appears to filter in for early next week, although the deterministic guidance still brings a few weak perturbations through from time to time. Thunderstorm coverage may decrease a bit from Sunday, but we're still looking for scattered activity across the area with western interior areas favored for the better coverage. Temperatures should remain near seasonal normals for this period. MARINE... Light and variable winds this morning will become northeasterly this afternoon before veering easterly tonight. Speeds will average 5 knots or less early this morning, increasing to around 10 knots this afternoon. Seas will generally be 2 feet or less. Scattered showers and thunderstorms are possible over the Atlantic and Gulf waters into tonight. Prevailing easterly winds are anticipated into this weekend with seas remaining around 2 feet or less. The greatest hazard to boaters through the weekend will be scattered thunderstorms which could produce locally higher winds and waves in addition to lightning. && .PRELIMINARY POINT TEMPS/POPS... West Palm Beach 76 88 76 87 / 30 40 40 50 Fort Lauderdale 79 87 77 87 / 30 40 40 50 Miami 76 87 76 87 / 30 40 40 50 Naples 74 89 73 89 / 40 70 20 60 && .MFL WATCHES/WARNINGS/ADVISORIES... FL...None. AM...None. GM...None. && AVIATION...33/Kelly
Hazardous Weather Outlook for South Florida National Weather Service Miami FL 941 AM EDT Thu Sep 20 2018 AMZ610-630-650-651-670-671-FLZ063-066>075-168-172>174-GMZ656-657-676- 210145- 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- 941 AM EDT Thu Sep 20 2018 ...SCATTERED TO NUMEROUS THUNDERSTORMS FAVORING INTERIOR AND WEST... ...LOCALLY HEAVY RAINFALL MAY CAUSE URBAN FLOODING... This hazardous weather outlook is for South Florida. .DAY ONE...TODAY AND TONIGHT Thunderstorms: Scattered showers and thunderstorms across South Florida mainly the western east coast suburbs, interior and west coast. The primary threat will be lightning and locally heavy rainfall. Flooding: With slow storm motion there is a chance of urban and poor drainage area flooding with locally heavy downpours. Temperatures:Daytime heat index values of around 105 degrees are possible over portions of northern Palm Beach County. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY Scattered mainly afternoon thunderstorms are forecast each day, especially over the western interior. The primary threats are lightning, heavy rain, and gusty winds. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed. For more information...visit the National Weather Service in Miami website at www.weather.gov/miami.
The Miami radar (KAMX), 75 km away, was scanning. The volume nearest the first event began at 19:02 UTC.
4 hail, 1 thunderstorm wind. Local standard time, as filed.
A trained spotter reported dime sized hail on 99th Avenue in Coral Springs. Multiple other reports of smaller hail in the area.
A trained spotter near the intersection of Coral Ridge Drive and Southgate Boulevard reported gusty winds enough to blow around some metal sheeting in a backyard. Radar estimates winds of 50 mph.
A trained spotter reported of dime size hail near intersection of Coral Ridge Drive and Royal Palm Blvd.
Members of the public and photos on social media show quarter sized hail fell near the BB&T Center in Sunrise.
A trained spotter reported 3/4 inch hail at Sawgrass Mills Mall in Sunrise.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Florida in 2018Every state in 2018This day in weather historyWarnings in Florida, September 2018
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: 786832, 786851, 786844, 786848, 786841.