A frontal boundary is draped over the Atlantic waters off the eastern sea board of the United States and across central Florida and into the Gulf of Mexico. Aloft, high pressure retreats into the central Gulf and western Caribbean with a mid-level trough amplifying across the peninsula.
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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 frontal boundary is draped over the Atlantic waters off the eastern sea board of the United States and across central Florida and into the Gulf of Mexico. Aloft, high pressure retreats into the central Gulf and western Caribbean with a mid-level trough amplifying across the peninsula. Additionally, a mesolow has developed along the frontal boundary off the Space Coast before pushing over the Lake Okeechobee region and into the Atlantic waters. This setup combined with increasing amounts of available moisture |created areas of more vigorous convection that produced torrential rainfall that eventually lead to flooding across areas of Palm Beach and Hendry counties.
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, 2:35 PM EST, 1 hour 55 minutes earlier.
Area Forecast Discussion
National Weather Service Miami FL
335 PM EDT Sun Sep 20 2020
.Short Term (Now through Monday)...
This Afternoon...
A complex pattern evolving today, with several features/impacts
to discuss. First, there is a notable mesoscale low, currently WNW
of Lake Okeechobee, which is evident in latest visible satellite
imagery. While model guidance has been somewhat disparate
regarding this feature, A SW track is forecast to occur, which
should bring the meso-low over near the western interior and
eventually into the Gulf waters. As this progression takes place
this afternoon, a broad surface trough is forecast to develop over
South Florida this afternoon. This isobaric gradient (trough)
becomes induced by both the relative convergent cyclonic wind flow
accompanying the meso-low as well as sufficient differential
heating that takes place, as portions of the interior are forecast
to reach up into the lower to mid 90s this afternoon. The
environment is characterized by deep tropical moisture (2.0-2.3
PWI) and weak steering flow (850-300 hPa mean winds < 5 kts).
Areas where high theta-e air intercepts localized sea-breeze
convergent wind maxima will be favorable for deep convection, of
which may be capable of producing torrential rainfall and strong
wind gusts. For this afternoon, the signal for highest storm
potential is presently over the interior, though activity is
forecast to increase over the Atlantic metros late this afternoon
and into the evening.
Tonight Through Monday...
The concern for heavy rainfall and flooding lingers overnight into
Monday morning. A vigorous shortwave impulse is forecast to
propagate from north to south, around the eastern portion of 500 hPa
anticyclone located in the Gulf of Mexico. A frontal boundary is
attendant with this feature, oriented across south central Florida
with a gradual southerly propagation. A narrow NE convergent wind
field exists ahead of this boundary. Additionally, a swath of high
precipitable water congeals over the Atlantic waters/metros Monday
morning. Higher boundary layer wind speeds associated with the
tightening pressure gradient will yield impressive moisture fluxes,
likely resulting in showers/thunderstorms over the Atlantic waters
overnight and into the morning. This activity may propagate into the
metros, which could present a localized flooding threat.
Furthermore, RAP prognostic data is parsing SFC-3km bulk shear
values of 15-20 kts. This could favor strong bowing segments, which
may be further enhanced by the uptick in synoptic wind speeds.
Therefore, the main impacts of concern tonight into Monday are
strong wind gusts and localized flooding.
Temperatures will be uncomfortable this afternoon, with max
temperatures in the lower to mid 90s across the region. Some relief
is anticipated for Monday, likely owing to widespread cloud cover
tomorrow morning as well as advection of a slightly cooler maritime
airmass. High temperatures for Monday are forecast to be in the mid
to upper 80s across the region.
.Long Term (Tuesday through Sunday)...
A drier air mass will move into the region for Tuesday and
Wednesday as high pressure continues to build in from the north.
At the same time, Hurricane Teddy will interact with the frontal
boundary well off to the northeast in the Atlantic. This will help
to continue the strong pressure gradient over South Florida which
will allow for the gusty conditions to continue throughout the
day on Tuesday. There will be a slight chance of showers as
enough lower level moisture will remain in place, however, any
shower that does develop will be fast moving and rather shallow.
The pressure gradient across the region will begin to decrease on
Wednesday and the dry air mass will remain in place. A slight
chance of showers cannot be ruled out during the day on Wednesday
as enough low level moisture still will be in place. Temperatures
during this time frame will be in the mid 80s across the east
coast metro areas to around 90 across the interior sections.
On Thursday, the weather pattern begins to change as the latest
computer model guidance show a mid level disturbance over the
central portion of the country beginning to interact with Tropical
Storm Beta in the western Gulf of Mexico. This interaction will
help to draw the frontal boundary in the Florida Straits back
northward slowly as a warm front as the mid level disturbance
moves eastward. This will allow for additional moisture to return
to the region which will increase the chances of showers and
thunderstorms from Thursday through the end of the week. The
timing of this frontal boundary moving northward is still
uncertain as the ECMWF is a bit slower then then GFS is. The
slower solution would delay the onset of increased chances of
showers and thunderstorms. With the increased amount of moisture,
locally strong convection could lead to heavy rainfall and gusty
towards the end of the week and into next weekend. This will
continue to be monitored as the week progresses.
&&
.Marine...
An approaching frontal boundary will result in an uptick in winds
speeds over the Atlantic waters. A surge of moisture will advance
ahead of the front tomorrow as well, which will increase the chance
for showers and storms across the region, mainly overnight into
Monday morning. Breezy NE winds in association with the front will
phase with swell emanating from Hurricane Teddy to produce hazardous
seas beginning this afternoon. The highest swell and wave heights
are forecast to be over the Palm beach waters initially, but will
protrude southward into Broward/Miami-Dade waters as well. Given the
aforementioned conditions, a Small Craft Advisory is currently in
effect. There could be periods where wind speeds meet gale force
criteria, however this does not currently merit a Gale Watch. Will
monitor and update as necessary.
&&
.Aviation...
Showers and storms will continue to develop along the sea breezes
this afternoon and affect the TAF sites. There should be a drop in
shower and thunderstorm activity this evening before increasing the
coverage over the east coast metro areas late tonight. The ceiling
and vis will be in the VFR conditions but fall into the MVFR or even
IFR conditions with the showers and thunderstorms.
&&
.Beach Forecast...
NE swell off the Atlantic coast will be increasing across the
Atlantic waters through at least the middle of this week allowing
for an elevated risk of rip currents to persist, with the highest
risk along the Palm Beach coastline. Therefore, a High Surf Advisory
is in effect for the beaches of Palm Beach County and a High Risk of
Rip Currents in effect for the east coast beaches of South Florida.
Astronomically higher than normal tides may result in minor coastal
flooding along coastal Miami-Dade, Broward, and Palm Beach counties
and isolated minor coastal flooding in Collier County through Sunday
evening. Considering this risk, a Coastal Flood Advisory is in
effect for the Atlantic coast and a Coastal Flood Statement in
effect for the beaches of Collier County.
&&
.Preliminary Point Temps/PoPs...
West Palm Beach 78 86 76 86 / 70 50 20 20
Fort Lauderdale 79 86 77 86 / 70 70 30 20
Miami 78 86 76 86 / 60 70 30 20
Naples 76 88 73 89 / 40 30 20 10
&&
.MFL WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk through Tuesday evening for FLZ168-172-173.
High Surf Advisory until 8 PM EDT Tuesday for FLZ168.
Coastal Flood Advisory until 8 PM EDT this evening for FLZ168-
172-173.
AM...Small Craft Advisory until 8 PM EDT Tuesday for AMZ610-650-651-
670-671.
Small Craft Advisory from 2 AM Monday to 8 PM EDT Tuesday for
AMZ630.
GM...Small Craft Advisory until 8 PM EDT Tuesday for GMZ656-657-676.
&&
Marine...09/Bhatti
Aviation...09/Bhatti
Beach Forecast...09/Bhatti
Short Term...09/Bhatti
Long Term...55/CWCHazardous Weather Outlook for South Florida National Weather Service Miami FL 452 PM EDT Sun Sep 20 2020 AMZ610-630-650-651-670-671-FLZ063-066>075-168-172>174-GMZ656-657-676- 210900- 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- 452 PM EDT Sun Sep 20 2020 ...Localized Flooding Possible Tonight... ...Hazardous Marine Conditions... ...High Risk of Rip Current Risk along Atlantic Coast... This hazardous weather outlook is for South Florida. .DAY ONE...TONIGHT Rip currents: A high risk of rip currents exists along the Atlantic beaches of South Florida. Beach erosion is possible along the Atlantic and high surf is forecast along the Palm Beaches. Coastal Flooding: Minor flooding of coastal locations is possible, particularly around the times of high tide due to astronomically higher tides. Thunderstorms: A few thunderstorms are possible across South Florida this evening. Lightning and locally excessive rainfall are the primary hazards. Strong wind gusts and funnel clouds are possible with a strong storm or two this evening. Waterspouts: A few waterspouts are possible today for all the local South Florida waters. Wind: Strong thunderstorms today could produce wind gusts to 50 mph. Increasing northeasterly winds of 20 to 25 knots with gusts to gale force this evening into tonight will pose hazardous marine conditions across all the South Florida waters. Flooding: Heavy rainfall from thunderstorms could lead to flooding, particularly in urbanized and poorly drained areas in the east coast metro areas this evening and tonight. Areas that drain to local bodies of water may also experience slower than normal drainage around the times of high tide due to the astronomically higher tides. Waves: Incoming swell and increasing winds will allow seas in the Atlantic to build to 7 to 12 feet, mainly over the Palm Beach coastal waters. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY The frontal boundary will push across the area on Monday with showers and thunderstorms capable of producing strong wind gusts, torrential rainfall, localized flooding, and lightning. Hazardous marine and beach conditions will linger through the week, particularly in the Atlantic. Thunderstorm chances return to the forecast later in the week. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. Please relay any information about observed severe weather and flooding to the National Weather Service forecast office in Miami while following all local, state, and CDC guidelines. For more information...visit the National Weather Service in Miami website at www.weather.gov/miami.
The national radar mosaic for the moment the first event began.
2 flood. Local standard time, as filed.
A trained weather spotter reported street flooding at the intersection of Forest Hill Boulevard and Southern Boulevard in Wellington, FL and vicinity due to passing storms. Rainfall estimates were around 2 inches within an hour.
Law enforcement reported street flooding near the intersection of Bridge Street and Oklahoma Avenue due to heavy rainfall from thunderstorms.
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, September 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: 920191, 920192.