Flood in Florida, August 20, 2017

Area Forecast Discussion...UPDATED
National Weather Service Miami FL
1041 AM EDT Sun Aug 20 2017

.UPDATE...
An opening round of Atlantic convection has pushed ashore of the
east coast metropolitan area and weakened as it progressed inland.
The morning MFL sounding shows a very moist atmosphere with a
precipitable water value of 2.22 inches, supported by 2.18 inches
at KEY. The main threat today will continue to be potential
flooding from heavy rainfall and cloud-to-ground lightning. This
morning's soundings do not show an environment as conducive for
strong wind gusts compared to previous days, but gusts of 35 to 45
mph certainly cannot be ruled out with boundary collisions later
today. Current forecast captures this potential focus over the
interior and Gulf coast well. No updates are currently planned,
with temperatures still appearing to be in line with the latest
guidance. Have a great Sunday!

&&

.PREV DISCUSSION... /issued 731 AM EDT Sun Aug 20 2017/

AVIATION...
Convection associated with a tropical wave is moving across South
Florida this morning, bringing MVFR and brief bouts of IFR to the
east coast terminals. Convection should spread north and west
today, with the potential to persist a good amount of the day.
Sub-VFR bouts will be possible with a need for short-fused
amendments through the day. Convection should begin to trend down
as the wave exits later this evening.

PREV DISCUSSION... /issued 416 AM EDT Sun Aug 20 2017/

DISCUSSION...

TODAY AND TONIGHT: The axis of the first of our tropical waves is
moving into the southern peninsula early this morning. The
ongoing convection over the local Atlantic and NW Bahamas has
waned over the past few hours, leaving only isolated light showers
as we approach daybreak. This may potentially be due to ongoing
shear from the upper level low over the eastern Gulf and/or a
weaker tropical wave limiting low level convergence.

Models have fallen into two camps this morning, either backing
off on convective development through mid morning or ramping up
activity along the local Atlantic and east coast right after
daybreak. While there has been a modest increase in light showers
in the past hour, have leaned towards the slower start based on
satellite/radar trends.

Derived TPW satellite shows PWATs of 2.2-2.3 inches encroaching
on the region, which should be firmly in place as we get on the
more convectively favored east side of the wave by mid morning.
Add some daytime heating, and expect rain to pick up across the
area later this morning. Don't foresee a significant flood threat
today, but given the anomalously moist environment, heavy rain
rates can't be ruled out as stronger convection develops. Expect
impacts to be limited to local flooding of streets and poor
drainage areas.

Showers with embedded storms will shift west later in the
afternoon as the wave tracks into the Gulf, with activity waning
from east to west later today and drier conditions tonight.

MONDAY: No change in the forecast thinking as the work week and
eclipse day starts out with the driest day of the week. Wave vapor
satellite shows well the area of subsidence and dry air in the mid-
upper levels to our east in between the departing tropical wave from
today, and the next wave (Invest 92L). There will still be enough
low level moisture for typical afternoon boundary layer cumulus, but
storm chances look isolated at best for most of the region. With
breezy east winds in place, the east coast sea breeze should be able
to get going and push pretty far inland, likely providing the main
focus for any isolated convection.

Overall partly cloudy skies look to be in place for the eclipse
Monday afternoon, though anyone in/near any storms will see
mostly cloudy conditions. Cloud cover from the next tropical wave
begins to invade from the east during the late afternoon, but
there is a reasonable chance thick clouds and showers will hold
off until after sunset for east coast viewers.

TUESDAY THROUGH THE END OF THE WEEK: Weather for the middle of the
weak across South Florida will still be driven by the arrival of
Invest 92L, or its remnants, moving west across the region on
Tuesday. Conditions are only expected to be only marginally
favorable for this system to develop any further, and model trends
support this with a somewhat drier, and weaker feature as it
arrives. Satellite data shows PWATs 2.1-2.3" pooled around this
feature currently, which models support arriving intact as it moves
into South Florida. So even with perhaps a weaker wave, the return
of tropical moisture as we get on the back side of the wave will
bring a return of numerous showers with embedded thunderstorms for
Tues and Wed.

Pattern remains unsettled into late week as deep upper low over
Canada drives digging trough through the eastern US, with an
associated frontal boundary sagging anomalously south into the
Florida peninsula. With both the low and mid level ridge axis
suppressed to the south, we will be under south-southwesterly flow
that will continue to tap into the tropical airmass to our south.
Numerous showers and scattered storms can be expected through the
period, likely with a diurnal maximum.

Given the potential for several days of active weather in a
tropical airmass, this period will need to be watched for local
flooding problems.

MARINE...High pressure to our north will keep prevailing east-
southeast flow in place over the local waters through mid week.
Multiple tropical waves passing through the region will maintain
generally moderate speeds, with fresh winds possible at time
starting late tonight through Monday night, requiring small craft to
exercise caution.

The increase in speeds will bring an increase in wave heights,
building to around 4 feet over the open waters tonight through
Monday night, before gradually decreasing mid week as winds decrease.

Expect scattered to numerous showers and storms over the waters
through today as a tropical wave crosses the region. Coverage will
briefly be lower on Monday, before increasing again Tuesday onwards
with the next tropical wave and an unsettled pattern.

BEACH FORECAST...An increase in east-southeast flow early this week
will raise the rip current threat at the Atlantic beaches through
Tuesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach  89  81  93  81 /  60  20  20  30
Fort Lauderdale  89  82  91  81 /  60  20  20  40
Miami            89  81  92  80 /  60  10  20  30
Naples           92  77  96  79 /  60  20  20  10

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...None.
GM...None.

&&

UPDATE...02/RAG
DISCUSSION...88/ALM
MARINE...88/ALM
AVIATION...02/RAG

Hazardous Weather Outlook for South Florida
National Weather Service Miami FL
409 AM EDT Sun Aug 20 2017

AMZ610-630-650-651-670-671-FLZ063-066>075-168-172>174-GMZ656-657-676-
202015-
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-
409 AM EDT Sun Aug 20 2017

...SCATTERED STORMS ARE EXPECTED WITH LOCALLY HEAVY RAINFALL TODAY...

This hazardous weather outlook is for South Florida.

.DAY ONE...TODAY AND TONIGHT

Thunderstorms: There is a chance of thunderstorms across South
Florida today. The primary impacts from the storms will be lightning
strikes and heavy rainfall.

Flooding: Ponding of water on roadways, especially in low lying
areas, and locations with poor drainage will be possible today.

No other hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

Increasing tropical moisture is forecast to bring better storm
coverage to South Florida for most of this week, as a tropical wave
moves into the area from the Bahama Islands. The primary impacts from
the storms will be lightning strikes and locally heavy rainfall.

Stronger easterly flow early this week may bring an increase threat
for strong rip currents, before decreasing late this week as the
easterly winds decrease.

No other hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Widespread spotter activation is not anticipated, however individual
spotters are encouraged to report 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.

Baxter

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MIAMI FL
1101 AM EDT SUN AUG 20 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0955 AM     MARINE TSTM WIND 8 SSE KEY BISCAYNE      25.59N  80.10W
08/20/2017  M43 MPH          AMZ651             FL   BUOY

            A MARINE THUNDERSTORM WIND GUST OF 37 KNOTS... 43
            MPH... WAS RECORDED AT FOWEY ROCKS...AN ELEVATED
            ANEMOMETER SITE... AT 955AM.

&&

EVENT NUMBER MFL1700343

HAGEN