Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 231200
AFDMFL

Area Forecast Discussion
National Weather Service Miami FL
800 AM EDT Sat Sep 23 2017

.AVIATION...
Morning showers will continue to develop through the day with
coverage of thunderstorms increasing this afternoon. Sea breezes
are expected to develop with a convective focus around boundary
collisions. Bouts of Sub-VFR conditions with convection could
require short-fused amendments today.

&&

.PREV DISCUSSION... /issued 434 AM EDT Sat Sep 23 2017/

DISCUSSION...

TODAY THROUGH SUNDAY: Large trough extending across the eastern US
is expected to develop into a weak upper level low that meanders
along the northern Gulf coast through the remainder of the weekend.
Also in place will be a robust area of deep moisture across most of
the state. PWATs from last evening`s MFL sounding were around 2.2",
with the potential for similar values today and tonight.

Temps aloft were seasonably cool from the sounding at around -6C,
but models show the potential for slight cooling to around -7C or so
today with the upper level feature at its closest point to the
region. While ENE flow will dominate, there will once again be the
potential for a Gulf breeze to develop near the coast.

Scattered showers and storms will likely develop late morning near
the east coast then spread inland through the afternoon. Steering
flow initially will be weak, with storms drifting SW, but
expected to pickup later in the day as Hurricane Maria lifts
northeast of the Bahamas and the local pressure gradient tightens.

The concerns today will be for a few stronger storms given the
proximity of the upper low, especially along boundary collisions,
and heavy rainfall. WPC has highlighted the eastern half of South
Florida under a marginal risk for excessive rainfall, keying on
the potential for coastal convergence and backbuilding storms
along with slow storm movement. With drainage difficulties from
sewers with debris still around from Irma, this could lead to some
urban type street flooding, especially along the east coast metro
areas.

The NE flow will bring a few Atlantic and east coast showers
overnight. A similar pattern to today is expected on Sunday, though
stronger winds should bring a little faster storm motion.

EARLY TO MID NEXT WEEK: Hurricane Maria is forecast to continue its
northward track roughly parallel, but east of the US coast through
mid week. As it lifts north of the region on Monday, west-northwest
mid level flow in it`s wake will bring a very dry airmass down the
peninsula. Enough moisture lingers for scattered showers and storms
Monday and Tuesday, with the steering flow favoring the east coast.
Coverage becomes more isolated Wednesday through Friday as PWATs
drop below 1.5", with areas north of the I-75 corridor
potentially remaining dry.

MARINE...Hurricane Maria is forecast to move to the north well east
of Florida and the Central Bahamas over the next few days. As the
storm moves north of the Bahamas, we will see an increase in the NE
swell that has been in place in the Atlantic. Seas may build to 5-
8ft offshore Broward and Palm Beach counties, with swells 4-6ft at
12-13 seconds from Sunday through midweek. Based on the timing of
the seas, a Small Craft Advisory is now in effect for the Palm Beach
waters starting this evening.

Pressure gradient will be strongest today with NE winds 10-15kts in
the Atlantic and around 10kts in the Gulf. Winds will diminish to
around 10kts in the Atlantic and 5-10kts in the Gulf by Sunday, with
prevailing winds becoming more northerly through early next week.

BEACH FORECAST...Increasing northeasterly swells will be the
concern into the upcoming week. Strong rip currents have continued
to be reported along the Palm Beaches, and will likely continue to
through much of the upcoming week. A High Risk for Rip Currents
remains in effect for Palm Beach County today, which will likely
have to be extended further south as we head into next week as the
swells from Maria move in.

With the northeast swell forecast to build to 5 to 6 feet,
especially off Palm Beach County, there will be the potential for
breakers over 10ft, especially at high tide, by Sunday night. High
surf and beach erosion are a significant possibility, which may
necessitate a High Surf Advisory as early as tomorrow..

&&

.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach  88  77  90  76 /  60  40  40  10
Fort Lauderdale  88  78  90  78 /  60  30  40  20
Miami            90  78  91  78 /  60  30  40  20
Naples           91  75  91  76 /  50  20  40  30

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk through this evening for FLZ168.

AM...Small Craft Advisory from 8 PM this evening to 5 PM EDT Monday
     for AMZ650-670.

GM...None.

&&

AVIATION...02/RAG



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