Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 182028
AFDMFL

Area Forecast Discussion
National Weather Service Miami FL
428 PM EDT Fri Aug 18 2017

.DISCUSSION...

...Heavy rain possible Saturday into Sunday for South Florida...

FRIDAY AFTERNOON THROUGH SUNDAY
A large, well-defined upper-level low is currently centered over the
region. Scattered thunderstorms are developing over the interior
this afternoon. Expect this activity to continue over the
interior and west coast through early evening. Several
thermodynamic ingredients from the 12Z adjusted sounding and RAP
model soundings indicate that some of the thunderstorms this
afternoon will be strong over the interior and west coast areas.
Cannot rule out one or two severe storms. Hail and gusty winds are
the main threats. Expect thunderstorm activity to diminish after
sunset.

On Saturday, a tropical wave will approach South Florida, bringing
rainier than normal conditions from Saturday afternoon through
Sunday morning, and possibly lasting through Sunday afternoon. Most
guidance indicate PWATs in the 2.0-2.4" range during much of the
period. There will be a risk of localized street flooding. There
is a chance for sunshine Saturday morning prior to the arrival of
the tropical wave, so can`t completely rule out some strong storms
on Saturday afternoon. Again, the primary threat on
Saturday/Sunday is for heavy rain and localized flooding.

SUNDAY NIGHT THROUGH FRIDAY
Sunday night and Monday, there will be an influence of mid-upper
ridging from the Bermuda high, which will serve as a short-lived
break from the higher than normal rain chances. A strong
mid/upper-level high pressure area will move westward and anchor
itself over the southeastern United States by Tuesday. At the same
time, the tropical disturbance currently located about 600 miles
east-northeast of the northern Leeward Islands (Invest 92L), is
likely to be approaching the region. NHC indicates a 60% chance of
development as their 2 PM Tropical Weather Outlook. Regardless of
development, this system is likely to bring a chance for enhanced
rainfall to South Florida early Tuesday through Wednesday. All
residents and visitors of South Florida need to continue to
monitor this tropical disturbance through the weekend.

Even though the threat from 92L should be gone by late next week,
the GFS and other models hint that we could remain in a rainy
pattern associated with a left-over trail of moisture from 92L
combined with a frontal boundary to our north. Low-mid level
southerly winds will advect deep tropical moisture over South
Florida toward the boundary, resulting in a continued rainy
pattern that lasts through the week.

&&

.MARINE...
Mostly good boating conditions are expected for South
Florida waters off both coasts through the first part of the weekend
with seas 2 feet or less. By Saturday night, winds increase to 15
kt and seas build to around 3 feet for the Atlantic waters.
Expect these 3 foot seas to continue through Sunday, with 2-3
foot seas for the Gulf waters. By Sunday night, seas build to 4
feet with a few areas of 5 feet possible for the Atlantic waters.
Seas averaging around 4 feet can be expected to last through early
next week for the Atlantic waters.

Small craft exercise caution conditions may be possible by late
Saturday night or Sunday morning for Atlantic waters due to winds
in the 15-20 knot range.

&&

.AVIATION...

Generally drier conditions along the east coast with
storms developing along sea breeze as it pushes into interior
towards APF. Convection should diminish overnight. Saturday may
be a bit of a transition day with a tropical disturbance near the
Bahamas potentially increasing rain chances near the tail end of
the TAF period. Any direct impacts to terminals by convection
could lead to sub-VFR conditions which will necessitate short-
fused amendments.

&&

.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach  81  94  80  91 /  20  60  60  70
Fort Lauderdale  82  92  80  91 /  20  70  50  60
Miami            81  93  80  91 /  20  70  50  60
Naples           77  94  78  91 /  30  40  40  60

&&

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

DISCUSSION...98/ABH
MARINE...98/ABH
AVIATION...02/RAG



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