Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 220019

Area Forecast Discussion
National Weather Service Miami FL
819 PM EDT Fri Jul 21 2017

Isolated showers, will continue over the coastal waters tonight.
However, coverage and confidence is not great enough to include a
VCSH category for the coastal sites in the latest TAF package.
Light southeast winds will prevail along the east coast, 8-10 KT
aft 22/1500Z, and a Gulf breeze along the west coast. VCTS conds
are expected to develop during the late morning into the
afternoon, due to sea breeze interaction.


.PREV DISCUSSION... /issued 349 PM EDT Fri Jul 21 2017/

Numerous thunderstorms developed today over South Florida with a
moist and unstable air mass in place. The downdrafts from these
thunderstorms joined forces to create a large and strong cold
pool. In fact, the temperature fell to 72 degrees at Miami
International Airport with this convection, which is the coolest
temperature observed there since June 7th!

The cold pool has pushed the unstable air south and east out of
the area, temporarily stabilizing the atmosphere. The leftover
stratiform rainfall from this convective system is still falling
out over the east coast counties as of 3:45 pm EDT, but will
gradually end by around 6 pm. It appears unlikely the air mass
will recover before nocturnal cooling sets in. Also, observational
data confirm model simulations of a dry Saharan Air Layer (SAL)
currently over Cuba and the Bahamas likely to overspread the
southern half of the region tonight. So POPs overnight will be
kept under 20% for most areas.

Saturday, models indicate broadly confluent flow continuing over
the area and we should start the day without much convection
around, allowing diurnal destabilization. The SAL moving in
tonight will likely still be in place over the southern part of
the Peninsula in the morning before shifting west into the Gulf
later in the day. With lower tropospheric confluence over the
region, plenty of heating during the morning and midday, and
gradually recovering moisture/instability, will likely see
another round of showers and thunderstorms, particularly the
northern half of the area where the SAL/low precipitable water air
is less likely to be a factor.

Sunday and Monday, global models tend to hint at some slightly
drier air rotating over the area around the Atlantic high, with
the axis of the Atlantic ridge nearly overhead. So POPs will be a
tad lower than previous days. But still some scattered showers and
a few thunderstorms will be possible, generally over the waters at
night and inland during the day.

Tuesday and beyond, the ridge axis shifts a little more
northeastward and weakens, as models hint at some mid level
troughing digging into the northeastern Gulf. This should open the
door to slightly deeper moisture and broad low level confluence
over the region. POPs will generally be near climatology with the
typical diurnal pattern indicated.

Generally good boating conditions in store outside of
thunderstorms with winds under 15 knots and seas under 3 feet.
Brief locally higher winds and seas possible near any

PREV DISCUSSION... /issued 135 PM EDT Fri Jul 21 2017/

Active convection is forecast to continue through the afternoon,
although it may become more spread out by the middle of the
afternoon. Even so, have kept Tempo and VC for TS for the rest of
the afternoon, and into the evening. The stronger storms should
have past, but some isolated storms could still bring strong wind
gusts. Also, brief IFR conditions will be possible under heavy
showers and storms.

West Palm Beach  77  90  78  92 /  10  50  30  30
Fort Lauderdale  79  90  79  93 /  10  50  30  30
Miami            79  91  79  93 /  10  40  30  30
Naples           77  90  77  93 /  10  40  20  30



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