Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 211818
AFDMFL

Area Forecast Discussion
National Weather Service Miami FL
118 PM EST Sat Jan 21 2017

.AVIATION...
High pressure is weakening ahead of a cold front that will
approach the region tomorrow. This has allowed for some isolated
showers to quickly move across the area. however, they are sparse
and should have little impact on the TAF sites. VFR is forecast
through the TAF period. The wind is struggling between south
southeast and south southwest, which may make it difficult in
runway decisions. The wind is forecast to turn southwest tomorrow
morning, and pickup to 15 to 20 kts, with gusts of 25 to 30 kts.
the cold front will bring deteriorating conditions late Sunday
into Monday.

&&

PREV DISCUSSION... /issued 508 AM EST Sat Jan 21 2017/

DISCUSSION...

.Strong to Severe Storms Possible Late Sunday and Sunday Night...
.Dangerous Marine Conditions Over Local Waters Early Next Week...

Today and Tonight: Fog has overspread much of South Florida this
morning with locally dense fog being reported in a few spots. A
Dense Fog Advisory may be needed if conditions become more
widespread.

Fog is expected to burn off within an hour or two of sunrise this
morning, leaving a mostly sunny and dry day, baring an Atlantic
sprinkle or two. Increasing low level flow out of the southwest
late tonight may bring a few showers, mainly over the local
waters.

Sunday and Sunday Night: This will be the main focus of the
forecast period as the threat continues for strong to severe
storms across South Florida with a strong cold front.

Upper level trough moving into the western US this morning is
expected to develop into an upper level low as it moves across TX
late tonight. A large surface low is expected to develop ahead of
the upper feature as it moves across the Deep South, interacting
with the quasi-stationary front across the northern Gulf coast. As
the lows lift out to the northeast late on Sunday, they will bring
a strong cold front through the FL peninsula late in the day.

A strong pre-frontal trough/squall line still looks to precede
the main front, though a few solutions still hint it weakening as
it moves into South Florida. The latest runs of the GFS have also
sped up the pre-frontal trough and cold front, putting both into
South Florida by late afternoon and clearing the peninsula before
daybreak. ECMWF and NAM12 remain closer to previous timing, with
the bulk of storms not reaching the region until midnight and
clearing around daybreak

Current thinking remains for two main rounds of showers and
thunderstorms, with a conservative average placing the main
severe weather threat from Sunday evening through daybreak
Monday. The first round is be with the passage of the pre-frontal
trough Sunday evening, and the other round will be with the
actual cold front pre-dawn Monday morning.

100-110kt jet moving into the FL peninsula with the trough will
bring a rather impressive low level jet with 925mb and 850mb winds
45-55kts. Models continue to keep flow fairly unidirectional and
veered more southwest, suggesting strong straight line winds will
be the main severe weather threat. However, embedded isolated
tornadoes can`t be ruled out, especially earlier in the evening
with any activity that develops ahead of the main convective
lines and with the pre-frontal trough/squall line.

Outside of convection, Sunday will be a windy day with south-
southwest winds 20-25 mph and gusts over 30mph. Despite increasing
cloud cover, this will also make Sunday a very warm day with
highs in the low-mid 80s. Wouldn`t be surprised if a few east
coast locations flirt with record highs if convective development
is delayed.

The Remainder of Next Week: While the main surface front and
threat for storms is expected to be south and east of South
Florida around daybreak Monday, the main upper level trough is not
forecast to cross the state until later in the day. Some moisture
wrapping around the main low as it lifts up the eastern seaboard
in the presence of the upper trough will keep a chance for a few
showers through Monday afternoon.

High pressure will remain in control for much of the remainder of
the week with dry and seasonably warm conditions. The next threat
for rain looks to be with a weaker front late week.

MARINE...South-southwest winds continue around 10 knots during
the day, gradually increasing later this evening and overnight to
15-20 knots. Latest forecast has winds reaching advisory level
across most of the waters by daybreak Sunday. Conditions then
rapidly deteriorate through the day, reaching 25 to 30 knots late
Sunday night as winds veer westerly behind the front. Frequent
gusts to gale force will be possible Sunday night into Monday over
all South Florida waters, with potential for sustained gale force
winds at times. The seas will increase to over 7 feet late Sunday
and potentially over 15 feet open Gulf waters by Monday morning.

A Small Craft Advisory is now in effect for all the local waters
starting late tonight, and a Gale Watch will likely be issued
later today.

BEACH FORECAST...Increasing southerly winds later today may lead
to an increase in the longshore current along both the Gulf and
Atlantic beaches. Windy southwesterly flow on Sunday will bring a
high risk of rip currents to the Gulf Beaches on Sunday, which may
linger through mid week as seas remain elevated.

With strong onshore winds expected Sunday night into Monday,
there will be a risk of coastal erosion and minor coastal flooding
of particularly vulnerable areas along the Gulf Coast of South
Florida. The magnitude of the risk will depend on the timing of
the strongest winds and whether this coincides with the time of
high tide.
&&

.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach  69  85  63  77 /  10  20  80  30
Fort Lauderdale  72  84  66  78 /  20  20  80  30
Miami            70  86  68  74 /  20  20  80  30
Naples           68  80  67  72 /  10  60  80  20

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...Small Craft Advisory from 4 AM Sunday to 7 AM EST Tuesday for
     AMZ610-630-650-651-670-671.

GM...Small Craft Advisory from 4 AM Sunday to 7 AM EST Tuesday for
     GMZ656-657-676.

&&


DISCUSSION...88/ALM
MARINE...88/ALM
AVIATION...13







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