Area Forecast Discussion
Issued by NWS Miami, FL

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000
FXUS62 KMFL 220059
AFDMFL

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

.UPDATE...
The 00Z MFL sounding shows moisture in the boundary layer with dry
air in the mid levels. Winds were light and southerly at the
surface, strengthening and veering to westerly with height.
Southerly winds 5 to 10 mph are forecast to persist through
tonight. These winds should keep the boundary layer from
decoupling, therefore have not included fog in the grids. Models
still indicate a strong cold front approaching South Florida
tomorrow. Ahead of this front, the surface pressure gradient will
tighten and southwesterly winds will strengthen. A wind advisory
may need to be issued on a later shift, depending the forecast
magnitude of these winds. A high rip current advisory has been
issued for the Gulf coast beaches of Collier County. Otherwise,
the rest of the forecast a appeared on track.

&&

.PREV DISCUSSION... /issued 631 PM EST Sat Jan 21 2017/

AVIATION...
The winds will be close to due southerly tonight over all of South
Florida taf sites before swinging to more of a southwest direction
late Sunday morning into Sunday afternoon. The wind speeds will be
5 to 10 knots tonight over all of the taf sites before increasing
to around 15G25KT Sunday morning and then to 25G35KT Sunday
afternoon ahead of a cold front.

The weather should remain dry tonight into Sunday morning, before
some showers develop over South Florida Sunday afternoon. The
threat of Thunder will more likely be Sunday evening into Sunday
night which could be strong to even severe. Therefore, VCSH will
be added for the afternoon hours for all of South Florida taf
sites, and will leave out thunder conditions at this time.

PREV DISCUSSION... /issued 506 PM EST Sat Jan 21 2017/

DISCUSSION...
This evening into tonight: Water vapor loop this afternoon
indicated an eastward moving low pressure center over northern
Georgia with deep convection stretching out ahead of this feature
from South Carolina to the Florida Panhandle. Further south, over
our region, a it was a much different story. Visible satellite
loop showed only few/scattered cumulus pushing rapidly northward
from the Florida Straits. Moistening conditions in the lower
levels have allowed for a some spotty light showers to develop
along the east coast metro, but no reported accumulation. Maximum
temperatures are topping out in the low to mid 80s, 6 to 9 degrees
above average for this time of year. Tonight, breezy southwest
flow in the interior should allow for decent mixing in the
boundary layer. Therefore, fog is not likely to form and have left
out of the grids.

Sunday into Sunday night: Both the GFS and ECWMF prog an deep upper
level trough to move eastward across the southern plains. In
response, a deep surface low will develop and interact with a quasi-
stationary front across the northern Gulf. By Sunday morning, these
models develop a vigorous cold front out ahead of the
disturbance, stretching from the Florida panhandle down through
the central Gulf of Mexico. Ahead of this front, Sunday afternoon,
surface pressure gradients will begin to tighten, strengthening
southwest winds, both over our local coastal waters and across the
peninsula. In addition, mid-range models develop a pre-frontal
squall line, far ahead of the actual front. This line of activity
may affect portions of Hendry, Glades, and Collier counties by
late Sunday afternoon. A strong southwesterly low level jet should
enhance the winds associated with the squall, and veering winds
with height may support a few spinning storms. As the actual cold
front nears, southwest winds will further increase. The GFS, NAM,
and ECMWF all advect a secondary squall across the peninsula from
late Sunday evening, to early morning on Monday. This is timeframe
where severe weather seems most likely. Thunderstorms associated
with the squall may produce strong, possibly damaging,
west/southwest winds, heavy rain, and small hail. An isolated
tornado can not be ruled out. By dawn on Monday, the front will
have pushed out into the Atlantic, ending the severe weather
threat.

Monday through Thursday: Winds will turn west/northwest behind the
front as South Florida remains wedged in between building surface
high pressure over the Gulf and deep low pressure over the Atlantic.
Residual low level moisture will extend the chance of showers
through the day, though strong convection is not expected. A
cooler airmass begins to move in from the northwest, with maximum
temperatures only forecast to reach the mid- 70s along the Gulf
and interior, and mid to upper 70s along the east coast metro. By
Tuesday, precipitation chances dwindle further with drier
filtering in, along with a decrease in overall cloud cover.
Temperatures will still remain on the cool side with maxes only
forecast in the mid 70s, a couple degrees below normal for this
time of year. High pressure riding will dominate the weather
pattern through Thursday with a slow warming trend.

MARINE...
South-southwest winds with gradually increase later this evening
and overnight to 15-20 knots. Latest forecast has winds reaching
small craft advisory level across most of the waters by early
Sunday morning. Conditions then rapidly deteriorate through the
day, reaching 25 to 30 knots late Sunday night with gusts near 40
KT at times. Frequent gusts to gale force will be possible Sunday
night into Monday over all South Florida waters. Thus, a Gale
watch has been issued for this timeframe. 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 is in effect from Sunday
evening through Monday evening.

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.

BEACH FORECAST...
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  70  85  67  78 /  10  20  90  20
Fort Lauderdale  72  83  69  80 /  20  20  90  20
Miami            71  85  68  79 /  20  20  90  30
Naples           68  81  71  73 /  20  50  80  20

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk from Sunday evening through Tuesday
     evening for FLZ069.

AM...Gale Watch from Sunday evening through Monday evening for AMZ650-
     651-670-671.

     Small Craft Advisory from 4 AM to 7 PM EST Sunday for AMZ650-651-
     670-671.

     Small Craft Advisory from 7 PM Monday to 7 AM EST Tuesday for
     AMZ650-651-670-671.

     Small Craft Advisory from 4 AM Sunday to 7 AM EST Tuesday for
     AMZ610-630.

GM...Gale Watch from Sunday evening through Monday evening for GMZ656-
     657-676.

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

     Small Craft Advisory from 7 PM Monday to 7 AM EST Tuesday for
     GMZ656-657-676.

&&

UPDATE...27/JT
DISCUSSION...27/JT
MARINE...27/JT
AVIATION...54/BNB
BEACH FORECAST...27/JT






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