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fxus62 kmfl 240102 
afdmfl

Area forecast discussion
National Weather Service Miami Florida
902 PM EDT Thu Mar 23 2017

Aviation...
tempos for thunderstorms and rain remain in most of the Atlantic terminals through
03z tonight as thunderstorms associated with the passage of a
cold front boundary. MVFR cigs will also accompany the
heaviest showers, along with possible reduced vis. Vcsh
continues through the overnight hours, but mainly VFR should
prevail once the active convection moves south of the area.
It will remain breezy tonight, then easterly winds in the 15 to
20 knots range with higher gusts are expected on Friday behind the
front.



&&

Previous discussion... /issued 742 PM EDT Thu Mar 23 2017/

Update...
as of 740 PM EDT...scattered shower and thunderstorm activity
continues to gradually wane across the region early this evening
with the loss of daytime heating. Earlier this afternoon and
evening, it was quite active for late March, with scattered to
numerous showers and thunderstorms producing locally strong to
borderline severe weather that primarily included small hail and
frequent lightning.

Over the next few hours, additional scattered showers and a few
storms will be possible, mainly across eastern areas as the
frontal boundary continues to push south across far southern
Florida. The threat for strong storms will be very minimal with
the loss of daytime heating and additional storms moving over
already worked over areas. After late this evening, there will
continue to be the potential for scattered showers streaming into
eastern areas off the Atlantic. The flow will become breezy at
times through the night, with northeast/east winds occasionally
gusting 15-25 mph at times especially over eastern areas. Skies
will remain mostly cloudy for most, although there will be some
gradual clearing along the Gulf Coast late. Low temperatures will
generally be in the 60s.

Previous discussion... /issued 325 PM EDT Thu Mar 23 2017/

Discussion...

Near term /through 6 am Friday morning/...

As of 325 PM EDT...scattered showers and thunderstorms continue
across South Florida this afternoon, especially across portions of
the interior and lake region as a weakening frontal boundary
moves south across the region. The convective activity has also
been supported by a piece of shortwave energy rotating through the
flow across central Florida, evident in the water vapor satellite
imagery. The Storm Prediction Center continues to highlight all
of South Florida in a marginal risk for severe thunderstorms,
mainly for isolated hail and damaging winds.

A special 18z upper air release performed at kmfl supports the
ongoing strong/severe thunderstorm risk, which looks to continue
into the early evening hours. Remnants of an eml continue to yield
rather impressive mid-level lapse rates between 7-8 c/km and near
record cold 500 hpa temp around -14.5 c for this time of year.
With plenty of surface heating through the morning and early
afternoon hours, high temperatures topping out well into the 80s
for most areas, coupled with low-level moisture pooling ahead of
the boundary, cape values of 1500-2000 j/kg have been observed
across the region, supporting occasional strong to borderline
severe storms.

Remnant convergence along the dissipating front, coupled with the
dynamics associated with the shortwave energy moving through
central Florida will continue to support a rather active remainder
of the afternoon and early evening across much of the region.
While a severe thunderstorm with large hail and gusty winds cannot
be ruled out, much of the activity should remain sub-severe, but
still have the potential to produce small hail, brief gusty winds
45-55 mph, frequent lightning, and locally heavy rainfall that may
lead to some poor drainage flooding issues in urbanized and low-
lying areas.

For tonight, any lingering thunderstorm activity should rapidly
wane through the evening hours with the loss of daytime heating,
and as the aforementioned shortwave energy exits east. Still,
some scattered showers will linger overnight especially across
eastern areas as gusty east/northeasterly flow rapidly moves into
the region in the wake of the frontal boundary. Wind gusts
overnight may occasionally be 15-25 mph at times, especially for
eastern areas. Low temperatures will generally be in the 60s.

Short term /6 am Friday morning through Saturday night/...

In the wake of the frontal boundary, which looks to eventually wash
out south of the region, strong high pressure will build to the
north, keeping a tight pressure gradient across the region between
the southern edge of the high and the exiting front. Brisk
east/northeast winds, especially along the East Coast, will
continue through the day Friday along with lingering isolated to
widely scattered showers. Slightly drier air will work into the
region beginning Saturday, lowering the threat for rain although
an brief shower can still not be ruled out.

High temperatures will range from the upper 70s to near 80 along
the East Coast, to lower and even some mid 80s in the interior and
Gulf Coast. Low temperatures will range from the upper 50s to
upper 60s.

Long term /Sunday through Wednesday/...

The long term period will be characterized by an easterly flow
regime, with weak upper-level ridging aloft. An upper-level trough
digging through the lower Great Lakes early next week will help to
break down the upper-level ridging further, allowing the flow to
become more southerly. Generally fair weather can be expected
through the period, although a few showers streaming in off the
Atlantic will be possible from time to time mainly across eastern
areas.

With the easterly flow in place, temperatures will be above normal
for the long term period. Humidity, although not oppressive, will be
higher as well compared to recent days.

Marine...
Small Craft Advisory conditions for much of the local waters
through tonight...

A frontal boundary, gradually weakening with time, will continue to
move south across the region through the rest of today, with marine
conditions rapidly deteriorating in its wake. This front will bring
scattered showers and thunderstorms to the local waters, especially
over the Atlantic and Lake Okeechobee. With the strongest storms,
locally erratic winds and small hail will be possible, with a low
chance of waterspouts as well.

Behind the frontal passage, expect east-northeast winds 20-25kts
over much of the local waters, including Biscayne Bay, through the
overnight hours with seas in excess of 7 feet over the offshore
Atlantic waters, highest in the Gulf Stream. Winds will also be
around 20 knots in the offshore Gulf waters, with seas 4-6 feet.

Winds and seas will begin to slowly diminish during the day Friday,
especially over the Gulf waters, but Small Craft Advisory conditions
are likely to continue for the Atlantic waters including Biscayne
Bay into Saturday morning. Hazardous marine conditions may linger
for the Atlantic waters into early Sunday as well, before better
boating conditions return for the second half of the weekend.

A Small Craft Advisory is in effect for the local Atlantic waters
including Biscayne Bay through Saturday morning, and the local Gulf
waters this evening through mid-Friday morning. Small craft should
exercise caution tonight in the Lake Okeechobee waters.

For more details on the marine forecast, see the coastal waters
forecast.

Beach forecast...
a high risk of rip currents will continue for the Atlantic beaches
through at least Saturday morning with strong onshore flow. The
rip current risk for the Atlantic beaches will likely remain
elevated well into next week as well with continued onshore flow.

Fire weather...
scattered showers and thunderstorms this afternoon and evening
should help mitigate fire weather concerns in the short term, with
many areas seeing a light to soaking rain as a frontal boundary
moves across the region. In the wake of the frontal boundary,
drier air will filter into the region by the end of the weekend
and into early next week, with relative humidity levels
potentially reaching critical values across portions of the
interior and Gulf Coast.

Aviation...
a cold front dropping southward across the region will continue to
generate unsettled weather over South Florida. Through 23/2200z,
thunderstorms in the vicinity conds will affect mainly portions of the East Coast taf sites
and adjacent waters. Expect scattered/bkn025 and bkn050, then
decreasing cloud cover and convective activity by late evening
into overnight. Small hail and gusty/erratic winds will be
possible the storms as they move southward along the peninsula.
Behind the front, east northeast winds will increase to around
15-17 knots with occasional higher gusts. However, at kapf, east-northeast
winds will be weaker, only around 12 knots. Breezy conditions should
continue through the night along the East Coast taf sites with
vcsh.
&&

Preliminary point temps/pops...
West Palm Beach 69 78 68 80 / 40 20 20 10
Fort Lauderdale 71 78 70 80 / 40 20 20 10
Miami 70 79 69 81 / 40 20 20 10
Naples 63 83 62 81 / 20 10 0 10

&&

Mfl watches/warnings/advisories...
Florida...high rip current risk through Friday evening for flz168-172-173.

Am...Small Craft Advisory until 8 am EDT Saturday for amz630-650-651-
670-671.

GM...Small Craft Advisory until 11 am EDT Friday for gmz656-657-676.

&&

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