Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 212020
AFDMFL

Area Forecast Discussion
National Weather Service Miami FL
320 PM EST Tue Feb 21 2017

.DISCUSSION...
Quiet weather today will being to give way to rain showers
overnight tonight. This will be caused by an approaching low
pressure system, currently over Alabama, moving east. Both the
ECMWF and the GFS have the upper level low digging to the
southeast through tomorrow, trying to cutoff from the main flow.
They then have the system moving right over South Florida on
Thursday. This will continue to spread showers and thunderstorms
across South Florida through the evening hours on Wednesday. The
initial showers will be caused by some isentropic lift well ahead
of the system.

Models are showing that a main line of showers, and possibly
thunderstorms will enter the area late Wednesday morning, and move
across the region, and should be off the Atlantic coast Wednesday
evening. While it is a cold front, it does not have the typical
cold front signature in the models, as the line is merged with
the surface low. However, it is out ahead of the upper level low,
indicating that the showers and storms may be somewhat elevated in
nature, or just higher ceilings then typical fronts. There is
also 500mb vorticity advection associated with the line of showers
and storms. The 500mb temps are showing to be around -10.5C to
-11C which would help support thunderstorms, along with some
possible small hail.

So far, SPC only has general thunderstorms, which is reflected in
the forecast with a slight chance in the morning, then a chance of
thunderstorms in the afternoon across the entire area. The models
have the main area of instability pushing off to the east
Wednesday night, and only some wrap around shower activity for
Thursday and Thursday night. By Friday, the system should be far
enough out that quiet weather returns to South Florida.

High pressure builds in behind the system, but is centered to the
north. It should keep the weather quiet through the weekend. This
will also allow an easterly flow to develop once again over the
area for the beginning of next week, which may allow for some
moisture and isolated coastal showers to begin to affect the
Atlantic coast by the middle of next week.

temperature wise, the front will not have a significant affect for
the surface temperatures, other than the high being about 5
degrees lower Wednesday and Thursday.

&&

.MARINE...
A low pressure system will bring showers and thunderstorms to the
South Florida waters for Wednesday and Thursday, with the
Atlantic waters possibly seeing some activity Friday as well.
However, the wind will be mainly southerly, then northwesterly,
and is not forecast to have a significant impact on the wave
heights for the South Florida waters. The wind may bring the need
for at least a small craft should exercise caution statement for
tomorrow, and possible a small craft advisory for portions of the
area.

The wind will also bring an increased risk of rip currents to the
Atlantic coastal areas tomorrow. With high pressure building to
the north over the weekend, the wind will pick up out of the east
once again for the beginning of the week, which may increase the
rick of rip currents for the Atlantic coast once again.

&&

.AVIATION...
VFR flying conditions will prevail early in the TAF period before
an approaching low pressure system brings deteriorating flying
conditions to all terminals by daybreak Wednesday. Cloud cover
will be on the increase especially after 00z as the system
approaches, with showers overspreading the region from west to
east beginning around 09z-10z. Conditions will initially start out
as VFR but decrease to MVFR as steadier rain overspreads the
region. Thunderstorms will also be possible towards the end of the
period as well. Winds will be out of the southeast around 10 knots
through 00z, before decreasing to generally 5-10 knots overnight,
and 10-15 knots after 12z.

&&

.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach  69  77  65  80 /  40  70  70  60
Fort Lauderdale  68  78  65  79 /  30  70  80  50
Miami            68  77  64  78 /  30  70  80  50
Naples           65  72  60  76 /  30  80  30  20

&&

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


DISCUSSION...13
MARINE...13
AVIATION...92/IRL







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