Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 222356

Area Forecast Discussion
National Weather Service Miami FL
756 PM EDT Tue Aug 22 2017

Scattered showers and thunderstorms will continue to develop
across interior and west coast through the evening hours with
possible brief MVFR cigs with passing TSRA. More showers are
expected after midnight along the east coast and increasing through
the day. Winds will diminish this evening before increasing again
to near 10 knots out of the east se by the middle of Wednesday
morning. VFR conditions will prevail throughout most of the forecast


Late-developing showers and thunderstorms still blossoming at this
early evening hour from Lake Okeechobee through Collier County
and over the nearshore Gulf of Mexico waters. This activity should
persist for another 2 hours or so as it moves SW and gradually
loses steam as temperatures cool. Earlier update to POPs accounted
well for this expected trend and no changes needed at this time.
Additional showers and thunderstorms are forecast to develop over
the Atlantic late tonight, especially after midnight, as the
trough over the Bahamas approaches South Florida. Increasing POPs
for the east coast metro as reflected in earlier update still look
OK. Flood threat tonight remains low, but not totally out of the
question, with the main threat beginning tomorrow night and
lasting through the remainder of the week and possibly into the
upcoming weekend.


.PREV DISCUSSION... /issued 436 PM EDT Tue Aug 22 2017/

..Wet and Stormy Remainder of the Week with Flooding Potential...

Relatively dry conditions late this afternoon across South Florida
as the trough of low pressure remains to our east over the western
Bahamas. Expect showers and thunderstorms to increase some over
interior and western areas until early evening in typical diurnal
pattern, while most of the east coast metro areas remains dry.

The trough will slowly make its way towards South Florida tonight,
ushering in a wet and stormy period which will likely last through
the end of the week (and maybe beyond). Precipitable water values
in excess of 2 inches seen in experimental GOES-16 total precipitable
water product lining up to our SE and this rich tropical moisture
will be pumped into South Florida as winds become SE through the
mid-levels through Thursday. Another round of scattered showers
and thunderstorms will move onshore the east coast tonight, increase
further in coverage on Wednesday morning and spread across the
interior and Gulf coast by midday and through the afternoon.
Timing/coverage of convection will still exhibit somewhat of a
diurnal cycle on Wednesday, but as a second mid-level trough
approaches South Florida from the SE Wednesday night and
Thursday, showers and thunderstorms should increase and become
widespread for most of that period. Models suggest that the
trough and mid-level low will shift north and east Thursday night
and Friday, placing South Florida in a S/SW wind flow. This raises
particular concerns for heavy rainfall/flood potential along the
Gulf coast Thursday night and Friday, especially if bands of
stronger showers and thunderstorms form over the SE Gulf of Mexico
and move onshore.

While overall moisture profile is certainly adequate enough for
us to be concerned about the potential for flooding across much of
South Florida, more precise timing and coverage of heavier rain
is still somewhat in question due to the rather complex nature of
the weather pattern over the region, especially with how the
surface and low level trough interacts with the mid-level low.

It`s important to note that regardless of any low development over
the next few days, the overall pattern is conducive for at least
the potential for flooding rains over parts of South Florida. If
present trends continue, a Flood Watch may have to be issued
either Wednesday or early Thursday for at least parts of South
Florida, with the threat of flooding rains possibly extending
through Friday.

For the upcoming weekend, GFS and ECMWF show surface low pressure
hanging around north of the western Bahamas, which would continue
to place South Florida in a moist SW flow. Therefore, no break
from the wet and stormy pattern in sight until perhaps early next

After a hot day today, max temperatures will trend downward as
clouds and rain coverage increase over the next few days.

Southeast winds 10 to 15 knots will increase to 15 to 20 knots
over the Atlantic waters Wednesday night and Thursday, then
gradually become south to southwest Thursday night and Friday.
Seas will be 4 feet or less, except locally higher in showers and
thunderstorms from Wednesday night onward.

West Palm Beach  80  88  78  88 /  50  70  50  80
Fort Lauderdale  79  87  78  87 /  50  70  70  80
Miami            79  89  78  89 /  50  70  70  80
Naples           78  89  77  89 /  40  80  40  70



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