Area Forecast Discussion
Issued by NWS Miami, FL

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000
FXUS62 KMFL 211146
AFDMFL

Area Forecast Discussion
National Weather Service Miami FL
746 AM EDT Mon Aug 21 2017

.AVIATION...

VFR conditions will prevail today with little in the way of any
shower activity. Expect mainly east winds around 15 kts with gusts
around 20-23 kts likely during the midday and afternoon hours for
the east coast terminals of MIA, FLL, PBI. A tropical wave will
approach from the east tonight, so carrying VCSH for east coast
terminals after 00Z. Shower activity overnight will likely be
mostly isolated. Any showers would be in the form of short
duration passing showers and would not have a significant impact
on airport operations.

&&

.PREV DISCUSSION... /issued 407 AM EDT Mon Aug 21 2017/

DISCUSSION...

TODAY: Drier air is upon us as derived TPW satellite estimates mark
out well the subsident airmass moving in from our east with PW
values only around 1.2 inches. If these values managed to make it
into the area without modifying, they would be near the lowest
values recorded for this time of year.

Rain chances will be much below normal for this time of year,
isolated at best, and a few models keep the day entirely dry. With
forecast soundings still showing a shallow capping inversion above
the moist boundary layer, this is an entirely reasonable scenario.
However it is tough to bet again at least a few showers/storms along
the seabreeze in August.

The forecast for the eclipse viewing period across South Florida is
for partly cloudy skies under scattered cumulus clouds. There may be
a shower/storm or two later in the afternoon, with the best shot for
this over the interior and Gulf coast.

TONIGHT AND TUESDAY: The next tropical wave (92L) is expected to
continue its westward march today, reaching the NW Bahamas this
evening and moving across South Florida on Tuesday. This wave
appears to be slower-moving, and it will begin interacting with the
trough/frontal axis across the northeastern US, and likely stall
over or near South Florida.

Current timing based on satellite has the plume of moisture
associated with this feature arriving this evening. Coverage of
showers and storms is expected to quickly ramp up overnight into
Tuesday, especially once the wave axis crosses the area Tuesday
morning. Numerous showers with embedded storms are expected during
the day on Tuesday. As has been highlighted the past few days, there
will be the potential for periods of heavy rain. There is potential
for much heavier local amounts than the areal averages, especially
along the east coast with coastal convergence. WPC has already
placed much of the area under a marginal risk for excessive
rainfall for this period.

WEDNESDAY THROUGH SATURDAY: Deepening mid-upper level trough across
the eastern US will absorb the remnant low-level vorticity from 92L
late in the week, while a weakening front pushes into northern
Florida. The south-southwesterly flow that develops across the
region as a result of these features will continue to pump tropical
moisture across the area. Several models still show the potential
for cyclogenesis over the Gulf Stream northeast of our region
late week as the remnants of 92L interact with the frontal
boundary. NHC continues to monitor this feature, and has a 40%
chance of development into a tropical cyclone in 5 days when it is
in our vicinity.

Regardless of whether a surface low forms or not, the combination of
a trailing shear axis and deep south/southwest flow providing a
continuous moisture stream, which would argue for periods of rain
and thunderstorms (especially east coast). The threat with this
pattern also remains for heavy rain at times, with NCEP Weather
Prediction Center is forecasting an areal average of 3 to 4+ inches
of rain over much of the region this week. This would indicate the
potential for much heavier amounts locally, driven by mesoscale
processes. This calls for careful monitoring of the flood potential
throughout the week.

MARINE...Moderate to fresh east-southeast winds will continue
through around daybreak in the wake of yesterday`s tropical wave.
Speeds through most of the day will be around 10-15kts, then picking
up again from the east-northeast this evening into Tuesday morning
as another tropical wave approaches. Winds become more southerly at
10-15kts late week as the western Atlantic ridge axis drops further
south. Choppy seas can be expected, especially in the open waters,
with wave heights 3-4ft, occasionally 5ft in the Atlantic.

Mostly dry conditions are expected today, before increasing late
tonight from east to west with another tropical wave. Coverage is
expected to remain high through the remainder of the week as we
remain in an unsettled pattern. Winds and waves will be locally
higher near any thunderstorms.

BEACH FORECAST...Breezy onshore flow will keep a moderate risk
of rip currents at the Atlantic Beaches today. The risk is
expected to diminish by mid week as winds subside.
&&

.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach  92  81  91  79 /  10  50  70  50
Fort Lauderdale  91  81  90  79 /  10  50  60  50
Miami            93  81  91  79 /  10  30  60  50
Naples           96  79  92  77 /  20  10  60  40

&&

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


DISCUSSION...88/ALM
MARINE...88/ALM
AVIATION...98/ABH
BEACH FORECAST...88/ALM






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