FXUS62 KMFL 211957
Area Forecast Discussion
National Weather Service Miami FL
357 PM EDT Mon Aug 21 2017
Scattered cumulus clouds dot the South Florida sky at mid
afternoon as the eclipse comes to an end. The area is under a
subsident regime between two tropical waves with a well-defined
capping inversion on the MFL 12Z sounding. GOES-16 imagery
indicates the next tropical wave (called Invest 92L by the
National Hurricane Center) rapidly approaching from the east. In
fact KAMX 88D indicates scattered showers already beginning to
cross the east coast.
Tonight and Tuesday: Coverage and intensity of showers and a few
thunderstorms are expected to steadily increase tonight over the
east coast. Activity may hold off til closer til sunrise near the
Collier Gulf Coast and Glades/Hendry Counties. High resolution
guidance suggests convection that moves in will have the
potential for efficient rain rates especially toward sunrise and
during the day. Coverage increases Tuesday as the axis of the
tropical wave moves over and then just northwest of the area and
the region enters the more favorable sector for upward motion.
Wednesday through Friday: The leftover vorticity associated with
the tropical wave comes nearly to a halt over the area Wed-Thu.
This will yield a deep southeasterly fetch tapping rich tropical
moisture with several weak disturbances bringing periods of
convection. Whether 92L develops a surface cyclone near the region
is not the most important thing to focus on in terms of impacts.
Regardless of the scientific classification of the system, the
most significant impacts are likely to be from periods of heavy
This weekend: The trailing front from the Canadian low gradually
sinks into the southeast US and approaches northern Florida. This
front will likely absorb whatever vorticity remains of 92L just
northeast of our region. This will keep southerly/southwesterly
flow with rich moisture overhead, favorable for continued periods
of showers and thunderstorms with locally heavy rain.
Impacts from heavy rain through the weekend: Typically prone
areas of poor drainage will be at increased risk of ponding water
and occasional minor flooding. Areas of street flooding are also
likely to be an issue during periods of heavy rain. While there is
some risk for more significant flooding problems beyond the usual
vulnerable roads and low spots, there is not enough confidence
yet regarding timing/location of the greatest threat to justify a
Flood Watch. However, a watch may still be needed later in the
week as the ground saturates.
Over the Atlantic waters, a fresh easterly breeze today will
gradually decrease Tuesday to gentle as winds turn out of the
southeast, eventually swinging to southerly or southwesterly by
the weekend. Over the Gulf waters and Lake Okeechobee, a moderate
easterly breeze tonight will become variable in both direction
and speed from Tuesday into the weekend, but remaining generally
below 15 knots. A moderate chop and seas to 4 feet tonight will
gradually improve Tuesday into the latter half of the week.
Periods of showers and thunderstorms can be expected tonight
though the coming weekend, with locally gusty winds and higher
waves near thunderstorms.
A moderate risk of rip currents will continue through the night at
the Atlantic Beaches as moderate/gusty onshore winds continue. The
risk will gradually diminish back to slight levels Tuesday.
.PREV DISCUSSION... /issued 150 PM EDT Mon Aug 21 2017/
VFR conditions will prevail through this evening. Winds this
afternoon will be east around 15 kts gusting to 20-23 kts for
east coast terminals. Tropical wave approaching from the east will
bring VCSH tonight for east coast terminals. Increasing coverage
of showers along with some thunder possible after 09Z and
continuing into Tuesday for east coast sites. MVFR conditions
likely at times on Tuesday morning for east coast sites. Showers
are unlikely to be near APF until after 15Z. Future shifts will
evaluate potential for TEMPO groups and possibly SHRA in
.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach 82 93 80 91 / 40 50 40 60
Fort Lauderdale 81 90 80 90 / 50 50 50 60
Miami 81 91 79 90 / 50 60 50 60
Naples 79 92 77 92 / 10 70 50 60
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