Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 202339 AAB

Area Forecast Discussion...UPDATED
National Weather Service Miami FL
739 PM EDT Sat Jul 20 2019

The weather will remain mostly dry through the evening hours
before showers starts to work into the east coast taf sites from
the Atlantic Waters after 5/6Z tonight leading to VCSH conditons.
Thunderstorms will then affect the east coast taf sites after 15Z
Sunday leading to VCTS. KAPF taf site will see VCSH taf site until
02Z then dry conditons until 18Z Sunday then VCTS for the afternoon
hours. Winds will be easterly 5 to 10 knots through Sunday, except
KAPF taf site where they will be westerly after 18Z Sunday.


.PREV DISCUSSION... /issued 713 PM EDT Sat Jul 20 2019/

21Z TAFB analysis has a trough across the western fringes of
South Florida. The presence of this trough has allowed for
convection to persist throughout most of the day today with some
showers/thunderstorms popping up along the boundary. Overnight,
increased moisture with the trough and some vort maxima passing
through will keep showers/thunderstorms in the forecast,
particularly for the Atlantic waters and the east coast. Current
models trend to show the higher chances along the coastal Atlantic
waters and extreme southern portions of the peninsula. Just minor
adjustments to the current forecast to account for current radar
and latest model trends.


PREV DISCUSSION... /issued 334 PM EDT Sat Jul 20 2019/

Ongoing convection across much of South Florida is expected to
continue throughout the remainder of the afternoon and into the
evening hours as unsettled weather begins to take precedence.
Focus of most of the storms will be across the Gulf Coast and Lake
Okeechobee region, though the Atlantic waters and east coast metro
are not in the clear, especially as an inverted trough pushes
into South Florida from the Bahamas. Main hazards for the
remainder of today will be gusty winds, frequent lightning, and
small hail. Overnight lows tonight are forecast to be in the upper
70s to near 80 along the east coast with low to mid 70s

Things get spicy overnight tonight into tomorrow as the
aforementioned inverted trough creeps towards South Florida. The
environment will still feature ample moisture (PWs in the 2.00 to
2.50 inch range) with additional moisture reinforcements coming
with the trough. A parade of mid-level vort maxima (most evident
in the 500 mb levels) march across the west coast of South Florida
overnight as well, further aiding in the instability. To add to
this already complex forecast are relatively cool 500 mb temps.
GFS guidance suggest temps to waver in the -8C to -9C range from
now through Monday with slightly warmer temps advecting in
afterwards (-6C to -7C Monday afternoon through the remainder of
the forecast period). To put these temperatures into scope, the
average 500 mb temp for this time of year is around -7.4C.

With all of this in mind, higher rain chances will be possible
Saturday night into Sunday morning compared to South Florida`s
normal diurnally driven weather pattern. Scattered to numerous
storms are forecast Sunday afternoon and Sunday evening,
especially as the atmosphere heats up. Main hazards besides the
routine lightning, gusty winds, and heavy rainfall will be the
concern for possible minor localized flooding, particularly for
urban areas.

Taking a quick side note for two sentences -- models are showing
a very brief and shallow coverage of the Saharan Air Layer (SAL)
Sunday with surface concentration at only about 20-40 micrograms
per cubic meter. Essentially this will need to be monitored in
regards to the precipitation size spectrum and potentially
stronger updrafts.

For the beginning of next week, Monday looks to be the quietest
day weather wise. A ribbon of drier air (PW`s around 1.50 inches)
drags across the region but this is short lived as an approaching
mid-level trough and associated surface boundary pushes into the
region from the north. The amplification of the mid-level trough
axis continues to reach into the northeastern Gulf of Mexico by
late Wednesday into early Thursday. As the trough sits to the
north and west of our area and the ridge retreats a bit back into
the Atlantic, the rest of the week could see quite the unsettled
weather pattern with scattered to numerous showers and
thunderstorms outside of the diurnal sea breeze norms. Eventually
by the end of the extended forecast period, high pressure will
attempt to regain control, but until we reach that point in time,
the pattern will bear watching for the potential of excessive
rainfall and gusty winds.

While the overall pattern with the ridge of high pressure at the
surface will keep a generally light southeasterly flow across the
area most of the period, there will be periods of unsettled
weather this weekend into next week that mariners should maintain
awareness of. In particular, the passage of a trough late tonight
through Sunday and the approach of another trough early in the
week could cause an increase in storms over the waters. The main
concern with any storms remains gusty winds, lightning, and heavy

The persistent southeasterly flow will continue to permit a non-zero
rip current risk along the Atlantic beaches of South Florida through
the weekend and into next week. It is possible, particularly if the
passing troughs into early next week develop a bit stronger wind and
create surges of southeasterly to easterly flow that could enable a
moderate rip current risk at times along the Atlantic beaches.

Showers and thunderstorms are ongoing and continue to develop over
the interior and west coast. MVFR/IFR conditions for vis and cigs are
possible for KAPF with the Gulf sea breeze developing. For the
east coast taf sites most of the activity has moved west of the
terminals however there is additional development in the Atlantic
moving towards east coast. Have reintroduced VCSH FLL and points
southward to account for development in the Atlantic moving NW.
Southeast flow will prevail throughout along east coast.

West Palm Beach  78  89  78  90 /  30  40  20  30
Fort Lauderdale  79  88  79  88 /  30  40  20  30
Miami            78  89  79  90 /  40  40  20  30
Naples           75  89  74  90 /  20  60  40  40



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