Area Forecast Discussion
Issued by NWS Melbourne, FL

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FXUS62 KMLB 220156

Area Forecast Discussion
National Weather Service Melbourne FL
955 PM EDT Mon May 21 2018


Widespread precip tapered off to isolated light rain showers a
little after sunset across just about all of the area. Local radars
show spotty showers continuing upstream over the Atlantic, with much
higher coverage and intensity of precip over the Keys/Straits and
offshore south Florida. Local RAOB and DRWP data show SE to SSE flow
in the surface to 2KM layer, which supports at least some onshore
component to marine shower motion, especially farther south along
the Treasure Coast. Some redevelopment is likely given the favorable
setup aloft, high PWAT air mass in place, an approaching nocturnal
marine instability cycle. have trimmed POPs back to 20 north and
interior, trending up to 40 for the Treasure Coast. Min temps near
70/L70s once again.


.AVIATION...VFR most areas. MVFR to local IFR VSBYs (possibly MVFR
CIGs as well) near 2-3SM/BKN025 in showers overnight, with the best
chance along the MLB-SUA corridor.


.MARINE...SE flow averaging about 15KT will continue overnight. Seas
3-4FT near shore and 5FT well offshore. Expect coverage of showers
(and an isolated storm or two) to increase later tonight especially
over the Gulf Stream.


IMPACT WX...Weitlich


.PREV DISCUSSION... /issued 328 PM EDT Mon May 21 2018/

...Heavy Rain Possible Again Tuesday, Especially Near the Coast...

Tuesday...Axis of Atlantic surface ridge will extend into north
Florida.  This will maintain a moist, breezy southeast flow in the
lower levels.  The upper level trough in the eastern Gulf of Mexico
will weaken, but broadly diffluent flow aloft is still shown across
the area.  Little change in the extensive cloud cover is expected
with these conditions remaining in place, so high temps are forecast
in the upper 70s to lower 80s.

MOS guidance continues to have high rain chances (60-80%), along
the Space/Treasure Coasts tonight, then areawide on Tue. This
very moist pattern is not likely to come to a halt as fast as the
NAM based guidance suggests, so have bumped up PoPs to likely.
Locally heavy rainfall will continue to occur especially along the
coast where the flood threat has been increasing.

Wednesday...The axis of the Atlantic surface ridge is forecast to
settle a little closer to the local area.  Low level flow looks a
little more southerly and slightly weaker.  Therefore, early morning
Atlantic showers should not be pinned at the coast as much as recent
mornings, and with precipitable water forecast to start off a
little lower, convection may become more due to daytime heating.
MOS guidance supports this, showing high temps in the mid 80s at
the coast to around 90 inland. Expect showers/storms to be more
scattered as influence of the upper level trough wanes, so will
have 40-50% rain chances for now.

Previous Discussion...

Thu-Sun...The ridge axis does gradually sink south and east while
weakening slightly during the period. Unfortunately the deep plume
of moisture continues across the area into the weekend. Medium range
models show weak surface low development over the southern Gulf by
Thu with both GFS/ECMWF lifting this feature toward the Louisiana
coast by Sat. The ECMWF remains a bit deeper with this low pressure.
Aloft, troughing will deepen and take up residency across the Deep
South to include much of the GOMEX. This will strengthen the S/SWRLY
steering flow into the holiday weekend as well as send occasional
shortwave impulses over the region. This will signal increasing rain
chances with a threat for heavy rainfall and localized flooding over
already saturated ground. It will remain humid with max temps in the
L-M80s with min temps continuing in the U60s to L70s.


.AVIATION...Moderate to heavy showers will continue to occur this
afternoon in Volusia County and along the Treasure Coast. These
heavy downpours are resulting in IFR visibilities of 1-2 SM at
KDAB, and MVFR CIGs of BKN-020-030 at KDAB and KMLB-KSUA. Included
TEMPO groups in the TAFs to account for ongoing rain through
21/21Z at all coastal terminals. It is possible that this heavy
rainfall extends beyond the current TEMPO groups, so amendments
may be needed later this afternoon if the rain persists. The
inland terminals have dodged most of the heavy rainfall so far
today with some light rain and occasional MVFR CIGs, but otherwise
VFR conditions. As showers move inland this afternoon some
terminals may see periodic MVFR/IFR conditions with any moderate
to heavy shower activity. High resolution models, HRRR and local
WRF, indicate most of the showers will end after 21/24Z with VFR
conditions prevailing through the overnight. If the last couple of
days are any indication there may be shower development early in
the morning after 22/06Z, as a result I have continued VCSH at all
coastal terminals through the overnight. However, there is too
much uncertainty to include SHRA in the TAFs at this time. Due to
the abundance of moisture and high chances of rain for Tuesday,
have included VCSH prevailing at all terminals after 22/14Z.


Tonight-Tuesday...The pressure gradient still looks tightened enough
to maintain 15 knot southeast flow, and possibly up to 20 knots
offshore at times. This will continue to produce poor boating
conditions with seas 3-5 feet and up to 6 feet offshore. The
weather conditions also look poor as scattered to numerous showers
and isolated storms are indicated late tonight in the southern
waters, then spreading northward through Tue.

Wednesday-Thursday...The Atlantic ridge is still forecast to settle
close to the waters Wed while weakening. This will diminish
south/southeast winds and allow seas to subside to 3-4 feet.
Moisture will remain high enough for at least scattered showers and
isolated storms.

Friday-Saturday...The forecast for the start of the Memorial Day
weekend is still uncertain as the models don`t agree on the
evolution of low pressure forecast to develop over the
central/eastern Gulf of Mexico. The Atlantic ridge looks like it
is going to become well established again with an axis to our
north. This will provide a moist southeast wind flow, and while
the speed forecast is uncertain, at least some increase towards
15-20 knots would be expected.


DAB  71  80  70  84 /  40  60  40  40
MCO  70  82  70  88 /  30  70  30  50
MLB  73  80  73  84 /  50  70  40  50
VRB  73  81  72  85 /  60  70  40  50
LEE  71  83  70  88 /  30  70  30  50
SFB  70  81  70  87 /  40  70  40  50
ORL  70  81  70  87 /  30  70  30  50
FPR  72  81  72  84 /  60  70  40  50



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