Area Forecast Discussion
Issued by NWS Melbourne, FL

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FXUS62 KMLB 260740
AFDMLB

Area Forecast Discussion
National Weather Service Melbourne FL
340 AM EDT Mon Jun 26 2017

...Afternoon Rain Chances Building Into Mid Week...

.DISCUSSION...
Today/Tonight...The dominant ridge that has been parked over the
area since late last week will finally yield to the mid/upper
trough developing over the eastern CONUS. At the surface, a weak
front will push toward north Florida and further weaken the
western flank of the subtropical ridge. When combined with
steadily increasing moisture, especially in the vicinity of the
surface boundary, these features will bring about a greater
coverage of afternoon showers and storms this afternoon and
evening.

Model soundings suggest there will be quite a spread in available
moisture from SE to NW across the area, with the lowest values
along the Treasure Coast. Given this area is further removed
from the surface boundary and will see a faster inland movement of
the sea breeze, afternoon shower and storm coverage is expected to
be quite low when compared to what is forecast to the north and
west. Along the I-4 corridor, precipitable water values around
2.00" will combine with cooling temperatures aloft to produce
numerous showers and thunderstorms from mid to late afternoon.
With light westerly steering flow aloft, some of this activity is
expected to shift back toward the coast, mainly north of
Melbourne. Rain chances for this afternoon have been distributed
with this in mind: lowest along the Treasure Coast (20-40%) and
highest along the Interstate 4 corridor (60-70%).

Expect storms to have a bit more vigor this afternoon with
frequent to excessive lightning, brief gusty winds, and very heavy
rainfall the primary threats. Steering flow will be quite weak,
so localized flooding from quick 2- to 3-inch downpours remain a
possibility. Greater cloud cover should keep temperatures down a
degree or two from their highs on Sunday and closer to their
seasonal averages for late June (89-92).

With the best boundary interactions expected to take place late
this afternoon and early this evening, scattered (30-50%) chances
for showers and storms will be carried through midnight to account
for lingering debris rain and leftover convection. Overnight lows
generally in the mid 70s.

TUE-WED...Period begins with a weak sfc trough oriented roughly
parallel and just offshore of the Georgia-Carolina Coast between two
dominate and shifting high pressure ridges. While one shifts
seaward, the other is intended to overspread the Eastern CONUS. The
sandwiched trough will struggle to maintain identity as it fills
and associated moisture redistributes. Nonetheless, the vicinity
presence of said boundary offers an intriguing synoptic backdrop.
The boundary will drape across North Florida Tue and then sag toward
Central Florida for Wed as the large continental high pressure
transitions off the Eastern Seaboard. Low-level winds for Tue will
show a northerly component north of the boundary and a southerly
component south of it, but diurnally augmented overall with an
onshore component driven by a late morning and afternoon sea breeze.
For Wed, these winds are expected to be more uniform onshore. High
pressure aloft gets shunted a bit farther south as broad mid-level
troughing swings eastward but with significant effects well-north of
the forecast area. Even so, local concentrations of moisture should
be more than sufficient to promote rain chances on the higher side
of normal, especially since temperatures aloft will be a degree or
two cooler to help with convective overturning. Storms will be slow
movers and able to dump locally heavy rain totaling a couple of
inches in spots. Max Temps in the U80s/L90s each day with Min Temps
in the L/M70s.

THU-SUN...Mere vestiges of the old decaying boundary still present
with pools and pockets of associated moisture. These will tend to
gather over North Florida as embedded in the SE wind flow courtesy
of the seaward-moving high pressure area off the Mid-Atlantic and
New England Coasts. Then, gathering moisture over the Northern Gulf
of Mexico will spread east toward Florida to team with remaining
residual moisture to support 40-60 percent PoPs late-week and into
the weekend. Onshore flow will favor an inland skew to convective
distribution, especially for the afternoon and early evening. Yet a
chance of morning showers also included for the coast. Max Temps in
the U80s/L90s with Min Temps M/U70s.

&&

.AVIATION...
Generally VFR through the forecast period outside of brief
reductions due to afternoon shower and thunderstorm activity.
Greatest coverage of SHRA/TSRA anticipated from KMLB to the north
and west with lower chances along the Treasure Coast terminals
(KVRB-KSUA). Have introduced tempo groups where chances are
highest; users should monitor for timing adjustments as we
monitor trends in convective development through the day. Activity
should gradually diminish between sunset and midnight. Winds
generally 10 knots or less outside of gusty winds due to
thunderstorm activity.

&&

.MARINE...
Today/Tonight...The western extent of the Atlantic subtropical
ridge continues to lay across our waters. Winds will remain light
through the next 24 hours, generally at or below 10 knots outside
of thunderstorm activity. Seas 1 to 2 feet. Expect a greater
coverage of afternoon showers and thunderstorms over the mainland,
with a few pushing toward the intracoastal and nearshore Atlantic
waters this afternoon and evening, mainly north of Melbourne.

TUE-FRI...A weak frontal trough over the North Florida Atlantic
waters will sag slowly south toward the Central Florida waters by
Wed as it gradually dampens and erodes. Associated moisture will
prompt rain chances to be higher than normal through mid-week. By
Thu, a large area of high pressure will transition off the Atlantic
Seaboard causing local wind flow to become prevailing from the east
and onshore. By Fri, local winds turn southeast as the high pressure
transition`s farther seaward off the Mid-Atlantic Coast. Surface
winds expected to remain at or below 10 knots outside of
thunderstorm activity with seas generally 2 feet through mid-week.
Then, building onshore wind flow of 10 to 15 kts will support seas 2-
3 feet.

&&

.PRELIMINARY POINT TEMPS/POPS...
DAB  89  74  85  72 /  60  40  60  30
MCO  92  74  88  74 /  60  50  70  30
MLB  91  76  86  73 /  50  40  70  40
VRB  91  74  87  73 /  40  20  60  40
LEE  91  74  88  74 /  70  50  60  30
SFB  90  74  88  73 /  70  50  70  30
ORL  92  74  88  74 /  70  50  70  30
FPR  91  74  88  72 /  40  20  60  40

&&

.MLB WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...None.
&&

$$

Ulrich/Sharp


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