Area Forecast Discussion
Issued by NWS Melbourne, FL

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FXUS62 KMLB 300846

Area Forecast Discussion
National Weather Service Melbourne FL
446 AM EDT FRI SEP 30 2016


Today...A weak frontal boundary oriented NNE-SSW located over the
eastern panhandle extending into the northeast Gulf of Mexico is
forecast to stall over the northern peninsula today. GFS shows
some intrusion of dry mid level air across northern sections with
quite low PoPs near 20 percent across north Lake and Volusia.
Deeper moisture to the south of Orlando should support a higher
coverage of storms (near 50 percent). But with cool temps aloft
and a boundary to focus low level convergence, have raised the
MOS PoPs to 30-40 percent across the north. The offshore
(southwest) flow should be lighter today and allow the east coast
sea breeze boundary to form earlier and penetrate inland,
providing another focusing mechanism for storms. A few strong
storms are expected especially resulting from boundary collisions,
containing frequent lightning, downburst winds and small hail.

Tonight...The storms will push offshore this evening but support
aloft should maintain some convection as residual instability gets
worked over. Will gradually taper rain chances off over the
interior by midnight but will keep a small PoP along the coast

Zonal jet pattern over Canada will push a large blocking ridge from
the eastern provinces into the NW Atlc over the weekend. This will
allow a large H100-H70 cutoff low dominating the WX pattering over
the SE CONUS to slowly lift north around the backside of the ridge
into the Great Lakes region. There it will gradually become absorbed
by the northern stream.

As the low lifts north, the Atlc ridge axis will rebuild northward
acrs the central peninsula on Sat, then into the panhandle region on
Sun. Mean winds through the H100-H70 lyr will respond by shifting
from SW to SE on Sat, then to due E on Sun. Source region has
sufficient moisture to maintain at least sct PoPs thru the weekend.
Will keep PoPs blo 50pct on Sat as lingering pocket of dry H70-H30
air keeps PWat values in the 1.50"-1.75" range and impedes
convective development. PoPS increasing to 50-60pct on Sun as winds
thru the H85-H50 lyr shift out of the south and tap increasing
tropical moisture, PWat values increasing to 1.75"-2.00". No sig
change in airmass...temps will be within a deg or two of recent
readings with maxes in the U80s/L90s...mins L/M70s.

Convective potential will be enhanced this weekend by relatively
cool/unstable mid lvl air...H70 temps btwn 9C-10C and H50 temps btwn
-8C/-9C over the SW Atlc are yielding lapse rates of 6.5-7.0C/km
acrs the Bahama Bank and points eastward. Mid upr lvl dynamic
support should be present as well as the H85-H50 trof extending from
the cutoff low should extend far enough into the Deep South thru the
weekend to add weak upward vertical motion to the equation.

Persistent onshore flow will continue thru the first part of the
upcoming week as the Atlc ridge gradually breaks down in response to
a troffing pattern over the eastern CONUS and the forecast approach
of Hurricane Matthew from the south. Easterly flow thru the H100-H70
lyr on Mon...veering to the NE on Tue as the outer fringes of
Matthew`s circulation begin to impact the lcl WX pattern. No
significant drying anticipated, will keep sct/nmrs shras/tsras in
the forecast each day.

The easterly flow should focus afternoon storms over the interior
and west side of the peninsula on Mon... while NE flow and warming
mid lvl temps on Tue will support lower topped convection that tends
to focus more on the coastal zones. Mostly cloudy skies should keep
max temps in the U80s over much of the area each day...min temps in
the L/M70s.

Forecast will hinge on the future NHC track of Hurricane Matthew in
the central Caribbean. The system is forecast to move generally
westward through Saturday evening before turning north toward the
Windward Passage/eastern Cuba early next week. Reliable model
guidance suggests "Matthew" could lift north across the Bahamas
sometime next week. At a minimum, this would result in
breezy/windy conditions especially at the coast with building
seas/surf and dangerous rip currents at the beaches. Beyond that,
it is too early to speculate on specific impacts to east central
Florida or their timing. Climatologically, we remain in the heart
of the Atlantic hurricane season.


Light SW flow this morning will turn E/SE at coastal terminals in
a sea breeze around 17Z. A weak frontal boundary will approach
LEE/DAB during the day from the NW with some drier air aloft
filtering in. Deeper moisture south of MCO should produce the best
chance for storms and have included late day TEMPO groups from
MLB-SUA for storms pushing off the coast aft 21Z. Even across the
north, there will be a chance for storms and will add VCTS to
LEE/DAB/SFB in the next TAF issuance.


Today...Southwest winds around 15 knots over the Atlantic waters
early this morning will decrease to 10 knots by late morning as
pressure gradient weakens which will allow an E/SE sea breeze
to develop near the coast. A weakening frontal boundary will stall
across the northern FL peninsula today. Scattered lightning storms
are forecast to develop ahead of this front and sweep offshore
during the afternoon and early evening containing frequent
lightning and gusty downburst winds, posing a threat to boaters
on the intracoastal and near shore Atlc waters. Seas 2-3 feet.
Tonight...Scattered storms may persist near and offshore the coast
into the overnight supported by divergence aloft and an inverted
trough developing in the low levels.

Sat-Sun...Bermuda Ridge axis over the FL Straits will lift north
acrs the central FL Peninsula on Sat...then into the panhandle on
Sun. Sfc/bndry lyr winds will respond by shifting from a light S/SW
breeze to a light to gentle E/SE breeze on Sat...then a gentle to
moderate easterly breeze on Sun. The prevailing easterly component
will push a small swell into the lcl Atlc waters, enhancing wave
heights thru the weekend. Seas 2-3ft Sat building to 3-4ft Sat
night...contg thru Sun night.

Mon-Tue...Fcst will increasingly hinge on the future track of
Hurricane Matthew currently located over the central Carib. While
the official forecast keeps Matthew out of the immediate area
through Mon night...the latest NHC fcst track would begin to buckle
the lcl pgrad by late Mon night/early Tue morning...forcing winds to
back to the E/NE by daybreak Tue. Lcl pgrad would tighten steadily
on Tue with sfc winds continuing to back to the NE with speeds
approaching SCA criteria by sunset. Deteriorating conditions aft
sunset Mon as the freshening easterly flow pushes increasing swell
energy into the east FL coast. Seas building to 3-4ft nearshore and
4-5ft offshore Mon night...then 6-8ft nearshore and 7-9ft offshore
aft sunset Tue.


DAB  87  69  86  72 /  40  20  40  20
MCO  89  70  89  73 /  40  20  40  20
MLB  88  70  89  73 /  40  40  30  30
VRB  88  72  89  74 /  50  40  30  30
LEE  89  68  87  72 /  20  20  40  20
SFB  90  70  89  72 /  30  20  40  20
ORL  90  71  89  73 /  40  20  40  20
FPR  88  71  88  73 /  50  40  30  40


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