Area Forecast Discussion
Issued by NWS Melbourne, FL

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FXUS62 KMLB 190842
AFDMLB

Area Forecast Discussion
National Weather Service Melbourne FL
345 AM EDT Thu Jul 19 2018

.DISCUSSION...
Today-Tonight...lcl wind profilers show a deep SW flow acrs the FL
Peninsula as a frontal trof stalled over the Deep South/W Atlc is
keeping the Bermuda Ridge axis pinned over the FL Straits. Evng
RAOBs showed relatively high moisture thru the column with PWat
values arnd 2.00".  However, much of this moisture is trapped abv
the H50 lyr as latest RAP40 analysis shows H85-H50 dewpoint
depressions btwn 5-7C along an north of the I-4 Corridor, and btwn 7-
10C over the Treasure Coast/Lake-O region.  H100-H70 analysis shows
a similar moisture profile with the 70-80pct mean RH over I-4/Space
Coast, decreasing to AOB 70pct over Lake-O.

SW flow patterns tend to produce abv avg temps acrs east central FL,
and this case will be no different...max temps similar to Wed with
readings topping out in the L/M90s. This heating will provide
sufficient sfc instability to trigger shras/tsras as fcst soundings
indicate convective triggers in the U80s/L90s. However, while the
prevailing SW flow will favor the east central peninsula for diurnal
precip, the general lack of low/mid lvl moisture will be a limiting
factor. Furthermore, lcl profilers are measuring winds arnd 15KT at
least thru the H100-H85 lyr. This will at least delay the formation
of the east coast sea breeze until late aftn, if not suppress its
formation all together. Finally, mid lvl instability is on the low
side as H70 temps btwn 9-10C suggest a weak thermal ridge overhead,
while H50 readings btwn -6C/-7C are yielding lapse rates on the
order of 6.0C/KM.

PoPs will mirror the lcl moisture profile with 30pct over the
Treasure Coast/Lake-O region, increasing to 60pct for N
Brevard/Coastal Volusia. Will carry chc/slgt chc of tsras into the
evng hrs, but precip should dissipate well before midnight.
Overnight mins in the M70s.

Fri-Sat...low-level ridge axis extending across southern peninsula
Fri weakens and shifts SE Sat as mid/upper trough associated with
Great Lakes cut-off deepens/extends southward toward N/C FL. Surface
boundary remain N of state Fri, but drops into northernmost
peninsula Sat preceded by band of deep-layer moisture (Precipitable
Water values increasing toward 2.0-2.2 inches across far N CWA Sat).
This pattern will promote 15 kt SW boundary layer/steering flow
across most of CWA (except closer to 10 kt southern areas) which
should restrict east-coast sea breeze, at least Brevard County
northward. Coastal winds may back to an along-shore component across
southern areas both afternoons. With N-S moisture gradient, have
tempered POPs from 50% N to 40%C and 30% S both days, with low-end
scattered convection lingering into the evenings. Max temps low-mid
90s (even near the coast), with mins low-mid 70s; both 2-4 degrees
above climo.

Sun-Wed...GFS/ECMWF remarkably similar with depiction of mid-level
cutoff ever-so-slowly meandering southward, to OH Valley Sun, TN
Valley Mon, to central Gulf Coast Tue/Wed. This evolution should
allow surface boundary to drop well south down the peninsula, into
and possibly through CWA, before losing identify by early next week.
Rather broad swath of very moist air (albeit narrowing with time)
will accompany the boundary, with Precipitable Water values well
over 2 inches (possibly approaching 2.25 inches). For now, have
capped diurnal POPs at 60% through the period, but may need to raise
POPs for a portion of the period/area over coming days. Highest rain
chances Sun will remain across N/C areas, but should increase and
become fairly uniform CWA-wide during early-mid portion of next
week. Moderate Westerly low-level flow should again restrict
Atlantic sea breeze Sun (especially north half), then weaken while
becoming more SW/S Mon, then S/SE Tue-Wed, with sea breezes
dominating early-mid week, leading to above normal shower/storm
coverage. Clouds/precip should keep temps in check and near climo.

&&

.AVIATION...Thru 20/12Z.
Sfc Winds: Thru 19/12...S/SW 3-5KTS. Btwn 19/12Z-19/15Z...bcmg SW 8-
12KTS. Btwn 19/18Z-19/21Z...E of KMLB-KOBE bcmg S/SE 8-12KTs. Btwn
20/01Z-20/04Z...bcmg S/SW 3-5KTS.

Vsbys/WX/Cigs: Btwn 19/16Z-19/24Z...N of KISM-KTIX...nmrs MVFR
shras/IFR tsras...S of KISM-KTIX sct MVFR shra/IFR tsras. Btwn
20/00Z-20/03Z...chc MVFR shras/IFR tsras.

&&

.MARINE...
Today-Tonight....Frontal trof extending from the Deep South to the
Canadian Maritimes will keep the axis of the Bermuda ridge pinned
over the FL Straits. Gentle to moderate S/SW breeze will prevail,
which should be strong enough to prevent the formation of the east
coast sea breeze until late aftn. Even then, windshift will be to
S/SE and limited to points south of Cape Canaveral. Seas 2-3FT
nearshore and 3-4FT offshore. Sct-nmrs shras/tsras moving offshore.

Fri-Mon...Persistent eastern US trough will keep surface ridge axis
well south of the CWA. Moderate SW breeze will prevail Fri-Sun,
likely strong enough to restrict sea breeze formation Brevard
northward, with winds backing near the coast farther south each
afternoon. Gradient flow will become more southerly and a little
lighter Mon. Seas generally 2 ft nearshore and 3-4 ft offshore.
Scattered offshore-moving thunderstorms Fri/Sat afternoon/evening,
becoming locally numerous Sun/Mon.

&&

.HYDROLOGY...The Saint Johns River is either above Action Stage
or just above Flood Stage between Geneva and Astor. Little change is
expected into the weekend.

Near Geneva, just south of Lake Harney, the most recent stage was
8.1 feet, which is above Flood Stage (8.0 feet). The river is
forecast to fall slightly but remain near Flood Stage into the
weekend. A River Flood Warning remains in effect for this area.

At Sanford, the most recent stage was 5.1 feet, which is above
Action Stage (4.2 feet). The river is forecast to remain nearly
steady, staying below Flood Stage (5.5 feet) into the weekend.

Near Deland, the most recent stage was 3.5 feet, which is right
around Action Stage (3.5 feet). The river is forecast to remain
nearly steady into the weekend.

At Astor, the most recent stage was 2.3 feet, which is right around
Flood Stage (2.3 feet). The river is forecast to remain nearly
steady into the weekend. A River Flood Warning remains in effect for
this area.

.PRELIMINARY POINT TEMPS/POPS...
DAB  91  76  89  75 /  60  30  50  20
MCO  92  74  91  75 /  60  30  40  20
MLB  93  75  92  76 /  40  30  30  20
VRB  95  74  93  74 /  30  30  30  20
LEE  91  76  88  76 /  60  30  50  20
SFB  93  75  91  76 /  60  30  40  20
ORL  92  75  91  77 /  60  30  40  20
FPR  95  73  93  73 /  30  30  30  20

&&

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

&&

$$

SHORT TERM: Bragaw
LONG TERM: Spratt


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