089 
FXUS62 KMLB 120755
AFDMLB

Area Forecast Discussion
National Weather Service Melbourne FL
355 AM EDT Tue Sep 12 2023

...New MARINE, AVIATION...

.DISCUSSION...

Key Messages:
-HIGH Risk of Deadly Rip Currents At All Atlantic Beaches
-Marginal Risk For Late Day Severe Storms Inland Again
-Seas and Surf Building From Early Wednesday Onward
-Heat Index Up To Around 106 degrees This Afternoon

Current...Convectively active evening ended with numerous reports
of wind damage/large hail, along with local flooding and frequent
to continuous lightning in some storms. Current KMLB radar shows 
scattered Atlantic showers north of Melbourne Beach moving slowly 
N-NNE with convective CS debris dissipating as it moves offshore. 
3AM temps were in the L-M70s inland and U70s-80F near the coast.

Today-tonight...H50 high center over SOFL/Bahamas will flatten
as zonal flow to its north expands south across the peninsula. 
A surface ridge extending NE from the northern half of FL to just 
offshore the SE seaboard will weaken tonight as it starts to get 
squeezed by Hurricane Lee, which will turn northward, well east 
of the northern Bahamas.

Light winds ENE-E winds will allow the Atlantic sea breeze to form
and move steadily inland, with mean PWAT values remaining in the
1.8" to 1.9" range. While the H25 jet won't be in as favorable of
a position to help forces ascent as it was on Mon, another weak 
vort lobe will slide east in across north-central FL late this 
afternoon-early evening, helping to compensate for this. Similar
to Mon, CAMS guidance forecasts surface-H50 bulk shear values of
around 30kt, with H50 temps cooling another degree (to -8C/-9C),
which will steepen mid level lapse rates further.

Late day boundary collision over the western interior (near or 
just west of Lake Co.) is expected to produce rapid development of
strong to severe storms toward sunset once again. H85-H50 mean 
steering flow of 10-12kt will try to push activity E-SE across the
interior through early evening, though activity may not make it 
all the way back to the Atlantic coast.

POPs today will range from 30 along the coast (probably generous 
again) to 50-60 across the interior, highest from western Osceola 
northward. Raised POPS to 30-40 in this same area to cover storms 
lingering through mid-late evening. SPC 'MRGL' risk for severe 
storms in place for all of the interior of ECFL. Wind gusts to 
around 60 mph. hail 1" or slightly larger, frequent to excessive 
lightning and torrential 1-3"+ downpours expected in the most 
intense activity. Max temps 88-90F along the coast and L90s inland.
Mins in the L70s inland/M70s near the coast.

Wednesday... Some modest changes in the guidance for the middle of 
the week, as the latest data suggests somewhat higher moisture than 
previously noted (PW's ~ 1.8" / 0-3km mixing ratio's ~ 13 g/kg). A 
trough will be traversing over the Great Lakes, with its attendant 
cold front up across the Deep South. Weakening high pressure will be 
nestled just to our north, with light NE flow in the boundary layer 
and W/NW flow aloft. Scattered showers/storms are expected to flare 
up in the afternoon on both sea breezes, with the collision likely 
over our interior counties in the afternoon and early evening. 
Warmer mid-level T's (H5 ~ -5C) and weaker bulk shear should lessen 
the intensity of these storms, so expect more of the typical wet-
season variety. Highs 88-93 coast-interior. As Lee churns well out 
in the Atlantic basin, beach conditions become increasingly 
hazardous with surf becoming rough at 3-6 feet as the HIGH risk of 
rip currents continues.

Thursday-Saturday... Hurricane Lee will finally begin to move 
northward. As it does, northeast flow will pick up, forcing the 
increasingly diffuse 'cold' front southward across the state. 
Moisture will pool along this boundary, with its axis moving from 
Central/North FL on Thursday to South FL by Saturday. Rain/storm 
chances will follow suit: 60-70% near I-4 / 50% Treasure Coast on 
Thursday, then a broad 50-60% coverage on Friday. By Saturday, storm 
chances drop to 20-30% along I-4 but remain around 50% down near 
Lake O. With the increasing NE flow, a few onshore-moving showers 
will remain possible (20-30%) during the overnight periods as well. 
H85 T's will fall from +18C Thu to around +16C on Saturday. This 
will allow high temps to drop from the upper 80s-low 90s Thursday to 
the mid-upper 80s on Saturday. Barrier islands north of Cape 
Canaveral may even struggle to reach 85F Friday and Saturday with 
the onshore flow; this also spells a healthy overnight temperature 
gradient with mid/upper 70s at the coast, and upper 60s/low 70s 
inland by Friday night.

This will also be the timeframe where coastal impacts will maximize 
from Hurricane Lee's swells and moderate onshore winds.  The risk of 
deadly rip currents will undoubtedly remain very high. In the surf 
zone, 5-8 ft breakers are forecast by Friday, and beach/dune erosion 
could become an issue. Beachside communities, particularly across 
Volusia County, should begin considering steps to protect property 
known to be vulnerable to high surf events. A High Surf Advisory is 
certainly on the table during this timeframe; check back for further 
updates as we refine the forecast.

Sunday-Early Next Week... Ensemble cluster analysis reveals that the 
multi-model consensus keeps a trough across the Eastern U.S. this 
period, reinforced by additional shortwave energy entering the 
pattern from the Northern Plains. Details remain fairly murky, with 
individual clusters disagreeing on the depth and positioning of the 
trough. At the jet stream level, a split flow regime is forecast, 
with the subtropical jet extending across the extreme Southern U.S. 
before weakly phasing with the northern stream along the Eastern 
Seaboard. This will place Florida and the Gulf of Mexico in the 
right entrance region of the upper jet, favorable for broad synoptic 
lift. 

On cue, many ensemble members are ramping up rain/storm chances 
during this timeframe, but timing and intensity are both too early 
to call. However, with that old front hanging up just to our south, 
it is conceptually reasonable to expect that plume of moisture and 
slightly lower pressures to retreat northward across Central 
Florida, which will also act to percolate our rain chances. For now, 
trended coverage generally toward statistical guidance (40-60%), 
focusing higher as one travels south across the area. Highs will 
remain near normal, upper 80s to near 90. Surf will slowly subside 
late in the weekend, with 3-5 ft waves forecast on Sunday.

&&

.MARINE...
Issued at 355 AM EDT Tue Sep 12 2023

Today-tonight...As Hurricane Lee edges NW toward the latitude of 
the northern Bahamas, swells will begin to build into the local
waters. Seas will reach 3-5ft this afternoon, and up to 6ft in the
far outer Volusia water by sunset. Swells will continue to build
overnight, pushing seas to 4-6ft over most of the local Atlantic,
except for of 3-4ft along the immediate Treasure Coast, and up to
7ft well offshore from the Cape northward toward sunrise Wed, and
a SCA will be needed by then, if not a few hours earlier.

It bears repeating that seas, Boating and beach activities will 
become increasingly dangerous through the end of the week due to
building seas and surf and an increasing frequency of deadly rip 
currents!

Wednesday-Saturday... Small Craft Advisory conditions are expected 
in the offshore waters Wednesday before encompassing much of, if not 
the entire, marine area by sometime Thursday.  Due to the long-
period swell from Hurricane Lee, seas will continue to build. Expect 
seas to peak sometime Thu/Fri, highest in the Gulf Stream (see 
below). Winds will remain NE through the period, from 5-12 KT 
Wed/Thu before freshening to 10-15 KT Fri/Sat. A weak front will 
move through the area, prompting scattered shower/storm chances 
through the period.

 Seas           Nearshore (0-20 nm)      Offshore (20-60 nm)
------               ------                   ------
 Tue                 2-4 ft                   3-6  ft
 Wed                 3-6 ft                   4-8  ft
 Thu                 5-9 ft                   5-11 ft 
 Fri                 5-9 ft                   6-10 ft
 Sat                 4-8 ft                   5-9  ft

Note, occasionally higher seas can be expected.

&&

.AVIATION...
(06Z TAFS)
Issued at 355 AM EDT Tue Sep 12 2023

VFR giving way to increasing SHRA/TS chances, mainly after 21Z.
06Z TAF package added TEMPO TS groups for all interior aerodromes
in the 23Z-02Z time frame. Expect at least some sites will need to
have short fuse AMDs to add IFR VSBYs and convective gusts 30-50kt
once activity gets going.

&&

.PRELIMINARY POINT TEMPS/POPS...
DAB  88  74  88  74 /  40  40  50  20 
MCO  93  75  92  75 /  60  40  50  20 
MLB  90  76  89  75 /  30  20  40  10 
VRB  90  75  90  74 /  30  10  40  10 
LEE  93  74  92  74 /  60  40  50  20 
SFB  92  74  92  74 /  60  40  50  20 
ORL  93  76  92  75 /  60  40  50  20 
FPR  90  76  90  75 /  30  10  40  10 

&&

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

$$

SHORT TERM...Cristaldi
LONG TERM....Heil
AVIATION...Cristaldi