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Area Forecast Discussion (AFD)

Issued by Melbourne, FL (MLB)

                            
000
FXUS62 KMLB 130830
AFDMLB

Area Forecast Discussion
National Weather Service Melbourne FL
430 AM EDT Mon Aug 13 2018

.DISCUSSION...
Latest RAP40 analysis shows a high amp H100-H70 trof extending from 
the NE GOMex into the Carolinas butting up against the wrn flank of 
the Bermuda ridge over the FL Straits. Resulting H100-H70 mean flow 
is SW arnd 15KTS. Evng RAOBs measured PWat values btwn 1.75"-2.00" 
over most of central/south FL, except arnd 1.50" at KMFL. RAP40 
analysis shows the pocket of relatively dry air has pushed into the 
Bahamas under the SW flow as latest PWat values have recovering to 
arnd 2.00" areawide...up to 2.25" north of I-4. H100-H70 mean RH 
values btwn 70-85pct over most of the CWA...btwn 60-70pct over the 
Treasure Coast/Lake-O region. However, again, the relatively dry air 
is embedded within deep SW flow that will push it offshore by 
daybreak. Mid lvls on the dry side south of I-4 with H85-H50 
dewpoint depressions btwn 5-7C...along and north of I-4 depressions 
btwn 3-5C.

With SW flow dominating the H100-H0 lyr, the east FL coast will be 
focus for today's round of diurnal convection. Dynamic instability 
is present with an H85-H30 vort lobe over south FL embedded within 
srly flow, and a strong pocket of H30-H20 divergence over the wrn 
GOMex, though the latter feature has undoubtedly been enhanced by a 
large and persistent pocket of nocturnal convection. Thermodynamic 
support is modest: H70 temps btwn 8C-9C and H50 temps btwn -7C/-8C 
will yield lapse rates btwn 5.5-6.0C/KM.

With central FL on the ascending side of the trof axis to the NW, 
high PWat values, and sfc dewpoints in the L/M70s, another round of 
high PoP is in store for the CWA. No sig mid lvl thermal cap 
suggests precip could get an early start, though lcl HRRR/WRF models 
suggest initiation holding off until arnd 18Z. Given the SW steering 
flow, will go with 50-60pct over the interior and 60-70pct along the 
coast today...lower numbers to the south to account for the Lake-O 
shadow. Precip lingering thru 02Z with PoPs AOB 20pct. Temps near 
avg with aftn maxes in the U80s/L90s, overnight mins in the L/M70s. 

Tuesday...Low level flow will remain from the southwest on Tuesday 
as the low level ridge axis lift from south FL toward Lake 
Okeechobee. GFS is not indicating much morning convection but should 
see early to mid afternoon showers/storms along the Treasure coast 
sea breeze and also across far nrn sections in the low level SW flow 
and in an area of deeper moisture across the nrn peninsula. Will 
keep pops mainly in the 30-40 percent with scattered afternoon 
coverage expected. Highs will range from the lower to mid 90s across 
the nrn interior. 

Wed...Wednesday looks to be a transition day as the low level ridge 
moves north toward southern portions of east central Florida. This 
will allow the recent persistent low level SW flow to transition 
gradually to the SE to S in the afternoon. GFS has low level 
convergence maximized in the late afternoon from Osceola across 
eastern Orange/Seminole and Volusia counties with late day sea 
breeze interactions will keep shower/thunderstorm coverage in the 
scattered range with rain chances up to 40 percent. Highs lower 90s 
coastal to some mid 90s across the nrn interior.

Thu-Sun...GFS/ECMWF models have the mid level ridge strengthening 
across central FL into Thu and Friday with 500 mbs heights to 594 DM 
over the area. The low level ridge will also lift slowly northward 
across northern portions of east central Florida into late week. 
This will spell a drier airmass across the region with more limited 
sea breeze convection expected. Will indicate rain chances below 
normal in the 20 percent range near the coast and up to 20-30 
percent for the interior. Mid level heights are forecast to decrease 
slightly at 500 mbs over the weekend though the center of the mid 
level ridge aloft will remain across central FL. This should 
continue the trend of below normal rain chances (20 percent coastal 
to 30 percent interior) and hot temperatures in the lower 90s 
coastal to the mid 90s across interior sections.  

&&

.AVIATION...Thru 14/12Z.
Sfc Winds: thru 13/12Z...S/SW 3-6KTS. Btwn 13/12Z-13/15Z...bcmg S/SW 
6-9 KTS. Btwn 13/15Z-13/18Z...coastal sites S of TIX bcmg SE 7-
11KTS. Btwn 13/22Z-14/01Z...bcmg S/SW 5-8KTS. Btwn 14/03Z-14/06Z... 
bcmg vrbl AOB 3KTS. 

Vsbys/WX/Cigs: Btwn 13/15Z-13/18Z...slgt chc MVFR shras/IFR tsras. 
Btwn 13/18Z-13/24Z...cigs btwn FL060-080...nmrs MVFR shras/IFR tsras 
slgt chc LIFR tsras with sfc G35KTS. Btwn 14/00Z-14/02Z...cigs btwn 
FL100-120...slgt chc MVFR shras/IFR tsras. 

&&

.MARINE...
Today-Tonight...Weak trof extending from the FL Big Bend into the 
Carolinas will combine with the wrn flank of the Bermuda Ridge over 
the FL Straits to generate a light to gentle S/SW breeze acrs the 
lcl Atlc thru midday. Winds shifting to a gentle to moderate S/SE 
breeze over the nearshore waters by early aftn as the east coast sea 
breeze dvlps. Seas generally AOB 2FT...up to 3FT in the Gulf Stream 
north of Cape Canaveral. The offshore wind component will generate 
choppy wind waves over the nearshore leg with dominant pds AOB 4sec. 
Primary boating hazard will be sct/nmrs shras/tsras moving offshore 
btwn midday and early evng. 

Tuesday...SW winds Tue morning will become southerly in the 
afternoon and SE near the immediate coast. Some late afternoon and 
evening storms will be possible across the intracoastal and near 
shore waters.

Wed-Fri...SE/S winds Wed will become SE/ESE into late week as the 
surface ridge lifts northward. Overall coverage of showers and 
storms will be limited this period with mainly isolated showers/ 
storms expected across the east central FL Atlantic waters.

&&

.HYDROLOGY...
No sites along the Saint Johns river are at or above Flood Stage, 
with Astor, Sanford and Lake Harney forecast points remaining in 
Action Stage. Recent rains this weekend may cause additional sites 
to near Action Stage. Refer to the latest Hydrologic Statements 
(RVSMLB) for the latest stage and forecast information.

&&

.PRELIMINARY POINT TEMPS/POPS...
DAB  90  73  91  74 /  70  20  40  30 
MCO  92  73  94  75 /  60  20  30  30 
MLB  90  74  91  75 /  60  20  30  30 
VRB  90  73  91  74 /  60  20  30  30 
LEE  91  74  93  76 /  60  20  40  20 
SFB  92  73  94  75 /  60  20  30  30 
ORL  92  74  94  77 /  60  20  30  30 
FPR  90  73  90  74 /  50  20  30  20 

&&

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

&&

$$

Short Term/Aviation...Bragaw
Long Term/Impact WX...Volkmer