Area Forecast Discussion
Issued by NWS Melbourne, FL

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FXUS62 KMLB 190823

Area Forecast Discussion
National Weather Service Melbourne FL
423 AM EDT Sat Aug 19 2017


Today-Tonight...Main forecast problem is how the models are handling
moisture fields.  Mid-upper level low is moving slowly west across
the lower Florida Straits and all the models are indicating some
drier air aloft rotating into the area from the southeast.  The GFS
shows POPs less than 20 percent through tonight, but how pervasive
this drier air will be, looks questionable.

POPs today will certainly be low as the GOES 16 total precipitable
water product shows values 1.2 to 1.3 inches already reaching our
southern sections.  However, this product also shows the dry ribbon
being quite narrow.

Surface high pressure ridge axis will start off across central
Florida then will gradually nudge north as frontal trough to the
north along the eastern seaboard weakens.  This will lead to a light
onshore gradient wind developing across the south, which should be
conducive for gradual re-moistening. The ECMWF shows deeper
moisture returning along the Space & Treasure Coast tonight.

Have trimmed POPs back today to 20% or less, except 35% in
Martin county and 30 percent around the Ocala National Forest.
Will stay close to our previous forecast tonight and have chance
POPs along the Treasure Coast, with slight chance along the Space

Sunday...GFS/ECMWF consistent with axis of weak inverted trough
(tropical wave) reaching SE FL coast early Sunday then crossing
into the Gulf by late Sunday. Wave amplitude suggests greatest
return of deep moisture should remain across southern half of CWA.
Increasing coverage of onshore moving showers and embedded storms
likely during the day associated with SE flow and surge of
tropical PW to 2.00-2.25 inches. While some heavy rainfall will be
possible, given only weak SE flow, will not highlight in forecast
at this time. Steering flow progged to be light SE/SSE. If flow
was stronger and more southerly, would be more concerned about
training of cells along coast. POPs lowering to 20/30 percent
across the far north. Will retain scattered showers/storms for the
coastal counties and isolated coverage inland overnight given
moist onshore flow. Max temps near climo with above normal mins.

Mon-Tue...As tropical wave exits far west into the Gulf and
weakens further, a region of drier air upstream over the Atlantic
likely to work across CWA early in the week, resulting in POPs
falling to near or perhaps even a little below typical late August
coverage. Near normal high temps, with mins continuing several
degrees above normal (+5 to +8 degrees along the coast due to
onshore flow across warm waters).

Wed-Fri...Next inverted trough approaches the FL coast early
Wednesday then moves slowly across the state and into the Gulf
overnight. Global models refrain from organizing the tropical
disturbance as it approaches/crosses the area, but system may be a
fairly strong tropical wave. PW values increase significantly
again mid-late week with influx of deep SE flow. Rain chances
rebound Wednesday (especially aross the southern half of CWA),
then above normal coverage area-wide Thu/Fri. Could be some areas
of beneficial multi-day rain total by late in the week. No changes
with temp trend.


.AVIATION...Conditions look mainly VFR today as drier air aloft
spreads across the area from the southeast. This will result in a
much lower coverage of afternoon lightning storms. The greatest
chance might be near KLEE late in the day as the east & west coast
boundaries interact, but even there probabilities look too low to
mention in the TAF. Moisture should start to return from the
southeast tonight and bring small probabilities for showers or
storms to the coastal TAFs south of Canaveral.


Today-Tonight...Surface high pressure ridge axis will slowly nudge
north into our northern waters.  This will generate a light
southeast gradient wind, except remaining light southerly in the
north.  Seas will remain 2 feet or less today and might bump up to 2-
3 feet tonight offshore.  There is little prospect for showers or
storms today, but activity is expected to pick up tonight offshore
the Space & Treasure Coast.

Sun-Mon...As axis of tropical wave passes Sunday, light E/SE flow
early Sunday will become a little stronger from the SE, allowing
seas to build slight, reaching up to 4 feet offshore. Increasing
coverage of onshore moving showers and storms.

Tue-Wed...Light east flow Tue becomes more SE Wed as next tropical
wave axis approaches. Long fetch of onshore flow builds seas to
3-5 ft in the Gulf Stream. Lower shower/storm coverage Tue,
increasing markedly Wed to east of inverted trough axis.


DAB  91  76  89  78 /  20  10  30  30
MCO  94  77  91  77 /  20  10  30  30
MLB  92  78  89  79 /  10  20  50  40
VRB  92  77  89  78 /  20  40  60  40
LEE  94  77  93  77 /  30  10  30  20
SFB  95  77  91  77 /  20  10  30  30
ORL  95  78  91  77 /  20  10  30  30
FPR  92  76  89  78 /  20  40  60  30





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