Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Melbourne Florida
307 PM EDT Tuesday Sep 16 2014
current-tonight...the East Coast sea breeze boundary has developed
this afternoon from the cape southward through Jupiter Inlet.
Isolated showers and storms have already developed along it. Other
activity across east central Florida has been slow to develop thus
far due to cloud debris from earlier activity north of the area.
However...with deep moisture around...continued heating through the
afternoon...various boundaries around and weak impulses aloft we
should still see increasing coverage of showers and storms through
this evening. Movement of cells will be out of the northwest at
around 10 miles per hour. Main threats from storms continue to be frequent cloud
to ground lightning in a few cells...gusty winds of 40 to 50 miles per hour and
heavy rainfall. Some heavier cells may create ponding of water on
roadways and nuisance urban/small stream flooding for a short time.
A weak frontal boundary to the north will slide southward into
north-central Florida late overnight. Showers/storms will be on the
decrease into the late evening as it pushes offshore. Will still
maintain a slight chance for convection overnight due to the
proximity of the front and moist airmass in place. Mostly cloudy
skies expected with lows in the low to middle 70s. Light west-southwest
winds are forecast tonight.
..previous extended forecast discussion...
Wed-Thu...a 70-90kt h30-h20 jet streak extending from the Ohio/Tennessee
River valleys into New England will produce strong upper level
divergence over the deep south. This will induce a broad surface low
along a stationary front that will slowly crank it through central Florida
on Wednesday...then into S Florida on Thursday. Frontal motion will be slow but
steady as the Atlantic ridge over Florida and the Florida Straits is quite weak
and will not be able stall the advance.
Deep moisture pooling within the trough with precipitable water values running between
2.1"-2.2". This moisture...coupled with a respectable 850 mb-h50 vorticity
band in the vicinity of the front and h50-h70 lapse rates between
5.5-6.0c/km will produce a wet Wednesday with probability of precipitation above 50pct areawide.
Probability of precipitation will drop back to 20-30pct on Thursday as the Central Peninsula
gains the backside of the front and steering winds veer to the north/northwest
and pull drier and more stable middle level air across the County Warning Area with precipitable waters
dropping below 1.5".
On Wednesday...models indicate a nearly saturated airmass above h50 that
should produce middle/upper level cloud decks that will hinder surface heating.
However...ruc40 regional analysis shows h50 temperatures near the frontal
trough running around -8c that should provide sufficient instability to
keep scattered thunderstorms and rain showers in the forecast. Overall instability looks modest at
best...strong/svr thunderstorm threat will be quite low.
Cloud cover and rain cooled air will keep maximum temperatures near average
(m/u80s) on Wednesday despite the usually warmer wrly flow that will
prevail. Low precipitation/cloud coverage on Thursday will allow maximum temperatures to
warm back into the u80s/l90s. Min temperatures near average (l70s) as well as
light nearly winds push slightly lower dewpoints into central Florida.
Fri-Mon...frontal boundary will remain over S Florida through Friday as the Post
frontal hi pressure ridge works its way across the eastern Continental U.S. And off the
middle Atlantic/New England coast. North/NE surface/steering winds will keep the
relatively dry and stable middle level air mass in place with relatively
lower precipitation chances through the latter half of the week. The remnants
of the front will drift back northward on Sat as the h100-h70 flow veers
more to the E/NE...but by then it will be have little more than a
middle level Theta-E reflection than true frontal properties. Probability of precipitation on Sat
may creep up to the 50pct mark across the Treasure Coast...but precipitation
chances will remain at or below 40pct for most of the area into early next
week as broad hi pressure reestablishes its hold over the Gomex/western Atlantic.
No sig cool air advection as the front has been meandering over the
deep south for the past few days. Furthermore...with surface/low level
winds shifting onshore...ocean modification will occur quickly.
Maximum/min temperatures not expected to deviate from climatology avgs by more than
Aviation...the East Coast sea breeze has developed from the cape
southward this afternoon. Inland push will be slow due to
west/northwest flow at/above surface. Winds will back to an easterly
onshore flow component behind this feature. Increased convection
chances through this afternoon and evening. A surface boundary will
sink into north-central Florida by sunrise Wednesday morning. Tempo IFR/MVFR
conds will occur with any showers/storms with gusty downburst winds.
Rain chances will decrease into the evening but could still see a
few showers developing over the region overnight due to higher
moisture and the surface boundary's presence. Light west-southwest
winds forecast tonight. Higher rain chances continue into Wednesday with
front around the area.
Marine...current-tonight...weak front across the deep south will
sag into north-central Florida by daybreak Wednesday morning. Winds have backed
to easterly along the coast south from the cape where the ecsb has
formed. Offshore flow returns again tonight across much of the
waters. Main concern for boaters remains for scattered storms
producing gusty winds as they move offshore into this evening
especially north of Sebastian Inlet. Wind speeds may approach 15 kts
away from the coast overnight. Current seas around 2 feet will
gradually build to 3-4 feet offshore in increasing long period swells
..previous extended marine discussion...
Wednesday-Wednesday night...a weak frontal trough over the deep south push through
central Florida and suppress the Atlantic ridge axis into the Florida Straits.
Interaction between the two systems will tighten the local pgrad
sufficiently to produce a gentle to moderate wrly breeze across the
local Atlantic...no seabreeze is anticipated. Seas building to 3-4ft
nearshore and 5-6ft offshore...largely due to a very long period swell
(aoa 15sec) from distant Hurricane Edouard. Dangerous rip current
conditions are expected along the coast.
Thu-Fri...frontal trough will push into S Florida on Thursday...allowing a light
to gentle west/northwest breeze to veer to the north/NE through the day on Thursday...then
gradually to the east/NE through Friday. Swells will gradually dampen out on
Thursday with seas subsiding to 2-33ft nearshore and 3-4ft offshore by
sunset Thursday...continuing through Friday.
Sat-Sat night...the front will wash out over the S half of the
peninsula as it drifts back to the north...light to gentle east/southeast
surface/boundary layer breeze will prevail. A new swell train will work its
way into the local Atlantic as a large high pressure ridge pushes off the middle
Atlantic/New England coast and generates a tight pgrad along the eastern
Seaboard. Seas 2-3ft areawide at daybreak...building to 3-4ft
nearshore and 4-5ft offshore after sunset.
Preliminary point temps/pops...
dab 74 86 73 86 / 60 60 30 20
mco 74 88 73 90 / 60 60 30 30
mlb 76 86 73 86 / 50 60 40 30
vrb 74 87 72 86 / 50 60 40 40
Lee 74 89 73 90 / 60 50 30 20
sfb 74 89 74 90 / 60 60 30 20
orl 75 88 74 90 / 60 60 30 20
fpr 73 87 72 86 / 50 60 40 40