Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Melbourne Florida
349 am EST Sat Feb 13 2016
..poor to hazardous boating conditions this weekend...
latest analysis shows a dry cold front pushing into the Panhandle...
a little slower than anticipated. The 00z kjax/ktae radiosonde observations indicate
precipitable waters only around 0... latest Sat pics show a few cloud bands
developing ahead of the front in tandem with a band of h100-850 mb dewpoint
depressions between 3-5c over the Northern Peninsula. Ahead of the front...
however...a dry/stable airmass remains in place. The 00z radiosonde observations at
kxmr/ktbw/kmfl measured precipitable water values around 0... rap analysis
indicates h100-850 mb dewpoint depressions between 5-7c along the I-4
corridor...around 15c over Lake Okeechobee and the Treasure Coast.
As expected...the approaching frontal trough has eroded the h100-h70
ridge/anticyclone axis that was in place over the Florida Peninsula on
Friday. The ridge has effectively split in two with the western half
retrograding into the western Gomex...the eastern half pushing well east of the
Bahama bank to merge with the Atlantic subtropical ridge. This will
leave the front with little impedance to slow its forward motion...
especially given the rap40 indicates average h100-h70 flow behind it is
northwest at 25-30kts.
Another quiet weather day in store as frontal moisture is simply too low
to support the formation of anything more than a low level cloud
deck...mean relative humidity values through the h100-850 mb layer are at or below 80pct.
Furthermore...radiosonde observations show a lingering subsidence inversion in the
h90-h80 layer that will pancake any cloud deck below 5kft.
Temperatures will be a bit on the cool side from Brevard/Osceola Colorado northward
once the front pushes through as nwrly flow develops...keeping afternoon
readings in the l/m60s despite near full sun. Treasure Coast/Lake
Okeechobee areas well have time to warm into the l70s before the
frontal passage...but even these will be 3-5f below average. Tightening pgrad behind
the front will allow nearly winds to persist overnight...resulting in
a cool air advection pattern that will allow min temperatures to fall into
the l/m40s west of I-95. Marine influence will keep coastal temperatures a few
degrees warmer...generally u40s/l50s.
a high pressure ridge along the eastern Seaboard will shift
offshore. An early morning coastal trough will exist then
dissipate...giving way to an easterly wind flow in the afternoon.
The air mass will initially be very dry so coastal rain chances
look to be 10-15 percent. Will leave small probability of precipitation along the immediate
coast through Sunday night. Forecast soundings are still supportive
of stratocumulus spreading inland from the Atlantic. So despite
the more mild east wind flow...this cloudiness should keep daytime
highs a little below those from today...mainly middle 60s north and
upper 60s south. Onshore low level winds will keep overnight lows
more mild...lower 50s north interior and upper 50s South Coast.
Monday into early Tuesday...
this period is the main item of interest for the upcoming week. A
shortwave trough is forecast to move across the southern states
and spin up a surface low. The 00z GFS shows a weaker system farther
north than 24 hours ago. Hence the local low level wind fields are
forecast to be weaker. Precipitable water is still shown to only
recover to about 1.3 inches with surface dew points in the upper
50s to lower 60s. MOS probability of precipitation have backed off to 30-40 percent for
Monday night. The European model (ecmwf) also shows a weaker system but the pop values
are a lot higher than the GFS.
Do not want to make significant changes to the forecast just yet
as the subtropical jet core will be nearby and temperatures aloft will
be quite cold...so expect that there could be enough support for
convection over the Gulf of Mexico to spread well inland. Have
trimmed probability of precipitation back to 50 percent for Monday night but kept slight
chance for thunder. Recent weaker model solutions for this system
suggest some shower chances may linger into Tuesday.
Rest of week...
cold front is forecast to push east of the area Tuesday or Tuesday night...
bringing drying and weak cold air advection. A surface high
pressure ridge will then build from the Midwest to off the
Atlantic Seaboard by Sat...with a ridge axis settling into the
local area. Temperatures look close to normal. Late week onshore flow
should push a few showers towards the coast...but probability of precipitation are too low
to mention. Otherwise it looks dry.
surface winds: through 13/12z...W/SW 4-8kts. Between 13/12z-13/15z becoming north/northwest
8-12kts. Between 13/15z-13/23z...N/NW 12-15kts occasional g18-22kts. Between
13/23z-14/02z...becoming north 4-7kts.
Visibility/wx/cigs: VFR all sites.
today-tonight...poor boating conditions as a dry cold front pushes
through the local Atlantic waters. A moderate to fresh wrly breeze through
daybreak will veer to north/northwest by midday as the front pushes through. Rough
seas as winds make the shift from an offshore component to a nearly
component that will blow opposite to the Gulf Stream current.
Prevailing wave heights increasing from 2-4ft to 4-6ft nearshore...
and from 4-6ft to 5-7ft offshore. Steep waves with dominant periods between
5-7sec. Current advisory/caution orientation looks fine for now...
but may need to expand the advisory to include nearshore Treasure
Coast waters by late afternoon due to the Gulf stream's closer proximity
to the coast.
Sun-Mon...breezy northeast/east winds sun will veer to southeast
on Monday. This will keep conditions poor for small craft operation.
Monday night-Wed...breezy south flow is indicated for Monday night. This
will transport moisture northward and bring a chance of showers
and a slight chance for storms. Models differ a bit on the Tuesday-
Wednesday winds but overall the trend is for a weaker frontal passage.
Preliminary point temps/pops...
dab 60 45 63 54 / 0 0 20 20
mco 68 44 67 54 / 0 0 10 10
mlb 67 50 65 58 / 0 0 20 20
vrb 69 51 68 58 / 0 0 20 20
Lee 65 41 66 52 / 0 0 10 10
sfb 65 43 66 53 / 0 0 10 10
orl 67 44 66 53 / 0 0 10 10
fpr 69 52 68 58 / 0 0 20 20
Am...Small Craft Advisory until 4 am EST Sunday for Sebastian Inlet
to Jupiter Inlet 20-60 nm.
Small Craft Advisory until 4 am EST Sunday for Flagler Beach to
Volusia-Brevard County line 20-60 nm-Volusia-Brevard County
line to Sebastian Inlet 20-60 nm.