Weather

424 
fxus62 kmlb 291851 
afdmlb 


Area forecast discussion 
National Weather Service Melbourne Florida 
250 PM EDT Friday Aug 29 2008 


..swells from Tropical Storm Hanna could affect the Atlantic waters 
during the Labor Day weekend... 


..a very tenuous extended forecast with tropical cyclones on either 
side of the state... 


Discussion... 


Tonight...onshore flow will increase across the southern peninsula 
overnight as high pressure moves northward. Low level airmass is 
initially very dry across the southern County Warning Area as seen on the 15z cape 
sounding with a dry layer between 900-800 mbs and vsbl satellite 
imagery with sparse cumulus across the much of the forecast area. Will 
carry a slight evening shower/thunderstorm chance for Lake County into the 
evening and then inroduce a coastal shower chance south of the cape 
after midnight as onshore flow increased to around 15 knots over the 
Atlantic waters. 


Sat...onshore flow will continue to increase as pressure gradient 
tightens just a bit between Gustav and the high pressure center off the middle 
Atlantic. GFS/NAM increase 925 mb winds to 20-30 knots from the east/east-southeast 
through the day with deeper moisture making it up across the 
Treasure Coast in the afternoon. Should see an increase in Atlantic 
shower activity which will move onshore...and will advertise highest 
rain chances around 50 percent across the southern counties and taper probability of precipitation to 
around 40 percent northern sections. Highs in the middle-upper 80s coast and 
aroudn 90 interior. East swells will continue across the Atlantic waters 
and heighten the risk for rip currents. 


Sun-Mon...have trended probability of precipitation highest south and gradually decreased 
toward the NE sections. Highest probability of precipitation occurring south as southeast 
flow and some enhanced moisture well to the east of Gustav should 
increase probability of precipitation a little...especially southern sections. If Gustav 
trends a little west or east...the probability of precipitation may decrease/increase somewhat 
accordingly. See latest NHC discussion/forecast track of Gustav. 


Previous extended discussion... 
Tue-Fri...forecast remains very uncertain and highly dependent upon the 
track and strength of Hanna. One trend noted on the more reliable 
global model guidance is that the upper level pattern becomes quite 
hostile from late Monday Onward over the western sargasso sea area 
..where Hanna is forecast to be..as a 40-50kt north-northwest-north jet is forecast to 
develop on the east side of the eastern Continental U.S. Dlm ridge. This is 
reflected in significant slowing in forward speed along with a turn toward 
the SW...and a reversal of the intensification trend...by Mon-Tue. 
We will continue to watch the progress of Hanna closely here along 
the East Coast of Florida. 


Regardless...surface high pressure to the north should produce rather brisk 
onshore flow through much of the xtd range...which would continue the 
regime of nighttime/morning rain showers and scattered afternoon rain showers with limited 
coverage of ts. Coverage could wind up unusually low for August 
should mean layer drying be stronger than what guidance is indicating. 
On the other hand...with a T.C. East of the Bahamas...confidence in 
any scenario right now is pretty low. 


&& 


Aviation...isolated rain showers/thunderstorms and rain possible klee vicinity through around 23z. 
Isolated rain showers may also affect coastal terminals from kmlb-kvrb after 06z 
into Sat morning. 


&& 


Marine...east winds will increase overnight into Sat to around 15 
knots with seas 3-4 feet northern sections and building to 3-5 feet across 
the southern waters. Isolated showers overnight expected to become scattered 
on Sat. (Prev ext) model guidance continue to strengthen the 
easterly flow and begins to show some swell pushing into the near 
shore Atlantic waters from this weekend Onward. Based upon the GFDL have 
raised offshore seas by about 1-2ft for days 3-5. Will likely see some 
sort of cautionary stmt for the offshore waters later in the 
weekend... with Small Craft Advisory conds (or worse) possible by the middle-late next week. 


&& 


Hydrology...rate of rise at Lake Harney has been minimal past 24 
hours...only about 0.02 feet. However...with river level as high as 
this and levels becoming nearly steady or only falling very slightly 
in the coming several days...significant flooding problems will 
persist in that area through next week. 


Still expect to see a little more of a slow rise through Sanford and 
Deland this weekend...but again... even after the river begins to 
level off...the subsequent decrease will be very slow. Interests on 
the St Johns River will also need to remain mindful that heavy 
afternoon rainfall with thunderstorms will aggravate the ongoing 
situation. We will also need to keep a close eye ahead through the 
end of next week with respect to the eventual path of tc Hanna... 
since the present high water levels through central Florida could 
become even more problematic should the eventual path of Hanna place 
ec Florida in persistent rain bands. See the latest flood statement 
/miaflsmlb/ for latest information on flooding on the St Johns River. 


&& 


Preliminary point temps/pops... 
dab 77 87 77 89 / 10 30 30 40 
mco 76 90 76 90 / 10 40 30 50 
mlb 80 88 79 88 / 20 40 30 50 
vrb 79 89 78 88 / 20 50 40 50 


&& 


Mlb watches/warnings/advisories... 
Florida...none. 
Am...none. 
&& 


$$ 


Volkmer/glitto