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Area forecast discussion 
National Weather Service Tampa Bay Ruskin Florida
407 am EDT Tuesday Oct 21 2014

Short term (today through wednesday)...
currently at the surface...a broad area of low pressure is located
over the Bay of Campeche with a surface trough extending
east-northeastward into the Florida Keys. Infrared satellite
imagery shows cloudy or mostly cloudy conditions in place across
the forecast area...with radar imagery showing some convection
between the Florida Keys and the southwest Florida coast. Main
short term concern for today revolves around probability of precipitation.

Today...
a shortwave trough currently seen in water vapor imagery stretching
from the central Carolinas southwestward into the Florida Panhandle
will shift slowly southeastward and into central Florida by this
evening. This in combination with a strengthening 110+ knot upper
level jet over North Florida will allow the trough of low pressure
and associated deeper layer moisture to edge northward into
southwest Florida through the day. The nam12 shows h925-700 mb
condensation pressure deficits dropping to 30 mb or less roughly
along a Sarasota to Lake Kissimmee line...with decent forcing for
ascent provided by the right rear quadrant of the upper level jet and
middle/upper level qg forcing associated with the approaching shortwave
trough. Will generally use this Sarasota to Lake Kissimmee line to
delineate between rain in the forecast and rain free conditions.
Will show rain chances ranging from 20 percent along the northern
periphery of the deeper layer moisture to around 60 percent across
the far south where the moisture will be the deepest. Given the
extensive middle-high cloud across central and southern zones...the
potential for thunder will be low...but will include a mention of
isolated thunderstorms in the forecast given the decent dynamics
moving overhead. High temperatures are expected to top out in the
low to middle 80s.

Tonight...
the shortwave trough will shear out as it shifts further
southeastward and into South Florida...pushing the surface trough of
low pressure back into South Florida as well. Will show some slight
chance probability of precipitation in the evening across the interior...with rain free
conditions then expected in most locations overnight. The one
exception will be across Charlotte and Lee counties where some
isolated showers/storms may try to develop after midnight due to
some weak forcing for ascent provided by the right rear quadrant of 90+
knot upper jet and h925-700 mb condensation pressure deficits dropping
to around 30 mb...so will include some slight chance probability of precipitation here.
Overnight lows are expected to bottom out in the middle 50s across
the Nature Coast and in the 60s to around 70 degrees across
central and southern locales.

Wednesday...
the surface trough of low pressure and deepest layer moisture will
remain nearly stationary across South Florida. Most locations are
expected to be free from rain through the day...but will include
some slight chance/low chance probability of precipitation across Charlotte/Lee counties and
the far southern portion of Highlands County...where marginal deep
layer moisture and weak forcing for ascent may be enough to allow
for the development of a few showers/storms. High temperatures are
expected to top out in the low 80s across far northern areas and
in the middle to upper 80s across central and southern zones.

&&

Long term (wednesday night-tuesday)...we continue to watch the area
of disturbed weather across Bay of Campeche that NHC now shows a 50%
chance of tropical development over the next 5 days as it moves east
toward Cuba. That said models have trended towards a dry forecast
for the extended as one upper low across the eastern US lifts NE but is
quickly replaced by another trough by the weekend...although this
trough will be a bit more progressive as it pushes east into the western
north atl. This means cool and dry high pressure at the surface will be
reinforced by Sat and this helps keep high moisture confined to deep
S Florida and also helps steer any potential organized tropical system
well south of the region as it tracks due east. Based on this will
continue to confine mention of some very low probability of precipitation across the far
south near the strong moisture gradient on Friday. Very dry airmass
will promote large diurnal temperature ranges with lows mostly in the 50s
and 60s and highs generally in the low to middle 80s. Only downside
to the forecast may be the winds which will remain elevated from
the north-northeast through the weekend with caution level at times across
marine areas (esp offshore zones). Temperatures will climb late in the
period as upper ridging slides east from Texas toward the southeast US.

&&

Aviation...
scattered rain showers and isolated thunderstorms and rain are expected across southwest
Florida today...with the potential for some reduced ceilings/visibilities as
they move through kpgd/krsw/kfmy. Will handle with vcsh/thunderstorms in the vicinity for now
and amend as timing becomes more clear. Across the northern
terminals...VFR conditions are expected to prevail through the
period.

&&

Marine...
a trough of low pressure will remain across the Florida straights
through the work week and into the upcoming weekend with high
pressure in place north of the region...keeping east to northeast
winds in place across the marine area. A strengthening pressure
gradient across may result in periods of exercise caution and
possibly advisory level winds Wednesday night through Saturday.

&&

Fire weather...
a trough of low pressure will remain across the Florida straights
through the work week and into the upcoming weekend with high
pressure in place north of the region. Isolated to scattered
showers/storms may periodically affect areas south of Tampa Bay
through the week...but rainfall amounts are generally expected to be
on the light side. Relative humidity values may approach 35
percent across portions of the Nature Coast Wednesday
afternoon...otherwise humidity levels should remain above
critical thresholds through the forecast period.

Fog potential tonight...some patchy ground fog is possible around
daybreak Wednesday...however no significant or widespread fog is
expected.

&&

Preliminary point temps/pops...
tpa 84 67 85 64 / 10 10 10 0
fmy 83 70 86 68 / 60 20 30 10
gif 85 66 85 62 / 10 10 10 0
srq 83 67 86 65 / 10 10 10 0
bkv 86 56 85 53 / 10 0 0 0
spg 84 71 85 69 / 10 10 10 0

&&

Tbw watches/warnings/advisories...
Florida...none.
Gulf waters...none.

&&

$$

Short term/aviation/marine/fire weather...jelsema
long term/decision support...gittinger

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