Scientific Forecaster Discussion
fxus62 ktbw 211150
Area forecast discussion
National Weather Service Tampa Bay Ruskin Florida
750 am EDT Sat Oct 21 2017
VFR conditions next 24 hours. Enhanced easterly flow should
keep sea breezes from developing today.
Prev discussion... /issued 254 am EDT Sat Oct 21 2017/
Short term (today - sunday)...
the upper level trough has moved eastward over Bermuda and extends
southwest over the eastern Bahamas. An upper level high and
associated ridging extends from the Florida northward over
the eastern Seaboard. This ridge will slowly shift east
through the weekend and will be the dominant upper feature
through the period. On the surface, the main influence to
the weather over Florida will be from strong high pressure
to the north over the mid-Atlantic states. This will keep an
east-northeast wind flow over the region into the weekend
with seasonal rain chances between 20-40 percent each day.
Winds will generally be below 15 knots, however some gusts
near 20 knots will be possible over the coastal waters.
Long term (monday through next friday)...
first fall-like cold frontal passage for west-central and southwest
Florida to occur Tuesday through Tuesday night.
The new work week will begin with a rather complex upper level
pattern evolving over the eastern half of the country. A strong
piece of cut off shortwave energy will be spinning over the lower MS
valley early Monday morning...with a broad associated surface
reflection low from the north-central Gulf of Mexico to the lower MS
valley. Large upper ridging that will have brought generally fair
and warm weather to the Florida Peninsula during the previous weekend
will be shifting eastward into the Atlantic in response to the
approach of this energy from the west. While no doubt this shortwave
and surface low will be supporting plenty of showers/storms over the
eastern Gulf and deep south early Monday, the last residual
influence of the upper ridge looks as though it will allow our
forecast Monday to begin generally benign, warm, and humid. As we
head through the day, the deep layer flow aloft will become
increasingly cyclonic in nature, as the shortwave gradually evolves
eastward. In the upper levels of the troposphere, a broad swath of
diffluent flow associated with jet energy along the approaching
height gradient will provide some extra support for synoptic lift
over our region by the second half of Monday. Although convection
directly associated with the cold front over the Gulf will still
likely be offshore Monday afternoon/evening, deep moisture, diurnal
heating (leading to developing of a partly onshore flow component),
and added broad synoptic lift should support sct-nmrs shower/storm
development over the peninsula after midday. The greatest coverage
of showers would likely exist over the central and northern parts of
the area in closer proximity to the best large scale ascent.
However, could buy sea-breeze storms filling in further south as
well...given the favorable environment.
The details of this shortwave's evolution are still not in 100%
agreement among the guidance members, but the general pattern among
most members would suggest this shortwave becomes more progressive
Monday night, becomes an open wave again, and becomes negatively
tilted as it progresses through Alabama/GA/northern Florida. This
evolution would support a narrower band of showers/storms moving
slower into the Florida Peninsula with the actual cold front Monday
night/Tuesday morning. Although think rain chances are high across
much of our region Monday night/Tuesday morning, large scale ascent
certainly suggest the more widespread and heavier rainfall potential
stays to our north. The NAM remains an outlier, with a much slower
progression eastward later Monday into Monday night...and will not
be used in this forecast.
Tuesday morning, the cold front looks to be across the central
Florida Peninsula with a broken band of showers and some storms. At
this point, the front looks to be moving rather slowly with the
parent shortwave rapidly ejecting up the eastern Seaboard. The big
change in airmass will likely still be just off to our northwest.
However, do not worry, its along a slight delay. All reliable
guidance are in agreement showing a strong secondary source of
energy amplifying over the eastern Continental U.S. During the day Tuesday.
This trough will provide the real push of cooler/drier air into the
region later Tuesday and especially Tuesday night. The slower
frontal system during Tuesday awaiting the secondary push from the
north may keep a shower threat going down toward Fort Myers into
Tuesday evening, but by sunrise Wednesday, all areas should be
enjoying a dry forecast.
The warm and muggy airmass of the preceding days looks to be a thing
of the past by Wednesday morning, as a cooler and much drier flow
from the north clears the region. High temperatures both Wednesday
and Thursday are currently expected to stay below 80 region-wide.
The coolest night appears to be Wednesday night/early Thursday, when
a few upper 40s can not be ruled out over the Nature Coast.
Widespread middle to upper 50s look common elsewhere. Get ready to
open those windows and give that ac a break.
Moderating temperatures and increasing moisture commence Friday
ahead of our next potential weather system by Friday night or
Saturday of next week weekend.
VFR conditions will prevail through the period with dry conditions
expected at all terminals. Winds will remain out of the east-
northeast with some gusts around 15 knots during the afternoon
hours. No other aviation impacts expected.
strong high pressure to the north will be the dominant surface
feature influencing the weather over the coastal waters for the next
several days. Storm/rain chances will be very low, but the main
marine concern will be gusty east-northeast winds reaching Small
Craft Advisory level at times over the next couple of days. The
weather pattern will change by the beginning of next week as a cold
front approaches the area. Winds will shift to the south by the
Monday ahead of the front and rain/storm chances will be on the
increase. Winds will further shift to the north-northwest by the
middle of next week in the wake of this front. Drier air and
decreasing rain chances expected into next week. No other marine
high pressure will influence the weather over the region for the
next few days will minimal rain chances expected. A cold front will
move through the area by the beginning of next week with increasing
rain chances expected. Drier air will move into the area in the wake
of this front, but still expected to remain above any critical fire
weather threshold. No other fire weather impacts expected.
Preliminary point temps/pops...
tpa 88 74 87 75 / 0 0 30 10
fmy 88 74 89 74 / 10 0 10 10
gif 87 72 88 73 / 0 0 20 10
srq 89 75 88 74 / 0 0 30 10
bkv 88 70 88 72 / 0 0 30 10
spg 86 75 87 75 / 0 0 40 10
Gulf waters...Small Craft Advisory until 11 am EDT this morning for
waters from Bonita Beach to Englewood Florida out 20 to 60
nm-waters from Englewood to Tarpon Springs Florida out 20
to 60 nm-waters from Tarpon Springs to Suwannee River
Florida out 20 to 60 nm.