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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KJAX 160054
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
854 PM EDT Tue Oct 15 2019

.UPDATE...

Latest analysis shows nearly stationary front near the I-10 corridor
with the best instability over northeast FL, although weak,
supporting a little more convective echoes per radar trends with
scattered showers and an isolated embedded thunderstorm or two. SB
CAPE instability is about 400-800 J/kg over northeast FL, which
will more or less remain intact overnight based on latest
forecasts from RAP. Further north over southeast GA, better rain
chances exist as shortwave disturbances traverse that area from
west to east, enhancing lift and spreading stratiform rains and
embedded showers there. A few storms will be possible overnight
but weak lapse rates and little instability aloft should keep them
brief and isolated.

As sfc frontal wave over TN valley consolidates and moves east-
northeast tonight, the frontal boundary near I-10 will push
northward. Scattered to numerous showers and an isolated storm
expected and not expecting much change in the forecast at this
time. Lows in the upper 60s to lower 70s tonight.

&&

.AVIATION...
[Through 00Z Thursday]

Multilayered clouds with periods of showers and possible isolated
thunderstorm expected through Wednesday aftn, with MVFR at times
for SGJ and SSI in the near term. Additional showers expected by
Wed morning and MVFR vsby and cigs will be possible from around
09z-15z. T.-storm chances are too small to include in the TAFs at
this time.

&&

.PREV DISCUSSION [357 PM EDT]...

.NEAR TERM [Through Wednesday]...

Stationary front over SE Georgia this afternoon is the focus for
areas of rain with embedded showers and a few thunderstorms,
primarily along and north of the front over SE Georgia. Mid/upper
level impulses riding east in zonal flow over the SE U.S. will
prevent the front from moving much through tonight. As a result,
the highest rain chances will remain over SE Georgia for much of
the near term, along with a chance of a couple of stronger
thunderstorms late this afternoon through the overnight,
especially given the 30-40 knot wind maximum at 850 mb moving
through the area and increasing shear/helicity values. Locally
heavy rainfall will be enhanced tonight by a surface low pressure
area moving east along the front, with the Weather Prediction
Center placing SE Georgia in a marginal risk for excessive
rainfall through sunrise Wednesday.

South of the front, scattered showers and thunderstorms developing
over the Florida panhandle this afternoon will move east and
approach NE Florida towards sunset, although timing suggests that
this activity will likely weaken due to loss of daytime heating and
associated instability. Nevertheless, there should be enough dynamics
to support scattered showers and a few thunderstorms across NE
Florida through the overnight. As is the case north of the front,
there could be a strong storm or two late this afternoon, especially
from Lake City west. On Wednesday, a sharp mid-level trough anchored
over the Great Lakes is expected to move east and sweep a longwave
trough through the SE states, acting to move the front east/south
across our area as the day progresses. Chances for showers and
thunderstorms will persist during the first half of the day, with
40- 50 kt mid-level flow providing enough support for a few
thunderstorms along and ahead of the advancing front. Lack of low
level convergence along the front and unidirectional flow should
preclude widespread stronger storms. Rain chances decrease from
west to east during the afternoon as the front moves through, with
most of the rain chances confined to our southernmost counties by
the end of the day on Wednesday where the front is expected to
lie at that time. Low temperatures tonight will remain in the
upper 60s to lower 70s, and high temperatures reaching the 80s
(warmest across NE Florida) on Wednesday.


.SHORT TERM [Wednesday Night Through Friday Night]...

Clearing skies and cooler air will overspread the region
Wednesday night in the wake of the front, with dry and pleasant
conditions on Thursday as continental high pressure builds in from
the NW. Low temperatures Wednesday night will drop into the 50s
north and west of JAX, and 60s from JAX south. High temperatures
on Thursday will remain in the 70s over much of the area, with
lower 80s south of JAX.

The clear skies will not last long, however, as a closed mid-level
low pressure area over Texas and a surface low over the extreme
western Gulf of Mexico help to spread mid and high level moisture
back over the area late Thursday night. This trend towards cloudier
skies will continue on Friday as the mid/upper low moves slowly
E-NE. Clouds should thicken during the day on Friday, especially
over NE Florida, with light rain possibly affecting far southern
areas by Friday night. Models differ somewhat in the timing of the
deeper moisture and precipitation onset, with the GFS faster/earlier
than the ECMWF and Canadian model, as well as the regional NAM.
With these timing differences in mind, will introduce low rain
chances Friday night mainly south of I-10. Low temperatures
Thursday night will dip into the 40s over SE Georgia away from the
coast, and 50s elsewhere. Highs on Friday will be in the 70s,
then moderating lows Friday night about 5-7 degrees warmer than
the previous night as clouds increase across the area and flow
turns E-SE advecting warmer air.


.LONG TERM [Saturday Through Early Next Week]...

The low pressure over the Gulf of Mexico and SE U.S. will lift NE
this weekend, and the wind flow will turn southerly across the
area in response. Models again showing some differences in the
location of the axis of deeper moisture return, with the GFS farther
east and the ECMWF a little to the west. All in all, expect scattered
showers and a few thunderstorms to return to the region this coming
weekend, especially on Sunday. This trend looks to continue into
early next week, as models are in good agreement at this time on a
deep longwave trough setting up over the eastern U.S. and the next
cold front approaching the area. Temperatures will warm up quite
a bit and highs will return to the 80s during this time frame,
along with humid conditions.


.MARINE...
Showers and thunderstorms will gradually increase over the next 24
hours as the stationary front over the SE Georgia waters eventually
moves SE and through the local waters Wednesday night. Increasing
S to SW wind to 20 knots or greater will result in a Small Craft
Advisory starting overnight and continuing through Wednesday
afternoon. Following the frontal passage Wednesday night, wind
turns NW to N and gradually decreases to 10 to 15 knots on
Thursday, then NE-E 10 knots on Friday. High pressure will move
over the western Atlantic this weekend, and wind will turn SE to S
and increase to around 15 knots for this coming weekend. Seas will
peak at 5 feet over the offshore waters Wednesday, then remain
mainly in the 2-4 ft range Thursday into the upcoming weekend.

Rip Currents: Persisting long period swells will result in a
moderate risk through Wednesday.


.FIRE WEATHER...
Cloudy and mainly wet/humid conditions tonight, then gradually
drying on Wednesday as a cold front moves through the area.
Minimum relative humidity values drop below 35 percent on
Thursday, mainly north of a St. Augustine to Gainesville line.
Transport winds and dispersion values will increase Wednesday and
remain at moderately high levels on Thursday.


.HYDROLOGY...
River levels will remain elevated along the St Johns River with
continued minor flooding in Putnam county during high tide into
tonight.

&&

.PRELIMINARY POINT TEMPS/POPS...

AMG  67  81  50  73  48 /  80  30   0   0   0
SSI  72  83  59  74  58 /  70  40  10   0   0
JAX  71  87  59  78  56 /  70  50  10   0   0
SGJ  72  86  65  78  61 /  20  60  20   0   0
GNV  71  86  62  79  56 /  60  90  20   0   0
OCF  72  86  66  82  59 /  50  80  20   0   0

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...Coastal Flood Advisory until 6 AM EDT Wednesday for Putnam.

GA...None.
AM...Small Craft Advisory from 2 AM to 5 PM EDT Wednesday for Waters
     from Altamaha Sound GA to Fernandina Beach FL from 20 to 60
     NM-Waters from Fernandina Beach to St. Augustine FL from 20
     to 60 NM.

&&