834 
FXUS62 KJAX 090902
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
502 AM EDT Fri Sep 9 2022

...FLOOD WATCH THROUGH TONIGHT FOR COASTAL SOUTHEAST GA...
...ROUNDS OF HEAVY DOWNPOURS CONTINUE THIS WEEKEND THROUGH
MONDAY, MAINLY DURING THE AFTERNOON AND EVENING HOURS...

.SYNOPSIS...
Issued at 500 AM EDT Fri Sep 9 2022

Early morning surface analysis depicts a wavy stationary frontal
boundary situated across the Deep South, with weakening low
pressure (1007 millibars) positioned along the front over the
lower Mississippi Valley. Meanwhile, high pressure (1016
millibars) was building over the eastern Great Lakes and the Mid-
Atlantic region in the wake of this front. Aloft...cutoff
troughing was only slowly filling as it remains stationary over
coastal Louisiana, while ridging takes shape off the southeast
U.S. coast in between this cutoff trough and Hurricane Earl, which
has made its closest approach to Bermuda as it accelerates north-
northeastward over the open waters of the North Atlantic.
Otherwise, a deepening trough was progressing southeastward from
the northern Rockies and across the Northern Plains states. A
round of thunderstorms and heavy downpours on Thursday evening
that resulted in 2-4 inches of rainfall in portions of Glynn and
Duval Counties has lifted northward towards the Savannah and
Charleston metropolitan areas, with convection during the predawn
hours confined to our adjacent coastal waters, while another area
of convection was located over Apalachee Bay and the FL Big Bend 
coast. Multi-layered cloudiness remains in place area-wide, with 
low stratus ceilings expanding at inland locations. Temperatures 
and dewpoints at 09Z were mostly in the 70-75 degree range. 

&&

.NEAR TERM...
(Today and tonight)
Issued at 500 AM EDT Fri Sep 9 2022

The cutoff trough will only slowly fill through tonight and will
begin to nudge northwestward across the lower Mississippi Valley
tonight as ridging aloft continues to build off the southeastern
seaboard. This weather pattern will keep a deep southerly flow
pattern in place locally, with a 60-knot jet streak at 250
millibars (around 35,000 feet) located in between these features
to the south of the FL panhandle coast. Meanwhile, strengthening
high pressure over the Mid-Atlantic region will wedge down the
southeastern seaboard through tonight, resulting in a tightening
local pressure gradient near the position of the wavy, stalled
surface boundary over southeastern GA. Breezy onshore winds should
develop over coastal southeast GA shortly after sunrise. This 
tightening pressure gradient will maximize surface convergence 
over coastal southeast GA, where some of the short-term, high 
resolution guidance indicates that a few bands of slow moving 
downpours will set up over Glynn and possibly portions of Camden 
Counties later this morning and into the afternoon hours. 
Additional rainfall amounts could exceed 2 inches over these 
coastal counties, which will increase the threat for flooding, 
especially at urban and normally flood prone locations such as 
Brunswick, which experienced flooding on Thursday evening due to 
2-4 inch rainfall amounts. Additionally, strengthening southerly
flow will result in increasing speed shear across our region this
afternoon, and the presence of the frontal boundary and
strengthening surface convergence could result in a few strong or
even an isolated severe thunderstorm this afternoon, especially
for locations from Waycross northward. An isolated tornado cannot
be ruled out near the stalled boundary through this evening.  

We expect that another round of morning convection will occur 
over portions of north central FL and the Suwannee Valley, as 
convection developing over the far northeast Gulf of Mexico 
advects north-northeastward. This convection will likely shroud a
good portion of our area in thick cirrostratus, which will again 
delay a majority of the downpours until the afternoon hours. PWATs
will remain elevated (above 2 inches), and relatively mild mid- 
level temperatures will result in efficient rainfall production 
within convection that develops this afternoon. A band of heavy 
downpours will again likely traverse much of our area through the 
early evening hours. Rainfall amounts of 0.5 to 1.5 inches is 
expected at most locations through this evening, with locally 
higher amounts possible. Localized flooding will be possible, 
especially across southeast GA and portions of the Suwannee Valley
and north central FL, where the Weather Prediction Center has 
indicated a slight risk of excessive rainfall through tonight. 
Plenty of cloud cover and afternoon convection should keep highs 
in the low to mid 80s across our area today.

Any downpours that linger into the evening hours at coastal
locations could result in an enhanced flood threat due to
astronomically high tides, which will peak later this evening.
Otherwise, a pocket of slightly drier air advecting northward
across the FL peninsula this afternoon will overspread our area
overnight. Additionally, the strengthening ridge off the
southeastern seaboard will likely lift the wavy frontal boundary
north of the Altamaha River basin tonight, which will result in
the best surface convergence shifting north of our region. Low
stratus ceilings will likely develop again towards the predawn
hours, with lows generally falling to the 70-75 degree range
throughout our area.

&&

.SHORT TERM...
(Saturday through Sunday)
Issued at 500 AM EDT Fri Sep 9 2022

Prevailing flow will continue to be out of the south this weekend
as the upper level low off to the west is gradually absorbed by
the prominent trough over the central US. Heavy rains capable of
producing localized flooding are expected during this period with
PWAT values measuring at times as high as 2 to 2.3 inches. Diurnal
convective developments will initially build in over the
westernmost portions of the forecast area and then expand eastward
as the afternoon progresses. Daily high temperatures during this
period will reach up into the upper 80s and lower 90s for areas to
the east of the I-75 corridor and in the mid 80s for areas to the
west of I-75 that are expected to receive convective developments
earlier in the day. Overnight low temperatures will drop down into
the lower 70s over inland areas and in the mid to upper 70s along
the coastline.

&&

.LONG TERM...
(Monday through Wednesday) 
Issued at 500 AM EDT Fri Sep 9 2022

The upper level low will become fully absorbed by the trough over
the central US as it moves eastward with the prevailing flow
shifting about to become more out of the southwest-west. Chances
for heavy rainfall will continue on into Monday ahead of the
approaching frontal boundary from out of the west-northwest. Drier
air will settle in over the region with reduced chances for
precipitation expected through midweek. Temperatures for next 
week will be in line with the seasonal average.

&&

.AVIATION...
[Through 06Z Saturday]

Periods of MVFR conditions will be possible overnight at the
regional terminals as showers and low clouds progress northward
across our region. IFR ceilings will then likely develop at VQQ
and GNV after 08Z, with these conditions prevailing through around
14Z. Periods of MVFR conditions will then remain possible
throughout the day as showers and lower ceilings periodically
cross the terminals. Thunderstorms will then be possible after
15Z, and we have included PROB30 groups at each terminal for
briefly gusty winds and MVFR visibilities through the afternoon
hours. Brief periods of IFR conditions will also be possible
throughout the day during heavier downpours. Showers and
thunderstorms should then exit the area after 00Z, with VFR
conditions expected to prevail during the evening hours. East-
northeasterly surface winds will increase to 5-10 knots at SSI
after 08Z, with speeds elsewhere remaining around 5 knots or less
through sunrise. Surface winds at SSI will then increase to 10-15
knots by 15Z, with occasional gusts to 20 knots possible during
the afternoon hours. Outside of thunderstorm activity, southeast
to southerly surface winds will become sustained at 5-10 knots by
15Z at the regional terminals, with southeasterly winds then 
increasing to 10-15 knots at SGJ by 19Z. Prevailing winds will
then become southerly at the northeast FL terminals after 00Z,
with southeasterly surface winds remaining sustained around 10
knots at SSI through the evening hours.

&&

.MARINE...
Issued at 515 AM EDT Fri Sep 9 2022

A frontal boundary will remain stalled over the southeast Georgia
waters today and will briefly lift north of the Altamaha sound
tonight and Saturday. Meanwhile, high pressure will gradually
strengthen over the Mid-Atlantic region and New England through
Saturday. This weather pattern will create strengthening onshore
winds across the southeast Georgia waters this morning, with
speeds approaching Caution levels of 15-20 knots by late morning.
Combined seas will also build throughout our local waters due to 
long period swells originating from distant Hurricane Earl. Seas 
should remain just below Small Craft Advisory levels through 
Saturday, with 4-6 foot seas forecast throughout the Georgia
waters, as well as the offshore waters adjacent to northeast FL.
Seas of 3-5 feet will prevail over the nearshore waters adjacent
to northeast FL through Saturday evening. Periods of showers and 
thunderstorms will continue across our waters into early next 
week, as the frontal boundary sinks slowly southward late this 
weekend. Winds and seas will then subside by Tuesday ahead of 
another frontal boundary that will likely stall over the northeast
Florida waters late next week.

&&

.HYDROLOGY...
Issued at 500 AM EDT Fri Sep 9 2022

Additional rainfall amounts of 2-4 inches are possible today
across coastal southeast GA, possibly extending westward along the
Altamaha River basin, where bands of slow moving downpours will
likely develop along a nearly stationary frontal boundary. Locally
higher totals will be possible, and a Flood Watch has been issued
for Glynn and Camden Counties. Rainfall amounts elsewhere of 0.5
to 1.5 inches are expected through this evening, with locally
higher amounts possible, especially across inland southeast GA,
the Suwannee Valley, and north central FL, where multiple rounds
of downpours will be possible. Localized flooding is a concern at
these locations, especially for urban and normally flood prone
locations. Additional afternoon and evening downpours this weekend
will likely result in additional rises on area rivers and
tributaries, with "flashier" basins such as Black Creek in Clay
County being monitored, as basins become increasingly saturated.  

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  82  70  88  73 /  80  60  90  40 
SSI  84  75  89  77 /  80  60  80  50 
JAX  85  72  90  74 /  80  50  80  40 
SGJ  85  75  89  76 /  80  40  70  40 
GNV  85  72  90  72 /  90  40  90  30 
OCF  85  71  90  73 /  80  40  90  30 

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk through late Saturday night for FLZ124-125-
     133-138.

GA...High Rip Current Risk through late Saturday night for GAZ154-166.

     Flood Watch through late tonight for GAZ153-154-165-166.

&&

$$