National Weather Service Raw Text Product

744 
FXUS62 KJAX 301251
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
851 AM EDT Thu Sep 30 2021

.UPDATE...

Synopsis...Seasonally warm and continued mostly dry today with 
the main weather impact over the next 24 hrs late night fog inland
and a low chance of NE FL coastal showers Friday morning. 

A weak surface ridge axis extended across the local forecast area
this morning with high cirrus clouds spilling over an upper level
ridge building across the region from the the west. A couple weak
convergent bands of cumulus and the land breeze were noted in
early morning visible satellite imagery offshore of the local 
Atlantic coast, and as the land breeze converges with these bands 
a few coastal showers are possible through midday, mainly over the
FL outer waters. Cumulus were streaming inland just south of 
Flagler county early this morning, where some brief light 
sprinkles may develop, but the airmass remains very dry just above
the surface and very dry above 850 mb with PWAT down to 1.13 
inches per the 12z JAX RAOB, so prevailing dry weather will 
continue today as diurnal mixing ensues. 

The low level ridge will weaken and shift eastward today as a 
stronger surface high builds across New England. This pattern will
transition low level flow to the ENE into the afternoon, and 
shift a weak surface front SSW across the local waters late 
tonight into Fri bringing a low chance of coastal showers. 

With building heights aloft, temperatures will trend slightly
warmer today inland near 90 to the cooler mid 80s along the coast
under onshore flow. 

&&

.MARINE...

High pressure over the local waters will weaken today. A front 
will approach from the northeast late tonight and shift inland 
through Friday night. Light offshore flow (WNW) was across the
waters this morning with the land breeze with speeds 5-8 kts and
combined seas 1-2 ft composed of easterly swells. Winds will
transition to ESE into the early afternoon with speeds increasing
to 5-10 kts. Easterly winds increase Fri into Fri night to near
Exercise Caution Levels. Marginal advisory conditions are forecast
late Sat for the outer waters due to combined seas near 7 ft. 

Rip Currents: High risk NE FL beaches today, moderate for SE GA
beaches. Easterly long period swells have entered the local waters
with periods of 11-13 seconds and swell heights of 1-2 ft. Onshore
flow today will strengthen Friday and Saturday with high risk
conditions likely for all waters through the weekend as long
period swells persist.

&&

.HYDROLOGY...

The Santa Fe at Fort White and Three Rivers Estates remained in 
Minor Flood. The Satilla River at Atkinson also remained in Minor 
Flood. 

&&

.PREV DISCUSSION [749 AM EDT]...

.NEAR TERM [Through Tonight]...

With a slight increase in low-level moisture, patchy fog will be 
possible for inland areas in the pre-dawn hours. A weak surface high 
pressure ridge extending across northeast Florida continues to 
shift south today as strong high pressure expanding southward from
Hudson Bay, Canada, will push a backdoor cold front down the 
southeastern seaboard tonight. Another dry day is in store with a 
dry airmass lingering over the area. Low level easterly flow will 
begin to deepen as surface pressures begin to rise, while 
northwesterly flow aloft will advect a gradually thickening cirrus
shield over our area by the afternoon hours. High temperatures 
will be above seasonal average in the upper 80s to low 90s inland 
and, due to easterly flow, mid 80s along the coast. With an 
increase in cloud cover, overnight lows will be closer to average 
in the mid to upper 60s inland and low 70s along the coast.


.SHORT TERM [Friday Through Saturday]...

Our local pressure gradient will gradually tighten on
Friday as high pressure settles over the Mid-Atlantic
region and wedges down the southeastern seaboard. 
Easterly winds will become breezy at coastal locations, 
and convergent low level flow accompanied by PWAT 
values rising to around 1.5 inches will generate 
isolated to widely scattered showers on Friday morning
over our adjacent Atlantic coastal waters, with this
activity then moving onshore during the morning hours
and then progressing inland during the afternoon hours. 
Breezy onshore winds will keep coastal highs in the 
mid 80s, with inland highs reaching the upper 80s to 
around 90 before low level cloud cover increases during
the afternoon hours. Easterly winds will be slow to 
subside at coastal locations on Friday evening, and 
occasional brief showers may continue to move onshore
along the northeast FL coast throughout the night. Lows
will remain in the lower 70s at coastal locations, while
decoupling winds and less cloud cover inland will allow
lows to fall to the mid and upper 60s. 

High pressure will then slowly weaken as it pushes offshore 
of the southeastern seaboard by Saturday night. Deep onshore 
flow will continue to advect isolated and mostly brief showers
across our region on Saturday. Persistently breezy conditions 
at coastal locations will keep highs in the low to mid 80s, 
with upper 80s continuing inland. Our local pressure gradient 
will then loosen on Saturday night as high pressure weakens 
and pushes offshore, with a drier air mass also progged to 
advect westward across our region. This should limit shower
chances to coastal Flagler County overnight, with clearing
skies and decoupling winds resulting in inland lows falling
to the mid 60s, while a light onshore breeze keeps coastal 
lows around 70.


.LONG TERM [Sunday Through Wednesday]...

Troughing aloft will dig southward through the Plains States
on Sunday while ridging extending across the northern Gulf 
coast and southeastern states flattens throughout the day. 
Isolated showers will remain possible within the weakening
onshore flow regime across northeast and north central FL. 
Highs will continue to climb to the upper 80s inland and
the mid 80s at coastal locations. Low level flow will then
veer to southeasterly on Sunday night as low pressure takes
shape over the Great Lakes region, pushing a frontal boundary
through the Ohio, Tennessee and lower Mississippi Valleys.

Deep-layered moisture will gradually increase area-wide early
next week as low level flow continues to veer in advance of 
this decelerating frontal boundary. Isolated to widely scattered
mainly diurnal convection will be possible on Monday, with 
inland highs still climbing to the mid and upper 80s, while 
low to mid 80s continue at coastal locations. Convective
coverage may increase on Tuesday as troughing aloft begins
to cutoff to the west of our region, promoting strengthening
southwesterly flow aloft locally. Increasing humidity levels 
early next week will keep lows in the upper 60s inland and the 
lower 70s at coastal locations. 

The frontal boundary should move into our region towards 
midweek, although forecast confidence is rather low, as 
troughing aloft should remain cutoff to the west of our region.
Model blends currently depict numerous showers and thunderstorms
nearly area-wide by Wednesday afternoon as deep southwesterly
flow prevails. Increasing cloud cover and rain chances will 
likely keep highs in the low to mid 80s, with upper 80s possibly
continuing for inland north central FL.


.AVIATION...
[Through 12Z Friday]

VFR conditions through 06z under passing high cirrus and diurnally
driven cumulus with bases near 2 kft this morning rising to 3-5 
kft into the afternoon. Light and variable winds this morning < 4 
kts will increase late morning into the afternoon to the ESE with 
speeds increasing to 6-9 kts into the late afternoon as the east 
coast sea breeze shifts inland. Winds relax into the evening but 
maintain an ENE component along the coast and become near calm 
inland. A weak trough will slide down the SE Atlantic coast 
through early Friday morning, with low level cumulus increasing 
across coastal terminals toward 12z Fri morning. At this time 
trended bases near 3-3.5 kft with the best potential of MVFR at 
SSI but SREF probs are < 10% at this time. There could also be a 
few coastal showers approaching coastal terminals between 09-12z, 
but coverage and confidence are < 20% so refrained from TAF 
inclusion. Inland at VQQ and GNV, shallow ground fog will again 
will be possible after 07z-08z, and indicated MVFR for VQQ based 
on persistence and GNV to just 6SM BR for now.

&&

.PRELIMINARY POINT TEMPS/POPS...

AMG  89  65  89  65  87 /  10   0  20  10  20 
SSI  85  72  85  72  83 /   0  10  20  10  20 
JAX  87  68  87  68  86 /   0  10  30  20  20 
SGJ  85  71  86  72  84 /   0  10  30  20  20 
GNV  89  66  90  67  88 /  10   0  30  10  20 
OCF  90  66  90  67  88 /  10  10  30  10  20 

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk through late tonight for Coastal Duval-
     Coastal Flagler-Coastal Nassau-Coastal St. Johns.

GA...None.
AM...None.
&&