Area Forecast Discussion
Issued by NWS Jacksonville, FL
FXUS62 KJAX 300805
Area Forecast Discussion
National Weather Service Jacksonville FL
405 AM EDT FRI SEP 30 2016
.NEAR TERM /Through Tonight/...
The cold front is quickly pushing through southeast Georgia early
this morning, and will continue through northeast Florida this
morning. Significantly drier air advection will trail the frontal
boundary Today and it will be noticeably less humid across most of
the region. Although the air mass will be drier, it will still be
a warm day for a good chunk of our region. Given the setup, we
leaned on the warmer side of guidance for temps and on the lower
side of guidance for rain chances Today. A full day of sunshine
combined with southwesterly winds mixing down to the surface will
result in max temps closing in on 90 south of a line from Jesup to
Valdosta, with even a few lower 90s possible along the I-95
corridor of northeast Florida.
The significant dry air/subsidence aloft with PWATs falling well
below 1 inch will keep most of the area dry today with full
sunshine. With that said, there could be just enough low level
moisture to possibly support an isolated shower or storm across
our extreme southern zones as the cold front slows down and
possibly stalls and/or washes out across our southern zones later
We favored the cooler side of guidance with low temps tonight as
conditions will be rather favorable for strong radiational
cooling. All inland locations will be below normal, especially in
southeast Georgia and the Suwannee river valley of northeast
Florida where temps will fall as low as the mid 50s.
.SHORT TERM /Saturday through Sunday Night/...
The short term period begins with an upper level low over the
Ohio valley and a quasi-stationary frontal boundary stretching
across northeast Florida, roughly from a line southwest to
northeast from Ocala to Jacksonville. This keeps the region under
southwesterly flow above the surface, and a weak flow pattern at
the surface. The upper low will lift slowly northward into the
upper Great Lakes through Sunday and then eastward Sunday night
across the lower Great Lakes and into New York. The surface
boundary will also lift slowly northward in the second half of the
weekend, and moisture will begin to return.
Very dry conditions are forecast to the north of the boundary, with
precipitable water values (PWATS) around 0.5 inches in the
Suwannee Valley and northwestern half of Georgia Saturday morning.
PWATS are forecast to be around 1 inch near the surface boundary,
and near 1.5 inches across the far southeastern portions of the
region. Low level moisture will increase slightly throughout the
day from the southeast, and isolated to scattered showers and
storms are forecast for Flagler, Marion, Putnam and St. John`s
counties as the east coast sea breeze moves inland. Otherwise, dry
conditions will prevail with highs in the mid to upper 80s.
The axis of Atlantic ridging will continue to lift slowly northward
on Saturday night and Sunday, introducing a southeast low level
flow regime over north central Florida Saturday night and
northeast Florida on Sunday. Isolated showers are possible over
coastal locations Saturday night as the remnant front remains in
place and Atlantic moisture advects into the area. Overnight lows
will be warmer as moisture continues to increase, with lows near
60 across northwest portions of southeast Georgia and the Suwannee
Valley, to near 70 to the lower 70s along the east coast.
Scattered convection will remain possible over coastal locations
Sunday morning, with activity spreading inland by the afternoon as
the dry air mass departs inland portions of our region. Highs
again will generally climb to the upper 80s inland and the mid 80s
at the coast. A deepening onshore flow pattern will keep scattered
showers possible on Sunday night in the coastal counties, with
isolated activity possible inland. Lows will range from the upper
60s inland to the mid 70s at the coast.
.LONG TERM /Monday through Thursday/...
The hurricane hunter G-IV plane sampled the Bermuda high and
conditions around Hurricane Matthew Thursday afternoon. The GFS,
GFS ensemble mean, and Canadian models shifted slightly west
towards Jamaica in the medium term, and then turn the hurricane
northward into the Bahamas by Day 5. The GFS and its ensemble mean
slowed down, and were close to the ECMWF latitude timing through
Day 5. The operational European was slightly west of its previous
run and slightly faster through Day 5, but remained much further
east of the GFS. The models then continue to diverge significantly
beyond this time. The ECMWF is much slower and turns Matthew
well out to sea due to the old upper low stalling off the coast of
the northeastern conus and deepening. In addition, due to the
slower forward motion, the next upper level trough is then
forecast to pick up the hurricane and move it to the northeast. On
the other hand, the GFS and its ensembles are 200-250 miles east
of Jacksonville on Hurricane Matthew`s closes approach Wednesday
night and Thursday morning due to its faster forward motion ahead
of the next upper trough, and the GFS also shears out the upper
low instead of deepening it. Therefore, there remains considerable
uncertainty in the long range forecast, and the details will be
dictated by the size and track of Hurricane Matthew.
Regardless of the eventual track, a deep onshore flow pattern will
prevail over the region early next week, with scattered to
numerous showers and isolated embedded storms from Monday through
Wednesday. Locally heavy rains are possible in coastal northeast
Florida by Tuesday and Wednesday as tropical moisture begins to
push into the area. Breezy to windy conditions are possible
Wednesday into Thursday as the pressure gradient tightens,
assuming that Matthew continues northward as the GFS depicts.
Highs will generally remain in the 80s during this period, with
lower 80s expected by midweek at the coast as onshore winds
strengthens. Lows will generally remain in the upper 60s well
inland to the mid 70s at the coast.
Still a possibility of some patchy shallow ground fog across
portions of northeast Florida early this morning, otherwise VFR
conditions will prevail today.
A cold front will wash out over the waters Today with prevailing
winds generally out of the southwest around 10 to 15 knots. South
winds will increase some tonight, and small craft will need to
exercise caution across the Northeast Florida offshore waters.
Weaker flow will prevail over the weekend, then onshore flow will
gradually increase through early next week and headlines may be
needed by Tuesday evening.
Rip Currents: Low risk expected through the weekend, with an
elevated threat developing early next week.
.PRELIMINARY POINT TEMPS/POPS...
AMG 84 55 87 60 / 0 0 0 0
SSI 86 66 84 69 / 10 10 10 20
JAX 88 62 88 67 / 10 10 10 10
SGJ 88 69 86 70 / 10 10 20 20
GNV 89 62 87 65 / 10 10 10 10
OCF 89 64 87 67 / 20 10 20 10