Area Forecast Discussion
Issued by NWS Jacksonville, FL
FXUS62 KJAX 260824
Area Forecast Discussion
National Weather Service Jacksonville FL
415 AM EDT FRI AUG 26 2016
Currently...a few showers affecting the coastal areas and as far
inland as western Putnam and eastern Alachua counties. Moderate low
level moisture convergence due to inverted coastal trough noted in
latest analysis which will be slow to weaken through the morning
hours. Thus...isolated showers will likely continue through this
morning. Temps are in the 70s most locations except along the coast
where they are about 80.
Today and Tonight...Mid level high pressure system over ern TN will
slowly shift ewd to VA by Saturday morning. Weak upper level low
over NE FL early today will move wwd to the FL panhandle.
Meanwhile...weak vort lobes in lower to mid levels continue to
rotate around this system across northern FL peninsula with one of
these moving west through the FL big bend this morning and another
one moving west toward the ATLC coast tonight. Based on radar
trends...will continue with isolated to scattered showers across the
srn zones with the mean POP area shifting further wwd toward the N
FL I-75 corridor this aftn as drier low to mid level air filters in
on deep east to northeast flow. Isolated tstms at best as subsidence
inversion around 10 kft will prevent strong updrafts. Max temps
today around 90-95...with upper 80s along the coast. Breezy east to
northeast winds near 15-20 mph at the coast and 10-15 mph inland.
Tonight...lingering isolated showers toward inland NE FL area will
dissipate through the evening. Attention then focuses toward the
coastal zones again as potential will exist for ATLC shower activity
getting going again. Have placed in mainly isolated showers for the
coast after midnight with possible isolated thunderstorms as
instabilty increases over the warm waters coastal waters. Lows will
drop toward the upper 60s/70 inland SE GA and Suwannee Valley area
and lower to mid 70s toward the coast.
Saturday...deep layer flow is more veered but still decidedly
easterly with an increase in moisture expected late in the day. We
have gone with chance showers and tstms for NE FL and slight chance
for parts of SE GA. Shower activity mainly due to coastal convergence
and daytime heating. Max temps in the lower to mid 90s expected.
Breezy east to northeast flow expected for coastal areas.
Shower activity expected to increase over the adjacent Atlantic
waters Saturday night into Sun as low pressure 99L moves in the
Great Bahama Bank and drifts slowly WNW through Sun night toward
South Florida and Florida Straights. An inverted trough axis
extending north of the surface low will advanced toward the local
coastline through early Sun morning with a few showers moving inland
mainly along the NE Florida coast by sunrise.
By Sunday night the 00z ECMWF and 12z GFS bring 99L west or nw of
the Keys southwest of Cape Coral with the GFS showing an open wave
and the ECMWF as weak closed circulation. Again will utilize
NHC/WPC synoptic pattern consensus which indicated the low drifting
WNW over the eastern GOMEX during this period. Favoring any one
deterministic model solution at this time would be pointless and
ineffectual, going with the consensus. Either way...the local area
will continue to experience a big easterly fetch over the adjacent
Atlantic with increased coastal convergence.
Current forecast continues the trend of increasing clouds and rain
chances. Rain chances will increase from the ESE through Sun
afternoon and into Sun night as the parent surface low drifts
westward across the SSE Gulf of Mexico. Expect mainly showers with
clusters of isolated thunderstorms with diurnal enhancement.
On Sunday...high temps will range from the lower 90s well inland
toward I-75 to the mid/upper 80s along the coast. Muggy and above
normal minimum temperatures will continue with lows in the mid/upper
70s inland to near 80 along the coast and inland estuaries.
The extended period of onshore flow and building swells through the
weekend will increase the risk of rip currents. There will also be
an increased potential for elevated water levels along the coast due
to both the onshore flow and also above normal astronomical tides
with the new moon on Sept. 1st.
.LONG TERM...Mon through Thu...
The GFS continues to be less vigorous with the tropical wave with a
more gradual westward turn toward the north central Gulf which would
mitigate heaviest rain impacts. GFS has a veering trend with winds
easterly on Monday, ESE on Tuesday, SSW on Wednesday and WSW on
Thursday. Either way in this solution very deep moisture and high
cloud cover/rain chances will be in the forecast.
The 12z ECMWF trend (considerably weaker than the previous couple
runs) for early next week has been to indicate a rapid erosion of
the eastern CONUS/western Atlantic ridge. This would result in 99L
(again in whatever form it may take by that time) making a sharper
northward bend through the eastern GOMEX Monday-Tuesday, paralleling
very close to the Florida west coast, and eventually toward the
Florida Big Bend late Tuesday. Then picked up by the westerlies
moving through SE Georgia by Tuesday night and Wednesday and into
the Carolinas by late Thursday. If this situation were to pass, it
would extend the time frame of impacts through Thursday,
particularly in the shape of heavy rain and tornadic threats. The
local forecast area would be positioned on the ENE side of the low
circulation which is not only historically the wetter side and also
the more favored side for tornado formation.
The biggest change just came with 00z ECMWF where there is complete
dissipation of the upper ridge where the wave goes across the
central part of peninsula with best precipitation shunted across
south central Florida.
Given these stark differences, and no reason to prefer one model
more than another at this time, we will blend the guidance for
99L...indicated above normal rain chances spreading northward across
the local forecast area Mon-Thu as the circulation is progged at
this time to track northward across the eastern gulf coast region
and then across the deep south later in the week as it gets pick up
by a mid latitude trough. A low level trough axis will likely hang
back over the local forecast area if the low follows this general
track...and regardless of storm structure/intensity. This trough
axis amalgamated with ample tropical moisture content will bring the
potential for a widespread rainfall event across portions of Florida
and potentially SE Ga...especially along the coast and across the
Gulf Coast region. The potential for heavy rain should not be
continent much of the system`s strength, as weak tropical storms can
produce as much torrential rain as stronger systems.
.AVIATION...scattered to lcl broken stratocu and cumulus expected
through the period with a small chance of showers. Ceilings around
2500-4000 ft possible so brief MVFR cig/vsby possible esp in and
near showers. TSRA chances tool ow to mention in TAFS. ENE flow near
.MARINE...Rather poor small boating conditions will persist
through the next several days with easterly flow near 15 kt and
choppy wind-sea conditions. Chance of SCEC will exist...with better
chances during the weekend and especially early next week as a
tighter pres gradient seems likely. Seas generally 3-5 ft today with
the NWPS model doing a good job though a little bit under-forecast
near the 0-20 nm leg based on 41008 and 41112 reports.
Rip Currents: Solid moderate risk today with high risk possible from
persistent east flow and gradual increase in surf. Beachgoers are
urged to use extra precautions and ask lifeguards about conditions
before entering the water.
.PRELIMINARY POINT TEMPS/POPS...
AMG 94 68 93 73 / 0 0 10 10
SSI 88 77 88 78 / 0 10 20 20
JAX 91 72 90 76 / 20 10 30 20
SGJ 87 77 87 78 / 20 20 40 30
GNV 91 71 91 74 / 30 10 40 10
OCF 91 73 91 75 / 30 10 50 10