Area Forecast Discussion
Issued by NWS Atlanta, GA
FXUS62 KFFC 311934
Area Forecast Discussion
National Weather Service Peachtree City GA
334 PM EDT WED AUG 31 2016
...Tropical Storm Hermine likely to produce significant impacts
in parts of middle and east Georgia Thursday night and Friday...
.SHORT TERM /Tonight through Thursday/...
The next 24 hours should be fairly quiet, even with the active
tropics. The main impacts within the first three periods will be
increasing chances for precipitation...including locally heavy
rainfall by Thursday night.
Diurnal cu and showers should begin to diminish late this
evening/overnight with the loss of heating. Skies should mostly
clear out across the ATL metro...while lingering across central GA
The weak frontal boundary currently stretching from the eastern
Great Lakes back through the central US will slowly begin to sag
southward tomorrow. This boundary is expected to settle across
northern portions of GA by tomorrow night.
Not too confident on how far south this boundary will make it, but
the models are progging a brief wind shift to the NW tomorrow
afternoon before the synoptic flow turns back to the east ahead of
Hermine. For much of tomorrow, the pops should be highest across
northern GA (with the front) and central GA (showers coming off the
Atlantic in the deep easterly flow). Have gone ahead and painted a
slight chance across the I-20 corridor...as showers can pop up
anytime in this type of airmass.
.LONG TERM /Thursday Night through Wednesday/...
Primary concern is timing and impacts of Hermine. 12Z models not
backing off on intensity after Hermine makes landfall on North FL
coast around midnight Friday morning. While convection not as active
as it was this morning, looks much stronger than this time
yesterday. Still seeing a slight west/north shift and slower track
compared with previous runs.
Main message we want to share with partners is even when a storm
is nearing landfall, do *NOT* focus on the center of storm! Wind,
heavy rain and even isolated tornado impacts will be felt quickly
and WELL AHEAD of the the center reaching middle GA. This one
could surprise us.
Wind impacts may be substantial for what is only been just named
a Tropical Storm as strengthening, or at least a lack of
weakening, is forecast even after landfall. We have not seen
tropical storm force sustained winds in over 10 years in our CWA
based on our internal records. Sustained winds of 25 to 35 mph
with gusts to 50 mph may be possible as the center moves into our
southern and southeastern counties. Another impact is an isolated
tornado threat late thursday night and friday as this area is in
favorable northeast quadrant. Slight risk area in SPC day 2
outlook looks good given current forecast...but would need to be
adjusted north if track changes.
Finally heavy rain and flash flood threat may also be very
significant. Warm advection/warm front pattern expected to setup
east and northeast of Hermine, much like a PRE (predecessor rainfall
event), where heavy rain develops along and north of warm front like
feature. Models differ on where this PRE band of heavy rain will set
up exactly but expect heavy rain to develop Thursday night and
continue Friday as center tracks over south into east GA. At this
time...expecting 3 to 5 inches of rain thru Sat morning mainly
east of Lexington to Macon to Cordele line. Flash flood watch has
been issued but may need to be adjusted based on track of storm.
Another set of grid updates will be done around 5pm after the new
NHC package comes in. Based on this may need a Tropical Storm
watch shortly after.
The remainder of the extended forecast should be fairly quiet as
high pressure settles across the east half of the country. Temps
should be a little bit cooler and the airmass a bit drier behind
Hermine. Temps may end up dropping below 70 degrees overnight
Saturday night/Sunday morning...breaking the current streak.
PREVIOUS LONG TERM DISCUSSION /Thursday Night through Tuesday/...
The long term period begins during a critical time in the forecast
period as tropical system in the gulf makes landfall and makes
its closest approach to the local forecast area. Both the 00Z GFS
and Euro are further north with their tracks versus this time last
night with the ECMWF slightly more north than the GFS and the GFS
closer to current official track. Latest 06Z guidance coming in in
general varies between these solutions and again overall trend is
further north from 24 hours ago.
What this really means for the local area sensible wx wise is
very little chance from previous forecast with rain axis affecting
mainly extreme southeast portion of the area and winds remaining
less than 20 mph. The bigger potential impact is that we now have
very little wiggle room should system continue to trend northward.
Would not take much to get high percentage chances of tropical
storm force winds for the aforementioned SE corner.
Models are in better agreement with the ending of this system as
it pulls away from GA late Fri and surface front is dragged
southward behind it brining much drier air to the region. Still
looks like we are on track for a great Labor Day weekend depending
on which model verifies better. The GFS keeps dry conditions over
the whole area while the Euro continues to keep some deep layer
moisture over the southern portions. Have leaned toward the GFS
for now keeping conditions pop free through the weekend. Temps
have come up a few degrees in guidance for the extended weekend
which lines up better with ongoing forecast which already
reflected these numbers.
TAFS remain pretty quiet for now. Some sct low cu is possible
overnight and just after sunrise, but should lift to VFR cu for
the afternoons. Precip is too low to mention for now, but may have
to be changed iso/sct storms develop. Winds may end up being a
challenge during the day tomorrow. Models are progging wind speeds
to be 6kt or less, and the direction may end up going west of
north for a few hours during the day on Thursday.
//ATL Confidence...18Z Update...
Medium confidence on winds. High confidence remaining elements.
.PRELIMINARY POINT TEMPS/POPS...
Athens 71 92 72 79 / 10 30 50 60
Atlanta 73 91 72 83 / 10 30 40 50
Blairsville 65 86 66 77 / 20 30 40 50
Cartersville 70 92 71 84 / 10 20 30 40
Columbus 73 91 74 85 / 10 30 50 60
Gainesville 71 90 70 79 / 10 30 40 50
Macon 72 91 73 81 / 10 30 60 60
Rome 70 92 71 86 / 10 20 30 40
Peachtree City 70 91 72 83 / 10 30 40 50
Vidalia 73 90 74 83 / 30 40 80 80
Flash Flood Watch from late Thursday night through Saturday
morning FOR THE FOLLOWING ZONES: Baldwin...Bibb...Bleckley...