Area Forecast Discussion
Issued by NWS Atlanta, GA
FXUS62 KFFC 010103
Area Forecast Discussion
National Weather Service Peachtree City GA
903 PM EDT WED AUG 31 2016
Greatest upcoming forecast concern is Tropical Storm Hermine
currently located in the eastern Gulf of Mexico.
As per recent radar imagery...remaining shower/convective
activity mainly confined to north Ga where a lee sfc trough has
provided necessary lift amidst diurnal heating this afternoon.
Shower activity is also lingering across SE Ga where greater
tropical moisture and upper level support exists. Expect this
activity to diminish as the boundary layer decouples this
evening. Mainly clear skies expected across N Ga...with some pesky
low-mid level clouds lingering across C Ga. Low temps upper 60s
mountains to lower 70s elsewhere.
For Thursday...greater coverage of convection expected as TS
Hermine creeps towards the FL panhandle and a cold front
approaches the CWA from the NW. Expect highest coverage of precip
across the mountains ahead of the cold front and across central Ga
where deep layer tropical moisture resides. High temps in lower
TROPICS: TS Hermine`s mid-level circulation is located NE of
Yucatan penninsula with sfc reflection located a touch further
north. Hermine is expected to make landfall along FL coast after
sunset Thurs. It is possible Hermine could intensify into a
hurricane before making landfall...with SSTs well above normal
across the Gulf. Regardless of it being a hurricane or tropical
storms...feel threat of at least tropical storm conditions are
possible across parts of central Ga near the close of the work
week. After collaboration with neighboring offices this
afternoon...have put TS winds in the grids as well as issued a TS
and Flash Flood Watch. It is important to keep up to date with the
latest forecast information...as a slight shift in the projected
path could result in dramatic changes to the forecast. See
previous AFD discussion and latest information from NHC for
further details on this TS.
PREV DISCUSSION... /Issued 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.
Shower activity at 00z confined mainly to the north and SE of the
TAF sites. Expect clearing skies overnight across northern
sites...with some pesky low and mid level decks across CSG and
MCN. Potential exists for MVFR conditions around sunrise for CSG
and MCN as tropical moisture increases. Between TS Hermine pushing
towards the FL coast and a cold front approaching from the
NW on Thurs...shower and convective activity looks more likely at
all sites in the afternoon and evening. Have placed PROB30 at ATL
to covert this. Winds will perhaps be the trickiest part of the
forecast. Have elected to keep a southerly component at all
sites...with direction flirting between SW and SE the next 24
hours. Wind speeds 5-10kts. Will see a dramatic change in winds
and ceilings Thursday night into Friday as TS Hermine creeps in.
//ATL Confidence...00Z Update...
Medium on MVFR development...low on wind direction...high all
.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 / 20 30 30 40
Columbus 73 91 74 85 / 20 50 50 60
Gainesville 71 90 70 79 / 20 30 40 50
Macon 72 91 73 81 / 20 50 60 60
Rome 70 92 71 86 / 20 30 30 40
Peachtree City 70 91 72 83 / 10 40 40 50
Vidalia 73 90 74 83 / 30 50 80 80
Flash Flood Watch from late Thursday night through Saturday
morning FOR THE FOLLOWING ZONES: Baldwin...Bibb...Bleckley...
Tropical Storm Watch FOR THE FOLLOWING ZONES: Bleckley...Crisp...