Tropical Storm and Flash Flooding in Georgia, September 27, 2024

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
346 AM EDT Fri Sep 27 2024

.SYNOPSIS...
Tropical Cyclone Helene will move quickly north through Georgia this
morning, bringing continued heavy rainfall, significant flooding and
strong winds to our area. After the storm departs this afternoon,
expect a calmer weekend with temperatures near seasonal normals.

&&

.NEAR TERM /THROUGH TONIGHT/...
***A HISTORIC RAINFALL EVENT IS UNDERWAY FOR THE SOUTHERN
APPALACHIANS AND VICINITY WITH WIDESPREAD/LOCALLY CATASTROPHIC FLASH
FLOODING EXPECTED***

As of 315 am: Moderate to heavy rain continues across the forecast
area early this morning. Rainfall rates associated with the ongoing
activity are relatively tame...generally .25-.5" per hour (albeit
locally heavier). Nevertheless, flash flooding continues to steadily
worsen...especially across portions of the NC Blue Ridge. The center
of Hurricane Helene is currently near Vidalia, GA...and is already
accelerating (current speed ~40 mph) toward the north.   Tropical
rainbands...possibly producing rainfall rates of 1-2" per hour...
will begin to rotate across the CWA during the 08-12Z time frame.
This is when the flash flood situation...which is already severe in
some areas...will become potentially catastrophic... especially in
locations that received the brunt of the predecessor event over the
past 36 hours (i.e., counties encompassing the Blue Ridge
escarpment...note that this also includes the city of Asheville and
vicinity). It's very possible that ongoing warnings will be upgraded
to EMERGENCY designation in these areas. Reservoirs along the
Catawba River chain are also running high and these could be
breached as enuf water may not be able to be released beforehand.
Additional rainfall amounts of 3-6 inches are expected across all
but the southern and eastern fringe of the CWA (where 1.5-3" are
expected). This additional rainfall will result in...at the very
least..."run-of-the-mill" flash flooding across much of the
remainder of the CWA.

Winds remain a secondary concern...but nonetheless quite concerning,
as Helene made landfall as a Cat 4 last evening, and the fast-moving
nature of the cyclone isn't giving it a lot of time to weaken as the
expanding wind field advances toward the forecast area. Gusts of 35
to 45 kts are being reported as far north as Augusta...about 90
miles north of the cyclone center...and confidence is increasing
that damaging winds (gusts 55-65 mph) are going to be realized
across at least the western part of our area, especially as the
tropical bands around the center begin pushing in around daybreak.
Gusts across the higher elevations could reach 80 mph. The
combination of these wind gusts with saturated soil is likely to
result in widespread power outages across the western half of the
area.

Helene will continue to advance quickly W=>NW of the forecast area
late this morning into the afternoon, with quickly improving weather
conditions as the column dries quickly. However, flooding on some
larger tributaries will linger into at least Saturday, while main
stem river flooding will linger into early next week.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 310 am Friday: Stacked low pressure over the TN/OH Valley will
steadily weaken while moving very little during the short term.
Spokes of vorticity passing south of the low center and brushing the
southern Appalachians will interact with elevated moisture and weak
instability to result in development of scattered, mainly diurnal
showers Saturday and Sunday...primarily over the mountains. Rainfall
rates/amounts will generally be tame, but can't rule out some
locally heavy rainfall, especially on Saturday. Temperatures are
expected to be very close to normal through the weekend.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 300 am Friday: Upper low is forecast to be centered over the
Ohio Valley at the beginning of the extended, and is expected to
finally begin opening up and kicking into the Mid-Atlantic circa
Tuesday, as a strong short wave trough digs across the northern
Great Plains. This is expected to result in another round of mainly
diurnal showers on Monday. After that, it looks like we finally see
an end to precip chances for the remainder of the forecast period,
as drier air filters into the area in association with with
continental high pressure. Temperatures are expected to be slightly
above normal during the first half of the period, cooling a bit to
normal with the building surface high.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Flight conditions will deteriorate rapidly
over the next 3-6 hours as Hurricane Helene moves rapidly north
through Georgia. The main concern will be winds...as gusts in the
45-55 kts range...primarily from the E/SE are looking increasingly
likely from around 09-15Z. Some gusts as high as 60 kts are possible
at the upstate SC terminals and KAVL. Strong LLWS as high as 70 kts
will also develop at all sites later this morning. Otherwise, IFR
cigs are expected to prevail, although these will occasionally mix
up to MVFR as heavier rainfall rates/convective elements pass over
the terminals. Isolated TS are also possible...with VCTS included at
m most sites. Otherwise, winds will steadily diminish and tropical
rain bands taper off from late morning through early afternoon. Low
cigs are expected to become VFR by late afternoon, while gusts are
likely to subside after 00Z.

Outlook: Isolated to sct mainly diurnal/mainly mountain convection
(primarily showers) will be possible thru early next week. Morning
fog/low stratus will be possible each day, mainly in the mountain
valleys.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Flood Watch until 2 PM EDT this afternoon for GAZ010-017-018-
     026-028-029.
     Tropical Storm Warning for GAZ010-017-018-026-028-029.
NC...Flood Watch until 2 PM EDT this afternoon for NCZ033-035>037-
     048>053-056>059-062>065-068>072-082-501>510.
     Tropical Storm Warning for NCZ033-048>053-056-058-059-062>065-
     068>071-082-501>510.
     Wind Advisory until 2 PM EDT this afternoon for NCZ035>037-057-
     072.
SC...Flood Watch until 2 PM EDT this afternoon for SCZ008>014-019-
     101>109.
     Tropical Storm Warning for SCZ008>014-019-101>109.
&&

SYNOPSIS...JDL
NEAR TERM...JDL
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...JDL

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
1034 PM EDT Thu Sep 26 2024

GAZ010-017-018-026-028-029-NCZ033-048>053-056-058-059-062>065-068-
069-501>510-SCZ008-010-011-101>109-280245-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Avery-Madison-Yancey-
Mitchell-Swain-Haywood-Buncombe-Catawba-Graham-Northern Jackson-
Macon-Southern Jackson-Transylvania-Henderson-Cleveland-Lincoln-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-Rutherford Mountains-
Greater Rutherford-Polk Mountains-Eastern Polk-Cherokee-Anderson-
Abbeville-Oconee Mountains-Pickens Mountains-Greenville Mountains-
Greater Oconee-Greater Pickens-Central Greenville-
Southern Greenville-Northern Spartanburg-Southern Spartanburg-
1034 PM EDT Thu Sep 26 2024

...FLOOD WATCH IN EFFECT THROUGH FRIDAY AFTERNOON...
...TROPICAL STORM WARNING IN EFFECT...

This Hazardous Weather Outlook is for northeast Georgia, piedmont
North Carolina, western North Carolina and upstate South Carolina.

.DAY ONE...Tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   Tropical Storm Warning.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   Tropical Storm Warning.

Helene will track quickly northward overnight and will impact the
western Carolinas and northeast Georgia Friday, bringing gusty
winds, heavy rainfall, and flooding to the area.

.SPOTTER INFORMATION STATEMENT...

None.

NCZ070-071-082-SCZ009-012>014-019-280245-
Gaston-Mecklenburg-Union NC-York-Laurens-Union SC-Chester-Greenwood-
1034 PM EDT Thu Sep 26 2024

...FLOOD WATCH IN EFFECT THROUGH FRIDAY AFTERNOON...
...TORNADO WATCH 687 IN EFFECT UNTIL 8 AM EDT FRIDAY...
...TROPICAL STORM WARNING IN EFFECT...

This Hazardous Weather Outlook is for piedmont North Carolina and
upstate South Carolina.

.DAY ONE...Tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   Tornado Watch.
   Tropical Storm Warning.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   Tornado Watch.
   Tropical Storm Warning.

.SPOTTER INFORMATION STATEMENT...

None.

NCZ035>037-057-280245-
Alexander-Iredell-Davie-Rowan-
1034 PM EDT Thu Sep 26 2024

...WIND ADVISORY REMAINS IN EFFECT UNTIL 2 PM EDT FRIDAY...
...FLOOD WATCH IN EFFECT THROUGH FRIDAY AFTERNOON...

This Hazardous Weather Outlook is for piedmont North Carolina.

.DAY ONE...Tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   Wind Advisory.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   Wind Advisory.

.SPOTTER INFORMATION STATEMENT...

None.

NCZ072-280245-
Cabarrus-
1034 PM EDT Thu Sep 26 2024

...WIND ADVISORY REMAINS IN EFFECT UNTIL 2 PM EDT FRIDAY...
...FLOOD WATCH IN EFFECT THROUGH FRIDAY AFTERNOON...
...TORNADO WATCH 687 IN EFFECT UNTIL 8 AM EDT FRIDAY...

This Hazardous Weather Outlook is for piedmont North Carolina.

.DAY ONE...Tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   Tornado Watch.
   Wind Advisory.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.
   Tornado Watch.
   Wind Advisory.

.SPOTTER INFORMATION STATEMENT...

None.

PM

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