Flash Flood Warning 16, NWS Newport/Morehead City, NC

Area Forecast Discussion
National Weather Service Newport/Morehead City NC
717 PM EDT Tue Aug 6 2024

.SYNOPSIS...
Tropical Storm Debby will move off southeastern Georgia and
into the Atlantic today, then slowly lift through the
southeastern US Thursday and Friday. This system is expected to
bring impacts to eastern NC, mainly periods of heavy rainfall,
which could last for several days depending on the track and
speed.

&&

.NEAR TERM /TONIGHT/...
As of 7PM Tuesday...

 - Rain bands from TC Debby to continue impacting ENC with
   gusty winds, flooding rains, and a few tornadoes

 - Tropical Storm Watch now in effect for portions of the
   Crystal Coast

Not much has changed forecast wise for tonight as latest radar
imagery shows rainbands from tropical storm Debby making their
way across western Carteret and Downeast with additional steady
rain across our northern tier. Flash flooding remains a concern
through the night especially in any rainbands that make their
way across ENC this evening. As of this writing there is
currently a flash flood warning across portions of Pamlico and
Beaufort which should be allowed expire at 730PM. Will note
there will be breaks in the precip from time to time but general
trend

Prev Disc...Tropical Storm Debby is currently located near
Savannah, GA, and is moving slowly ENE. Debby is about to emerge
off the Georgia coast and out into the Atlantic. Through
tonight, Debby will move slowly up, or just off, the coast of
GA/SC. North of the center of the low, bands of rain and
embedded thunderstorms will continue to impact ENC with various
hazards outlined below.

1) HEAVY RAIN - The 18z MHX sounding shows a deep layer of
tropical moisture, with a PWAT of 2.27". This will support
efficient rainfall processes, and intense rainfall rates.
Ensemble guidance shows a decent signal for 1-2"/hr rainfall
rates at times, and given the depth of moisture and the enhanced
lift associated with Debby, I expect rates will exceed 2"/hr in
the heaviest bands. At the onset, FFG is 2-4" for 1-hr and 3-hr
timeframe. Through tonight, then, it will take some time to
work up to those values for an increased flash flood risk. That
said, urban and flood-prone areas will be susceptible to
flooding purely due to the higher rainfall rates. FFG values
will continue to fall as more rounds of rain move through, and
the flash flood threat should gradually increase with time.

2) WIND/TORNADO - The 18z MHX sounding shows over 1000j/kg
MLCAPE and 0-1 SRH has improved to 100-150 m2/s2. Based on
surface obs, a SW to NE oriented boundary exists across ENC, and
this boundary appears to be the delineation between the better
tornado/enhanced wind potential along the coast and less of a
wind/tornado threat inland. Short-term guidance suggest this
boundary won't move much through tonight, and I expect the
greatest tornado and convective wind threat to be focused along
and south of a line from Jacksonville to New Bern to
Swanquarter. Lastly, non-convective, gradient-driven wind gusts
of 25-35 mph will be common along the immediate coast, with a
quick drop off as you move inland.

&&

.SHORT TERM /WEDNESDAY/...
As of 315 PM Tuesday...

 - TC Debby impacts continue

On Wednesday, TC Debby is forecast to continue to be meandering
around the SC coastline on Wednesday. North of Debby, bands of
rain and embedded thunderstorms will continue to impact ENC with
gusty winds, heavy rain, flash flooding, and a few tornadoes.
Of note, the flash flood threat is expected to steadily
increase, especially for areas that see the heaviest rainfall
through tonight. Along the immediate coast, gradient-driven
winds of 25-35 mph will be common, with lower gusts further
inland.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
As of 0400 Tuesday...Wet pattern ahead with periods of moderate
to heavy rain ahead of TC Debby that is forecast to move Nward
over ECONUS mid to late week. Clouds and rain keep temps a few
ticks below normal through the period. Clearing late in the
weekend behind a cold front.

TC Debby forecast becomes very murky after today with steering
flow breaking down and the approach of cold front from the N
middle of next week, leading to a large amount of spread in
solutions for the progression of this system. Because of the
ambiguity of the long term, have stuck to NHC's official
forecast for the basis of the longterm. The Official NHC
forecast has Debby making another landfall in SC Thursday
evening and slowly moving toward the N. The official track has
the center of Debby passing W of the FA Friday evening and
departing to the NE through the day Saturday as a weak tropical
depression, although it will probably be transitioning to become
extratropical while it passes. Regardless of exact track, how
organized it is or is not, how it interacts with the approaching
front and its parent trough, barotropic vs baroclinic,
etc...all of which have vastly different explicit solutions, all
possibilities push the forecast to a wet week with even more
moisture getting pumped over the FA into an already fairly moist
column once Debby reaches the Atlantic later today. See HYDRO
section below for possible flooding impacts.

Conditions improve through the weekend as the passing of Debby
spurs a cold front through the FA with clearing skies and the
last stop on the week-long rain train.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
SHORT TERM /Wednesday/...
As of 715 PM Tuesday...

 - TC Debby to impact ENC over the next 24 hrs, and beyond

Tropical Storm Debby is centered near Savannah, GA this evening,
and is slowly moving ENE out into the Atlantic. Over the next
24 hours, Debby is forecast to continue to move slowly east,
just off the SC coastline. North of the center of Debby, bands
of SHRA and TSRA will continue to move quickly N/NW across ENC,
with reduced VIS, gusty winds to 35kt+, and possibly a brief
tornado. Latest obs show a mix of IFR and MVFR cigs and vis
across the area with only isolated spots with VFR cigs and vis
noted. Lowest obs within shower and thunderstorm activity. In
general still expect widespread MVFR to IFR cigs and vis tonight
though there could be some breaks to MVFR and even VFR at
times. COntinued widespread shower and thunderstorm activity
persists through Wednesday with a mix of MVFR to IFR conditions
noted across ENC.

Short term guidance has been fairly aggressive with IFR
CIGs tonight, but this may be overdone considering recent
trends in obs (going back to last night). For now, I've kept
CIGs in the MVFR range, with a SCT IFR layer to show the
potential.

LONG TERM /Wednesday through Saturday/...
As of 0410 Tuesday...TC Debby will impact the area for the
entire week, though still a lot of uncertainty exists.
Regardless of exact track/intensity, the long term will be a
rather wet period with 5-10+" possible over the next 7 days and
extended periods of flight restrictions likely before conditions
improve late in the weekend behind a clearing cold front.

&&

.MARINE...
SHORT TERM /through Tuesday/...
As of 300 PM Tuesday...

 - Increasingly dangerous marine conditions developing due to
   Tropical Storm Debby

Tropical Storm Debby will move slowly north along the GA/SC
coast over the next 24-36 hours, with building winds and seas to
the north of the system. Latest obs show seas of 6-9 ft south
of Cape Hatteras this afternoon, and 3-5 ft north of there.
Through Wednesday, seas of 8-11 ft are likely south of Cape
Hatteras, with seas of 4-6 ft to the north. Southeasterly winds
of 15-25kt will be common through Wednesday, with gusts up to
30-35kt (highest south of Cape Lookout). This will lead to
dangerous marine conditions through Wednesday, and beyond.
Additionally, bands of rain and thunderstorms will move north
across area waters, with areas of enhanced wind potential, as
well as a few waterspouts.

LONG TERM /Wednesday through Saturday/...
As of 0430 Tuesday...The main concern for this week across the
waters is TC Debby currently off the coast of Georgia. Still a
lot of uncertainty with this system, but current official
forecast has Debby moving slowly north through the far
southwestern Atlantic. From this point on through the rest of
the week, swell will build out of the SSW. Mariners should keep
a close eye on the forecast the next several days with potential
for strong winds and dangerous seas. Seas continually build
from S to N to 10-13ft by Thursday afternoon. Debby is currently
forecast to pass W of the area Friday and depart to the NE Sat
in conjunction with a cold front passing through from NW to SE
on Sunday.

&&

.HYDROLOGY...
As of 300 PM Tuesday...Flood Watch continues for the area
through Friday. Confidence remains fairly high in an extended
period of heavy tropical rains on the periphery of TC Debby
which will likely lead to areas of flash flooding across Eastern
NC, with the highest rainfall totals and greatest risk of flash
flooding generally south of US 70. Current forecast rainfall
totals of 5-10 inches, with isolated amounts up to 15 inches.
Though these totals are impressive it is important to note that
this rain will come over the course of the next 5 days and there
should be time for water to at least initially runoff without
much issue. Additionally, the risk for inland river flooding
will increase late this week and next week. It should be noted
that there is potential for significant river flooding to occur
if the current rainfall forecast holds.

&&

.MHX WATCHES/WARNINGS/ADVISORIES...
NC...Tropical Storm Watch for NCZ195-199.
     Flood Watch through Friday evening for NCZ029-044>047-079>081-
     090>092-094-193>196-198-199-203>205.
     Beach Hazards Statement until 8 PM EDT this evening for NCZ196-
     204-205.
MARINE...Small Craft Advisory until 8 PM EDT Friday for AMZ135.
     Small Craft Advisory from 8 AM Wednesday to 8 PM EDT Friday
     for AMZ136-137.
     Small Craft Advisory from 5 PM Wednesday to 8 PM EDT Friday
     for AMZ150.
     Small Craft Advisory until 8 PM EDT Friday for AMZ152-154-156.
     Tropical Storm Watch for AMZ158.
&&

SYNOPSIS...MHX
NEAR TERM...RM/RCF
SHORT TERM...RM
LONG TERM...CEB
AVIATION...RCF/CEB
MARINE...RM/CEB
HYDROLOGY...MHX

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