From Mike Powell@618:250/1 to All on Friday, July 26, 2024 09:22:00
AWUS01 KWNH 261353
FFGMPD
NCZ000-SCZ000-261852-
Mesoscale Precipitation Discussion 0734
NWS Weather Prediction Center College Park MD
953 AM EDT Fri Jul 26 2024
Areas affected...South-Central to Southeast NC...North-Central to
Northeast SC
Concerning...Heavy rainfall...Flash flooding possible
Valid 261352Z - 261852Z
SUMMARY...Slow-moving and very efficient convection with high
rainfall rates will be impacting areas of south-central NC into
north-central and northeast SC going through midday. Eventually
areas of southeast NC will also get into some of this activity
this afternoon. Some flash flooding is possible.
DISCUSSION...A very small-scale low-level circulation and
associated vort center is situated near the NC/SC border region
which is yielding some low-topped and extremely efficient
convection across areas of south-central NC and especially areas
of north-central SC. There is also evidence of a surface trough
axis extending eastward ahead of the weak low down across
northeast SC and some adjacent areas of southeast NC.
At least modest, but persistent moisture convergence along this
trough axis ahead of the low center along with a gradual increase
in boundary layer instability via the diurnal heating cycle should
facilitate a persistence and localized expansion of convection
going through the early afternoon hours. There is already a bit of
an instability gradient oriented in close proximity to this trough
from northeast SC into southeast NC where MLCAPE values are as
high as 1000+ J/kg.
The 12Z RAOB data from CHS and ILM show a deep tropical
environment with tall/skinny CAPE profiles. This will strongly
support a highly efficient warm rain set-up for very heavy
rainfall rates that will be capable of reaching 2 to 3 inches/hour.
Outside of the recent HRRR guidance, the early morning guidance is
not exactly handling the ongoing activity particularly well.
However, with the current radar and satellite trends, and slow cell-motions/efficient rainfall set-up, some localized storm
totals reaching 3 to 5 inches will be possible going through early
this afternoon.
Some areas of flash flooding will be possible as a result, and
especially with some areas already seeing moist antecedent
conditions.
From Mike Powell@618:250/1 to All on Monday, September 16, 2024 08:34:00
AWUS01 KWNH 160901
FFGMPD
NCZ000-SCZ000-161500-
Mesoscale Precipitation Discussion 1019
NWS Weather Prediction Center College Park MD
500 AM EDT Mon Sep 16 2024
Areas affected...Southeast NC...Northeast SC
Concerning...Heavy rainfall...Flash flooding possible
Valid 160900Z - 161500Z
SUMMARY...Heavy rainfall associated with Potential Tropical
Cyclone Eight will be advancing inland this morning across
southeast NC and northeast SC. A gradual increase in the threat
for flash flooding can be expected as rainfall rates increase.
DISCUSSION...The latest GOES-E Proxy Visible satellite imagery
along with radar and aircraft data shows the low center of
Potential Tropical Cyclone Eight centered approximately 95 miles
east-southeast of Charleston, SC at 09Z (5AM EDT). The storm
continues to advance slowly off to the northwest, and this will be
allowing for heavy rainfall focused around the northern quadrant
of the storm to begin cyclonically wrapping inland across the
coastal plain of southeast NC and northeast SC this morning.
The system still has a fair amount of baroclinicity associated
with it for the time being given the proximity of multiple frontal
features, but radar imagery shows pockets of very strong
convection north of the low center with extremely heavy rainfall
rates. This is also where there is much greater instability and
the latest RAP analysis confirms MLCAPE values of as much as 1500
J/kg near and to the northeast of the center where some of the
colder convective tops are noted.
Much more stable air is still noted along the immediate coastal
plain of the Carolinas, and this will tend to keep rainfall rates
a bit limited in the short-term across these areas as rains
offshore gradually push inland. However, in time as stronger
onshore flow arrives and the low center approaches by later this
morning, there should be an influx of greater instability and
stronger moisture convergence that will be conducive increasing
rainfall rates.
The 00Z HREF guidance supports rainfall rates in the 12Z to 15Z
time frame reaching 1 to 2 inches/hour across especially the
coastal areas of southeast NC around the Wilmington, NC vicinity.
Some of these heavier rainfall rates may also spread into
northeast SC near and to the north of Myrtle Beach.
Expect rainfall amounts by 15Z (11AM EDT) to reach as high as 2 to
4 inches with isolated amounts potentially up to around 5 inches.
These rains will gradually increase the threat for flash flooding
by later this morning.