NWS Charleston, SC wrote its last area forecast discussion before the first event at May 24, 9:46 AM EST, 2 hours 44 minutes earlier.
Area forecast discussion, May 24, 9:46 AM EST, 2 hours 44 minutes before
Area Forecast Discussion
National Weather Service Charleston SC
1046 AM EDT Fri May 24 2019
.SYNOPSIS...
Unseasonably hot high pressure will dominate into late next
week.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 1045 AM: Visible satellite indicated a well developed
land breeze over the coastal waters, with no cloud cover over
land. I will update the forecast to reduce sky cover over the
CWA through the day. In addition, based on latest MOS, I will
update to lower high temperatures a few degrees. However,
dewpoints will remain in the mid to upper 60s along the coast,
with low to mid 60s inland, resulting in a small change in peak
heat index.
Previous Discussion:
The RAP and H3R have trended about an hour slower with the
progression of the pinned sea breeze this afternoon. They both
have also increased highs by another degree with a sliver of
highs 99-100 from roughly Metter and Reidsville east to near
Springfield. Did not make any changes to the high temperature
forecast with the sunrise update, but if a slight increase in
highs may need to be introduced later this morning if short term
models continue to trend in this direction.
Today will be the first in a prolonged series of unseasonably
hot days for Southeast South Carolina and Southeast Georgia.
Deep layered high pressure will remain anchored across the
Southeast U.S. today with the local forecast area positioned
along the eastern flanks of the mid-upper level anticyclone
centered over west-central Georgia. The combination of a
downslope northwest flow aloft and rising H8 temperature to near
19C will promote an unseasonably hot day with little cloud
cover. Noted the latest NAEFS 1000 hPa temperatures are forecast
to be ~2-2.5 standard deviations above average for late May.
The synoptic pattern favors a pinned sea breeze scenario with
the circulation likely not making any inland progress until late
afternoon. This typically allows hot temperatures to reach all
the way to the Intracoastal Waterway. The various statistical
guidance packages typically under forecast high temperatures in
downslope flow regimes, especially in drought conditions, and
this was taken into account when constructing today's high
temperature forecast. Opted to nudge highs closer to the RAP/H3R
consensus which is about 2-3 degrees warmer yesterday's
afternoon forecast cycle. This places highs ranging from the
upper 90s inland to as far east as the Highway 17 corridor in
Southeast South Carolina and I-95 in Southeast Georgia to the
upper 80s/near 90 at the beaches. Even Downtown Charleston could
reach 95-97 degrees with west winds before cooling off the
passage of the sea breeze. There are signals that a few spots
in interior Southeast Georgia could reach 100 degrees, especially
in the Metter-Claxton-Reidsville corridor. Dewpoints are
expected to mix out into the lower-mid 60s away from the coast,
but will pool back into the lower 70s across parts of the
coastal counties in the vicinity of the late afternoon sea
breeze. The resulting heat indices should peak roughly in the
100-103 range for most locations which is below the usual pre-
July 1 Heat Advisory criteria of 105.
Since this is the first day of what will likely become a
prolonged heat event, an impact-based Heat Advisory will not be
issued for today per coordination with the neighboring NWS
Weather Forecast Offices (WFOs). A Special Weather Statement
will be issued to address today's heat instead. The need for
impact-based Heat Advisories will be coordinated over the coming
days on a case-by-case basis.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/...
Tonight: Modest radiational cooling is expected as the boundary
layer is poised to decouple quickly after sunset. A weak
backdoor cold front will approach the Santee River by daybreak
Saturday. Dry weather will continue under mainly clear skies.
Lows will range from the upper 60s/lower 70s inland to the
upper 70s at the beaches and Downtown Charleston.
Saturday through Monday: The mid-levels will consist of strong
high pressure hovering over the Southeast Saturday and Sunday,
with the high drifting southwards into the northern Gulf of
Mexico on Monday. Heights over our area will slowly drop through
the short term. However, this won't be very noticeable because
the high is unseasonably strong. NAEFS shows 500 mb heights
peaking at about 3 standard deviations above normal. It also
shows above normal temperatures at almost all levels of the
atmosphere. At the surface, a weakening front will pass just
north and then offshore of our area on Saturday. Otherwise,
areas of high pressure will stretch from the western Atlantic
into the Southeast states. The only risk of "convection" could
be across the Charleston Tri- County area Saturday afternoon.
But this will be a big hurdle to jump over given all of the dry
air in place across the area as shown by model soundings. Hence,
we have slight chance POPs in these locations and it's possible
this may be overdone. Otherwise, the main moisture will be fair
weather clouds each afternoon. Temperatures are forecasted to
approach or exceed record values throughout the short term. For
the high temperatures, we went with a blend of models, thickness
values, and accounted for the sea breeze (if any). Saturday
will be the "coolest" day with temperatures ranging from the
mid/upper 90s for most locations and maybe a few century marks
near the Altamaha River. Sunday, expect widespread upper 90s to
lower 100s. Monday may be the hottest day of the bunch because
the sea breeze may remain pinned to the coast. If so, most
locations away from the immediate coast could reach at least 100
degrees for highs. Lows each night will cool down into the 70s.
Heat indices are forecasted to be above 100 degrees each day.
Heat Advisories could be needed, especially Sunday and Monday.
Users who are curious about the records can look at the short
Climate section below.
&&
.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
The mid-level ridge will remain in place while surface high pressure
persists. Temperatures may trend downward a few degrees each day.
However, they are still forecasted to remain well above normal
throughout the long term. Additionally, no rainfall is in the
forecast. Heat advisories, poor air quality, and dry fuels that
could increase the risk of wildfires are all concerns. But the
details will need to be better defined as this time period gets
closer.
&&
.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
VFR.
Extended Aviation Outlook: VFR.
&&
.MARINE...
Today: West winds will back during the day as sea breeze
circulation develops along the beaches. Winds will increase in
the afternoon as an intense thermal gradient develops between
the ocean and inland locations. Winds are expected to peak 10-15
kt for most locations with 15 kt or 15-20 kt for the Charleston
County waters. Seas will average 1-3 ft.
Tonight: southwest winds will slowly veer to the west after
midnight as a backdoor cold front approaches from the north.
winds will remain 15 kt or less with seas 1-3 ft.
Saturday through Tuesday: Atlantic high pressure will prevail.
The sea breeze should develop along the coast each afternoon,
bringing periods of gusty winds. However, no advisories are
expected. Winds are then forecasted to ease somewhat each
evening. Waves will generally peak in the 3-4 ft range.
&&
.CLIMATE...
A significant, prolonged heat wave will challenge or break many
of these records:
ALL TIME RECORD HIGHS FOR MAY:
KCHS: 99 set May 21, 1938.
KSAV: 101 set May 30, 1898 and May 31, 1945.
KCXM: 99 set May 21, 1938 and May 26, 1953.
RECORDS FOR FRI 05/24...
Station Record High Year(s)
------- ----------- -------
KCHS 97 1953
KSAV 98 2011, 1953
KCXM 98 1953
RECORDS FOR SAT 05/25...
Station Record High Year(s)
------- ----------- -------
KCHS 97 2000, 1953
KSAV 100 1953
Station Record High Min Year(s)
------- --------------- -------
KCHS 75 1953
KSAV 76 1878
KCXM 79 1998
RECORDS FOR SUN 05/26...
Station Record High Year(s)
------- ----------- -------
KCHS 98 1953
KSAV 100 1953
Station Record High Min Year(s)
------- --------------- -------
KCHS 75 1998
KCXM 79 1998
RECORDS FOR MON 05/27...
Station Record High Year(s)
------- ----------- -------
KCHS 98 1989
KSAV 98 1989, 1962
KCXM 95 1962, 1926
Station Record High Min Year(s)
------- --------------- -------
KCHS 76 1991
KSAV 77 1878
KCXM 78 1991
RECORDS FOR TUE 05/28...
Station Record High Year(s)
------- ----------- -------
KCHS 97 1967, 1964
KSAV 96 1964, 1898
KCXM 93 2000
Station Record High Min Year(s)
------- --------------- -------
KCHS 76 2000
KSAV 76 1885
KCXM 80 2000
RECORDS FOR WED 05/29...
Station Record High Year(s)
------- ----------- -------
KCHS 95 1945
KSAV 98 1945, 1898
Station Record High Min Year(s)
------- --------------- -------
KCHS 76 2018
KSAV 75 1885
KCXM 77 1998
RECORDS FOR THU 05/30...
Station Record High Year(s)
------- ----------- -------
KCHS 95 2004
KSAV 101 1898
Station Record High Min Year(s)
------- --------------- -------
KCHS 75 1982
KSAV 75 1924
KCXM 78 1998
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
NEAR TERM...NED
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
CLIMATE...