![National Oceanic and Atmospheric Administration](/build/images/header/noaa.d87e0251.png)
![National Weather Service](/build/images/header/nws.4e6585d8.png)
![United States Department of Commerce](/build/images/header/doc.b38ba91a.png)
Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
665 FXUS62 KCHS 141944 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 344 PM EDT Wed Aug 14 2024 .SYNOPSIS... High pressure will build in from the north through late week. Another cold front may approach the area early next week, then remain nearby through late week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... A deep trough extending from low pressure aloft over Nova Scotia will cover the eastern states and western Atlantic, while a 5940-5950 meter anticyclone remains centered over the Arklatex region. We lie near the southern apex of the trough, and within a northwest flow that covers the entire vertical column locally above 700 mb. The trough will also cause TC Ernesto to lift northward to the east of the Bahamas. At the surface across the immediate region we find a fairly strong high pressure ridge to continue to build in, providing us with a noticeable change in air mass. An indication of that air mass change can be seen over the Charleston quad-county district, where many dew points are down in the mid and upper 60s. These dew points will push further south through the night, and will cover much of the northern and western counties after midnight. Through the evening there will continue to be isolated to scattered showers and a few t-storms, mainly near and inland from the sea breeze. The highest PoPs of 40-50% will be found in georgia for bryan, Liberty, Long, and Mcintosh County. This is where we find the best MLCAPE and moisture convergence, while further north there is actually some CINH and those areas are deeper into the drier air. As we go through the early evening this activity will fade, and we will be rainfree by about 9 pm. the HREF hints at a few showers developing across McIntosh overnight. But since the vast majority of guidance shows nothing at all, we ignored the HREF solution for now. As the diurnal cumulus clouds diminish this evening and winds decouple across much of the region, this will set us up for a less warm and muggy night that we`ve grown accustomed to the past few months. With the 1000-850 mb thickness to get down about 1401-1407 meters by daybreak, we`re looking at min temperatures dropping to the upper 60s and lower 70s most areas. The exceptions will be some middle 60s in the Francis Marion National Forest and maybe in upper Dorchester and far inland Colleton. While the barrier islands, the Charleston-North Charleston metro and the Savannah area will be mainly in the middle 70s. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... Thursday: A mid-level wave located over the Canadian Maritimes will wave break early Thursday and become vertically stacked. As this occurs, the newly formed area of closed low pressure will start to sink south as Ernesto accelerates towards Bermuda. For GA and SC, this will allow surface high pressure to build south and west across the coastal plain of SC and NC. PWATs are also forecast to be only around 1.25" (or around the 10th percentile for this time of year). 1000/ 850 mb thicknesses also respond, and are also only supposed to be around 1410 m Thursday afternoon. This will keep high temperatures at or just below 90 degrees, with no precipitation expected and dewpoints falling into the mid 60s. Friday: Sunrise will likely occur with temperatures in the low to mid 60s for most areas Friday morning along with mid 70s at area beaches. Surface high pressure will again remain directly overhead Friday with no precipitation expected as the region remains on the ageostrophic convergent side of the upper level trough axis. High temperatures on Friday look similar to Thursday as 1000/ 850 mb thicknesses hold at 1410 m. Low temperatures Friday night into Saturday morning do stay several degrees warmer compared to Friday morning or near 70 degrees. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As the weak upper ridge moves southward, an upper-level trough is expected to pass across the Great Lakes Saturday, and push into Southeast Canada and northern New England Sunday and Monday. A cold front extending southward from the associated trough is anticipated to approach the forecast area early next week. There is potential for this low to stall nearby into mid-week before a mid-level trough forces it offshore. Some guidance suggests that the upper-level trough will deepen as Ernesto passes nearby in the Atlantic off to the East. If this holds true, then it is possible to see an increase in instability and slightly cooler temps Sunday through Wednesday. However, the pattern should favor more unsettled weather conditions while the front and h5 shortwave energy provide sufficient forcing across ample moisture. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... KCHS/KJZI/KSAV: VFR will prevail through 18Z Thursday. The sea breeze boundary will generate isolated to scattered SHRA and a few TSRA this afternoon and early evening. However, coverage is less than recent days, so nothing more than VCSH is shown at KCHS and KSAV, with no mention at KJZI. The best chance for any brief flight restrictions would be at KSAV between 20Z and 23Z. Unlike the past two mornings, there doesn`t appear to be any chance for low stratus Thursday morning as the air mass drier than before. Extended Aviation Outlook: VFR conditions will prevail at CHS/JZI/SAV terminals through Saturday as surface high pressure remains in control. Brief flight restrictions are possible early next week to all terminals as a front brings showers/thunderstorms to the region starting Sunday && .MARINE... Tonight: The synoptic set-up is somewhat unusual for August, featuring a 1021 mb high centered over Pennsylvania that ridges south to Florida and the northern Gulf of Mexico. TC Ernesto will be found east of the Bahamas, and the resulting pressure difference between these two systems, will create NE and E winds of 15 or 20 kt. There will be some gusts at times approaching 25 kt, but the duration and coverage is not enough to hoist any Small Craft Advisories. Seas within this favorable fetch will be as high as 3-5 feet. Thursday: Surface high pressure will center across the coastal plain of SC/ NC on Thursday with winds out of the northeast 10 to 15 kt. Wind gusts up to 20 kt are likely with conditions remaining below Small Craft Advisory criteria. Friday: Winds will slowly veer around from the east on Friday as surface high pressure slowly nudges east. Also at this time, Hurricane Ernesto will be approaching Bermuda with increased swell, period, and wave height affecting all waters. Latest GFS spectral guidance has wave period approaching 15 feet Friday afternoon with wave heights nearing 7 ft. The wave height here is likely slightly underdone. Waves of 6 - 8 ft are likely out 20 nm. Small Craft Advisories might be required for all waters on Friday. Saturday - Monday: Through the weekend, surface high pressure will collapse as the next mid-level wave approaches the region. As this occurs, winds will veer around from the southwest near 10 kt through Monday. Each afternoon winds will back from the south and slightly increase in speed as a sea breeze circulation begins. Winds will then calm in the evening and veer around from the southwest once again. Small Craft Advisories may still be needed on Saturday due to swell from Ernesto, but wave heights will subside later Saturday below criteria. No advisories will then be needed for Sunday or Monday. Rip Currents: There is a low risk of rip currents on Thursday as wave heights remain around 4 ft with mainly 6 second or less period swell. On Friday however, Ernesto will be approaching Bermuda with 13 to 15 second swell reaching the SC and GA coast. This working in combination with onshore winds will produce a high risk of rip currents at all area beaches. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...Haines LONG TERM...Dennis AVIATION...Haines MARINE...Haines