Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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084 FXUS62 KCHS 221154 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 754 AM EDT Sun Sep 22 2024 .SYNOPSIS... High pressure will linger across the region through the early week. A weak cold front could approach from the west around mid to late week. && .NEAR TERM /THROUGH TONIGHT/... Today: Aloft, a ridge centered across southern TX will extend east across the Deep South and Southeast United States while a low and associated trough axis shift off the Northeast Coast. At the sfc, weak high pressure will prevail across the region, while weak low pressure develops across the Midlands and Upstate. Mid-upper ridging aloft is expected to gradually increase from the west with time while a weak downslope flow is also present. The setup suggests slightly warmer sfc temps than the previous day. In general, high temps should range in the upper 80s to lower 90s. Closer to the coast, high temps will be a bit cooler (low-mid 80s), likely due to onshore flow and sea breeze shifting inland during the afternoon. By mid-late afternoon, some guidance suggests weak sfc low pressure nudging into western most zones while weak mid-lvl vort energy arrives from the northwest late. Warm temps along with these subtle forcing features could be sufficient to produce a few late afternoon showers or even an isolated thunderstorm well inland given SBCAPE around 1000 J/kg along and west of the I-95 corridor. However, overall precip coverage should remain limited given the downslope flow in place aloft. Tonight: A few showers could linger across inland areas into early evening, but expect activity to diminish fairly quick with the loss of daytime heating. Weak sfc high pressure should then prevail for much of the night while additional ridging continues aloft. Light southerly winds under a few clouds should result in low temps that are noticeably warmer than the previous night. In general, lows should range in the upper 60s to lower 70s. Locations could stay in the mid 70s along the beaches. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... A deep upper ridge centered over the northwestern Gulf will traverse eastward across the Florida Peninsula Tuesday and shift over the Atlantic by Wednesday. Surface high pressure anchored over northern Maine extending southward along the Eastern Seaboard will persist through the period. A subsidence inversion around the 600-550mb layer noted via model soundings will limit convection, resulting in mostly quiet weather. Deep dry air aloft with some moisture trapped in the lower levels will result in a few low clouds, however mostly sunny skies are expected each day. There are some indications within the models that show spotty light showers far inland Monday/Tuesday, due to weak shortwave impulses aloft. However, low cloud tops indicate any showers that may develop should be brief with little measurable rainfall. We will continue with no mentionable rain chances (POPs less than 15%) in the forecast. Temperatures will be relatively mild through the period due to the ridge aloft. Expect highs in the upper 80s/low 90s each day. Both Monday and Tuesday night will feature lows around 70 degrees inland and low/mid 70s along the coast. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... An upper low over the Ohio Valley and elongated trough digging into the Deep South will propagate eastward pushing a cold front toward the area late Wednesday. With the trough progged to quickly lift out of the Southeast U.S. Thursday, the front will slow and weaken as it moves over the forecast area. Isolated to scattered showers are possible Wednesday night, and could potentially persist through Thursday depending on the progression of the front. From here on out, details for the long-term forecast will largely depend on the intensity, placement, and timing of a potential tropical system sourced from the Gulf of Mexico. See latest NHC Tropical Weather Outlook for the latest information. Based on the collaborated low position per WPC, the system is expected to remain west of the Carolinas. Given the FROPA, thick cloud cover, and anticipated rainfall, high temperatures are forecast to dip into the upper 70s/low 80s through the weekend. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... VFR conditions are expected at CHS/JZI/SAV terminals through 12Z Monday. Extended Aviation Outlook: VFR conditions expected to prevail through Wednesday. && .MARINE... Today and Tonight: Weak high pressure will lead to quiet marine conditions across local waters. In general, light northerly winds this morning will become southerly between 5-10 kt this afternoon while a sea breeze circulation develops, then shifts inland. Seas will range between 2-3 ft across nearshore waters and 3-4 ft across offshore Georgia waters today, then slowly subside about a foot during the night. Monday through Thursday: Weak, broad high pressure offshore will result in southeast winds around 10 kt or less. Seas will average 1- 3 ft for the nearshore waters out 20 nm and 3-4 ft for the outer GA waters from 20-60 nm. Near the end of the period, there could be an increase in winds and due to a potentially developing tropical system in the Gulf of Mexico. && .TIDES/COASTAL FLOODING... For today, a Coastal Flood Advisory will likely be needed during the early afternoon high tide cycle along Charleston and Colleton County coasts with moderate coastal flooding possible. Further south and into Georgia coastal areas, coastal flooding is less of a concern, but minor flooding levels could be met for a brief period. Should trends persist, a Coastal Flood Advisory could also be needed for the southern South Carolina and Georgia coasts. Positive tidal anomalies and high astronomical tides from the recent full moon will lead to elevated tides through early week. Although the astronomical high tides are lowering, coastal flooding is expected with each daytime high tide cycle along the Charleston and Colleton County coasts. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...DPB SHORT TERM...BRM LONG TERM...BRM AVIATION...BRM/DPB MARINE...BRM/DPB