942 FXUS62 KCHS 030607 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 207 AM EDT Fri May 3 2019 .SYNOPSIS... A weak low pressure system will effect the area late tonight into Friday. A cold front will then push through the region Sunday, followed by drier high pressure into the middle of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... As of 2 AM: Based on the latest CAMs, showers and thunderstorms should increase over the nearshore waters within an inverted surface trough during the first 1-2 hours of daylight. A surface low is forecast to track north over southern GA after 12Z. The circulation around the low should push the inverted trough inland from mid-morning through early afternoon. I will update the forecast to adjust PoPs and weather to latest timing adjustments. Previous Discussion: A mass of deep moisture associated with an inverted trough/surface wave, will continue to round the periphery of the ridge offshore. This pattern will advect Pwats in excess of 1.5 inches northward overnight across Southeast GA and southern SC. As deeper moisture and coastal convergence increase after midnight, we suspect more stratocu and layered clouds will tend to develop. At least isolated showers may develop from 09Z toward daybreak, especially along coastal zones. This pattern favors a lesser potential for late night fog, however we did mention patchy fog for a couple hours late tonight adjacent to the CSRA and SC Midlands where models paint some potential for stratus and fog. Given the increase in low-level moisture and clouds overnight, low temps should be quite mild ranging from the mid 60s inland to near 70 adjacent to the coast. && .SHORT TERM /6 AM THIS MORNING THROUGH SUNDAY/... Friday: A notable moisture increase is expected across the area as a weak wave/low rounds the western edge of retreating high pressure centered over the Atlantic. Chances of showers and thunderstorms remain the forecast with the greatest potential occurring late morning into the afternoon, but generally starting in Southeast Georgia early morning, then spreading into Southeast South Carolina mid morning into the afternoon as h5 shortwave activity associated with the wave/low encounters SBCAPE around 1000-1500 J/kg and PWATs up to 1.75 inches. At this time, convection is expected to remain sub-severe, but could briefly produce moderate/heavy downpours given a tropical moisture source. Temps will be a few degrees cooler than previous days given increasing clouds and precip activity across the area. In general, highs should range in the low/mid 80s. Any showers/thunderstorms should quickly wane during the evening due to diurnal heat loss, resulting in the overnight period being dry for all areas within a hour or two after sunset. Lows should remain mild, ranging in the mid/upper 60s. Saturday: A broad mid/upper lvl trough of low pressure will advance over the Central United States with subtle energy drifting across the Deep South. At the sfc, a south/southwest wind will help draw moisture from the Gulf of Mexico into the area by the afternoon, setting up chances of showers/thunderstorms mainly across areas away from the coast. Convection should remain sub-severe for the day, but sfc temps should warm a few degrees higher than the previous day, reaching the upper 80s across most locations away from the coast. Overnight, conditions will remain mild well ahead of an approaching cold front. Temps should only lower into the upper 60s to around 70. A few showers could develop across the area after midnight, starting inland as h5 shortwave activity approaches the region from the west. Sunday: A cold front will approach the Southeast United States, eventually shifting offshore over the course of the day. Ahead of the front, fairly warm and moist conditions will help spawn scattered showers and/or thunderstorms as h5 shortwave activity traverses the area. Wind fields are not particularly strong ahead of and during fropa and instability is modest with SBCAPE around 1000- 1250 J/kg. However, PWATs near 1.75 inches suggest showers or thunderstorms could produce brief heavy downpours until fropa occurs. Activity should quickly shift offshore and/or diminish as dry high pressure begins to build into the region post fropa late evening. In general, highs should peak in the low/mid 80s, highest away from the coast. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Moderate to high confidence this period. A cold front should move through Sunday night with drier high pressure building in starting Monday. Can't rule out some showers Monday and Tuesday but generally it looks dry for most areas. Rain chances will likely increase toward the middle of the week with the approach of deeper moisture ahead of a cold front. Temperatures will cool a bit early in the period, likely closer to normal Tuesday, but overall will stay above normal through the period. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... The primary forecast concern for the 6Z TAFs will be the timing and intensity of convection today. Based on the latest CAMs, showers and thunderstorms should increase over the nearshore waters within an inverted surface trough during the first 1-2 hours of daylight. A surface low is forecast to track north over southern GA after 12Z. The circulation around the low should push the inverted trough inland from mid-morning through early afternoon. The passage of the sfc trough should result in the peak coverage of showers and isolated thunderstorms, I will highlight the peak hours with a TEMPO from 15-19Z for MVFR vis during SHRAs. Periods of MVFR ceilings are forecast through the rest of the afternoon. Conditions should return to VFR this evening with light to calm winds. Extended Aviation Outlook: Fog and/or low clouds could impact both CHS and SAV terminals each morning through the weekend. However, greater chances of flight restrictions are possible with showers and/or thunderstorms on Sunday along/near a cold front that shifts over the terminals. VFR conditions should prevail at both terminals Monday. && .MARINE... Tonight: Onshore (southeast) flow will persist as a weak wave of low pressure moves northward along Florida's east coast. Winds near shore will average 10 kt with some stronger flow over GA waters beyond 20 NM closer to 15 kt with higher gusts. Seas have increased in response to a lengthened fetch and tighter gradient to the southeast. Near shore, seas 3 to 4 ft will be typical with 4-5 ft seas beyond the pilot buoys. We maintained a Small Craft Advisory tonight over 20-60 NM GA waters for seas in the 5-7 ft range. Friday through Tuesday: Atlantic high pressure will retreat east as an area of low pressure moves north near coastal waters early this weekend. Seas will generally build up to 2-4 ft across nearshore waters and up to 4-6 ft in offshore Georgia waters, resulting in the continuation of a Small Craft Advisory across offshore Georgia waters until early Friday afternoon. South/southeast winds should remain around 15 kt or less into early Saturday, before turning more south/southwest and increasing up to 15-20 kt Saturday afternoon into Sunday until a cold front pushes offshore by early Sunday night. Conditions should then improve and remain below Small Craft Advisory levels Monday and Tuesday as high pressure builds across the area early next week. Rip Currents...Increased swell, persistent onshore winds and enhanced astronomical influences with the approaching new moon will result in a Moderate Risk of rip currents at all of our beaches through Friday. && .CLIMATE... Record high min temps for May 4: KCHS: 70/1990 KCXM: 73/last set in 1990 KSAV: 70/last set in 1984 Record high min temps for May 5: KCHS: 70/last set in 1996 KCXM: 73/last set in 2012 KSAV: 70/last set in 2012 && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for AMZ374. && $$ NEAR TERM...NED SHORT TERM...DPB LONG TERM...DPB AVIATION...NED MARINE...DPB CLIMATE...