Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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815 FXUS62 KCHS 012235 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 635 PM EDT Mon Jul 1 2024 .SYNOPSIS... A cold front will impact the area tonight into early Tuesday before dissipating offshore. A hot and humid air mass will build over the region during the latter half of the week. By Monday, a weak cold front may reach coastal Georgia and South Carolina. && .NEAR TERM /THROUGH TUESDAY/... A quick forecast update to remove Berkeley and Dorchester Counties from the Flood Watch. In addition, based on radar trends and latest runs of the HRRR, hourly PoPs and Wx were adjusted to reflect the timing of the front and outflow boundaries. Temperatures were also aligned with recent observations. Impressive deep-layer moisture and moderate mixed-layer instability are in place along/south of the front. As surface moisture convergence increases and the front begins to zipper line down the weak sea breeze noted along the coast, expect showers/tstms to expand in coverage with an increase in rainfall rates. With PWATs nearing 2.50 at times, hourly rainfall rates near 3 in/hr look reasonable. Earlier this afternoon, showers/tstms produced about 2 inches of rain in less than 50 min at an unofficial mesonet site near Awendaw, SC. Storm totals of 2-4 inches with localized amounts in excess of 6 inches look on track. A Flood Watch remains in effect until 9 PM EDT. The near term flash flood threat looks to concentrate into two areas. The first being across eastern Berkeley and upper Charleston counties south into the Charleston Metro Area (including Downtown Charleston) where the latest WoFS Ens 90th% of Accumulated Precip product shows pockets of 5-6". Complicating things is heavy rain could falling as the 5 pm high tide approaches. The second being near the Savannah Metro area where convection developing near the city and working in from the south could merge. Trends are being closely monitored in both areas and Flood Advisories and/or Flash Flood Warnings could eventually be needed. Convection will wane this evening, but there are signals that ana area of renewed convection could fire after midnight along parts of the upper Georgia and far southern South Carolina coast near the southward moving front. This scenario is well supported by a number of the 01/12z CAMs. This activity could pose a risk for additional flooding. Lows tonight will range from around 70 well inland to the upper 70s and the beaches. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... Tuesday: The surface pattern is expected to feature a stalled boundary across SE GA with drier high pressure ridging across the SC Lowcountry. The environment along and south of the front should continue to feature deep instability and PW. The forecast will feature scattered to numerous showers and thunderstorms along and south of the front, keeping portions of inland SC dry. Using a blend of MOS, high temperatures are forecast to range in the mid to upper 80s. Wednesday: Short term guidance indicates that a 595 dm ridge will build over the Deep South and Southeast CONUS. At the sfc, the center of high pressure will remain off the NE and middle Atlantic states, resulting in ENE flow across the forecast area. This pattern will support a sea breeze to develop, serving as a focus for deep convection. Given the wide field of instability, scattered to numerous showers and thunderstorms are forecast to develop along the sea breeze. High temperatures are forecast to range around 90 degrees. A few counties across extreme SE GA may see heat index values peak between 100-105 degrees. Independence Day: Mid-level ridge will build over the forecast area on Thursday. Given high pressure over the western Atlantic, a sea breeze may develop during the afternoon. However, GFS forecast soundings indicate drier conditions compared to the first half of the week. Forecast soundings indicate PW around 1.5 inches with an inversion centered at H65. This profile indicates limited instability. The forecast will indicated isolated showers and thunderstorms. High temperatures are forecast to range between 90-95 degrees over dewpoints in the low to mid 70s. Heat index values are forecast to peak between 100-105 degrees. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Friday through Sunday, the feature of concern will remain the 595 dm ridge over the region. The forecast area under the strong ridge will feature high temperatures in the mid to upper 90s each day. In addition, dewpoints will climb in the mid to upper 70s. The max heat index will range between 105 to 113 each afternoon. This may result in either a Heat Advisory or a Excessive Heat Warning late this week into early next week. The forecast will indicate diurnal isolated to scattered showers and thunderstorms each day. On Monday, a weak front will approach from the west as the mid- level ridge shifts over the western Atlantic. Conditions across the forecast area will remain hot. However, storm coverage should increase, bringing some relief from the heat. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... 01/18z TAF Discussion: KCHS/KJZI/KSAV: Showers/tstms are expected to expand in area through the afternoon/evening as a cold front approaches. Prevailing tstms will be highlighted from 20-23z at KCHS and KJZI with TEMPO conditions as low as IFR at KCHS and LIFR at KJZI. For KSAV, impacts may be a bit later, closer to 23-02z. Amendments will be needed as convective trends become clearer. The front should move south of KCHS/KJZI by 00z and KSAV by 05z with VFR cigs filling in behind it. These will linger through the night. Extended Aviation Outlook: Brief flight restrictions are possible in showers and thunderstorms, mainly in the afternoon and evenings through the period. && .MARINE... Tonight: A cold front will work slowly south into the waters tonight. Winds will shift to the northeast behind the front with speeds reaching 15-20 kt in the South Santee-Edisto Beach nearshore leg late. Otherwise, winds speeds will remain 15 kt or less. Widespread showers/tstms could reduce vsbys to 1 NM or less at times. A few strong convective wind gusts in excess of 35 kt could also occur. Seas will average 2-4 ft. Tuesday through Saturday: Gusty ENE winds should develop across the nearshore SC waters on Tuesday. The region will remain between building high pressure and the front stalled to the south. Gusts are forecast to remain around 20 kts with 3-4 ft seas. Conditions are forecast to remain below Small Craft Advisory criteria through the rest of the week. A weak pressure gradient should support winds 15 knots or less and seas averaging 2-3 ft. && .CLIMATE... Daily Rainfall Records for July 1: KCHS: 2.66 set in 1948 KCXM: 1.64 set in 1966 KSAV: 2.76 set in 1871 && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Flood Watch until 9 PM EDT this evening for GAZ101-116>119- 137>141. SC...Flood Watch until 9 PM EDT this evening for SCZ042-043-047>052. MARINE...None. && $$ NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE...