Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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268 FXUS62 KCHS 172344 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 744 PM EDT Mon Jun 17 2024 .SYNOPSIS... High pressure will extend across the region through early next week. A tough of low pressure could approach the Southeast U.S coast by late this week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Early evening update: Inland convection has fizzled/moved inland. There are spotty showers in the coastal waters with some additional development anticipated tonight into Tuesday morning, particularly from Beaufort south. Just cosmetic tweaks made to the going forecast through tonight. Previous discussion... Tonight: Aloft a large ridge will remain centered across the Southeast and Mid-Atlantic states, favoring large scale subsidence across the local area. At the sfc, high pressure centered across the western Atlantic off the Mid- Atlantic and Northeast Coast extends south across the local area, providing an onshore flow throughout the evening and overnight period. Despite onshore flow, dry air depicted on water vapor imagery favors rain-free conditions across coastal areas and much of southeast South Carolina. However, a few showers (and perhaps a thunderstorm) could occur during the next few hours well inland, mainly across southeast Georgia where adequate moisture and SBCAPE between 1500-2000 J/kg reside. Subsidence aloft will limit the strength of convection across the noted area, but a few showers (or perhaps a thunderstorm) could produce gusty winds given low-lvl lapse rates around 7.5 to 8 C/km and DCAPE around 1000 J/kg. The window of opportunity should come to an end within an hour or two before sunset, as activity drifts further west. Conditions will remain quiet overnight while high pressure dominates the pattern near the sfc and aloft. Sfc dewpts will also generally range in the 60s tonight, and with winds weakening and partly cloudy to mostly clear skies in place, should yield slightly cooler min temps, generally in the mid-upper 60s inland to low-mid 70s near the coast. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/... A strong subtropical anticyclone will dominate the upper flow aloft over the eastern U.S. with local heights averaging 5920-5940 dam. At the surface, Atlantic high pressure centered offshore of the Mid- Atlantic states will prevail. A weak coastal trough is forecast to sharpen a bit just offshore by Tuesday and linger near the Northeast Florida, Georgia and far southern South Carolina coasts through late week. Although model soundings do show broad subsidence dominating aloft, a modest onshore flow and weak convergence in the vicinity of both the sea breeze and coastal trough will likely support isolated to scattered showers for mainly the coastal areas through the period. The greatest coverage looks to focus along the Georgia coast where some weak 850 hPa moisture transport and theta-e advection will occur, but even these fields are not overly strong. Pops were capped 20-40% as model QPF signals are not all that impressive suggesting deep convection will likely struggle given the degree of subsidence noted. Any mention of thunder was limited to slight chance. Highs each day will warm into the upper 80s to lower 90s away from the beaches with overnight lows ranging from the upper 60s well inland to the mid-upper 70s at the beaches. Breezy to locally windy conditions will occur at the immediate coast and beaches through the period. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... A well-defined TUTT located north of the Greater Antilles is forecast to meander closer to the Southeast U.S. coast later this week as Atlantic high pressure holds off the Mid-Atlantic coast. The operational GFS continues to be the most robust in developing a well- defined surface cyclone within the TUTT as it propagates to the west, but most of the guidance keeps any surface reflection as more of an open wave/inverted trough as it nears the coast. Overall confidence on how this scenario will unfold remains rather low, so further adjustments will likely be needed as trends become more apparent. For now, pops were limited to the chance category along the coastal counties with the highest probabilities centered along the Georgia coast. A broad upper trough will begin to dig across the Southeast U.S. Sunday as a cold front approaches from the northwest. As any surface reflection moves north in latitude, the heat will begin to build. Highs Friday will warm into the lower-mid 90s then increase to the mid-upper 90s Saturday and Sunday. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Prevailing VFR conditions are expected at CHS/JZI/SAV terminals through 00Z Wednesday. However, brief MVFR cigs are possible late tonight/early Tuesday with onshore flow off the Atlantic, particularly at the SAV terminal. Confidence remains too low to include in the latest forecasts. Otherwise, winds will further weaken tonight. But another round of gusty east winds (13-18 kt) is anticipated at the terminals Tuesday starting mid to late morning and persisting through the afternoon. Extended Aviation Outlook: Brief flight restrictions are possible in afternoon showers/thunderstorms with the best chances occurring at KSAV and KJZI. && .MARINE... Tonight: High pressure will remain the dominant weather feature, extending across the region from the north and enhancing the pressure gradient across local waters. The gradient along with some nocturnal low-lvl jetting will favor easterly winds between 10-15 kt with gusts to around 20 kt at times overnight. Seas will also slowly build during the period due to a prolonged onshore fetch. In general, seas should build to 3-4 ft across nearshore waters and 4-5 ft across offshore Georgia waters overnight. Tuesday through Friday: Solid northeast winds 15-20 kt will persist through much of the period. The gradient may tighten a bit as a trough of low pressure approaches late in the week. Seas will build due to a combination of increasing swell and continued breezy northeast winds. Seas will reach 6 ft in the Georgia offshore waters by early Tuesday evening, so a Small Craft Advisory has been issued for those waters through Friday. Seas 6 ft or greater will reach all nearshore legs by Wednesday and the advisory will likely need to be expanded into those waters overnight. Seas look to peak 5-7 ft across all waters Wednesday night into Friday morning. Rip Currents/High Surf: A Moderate Risk for rip currents will continue along all beaches into this evening. Many strong rip currents have been reported at Tybee Island today and with both winds and waves expected to increase a bit more on Tuesday and Wednesday, a High Risk has been advertised for both days for the Georgia beaches consistent with the latest rip current MOS. For the South Carolina beaches, local rip current calculators support a high-end moderate risk both days, but this may need to be upgraded to a high risk later, especially Wednesday. Breaking waves could reach 5 ft or greater Wednesday night into Thursday, especially along the Charleston County coast into Edisto Beach. A High Surf Advisory may be needed. && .TIDES/COASTAL FLOODING... Tides in the Charleston Harbor could reach minor flood levels with the evening high tides both Wednesday and Thursday. Coastal Flood Advisories could be needed for Charleston and Colleton Counties. Tides at Fort Pulaski look to hold below minor flood levels for now. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...High Risk for Rip Currents from Tuesday morning through Tuesday evening for GAZ117-119-139-141. SC...None. MARINE...Small Craft Advisory from 6 PM Tuesday to 6 AM EDT Saturday for AMZ374. && $$ NEAR TERM...Adam/DPB SHORT TERM...ST LONG TERM...ST AVIATION...Adam/ST MARINE...DPB/ST