Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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478 FXUS62 KCHS 180451 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1251 AM EDT Tue Jun 18 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 THIS MORNING/... High amplitude upper level ridge is planted along much of the East Coast with the center of high pressure over the Mid Atlantic. Surface high pressure is off the coast with ridging down through the southeast but a very subtle inverted surface trough off the southeast coast. Quiet weather prevails although with just a hint of showers trying to develop in the coastal waters within the prevailing easterly flow and very modest instability over the warm Atlantic waters. Pattern remains largely unchanged overnight. High res guidance continues to suggest further shower development in the coastal waters that try to sneak into coastal areas, particularly south of Beaufort. Low end precip chances were maintained in those areas overnight. Clear to partly cloudy skies and lighter winds will yield low temps in the mid-upper 60s inland to low-mid 70s near the coast. && .SHORT TERM /6 AM THIS 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 /06Z TUESDAY THROUGH SATURDAY/... Prevailing VFR conditions are expected at CHS/JZI/SAV terminals through 06Z Wednesday. However, brief MVFR ceilings are possible early this upcoming morning with onshore flow off the Atlantic, particularly at the SAV terminal. Confidence remains too low to include in the latest forecasts. The risk for any showers, especially at KSAV in the afternoon, is too low to justify any mention at this time. Otherwise, another round of gusty east winds peaking at least near 20 or 25 kt are anticipated at the terminals from about 15-16Z through sunset. Extended Aviation Outlook: Brief flight restrictions are possible in afternoon showers/thunderstorms with the best chances occurring at KSAV and KJZI. && .MARINE... Overnight: 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 around 15 kt with gusts to around 20 kt at times. Seas will also slowly build during the period due to a prolonged onshore fetch. In general, seas will build to 3-4 ft across nearshore waters and 4-5 ft across offshore Georgia waters. 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 8 AM EDT this morning through this evening for GAZ117-119-139-141. SC...None. MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT Saturday for AMZ374. && $$ NEAR TERM... SHORT TERM...ST LONG TERM...ST AVIATION... MARINE...