Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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258 FXUS62 KCHS 181949 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 349 PM EDT Tue Jun 18 2024 .SYNOPSIS... High pressure will extend across the region this week. A trough of low pressure will impact the Southeast U.S coast Thursday into Friday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... This Evening: Aloft, a large ridge will remain centered across the Mid-Atlantic and Southeast United States. At the sfc, high pressure centered across the western Atlantic off the Mid-Atlantic and Northeast Coast will extend southwest across the local area. The pattern will favor large scale subsidence across the region and with drier air depicted on water vapor imagery offshore, should suppress/limit convection. However, an easterly sfc wind along the southern edge of the sfc high centered north of the region will help drive low-lvl moisture onshore and should support few to perhaps scattered showers into evening hours. An isolated thunderstorm can not be ruled out as well until sunset. Overnight, little to no change in the pattern is expected aloft or near the sfc with high pressure dominating the pattern. Expect any shower or thunderstorm to wane or diminishing within an hour or so of sunset, with most areas remaining rain-free through the night. The only exception could be along the coast of southeast Georgia, where onshore flow maintains sufficient moisture for a light shower or two near daybreak. Although winds will diminish inland by late evening, gusty conditions could persist along the immediate coast. The pattern will support a fairly large range in temps late, with lows expected to dip into the mid-upper 60s inland to mid 70s near the beaches. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... Wednesday and Thursday: The southern flanks of the expansive upper level anticyclone centered over the eastern United States will begin to buckle just a bit as a well defined TUTT located north of the Greater Antilles approaches the Southeast U.S. coast. The operational GFS is has finally come in line with the rest of the global guidance in keep any surface reflection of the TUTT as an open tropical wave/inverted trough as it moves onshore late Thursday night into the day Friday. Given a modest northeast low-level flow is expected to continue ahead of the approaching tropical wave, steering trajectories favor coastal Georgia for the best chances for measurable rainfall. Still not seeing a strong QPF signal in the various guidance for any concentrated areas of showers given the development of deep convection seems unlikely with the degree of subsidence noted aloft, but isolated to scattered low-topped showers with a few tstms appear likely. Pops 20-40% were maintained for mainly the coastal counties, highest along the Georgia coast. Highs will warm into the upper 80s/lower 90s away from the coast both days with lows Thursday morning dropping into mid-upper 60s well inland to the mid-upper 70s at the beaches. Breezy to locally windy conditions will also persist along the immediate coast and beaches. Thursday Night and Friday: Rain chances will begin to ramp up late Thursday Night and especially Friday as the approaching tropical waves moves onshore. Shower coverage may lessen a bit Thursday evening as subsidence ahead of the tropical wave spread in from the east, but this will rapidly change as daybreak approaches Friday and the primary wave axis pushes inland. The wave will be accompanied by a ribbon of PWATS in excess of 2 inches. This coupled with some forcing with the weakening TUTT aloft and the convergent/east side of the westward propagating surface wave should be enough to support scattered if not numerous showers with a few tstms. Pops were trended up a bit to 40-60% (highest coast), but given the TUTT will likely be rapidly dampening as it approaches the expansive upper- level anticyclone, there is some hesitancy to go any higher with pops at this time. Further adjustments will likely be needed. Lows Thursday night will drop into the mid-upper 60s well inland to the mid-upper 70s at the beaches. Highs Friday will range from the upper 80s/lower 90s away from the coast with cooler conditions at the beaches. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... The tropical wave and associated TUTT aloft will quickly dissipate over the weekend with the region positioned along the eastern flanks of the large subtropical anticyclone. Despite the dissipation of the TUTT, a broad weakness looks to remain through early next week. This coupled with sea breeze influences and lingering deep-layered moisture featuring PWATS in excess of 2 inches will support scattered showers/tstms each day. The heat will also begin to build through the weekend and especially Monday with highs warming into lower-mid 90s Saturday with the mid-upper 90s into early next week. The warmest day looks to occur Monday where a few spots far inland could make a run for 100 before the onset of showers/tstms. Dewpoints do not look to really mix out during this period with heat indices expected to peak 100-103 Saturday, 102-105 Sunday and 105- 110 Monday, highest across the inland portions of the coastal counties. Heat Advisories could be needed at some point with Monday being the best day for reaching the Heat Advisory criteria of 108. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Prevailing VFR conditions are expected at CHS/JZI/SAV terminals through 18Z Wednesday. However, brief showers and therefore brief MVFR conditions could impact the SAV terminal this afternoon, then again late morning into early afternoon Wednesday. Otherwise, expect gusty east winds at all terminals this afternoon (20-23 kt), then again at a similar speed late morning into the afternoon Wednesday. Extended Aviation Outlook: Brief flight restrictions are possible in afternoon showers/thunderstorms Wednesday and Thursday, especially at KSAV. Chances of flight restrictions increase at KCHS/KJZI/KSAV terminals Friday and Saturday with lesser chances Sunday. && .MARINE... Tonight: A large and strong ridge of high pressure will encompass the coastal waters, with a subtle inverted trough to form nearby. The pattern will favor an enhanced pressure gradient across local waters through the night, with easterly winds gusting upwards to 20- 25 kt. Favorable long duration onshore fetch will also allow seas to build across local waters, eventually peaking between 4-6 ft across nearshore waters and 5-7 ft across offshore Georgia waters. Small Craft Advisories will therefore be in effect for all local waters outside the CHS Harbor tonight, but a brief lull in winds is possible this evening before 6 ft seas arrive across nearshore waters around midnight. Wednesday through Saturday: Gusty northeast winds will persist into Friday as a tropical waves approaches from the east and a modest gradient persists over the coastal waters. Northeast winds will average 15-20 kt with gusts to 25 kt during this time. Seas will remain above 6 ft through Thursday night within 20 NM and into Friday evening for the waters 20-60 NM offshore. Small Craft Advisories are in effect for these waters. Seas look to peak 5-6 nearshore waters and 6-8 ft in the offshore waters, mainly on Thursday. Winds in the Charleston Harbor will be near advisory thresholds, but are expected to hold just sky. The need for an advisory there will be reevaluated Wednesday morning. Both winds and seas will begin to diminish Friday night into Monday. Rip Currents/High Surf: Tybee Island Ocean Rescue is flying double red flags at all Tybee Island beaches where a number of very strong, dangerous rip currents have been observed. The waters have been closed here as a result. Expect the risk for strong and dangerous rip currents to spread into all beaches Wednesday which will persist into Thursday. A high risk for rip currents is being highlighted for all beaches for both days. NWPS breaking wave guidance shows breakers reaching 3-5 ft along the beaches on Wednesday and Thursday, highest in the Folly Beach area. Given only spotty instances of 5 ft breakers are being depicted, the situation for Wednesday looks to marginal for a High Surf Advisory at this time. && .TIDES/COASTAL FLOODING... Surface high pressure will remain off the coast of New England with a tight pressure gradient and elevated winds across the South Carolina and Georgia coast. A full moon on 6/22 will also cause the astronomical tides to slowly build. There is a chance that minor coastal flood stage could be reach on the Wednesday and Thursday evening high tides for Charleston Harbor. Tides at Fort Pulaski are forecast to remain below minor flood stage. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...High Risk for Rip Currents through Wednesday evening for GAZ117-119- 139-141. SC...High Risk for Rip Currents from Wednesday morning through Wednesday evening for SCZ048>051. MARINE...Small Craft Advisory until 6 AM EDT Friday for AMZ350-352-354. Small Craft Advisory until 11 PM EDT Friday for AMZ374. && $$ NEAR TERM...DPB SHORT TERM...ST LONG TERM...ST AVIATION...DPB/ST MARINE...DPB/ST