990 FXUS62 KCHS 100133 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 933 PM EDT Tue Oct 9 2018 .SYNOPSIS... Hurricane Michael will move north across the Gulf of Mexico before making landfall along the Florida Panhandle Wednesday. Michael will then weaken to a tropical storm as it moves northeast across Georgia and South Carolina Wednesday night into Thursday. Cooler high pressure will then build in through early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... The band of light to moderate rains has finally made it into the Charleston metro area, with it's westward extent into areas of Dorchester to Jenkins, and it's southern extent to near the Savannah River. Further south across the bulk of Georgia, the rain is more scattered. We have adjusted PoP based on radar trends, and since we lapse rates are poor and there is only minimal instability, we have removed mention of thunder prior to midnight. We remain on track for possible record high minimums at all 3 Climate sites. Since we are just past high tide, given the ongoing rains in downtown Charleston could certainly complicate the flooding situation. Previous discussion... A single wide band of moderate to locally heavy rainfall has setup from Metter and Millen east to Beaufort. Vsbys have been as low as 1/4 mile in the heavy rain. Could see a quick 1-2 inches of rain with this band as it moves slowly north, likely reaching the Charleston Metro area by 10 PM or so. Adjusted near term pops to reflect 100% pops for in the Millen-Charleston- Savannah-Metter corridor. While low, there is a non-zero tornado risk along the Georgia and far southern South Carolina coast. GOES-E visible imagery shows a ribbon of tropical moisture arcing from Southeast Georgia to offshore of the eastern Bahamas into the central Caribbean Sea. RAP and satellite derived data suggest PWATS of 2.25-2.50 inches are embedded in this tropical connection and is helping to support several large bands of heavy rainfall from southern Georgia and offshore of the Florida east coast. The band will slowly propagate north through the night as Hurricane Michael moves north across the eastern Gulf of Mexico and several mid-level perturbations embedded in the southeast-northwest oriented flow between subtropical high pressure moving farther offshore of the North Carolina Outer Banks of Hurricane Michael cross the area. Southeasterly low-level jetting as high as 35-40 kt will remain in lace through much of the night so any shower activity will have the potential of producing localized wind gusts of 40-50 mph. Otherwise, breezy conditions will continue at the beaches. Overnight pops will range from 70-100% along with a "rain heavy at times" qualifier. The risk for any freshwater flooding will be highest across the coastal counties, especially during the evening high tide. Widespread flash flooding is not expected through sunrise, thus a Flash Flood Watch will not be issued for this time period. It will be a warm and humid night for early October with lows ranging from the mid 70s inland to around 80 at the beaches. The record high minimum temperatures at all three climate sites could be challenged. See the climate section below for additional information on the records. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... On Wednesday the main feature will be the weak inverted trough off to the northeast of Hurricane Michael. The center of this trough will be along the SC/GA coastline at daybreak Wednesday, then move north-northeast through early afternoon. We expect numerous heavy showers with isolated tstms across the area during the morning with the greatest coverage and intensity over southern SC closer to the trough. Unseasonably high PWATs in excess of 2.1" will support torrential rainfall at times. During the afternoon the best convergence associated with the trough are is forecast to move north of the area though we then expect some outer rain bands from Michael to start rotating through the area. A bit of a lull is possible Wednesday evening, then the rain shield associated with Michael is expected to move into interior southeast GA with some outer bands farther to the north and east. The brunt of the torrential rainfall associated with Michael's circulation will move through on Thursday with the greatest effects over our inland zones. Latest storm total QPF shows 2-4 inches across coastal sections and 3-5" inland. The strongest winds will begin in southeast GA late Wed night and affect most of southern SC during the day Thursday. An enhanced tornado threat appears likely from Wednesday afternoon through at least Thursday morning based on model progs for low-level helicity and surface-based instability. Slightly cooler and drier weather expected late Thursday night into Friday. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Late this week, surface high pressure will build back into the region behind departing TC Michael. Precipitation potential is looking rather low Friday and Saturday as a dry column sits overhead, then rain chances will increase with increasing moisture levels ahead of an approaching cold front Sunday into the first part of next week. Temperatures look to remain above normal. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... A band of moderate to heavy rain will move north into the KCHS terminal by late evening and persist through about 07z. Expect vsbys as low as 1/2 mile at times with this line, but vsbys should generally average 2-3SM. Other banks are likely to develop overnight and impact both KCHS and KSAV. High resolution guidance supports such a line reaching KSAV 07z and lingering through about 10z. Again, prevailing vsbys should be MVFR and as low as 2SM at times. Rain should move out the terminals by 10z and expect mainly dry conditions to prevail for the remainder of the 00z TAF period. Steadier rains associated with Michael should hold off until after 00z, although it will be close at KSAV. Gusty winds will persist through the night and increase a bit Wednesday afternoon. Extended Aviation Outlook: MVFR or lower conditions likely at both terminals Wednesday afternoon through Thursday night as Hurricane Michael moves west of the area. The greatest chance for IFR ceilings and/or vsbys will be late Wednesday night through Thursday afternoon due to moderate to heavy rain. && .MARINE... Tonight: Nasty marine conditions will continue across all waters tonight with winds 20-25 kt with gusts to 30 kt. Shower activity will be capable of producing localized wind gusts to 40-45 kt. Seas will build through the night, reaching 5-8 ft nearshore waters and 9-11 ft offshore waters. Wednesday through Saturday: The impacts of Hurricane Michael are obviously the main concern with this package. Marine conditions will become increasingly treacherous during the day Wednesday with the strongest winds and largest seas Wednesday night into Thursday. Improving conditions Thursday night into the weekend as high pressure builds in. Rip Currents: A high risk for rip currents continues into Wednesday due to persistent, strong onshore wind, some swell and astronomical influences. The rip current risk will remain elevated through the week. && .TIDES/COASTAL FLOODING... Coastal Flooding: The decision was made locally to issue a long-duration Coastal Flood Advisory for all coastal zones, excluding Tidal Berkeley, to cover all high tides through the duration of Michael. Minor to locally moderate coastal flooding is expected through the period. At this time, levels are not expected to reach Coastal Flood Warning criteria for either Fort Pulaski or Charleston Harbor with average inundations above ground level expected to stay 2 feet or less. This will be watched carefully and warnings will be issued if needed. High Surf: Expect breakers of 5 to 8 feet to impact the surf zone before winds turn offshore in the wake of Michael. A High Surf Advisory has been posted for all beaches. && .CLIMATE... Record high minimums for 9 October: KCXM: 77/2017. Record high minimums for 10 October: KCHS: 75/2017. KCXM: 78/2017 and previous. KSAV: 75/2017. Rainfall record for 10 October: KCHS: 1.82/1990. KCXM: 2.13/1990. KSAV: 5.68/1990. Rainfall record for 11 October: KCHS: 4.48/1990. KCXM: 5.46/1990. KSAV: 4.43/1885. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Tropical Storm Warning for GAZ087-088-099>101-114>119-137>141. High Rip Current Risk through Wednesday evening for GAZ117-119- 139-141. High Surf Advisory until 8 PM EDT Thursday for GAZ117-119-139- 141. Coastal Flood Advisory until 2 PM EDT Thursday for GAZ117-119- 139-141. SC...Tropical Storm Warning for SCZ040-042>045-047>052. High Rip Current Risk through Wednesday evening for SCZ048>051. High Surf Advisory until 8 PM EDT Thursday for SCZ048>051. Coastal Flood Advisory until 2 PM EDT Thursday for SCZ048>051. MARINE...Tropical Storm Warning for AMZ330-350-352-354-374. && $$ NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE... TIDES/COASTAL FLOODING... CLIMATE...