618 FXUS62 KCHS 101817 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 217 PM EDT Wed Oct 10 2018 .SYNOPSIS... Hurricane Michael will move north through the Gulf of Mexico before making landfall along the Florida Panhandle this afternoon. Michael will then gradually weaken to a tropical storm as it moves northeast across Georgia and South Carolina tonight and Thursday. Cooler and drier high pressure will then build in through the weekend before a coastal trough and cold front affect the area bringing a return of some rain. && .NEAR TERM /THROUGH TONIGHT/... Early this afternoon: Regional radar imagery shows that a band of heavy rainfall setup across the Charleston Tri-County region and continued to feed inland into the Midlands. This band continues to shift toward the Santee River. Elsewhere, subsidence has largely won out and the visible satellite imagery shows plenty of clearing from around the Altamaha toward the Santee River. This area has seen isolated to scattered convection but little else. The main concern moving forward the arrival of the circulation around Michael and an environment supportive of some supercells and isolated tornadoes across portions of the forecast area. SRH values will be increasing into the 200-400 m^2/s^2 across southeast Georgia, with MLCAPE values of around 1500 J/kg. The Storm Prediction Center has increased the severe weather risk for today into the Enhanced category and it seems that a Tornado Watch will very likely be needed in the next few hours. Tonight: As poor as conditions will be today, they will steadily worsen tonight as Michael draws into closer proximity of the area. We anticipate tropical storm conditions will overspread the forecast zones from southwest to northeast, and depending on how quickly Michael diminishes in strength from a hurricane to a tropical storm, there is a low end probability that some hurricane force wind gusts might approach Candler, Jenkins, Sylvania and Allendale counties late. However, these odds are not high enough for a Hurricane Watch, so we continue with our Tropical Storm Warning. PWat will rise near 2.6 to 2.75 inches within a deep southerly flow as the tropical cyclone gets closer. This will allow for PoP to increase to as high as 70 to 100% probabilities by daybreak Thursday. We considered a Flash Flood Watch, but since the system is moving at a fairly steady northeast clip, we opted not to raise one at this time. There certainly could be Flash Flood Advisories issued, but the potential for any warnings seems low. The fast pace of the cyclone will lead to increased low level helicity and low level shear, with model guidance depicting a SIG TOR as high as 2 to 4 units and SHERBS3 near a unit of 1 that spreads in from southwest to northeast during the night. This will lead to a favorable environment for at least isolated tornadoes across the entire region. A Tornado Watch could become necessary. Elevated dew points within the warm southerly flow will prevent temps from getting any less than the mid or upper 70s, or about 15 to 20F above the normal low and close to normal daytime highs. In fact, record high minimums are in jeopardy at all 3 climate sites (See CLIMATE section below). && .SHORT TERM /THURSDAY THROUGH SATURDAY/... Based on the latest NHC forecast, weakening Tropical Storm Michael will be moving through the SC Midlands Thursday with the worst conditions across southeast SC/GA during this time. Several inches of rain for most places away from the GA coast and tropical storm force winds/isolated tornadoes everywhere are expected, beginning first in GA and then spreading into SC. Improving conditions are then expected Thursday night with diminishing winds and generally dry weather as Michael moves farther away. Long overdue cooler and drier conditions are then on tap Friday and Saturday as high pressure builds from the north. Temperatures should still remain at or above normal though through the period. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Late this week cooler and drier high pressure will build back into the region behind Michael. A weak coastal trough will then develop early next week ahead of a cold front which could move into the area as early as Monday night. Rain chances are not expected until early next week. Temperatures look to remain near to above normal levels. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... VFR conditions will likely continue through the afternoon, other than showers that could occasionally pass through KCHS. By this evening and into the overnight, conditions will deteriorate rapidly. Prevailing MVFR ceilings are expected at both sites, beginning roughly in the 08-10z time period and continuing through 18z Thursday. Showers and bands of very heavy rainfall will be possible, with at least TEMPO conditions of IFR visibilities. As the center of Hurricane Michael moves across interior Georgia and South Carolina, winds will pick up significantly, turning from southerly to more southwesterly with time. The TAF's feature wind speeds in the 25g35kt range, with higher gust possible within any showers or thunderstorms that pass through. Extended Aviation Outlook: Flight restrictions likely Thursday due to periods of moderate to heavy showers/tstms. Gusty winds expected Thursday as tropical cyclone Michael moves northeast to the west of the terminals. && .MARINE... Today and tonight: Dangerous marine conditions will impact the coastal waters, with tropical storm conditions to develop in response to Major Hurricane Michael that moves onshore of the western Florida panhandle this afternoon, and then into southern Georgia tonight, gradually diminishing in strength to a Tropical Storm late. The strongest winds and largest seas this period will occur tonight across the entire Atlantic waters and in Charleston Harbor. Mariners can expect isolated to scattered t-storms today and tonight, some of which will produce wind gusts of 40 or 45 kt. Plus there is an increased chance of at least isolated waterspouts given the favorable shear and helicity across the region, mainly late in the day and more so tonight. Thursday through Monday: Conditions will remain dangerous Thursday as Tropical Storm Michael moves northeast through the SC Midlands. Tropical storm force winds are expected during this time with wind gusts to near 50 kt and seas building to near 13 feet mainly off the Charleston County coast. Conditions will then improve late Thursday as the storm moves away and winds shift offshore. Cooler/drier high pressure will then build in from the north with some increase in winds/seas although likely staying below Advisory levels. A weak coastal trough should then develop early next week while a cold front approaches from the west, possibly arriving into the local area by the end of the period. Rip Currents: A high risk for rip currents continues today at all beaches due to persistent, strong onshore wind, some swell energy and astronomical influences. The rip current risk will remain elevated through at least Thursday or Friday. && .TIDES/COASTAL FLOODING... Coastal Flooding: Since the high tide last evening, levels have been running as much as 1.0 to 1.5 ft MLLW above predicted, and a similar trend will continue today and tonight, with even larger departures possible Thursday. As a result, we anticipate at least minor to moderate flooding will occur with the next three high tide cycles in Charleston, and at least minor flooding at Fort Pulaski during at least 2 or 3 of those high tides (including this morning). The actual high tide will likely occur around 30 minutes after the astronomical high tide, which will lead to the largest departures at that time. A Coastal Flood Advisory remains in effect for all but Tidal Berkeley at this time for the high tides today and this evening. There is however an increasing chance that we might require a Coastal Flood Watch and/or Warning for the South Carolina coast with the late morning high tide Thursday (for 8.0 ft MLLW or greater) and also the need for a Coastal Flood Advisory for Tidal Berkeley. These conditions will be considered at a later time. In addition, areas of erosion will occur due to strong onshore winds and elevated tide levels. High Surf: There will continue to be large breaking waves impacting the entire stretch of beaches today through Thursday, reaching as large as 5 to 8 ft, highest during Thursday with TC Michael at its closest approach. A High Surf Advisory will therefore remain in effect. && .CLIMATE... 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. && .EQUIPMENT... The KCLX radar will continue to be down through approximately 4 pm due to emergency repairs. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Tropical Storm Warning for GAZ087-088-099>101-114>119-137>141. High Risk for Rip Currents until 8 PM EDT this evening for GAZ117- 119-139-141. High Surf Advisory until 4 AM EDT Friday 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 Risk for Rip Currents until 8 PM EDT this evening for SCZ048>051. High Surf Advisory until 4 AM EDT Friday 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...BSH/33 SHORT TERM...RJB LONG TERM...RJB AVIATION...BSH/RJB MARINE...33/RJB TIDES/COASTAL FLOODING... CLIMATE... EQUIPMENT...