112  
FXUS62 KCHS 211113  
AFDCHS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHARLESTON SC  
713 AM EDT THU SEP 21 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL PREVAIL THROUGH THIS WEEKEND. THE HIGH WILL  
WEAKEN AND SHIFT INLAND AS HURRICANE MARIA TRACKS NORTHWARD OFF  
THE SOUTHEAST U.S. COAST THROUGH THE FIRST HALF OF NEXT WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
TODAY: A VERY WEAK SURFACE PRESSURE PATTERN WILL PERSIST ACROSS  
THE FORECAST AREA. AN UPPER LEVEL TROUGH AXIS EXTENDS THROUGH  
GA AND THE CAROLINAS WHILE PWATS LOOK TO BE MORE ELEVATED ACROSS  
OUR GA ZONES NEARING CONVECTIVE INITIATION THIS AFTERNOON. THE  
00Z NAM BEARS THIS OUT WITH A NARROW SLOT OF DRIER 850-500 MB  
RHS NORTH OF I-16 INTO SOUTHEAST SC DURING THE AFTERNOON HOURS.  
WITH LOW-LEVEL CONVERGENCE AGAIN QUITE WEAK DURING THE SEA  
BREEZE OSCILLATION PERIOD, WE HAVE MINIMAL POPS BUT DID MAINTAIN  
LOW-END CHANCE POPS IN OUR COASTAL HALF/SOUTHERN ZONES OF  
SOUTHEAST GA. ISOLATED SHOWERS AND TSTMS POSSIBLE ALONG THE SC  
SEA BREEZE. IT WILL BE ANOTHER WARM DAY WITH HIGHS JUST A DEGREE  
OR TWO WEDNESDAY'S HIGHS.  
 
TONIGHT: A FEW OF THE HIGH RESOLUTION MODELS SUGGEST ISOLATED  
EVENING CONVECTION COULD LINGER ALONG A SAGGING MID LEVEL  
TROUGH AXIS ACROSS OUR FAR NORTHERN ZONES AROUND THE SANTEE  
COOPER LAKES. WITH THE LOSS OF DIURNAL HEATING AND WARM MID  
LEVEL TEMPS, WE ONLY HUNG ONTO 20 POPS PRIOR TO MIDNIGHT WHILE  
SUSPECTING MODELS COULD BE OVERDONE. WE ALSO OPTED FOR PATCHY  
FOG MENTIONS ACROSS NORTHWEST ZONES LATE TONIGHT WHERE VARIOUS  
GUIDANCE PROGS SUGGEST THE HIGHER CHANCES.  
 

 
   
SHORT TERM /FRIDAY THROUGH SUNDAY/
 
 
WEAK UPPER TROUGHING AND SOME INCREASED MOISTURE WILL PERSIST  
ACROSS THE AREA FRIDAY INTO SATURDAY AND THIS ALONG WITH A  
FAIRLY WEAK SEA BREEZE WILL SUPPORT A FEW SHOWERS AND  
THUNDERSTORMS, MAINLY IN THE AFTERNOON ON FRIDAY AND JUST IN GA  
ON SATURDAY. BUILDING HIGH PRESSURE FROM THE NORTH LATER  
SATURDAY AND SUNDAY SHOULD KEEP THINGS DRY THIS PERIOD.  
TEMPERATURES WILL STAY ABOVE NORMAL, GENERALLY UPPER 80S DURING  
THE DAY AND AROUND 70 AT NIGHT.  
 

 
   
LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/
 
 
INLAND HIGH PRESSURE WILL PERSIST THROUGH EARLY NEXT WEEK WHILE  
CONFIDENCE IS INCREASING THAT HURRICANE MARIA WILL REMAIN OFFSHORE  
OF THE SOUTHEAST U.S. COAST AS IT TRACKS NORTH THROUGH THE MIDDLE OF  
NEXT WEEK. SOME SHOWERS COULD SKIRT COASTAL AREAS EARLY NEXT WEEK AS  
MARIA PASSES BY BUT OTHERWISE MAINLY DRY CONDITIONS ARE ANTICIPATED.  
TEMPERATURES LOOK TO STAY ABOVE NORMAL.  
 

 
   
AVIATION /12Z THURSDAY THROUGH MONDAY/
 
 
MAINLY SHALLOW GROUND FOG ALONG THE COASTAL CORRIDOR EARLY THIS  
MORNING, MOST NOTICEABLE AT KCHS. OTHERWISE, CONDITIONS WILL BE  
VFR TODAY AND INTO TONIGHT. CHANCES FOR CONVECTION AT THE  
TERMINALS STILL LOOKS LOW-END AT MID AFTERNOON ALONG THE SEA  
BREEZE. THE POTENTIAL FOR FOG EXISTS AGAIN LATE TONIGHT, MAINLY  
AFTER 06Z THROUGH DAYBREAK ON FRIDAY.  
 
EXTENDED AVIATION OUTLOOK: LOW PROBABILITY FOR BRIEF FLIGHT  
RESTRICTIONS IN EARLY MORNING FOG AND/OR LOW CLOUDS SATURDAY MORNING  
AND IN MAINLY AFTERNOON SHOWERS/THUNDERSTORMS FRIDAY AT KCHS/KSAV  
AND AT KSAV SATURDAY.  
 

 
   
MARINE
 
 
THROUGH TONIGHT, RELATIVELY TRANQUIL CONDITIONS WITH WINDS VARIABLE  
AT TIMES AS HIGH PRESSURE TO THE NORTH EVENTUALLY TURNING SYNOPTIC  
FLOW ONSHORE BY EARLY FRIDAY. WIND SPEEDS WILL BE BELOW 15 KT  
WITH SEAS 2-3 FT, MAINLY IN LONG PERIOD SWELL.  
 
THURSDAY THROUGH MONDAY: NO SIGNIFICANT CONCERNS BEFORE SWELLS FROM  
HURRICANE MARIA NEARING THE SOUTHEAST BAHAMAS LATER THIS WEEK BEGIN  
TO IMPACT THE WATERS THURSDAY NIGHT OR FRIDAY. ADVISORIES WILL BE  
LIKELY FOR THE OFFSHORE WATERS STARTING FRIDAY AND THE NEARSHORE  
WATERS STARTING FRIDAY NIGHT. SEAS COULD BUILD TO 10 FEET OR MORE  
NEAR THE GULF STREAM SATURDAY NIGHT AND PERSIST IN MONDAY, ALTHOUGH  
MUCH DEPENDS ON THE EXACT TRACK/STRENGTH OF HURRICANE MARIA.  
 
RIP CURRENTS: ASTRONOMICAL INFLUENCES AND A LINGERING LONG  
PERIOD GROUND SWELL COMPONENT WILL SUPPORT A LOW-END MODERATE  
RIP CURRENT RISK AT AREA BEACHES TODAY. SWELL FROM OFFSHORE  
HURRICANE MARIA WILL CREATE MORE SIGNIFICANT RIP CURRENT RISKS  
THIS WEEKEND INTO THE MIDDLE OF NEXT WEEK.  
 

 
   
TIDES/COASTAL FLOODING
 
 
ON THIS MORNING'S HIGH TIDE CYCLE, SOME SHALLOW COASTAL FLOODING  
IS POSSIBLE AROUND DOWNTOWN CHARLESTON BUT FOR NOW, WE HAVE  
HELD OFF ON A COASTAL FLOOD ADVISORY FOR LEVELS REACHING VERY  
CLOSE TO 7.0 FEET MLLW.  
 
POWERFUL SURF CREATED BY OFFSHORE HURRICANE MARIA WILL DRIVE  
SIGNIFICANT WAVE RUN-UP, WHICH COULD CAUSE FURTHER BEACH EROSION  
THIS WEEKEND INTO EARLY NEXT WEEK. ALSO, THE POTENTIAL FOR  
SHALLOW SALT WATER FLOODING WILL PERSIST THROUGH EARLY NEXT WEEK  
AROUND THE TIMES OF HIGH TIDE, PARTICULARLY ALONG THE SC COAST.  
 

 
   
CHS WATCHES/WARNINGS/ADVISORIES
 
 
GA...NONE.  
SC...NONE.  
MARINE...NONE.  
 

 
 

 
NEAR TERM...  
SHORT TERM...RJB  
LONG TERM...RJB  
AVIATION...  
MARINE...RJB  
TIDES/COASTAL FLOODING...  
 
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