000 FXUS62 KCHS 081125 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 625 AM EST SUN NOV 8 2009 .SYNOPSIS... HIGH PRESSURE WILL REMAIN THE DOMINANT WEATHER FEATURE THROUGH TONIGHT. THE COMBINATION OF HURRICANE IDA...OR ITS REMNANTS... LIFTING NORTHWARD THROUGH THE GULF OF MEXICO AND A COLD FRONT APPROACHING FROM THE NORTHWEST WILL RESULT IN UNSETTLED CONDITIONS DURING THE EARLY TO MIDDLE PART OF THIS WEEK. HIGH PRESSURE WILL THEN BUILD BACK INTO THE REGION BY THURSDAY AND REMAIN THE DOMINANT WEATHER FEATURE THROUGH THE FIRST PART OF NEXT WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL PREVAIL OVER THE SOUTHEASTERN UNITED STATES TODAY...WHILE EXPANSIVE HIGH PRESSURE AT THE SURFACE REMAINS OVER THE WESTERN ATLANTIC. GIVEN HIGH PRESSURE AT THE SURFACE AND ALOFT...STRONG SUBSIDENCE WILL BE IN PLACE TODAY. THE ONSHORE FLOW WILL ALLOW FOR A SLIGHT INCREASE IN LOW LEVEL MOISTURE...WHICH MAY SUPPORT THE DEVELOPMENT OF A FEW CUMULUS CLOUDS THIS AFTERNOON. THIN CIRRUS MAY ALSO BEGIN TO INCREASE FROM THE SOUTH DURING THE DAY. HOWEVER...SKIES WILL GENERALLY REMAIN SUNNY OR MOSTLY SUNNY ACROSS THE AREA. THE STRONG RIDGING ALOFT WILL RESULT IN ABOVE NORMAL TEMPERATURES TODAY...WITH LOW LEVEL THICKNESS VALUES SUPPORTING HIGHS OF 76 OR 77. AREAS ALONG THE IMMEDIATE COAST WILL BE SIGNIFICANTLY COOLER...AROUND 70...DUE TO THE ONSHORE FLOW. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... HURRICANE IDA IS FORECAST TO TRACK NORTH ACROSS THE CENTRAL GULF OF MEXICO BY THE NATIONAL HURRICANE CENTER...WHILE STRONG HIGH PRESSURE REMAINS IN PLACE NORTH OF THE REGION. THE SURFACE PRESSURE GRADIENT BETWEEN THESE TWO SYSTEMS WILL BEGIN TO TIGHTEN OVER THE REGION TONIGHT...PREVENTING WINDS FROM DECOUPLING ACROSS COASTAL AREAS. CIRRUS SHOULD BEGIN TO INCREASE/THICKEN FROM THE SOUTH TONIGHT...WHILE THE PERSISTENT LOW LEVEL ONSHORE FLOW COULD ALLOW SOME STRATOCUMULUS TO ADVECT INLAND LATER IN THE NIGHT. THE INCREASED CLOUD COVER AND/OR LACK OF DECOUPLED WINDS SHOULD LIMIT COOLING TONIGHT...KEEPING LOWS IN THE MID TO UPPER 50S TOWARD THE COAST. AREAS FARTHER INLAND COULD SEE LOWS AROUND 50 OR IN THE LOWER 50S DUE TO LIGHTER WINDS HOWEVER. && .LONG TERM /MONDAY THROUGH SATURDAY/... FAIRLY GOOD MODEL AGREEMENT THIS PERIOD EXCEPT FOR THE EVOLUTION OF TROPICAL CYCLONE IDA AND ITS REMNANTS FOR EARLY TO MID WEEK. HIGH PRESSURE TO THE NORTH WILL CONTINUE THROUGH MONDAY BEFORE THE THE HIGH BEGINS TO BREAK DOWN DUE TO THE APPROACH OF A SURFACE LOW PRESSURE FROM THE SOUTH /TROPICAL CYCLONE IDA/ AND AN UPPER-LEVEL TROUGH FROM THE WEST. ALTHOUGH TC IDA WILL BE TRANSITIONING INTO AN EXTRA-TROPICAL SYSTEM NEAR THE GULF COAST TUESDAY...PLENTY OF DEEP MOISTURE WILL BE PULLED INTO THE AREA AHEAD OF THE STORM AND THE UPPER TROUGH. WILL CONTINUE TO CARRY LIKELY RAIN CHANCES TUESDAY/TUESDAY NIGHT. IMPROVING CONDITIONS ARE THEN EXPECTED WEDNESDAY AS THE UPPER TROUGH SHIFTS OFFSHORE TAKING THE DEEP MOISTURE WITH IT. STILL LOOKING AT THE POTENTIAL FOR A FEW INCHES OF RAIN WITH THIS EVENT BUT WITH THE RECENT DRY WEATHER WE DO NOT EXPECT ANY FLOODING PROBLEMS AT THIS POINT. THUNDER PROSPECTS APPEAR TOO LOW TO MENTION AT THIS TIME...BUT THERE IS A CHANCE ON TUE/TUE NIGHT IF THE WARM SECTOR GETS INTO THE AREA. TEMPERATURES WILL GENERALLY BE NEAR NORMAL THROUGH THE PERIOD EXCEPT FOR WELL ABOVE NORMAL TEMPERATURES MONDAY AND SATURDAY. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH 12Z MONDAY. CLEAR SKIES AND CALM WINDS WILL PERSIST INTO MID-MORNING... WITH AN EASTERLY FLOW DEVELOPING LATE THIS MORNING AND THIS AFTERNOON WITH SPEEDS LESS THAN 10 KT. THE ONSHORE FLOW COULD RESULT IN A FEW CUMULUS DEVELOPING DURING THE AFTERNOON NEAR KSAV...OTHERWISE SOME INCREASING HIGH CLOUDINESS IS EXPECTED FROM THE SOUTH THROUGH TONIGHT. EXTENDED AVIATION OUTLOOK....VFR CONDITIONS WILL PREVAIL THROUGH MON. POTENTIAL FOR MVFR OR IFR CONDITIONS MON NIGHT THROUGH WED. LLWS ALSO POSSIBLE WED MORNING. VFR CONDITIONS EXPECTED WED NIGHT INTO THU. && .MARINE... RATHER BENIGN CONDITIONS ARE EXPECTED OVER THE COASTAL WATERS TODAY AS HIGH PRESSURE OVER THE WESTERN ATLANTIC REMAINS IN PLACE. WINDS WILL VEER FROM NORTHEAST TO EAST THIS AFTERNOON...WITH SPEEDS LESS THAN 15 KT THROUGHOUT THE WATERS. DESPITE A LACK OF SIGNIFICANT WIND WAVES...THE PERSISTENT ONSHORE FLOW COULD KEEP SEAS UP AS HIGH AS 2-4 FT AS WEAK EASTERLY SWELLS IMPACT THE WATERS. THE SURFACE PRESSURE GRADIENT BETWEEN HIGH PRESSURE OVER THE WESTERN ATLANTIC AND HURRICANE IDA MOVING ACROSS THE CENTRAL GULF OF MEXICO WILL BEGIN TO TIGHTEN OVER THE WATERS TONIGHT. THIS WILL CAUSE ONSHORE WINDS TO INCREASE TO AS HIGH AS 15 KT OVER THE NEAR SHORE WATERS AND 15-20 KT OVER THE OUTER GEORGIA WATERS. THE FAVORABLE FETCH WILL ALLOW SEAS TO BUILD AS WELL...AND A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE OUTER GEORGIA WATERS BEGINNING AT MIDNIGHT AS A RESULT. MONDAY THROUGH THURSDAY...HIGH PRES TO THE N WILL GIVE WAY TO A LOW PRES SYSTEM APPROACHING FROM THE SW /TC IDA OR ITS REMNANTS/ MON AND MON NIGHT. MEANWHILE...AN APPROACHING UPPER TROUGH OF LOW PRES LOOKS TO PICK UP TC IDA /OR PART OF THE SYSTEM/ AND MOVE IT NE OVER/NEAR THE MARINE AREA TUE/TUE NIGHT. HIGH PRES WILL THEN BUILD IN BEHIND THE DEPARTING LOW WED/THU. DUE TO THE CONSIDERABLE UNCERTAINTY WITH THE EVOLUTION OF TC IDA AND ITS REMNANTS...MARINERS ARE REMINDED THAT THERE IS QUITE A BIT OF FORECAST UNCERTAINTY AT THIS TIME. ONGOING SCA CONDITIONS ACROSS THE GA WATERS BEYOND 20 NM ARE LIKELY TO TRANSITION INTO THE COASTAL WATERS WITHIN 20 NM MON NIGHT AS SEAS BUILD TO 6 FT. A VERY STRONG PRES GRADIENT WILL EVENTUALLY SET UP B/W THE DEPARTING LOW AND A BUILDING HIGH PRES SYSTEM INLAND TUE NIGHT/WED. IT IS DURING THIS TIME THAT GALES ARE POSSIBLE...ESPECIALLY ACROSS THE WATERS BEYOND 20 NM FROM SHORE. IMPROVING CONDS EXPECTED THU WITH NO HEADLINES EXPECTED WITHIN THE NEARSHORE WATERS BY THU NIGHT. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM EST FRIDAY FOR AMZ374. && $$ JAQ/RJB