AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 349 AM EDT FRI JUL 29 2011 ...HOT AND HUMID WEATHER TO RETURN THIS WEEKEND WITH HEAT INDICES APPROACHING 110 DEGREES... .SYNOPSIS... ABOVE AVERAGE TEMPERATURES AND HIGH HEAT INDICES WILL BE THE MAIN WEATHER STORY THIS WEEKEND WITH BELOW AVERAGE AFTERNOON THUNDERSTORM CHANCES FOR TODAY AND SATURDAY. THE BEST CHANCE OF AFTERNOON THUNDERSTORMS THIS WEEKEND IS EXPECTED TO BE OVER THE FLORIDA BIG BEND. MAXIMUM HEAT INDICES MAY APPROACH THE LOCAL HEAT ADVISORY CRITERIA OF 110 DEGREES ON BOTH SATURDAY AND SUNDAY. && .SHORT TERM... (TODAY THROUGH SUNDAY) MODELS AGREE THAT A STRONG UPPER LEVEL RIDGE WILL BUILD OVER THE AREA ON SATURDAY AND THEN START TO RETROGRADE WEST OF THE AREA ON SUNDAY. THIS RIDGE WILL ACT TO SUPPRESS CONVECTION OVERALL AND INCREASE TEMPERATURES. GIVEN THAT THE 1000-700 MB MEAN WIND IS FORECAST BE LIGHT TO MODERATE OUT OF THE NORTH...A TYPE 8 SEA BREEZE REGIME LOOKS PROBABLE FOR THE WEEKEND. THIS REGIME TYPICALLY RESULTS IN THE HIGHEST THUNDERSTORM CHANCES ACROSS THE FLORIDA PANHANDLE AND BIG BEND WITH THE SEA BREEZE HAVING A TOUGH TIME MOVING NORTHWARD AGAINST THE PREVAILING SYNOPTIC WIND FLOW. SOME ENHANCEMENT IN THUNDERSTORM CHANCES FROM THE EAST COAST SEA BREEZE COULD OCCUR ACROSS THE BIG BEND AND WILL SHOW THE HIGHEST PRECIP CHANCES IN THIS AREA FOR THE WEEKEND (40-50 PERCENT). AS THE UPPER LEVEL RIDGE RETROGRADES TO THE WEST ON SUNDAY...THERE ARE SOME INDICATIONS THAT WEAK SHORTWAVE ENERGY MAY MOVE INTO THE AREA FROM THE NORTH AND PROVIDE A SLIGHTLY HIGHER CHANCE OF AFTERNOON SHOWERS AND THUNDERSTORMS. TEMPERATURES WILL LIKELY SOAR INTO THE UPPER 90S TO LOWER 100S ACROSS THE INTERIOR WITH MID 90S EVEN AT THE COAST GIVEN THE PRESENCE OF THE UPPER LEVEL RIDGE AND MEAN NORTHERLY FLOW WHICH IS USUALLY WARM DURING THIS TIME OF YEAR. THIS COMBINED WITH SEASONABLY HIGH DEW POINTS COULD RESULT IN HEAT INDICES EXCEEDING 110 IN SOME AREAS BOTH DAYS THIS WEEKEND AND A HEAT ADVISORY COULD BECOME NECESSARY. .LONG TERM... (SUNDAY NIGHT THROUGH NEXT FRIDAY) THE LARGE SCALE LONGWAVE PATTERN COMMENCES WITH EXPANSIVE RIDGE FROM WEST COAST EWD. IN NRN STREAM RIDGE EXTENDS TO ERN STATES BUT IN SRN STREAM SUB- TROPICAL RIDGE EXTENDS WELL INTO WRN ATLC. AT SURFACE... LOW OFF NEW ENGLAND COAST WITH TRAILING FRONT SSW TO WEAK LOW OVER COASTAL CAROLINA THEN WEAK TROUGH ACROSS CWA. BERMUDA HIGH PRESSURE FROM WRN ATLC CROSS CNTRL PENINSULA. THIS PLACES LOCAL AREA IN ONSHORE FLOW BETWEEN BOTH SYSTEMS WITH SURFACE BOUNDARY PROVIDING FOCUS FOR CONVECTION INTO THE WORK WEEK. MODELS ARE IN AGREEMENT THAT BEGINNING ON MONDAY THE UPPER LEVEL HIGH RETREATS BACK TO SRN/CNTRL PLAINS AND PERSISTS THERE. AT SURFACE...BERMUDA HIGH SAGS SWD TO SRN FLORIDA PENINSULA BY MIDWEEK. AT SAME TIME...A STRONG CANADIAN TROUGH MOVES ACROSS THE NRN TIER STATES GRADUALLY AMPLIFYING REACHING THE NERN STATES WED. IN RESPONSE...UPPER TROUGH DEEPENS ALONG AND JUST OFF NE/MID-ATLC SEABOARD AND DIGS DOWN THE EXTREME WRN ATLC. SO LOCAL AREA IN DIVERGENT FLOW BETWEEN RETREATING HIGH TO WEST AND AMPLIFIED TROUGH TO EAST. ASSOCD WEAK VORT MAXES MAY ROTATE WWD FROM TROUGH THRU PERIOD AND PROVIDE BRIEF LIFT OF CONVECTION MOST DAYS. BY FRI LOW CUTS OFF FROM BASE OF TROUGH OFF SE FL WITH CYCLONIC FLOW INCHING TOWARDS LOCAL AREA. WITH SHORTWAVES SLATED TO REMAIN WELL TO OUR WEST...PRECIPITATION WILL BE FOCUSED ALONG SEA BREEZE THROUGH THE ENTIRE PERIOD. WITH MID AND SOME UPPER LEVEL MOISTURE REMAINING HIGH ESPECIALLY END OF PERIOD...THE SEA-BREEZE WILL BE SOMEWHAT ENHANCED. WILL GO WITH LOW-MID SCT POPS SUN NIGHT THRU TUES (HIGHEST MON AFTN) AND WDLY SCT-LOW SCT POPS REST OF DAYTIME PERIODS. GENERALLY WDLY SCT OR BELOW AT NIGHT. MIN AND TEMPS WILL REMAIN 3 TO 5 DEGREES ABOVE CLIMO THRU THE PERIOD. (AVG INLAND MAX/MIN TEMPS ARE 71/92 DEGREES). THE COMBINATION OF TEMPS IN THE MID 90S AND HIGH HUMIDITIES WILL ALLOW MAXIMUM HEAT INDICES WILL RISE TO 105 TO 110 DEGREES MOST AFTERNOONS. && .AVIATION... GUIDANCE IS IN GOOD AGREEMENT SHOWING VERY LITTLE IN THE WAY OF EXPECTED VIS/CIG RESTRICTION THROUGH THE EARLY MORNING HOURS. WITH ALL THE RAIN THE PAST FEW DAYS..SOIL MOISTURES ARE HIGH...SO PATCHY MVFR VIS RESTRICTIONS WILL BE POSSIBLE...ESPECIALLY TOWARD DAWN...SO MINIMAL MVFR VSBYS 08Z-12Z ALL SITES. OTHERWISE...VFR WILL PREVAIL THROUGH MUCH OF THE DAY WITH THE ONLY EXCEPTIONS OCCURRING IN PROXIMITY TO ANY TYPICAL AFTERNOON SHOWERS AND STORMS. CHANCE OF RAIN TOO LOW TO INCLUDE IN TAFS...BUT WITH GO WITH CB IN ALL 18Z-00Z. && .MARINE... THE PRESSURE GRADIENT WILL CONTINUE TO DIMINISH AS DON MOVES FURTHER AWAY FROM THE AREA AND MAKES LANDFALL. SWELLS FROM DON APPEAR TO HAVE PEAKED FOR THE LOCAL AREA AND A SLOW DOWNWARD TREND HAS COMMENCED. SEAS AROUND 2 FEET ARE EXPECTED OVER THE WESTERN LEGS BY SATURDAY WITH 1 TO 2 FEET EXPECTED BY THE END OF THE WEEKEND AS THE SUBTROPICAL RIDGE ONCE AGAIN BECOMES THE DOMINANT FEATURE OVER THE MARINE AREA. && .FIRE WEATHER... DESPITE LOWER RAIN CHANCES AND HIGHER TEMPERATURES...RELATIVE HUMIDITY VALUES WILL REMAIN WELL ABOVE 35 PERCENT THROUGH THE WEEKEND. && .PRELIMINARY POINT TEMPS/POPS... TALLAHASSEE 96 75 99 76 97 / 30 20 30 20 50 PANAMA CITY 90 76 94 78 93 / 30 20 30 20 40 DOTHAN 96 75 98 76 97 / 20 10 20 10 50 ALBANY 96 75 100 76 100 / 20 10 20 10 50 VALDOSTA 97 74 101 75 100 / 20 10 30 20 50 CROSS CITY 96 74 96 75 95 / 20 10 40 30 50 APALACHICOLA 90 77 94 79 93 / 20 10 30 20 30 && .TAE WATCHES/WARNINGS/ADVISORIES... AL...NONE. GA...NONE. FL...NONE. GM...NONE. && $$