000 FXUS62 KMFL 241428 AFDMFL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MIAMI FL 928 AM EST TUE NOV 24 2009 .UPDATE...LATEST SURFACE ANALYSIS SHOWS W/E SURFACE BOUNDARY ACROSS THE SOUTH CENTRAL GULF CROSSING THE STATE ACROSS SOUTH FLORIDA AND TURNING NORTHEAST INTO BROAD AREA OF LOW PRESSURE OFF THE MID ATLANTIC STATES. AT THE UPPER LEVELS H2-3 ANALYSIS REVEALS HIGH AMPLITUDE TROUGH ACROSS THE MIDDLE SECTIONS OF THE COUNTRY STRETCHING ALL THE WAY DOWN INTO MEXICO WITH S/W ROTATING AROUND ITS BASE FROM SOUTHERN TX INTO WESTERN GULF AT THIS TIME. ALL THESE FEATURES HAVE COME TOGETHER RESULTING IN INCREASING CONVECTION ALONG BOUNDARY ACROSS WEST CENTRAL PORTIONS OF THE GULF OF MEXICO. BLENDED SSMI/AMSU/GPSMET TPW PRODUCT SHOWS TWO AREAS OF PWAT AROUND 40-50% ABOVE NORMAL. ONE IS STRETCHING ACROSS THE CENTRAL GULF INTO CENTRAL FLORIDA AND THE OTHER ONE EXTENDING FROM CUBA ACROSS THE CENTRAL BAHAMAS. ALL THESE FEATURES AND THEIR EVOLUTION OVER NEXT COUPLE OF DAYS WILL RESULT IN INCREASING CHANCES OF RAIN FOR SOUTH FLORIDA. ALL MODELS ARE CONSISTENT WITH THAT INCLUDING THE ENSEMBLE SREF AND EKDMOS GUIDANCE. BUT FOR TODAY...12Z UPR LEVEL DATA STILL SHOWS THE AREA UNDER THE INFLUENCE OF A LOW LEVEL RIDGE WITH MARGINAL OR LESS THAN MARGINAL THERMODYNAMIC INDICES. LOW LEVEL DEEP EASTERLY FLOW IS STILL IN PLACE ACROSS THE AREA AND WITH PWAT RUNNING AROUND 20% ABOVE NORMAL DECIDED TO RAISE POPS FOR PORTIONS OF INTERIOR SOUTH FLORIDA FOR THIS AFTERNOON AND EVENING TO 30% AND LEAVE THEM AT 20% ELSEWHERE BUT STILL IN THE FORM OF SHOWERS MAINLY WITH PERHAPS AN ISOLATED THUNDERSTORM. FOR TONIGHT...TWEAKED POPS A LITTLE BUT THE INCREASING TREND IN THE RAIN CHANCES FOR TONIGHT IS STILL IN PLACE AS WE TRANSITION INTO WEDNESDAY. NO OTHER CHANGES MADE TO THE FORECAST AT THIS TIME. && .PREV DISCUSSION... /ISSUED 616 AM EST TUE NOV 24 2009/ AVIATION...WEAK SFC TROF STALLED OVR LAKE OKEE AREA AND WL PERSIST THRU PD. WDLY SCT SHRA MOVG W THRU ATLC COASTAL WATERS OFF OF PALM BEACH AND VCSH KPBI THRU 14Z. LTR TDA SCT SHRA/ISOLD TSRA PSBL ALG STALLED TROF BUT ONLY VCSH AT KPBI AFT 16Z ATTM. PSBL VCSH KAPF AFT 00Z AS SHRA OVER GULF MOVS NE TWD S FLA. SFC WND CALM TO ESE 3-5 KTS INCRG AND BCMG E 8-11 KT AFT 16Z XCPT W COAST SEA BREEZE AT KAPF AFT 18Z. PREV DISCUSSION... /ISSUED 439 AM EST TUE NOV 24 2009/ DISCUSSION... CURRENT IR SATELLITE IMAGERY INDICATES MOSTLY CLOUDY SKIES ACROSS MUCH OF SOUTH FLORIDA THIS MORNING...WITH A GOOD COVERAGE OF CI/CS MOVING OVERHEAD IN SOUTHWEST FLOW ALOFT. HOWEVER...SOME BREAKS IN THE OVERCAST CONDITIONS ARE OCCURRING ACROSS THE NORTHWEST INTERIOR...AND THIS -- COUPLED WITH LOCALLY HIGHER LEVELS OF SOIL MOISTURE DUE TO THUNDERSTORM ACTIVITY ON MONDAY AFTERNOON -- HAS ALLOWED WIDESPREAD FOG TO FORM IN THIS AREA. OVERALL...EXPECT SIMILAR WEATHER CONDITIONS TO MONDAY TO PREVAIL TODAY...AS MODEL GUIDANCE HAS CHANGED VERY LITTLE REGARDING PROMINENT FEATURES TO AFFECT THE AREA. STRONG SOUTHWESTERLY FLOW ALOFT WILL CONTINUE OVER THE FLORIDA PENINSULA TODAY...AS THIS REGION WILL REMAIN SITUATED BETWEEN A DEEPENING UPPER LOW MOVING EASTWARD ACROSS THE CENTRAL PLAINS AND A STUBBORN MID-LEVEL HIGH CENTERED ACROSS THE GREATER ANTILLES. THE HIGHEST RAIN CHANCES WILL STILL BE ACROSS THE NORTHERN INTERIOR AND NORTHEAST ZONES..IN VICINITY OF STALLED FRONTAL BOUNDARY...AND BASED ON FORECAST SOUNDINGS AND PERSISTENCE...WILL MENTION SHOWERS AND ISOLATED THUNDERSTORMS. ALL MODELS ARE IN GOOD AGREEMENT THAT SEVERAL LOW AMPLITUDE WAVES WILL TRANSLATE EITHER ACROSS OR VERY CLOSE TO SOUTH FLORIDA IN THIS SOUTHWESTERLY FLOW REGIME OVER THE NEXT COUPLE OF DAYS...AS AN ACTIVE SUBTROPICAL BRANCH OF THE UPPER LEVEL JET CONTINUES. FURTHERMORE...BROAD/WEAK SURFACE CYCLOGENESIS IS STILL EXPECTED TO OCCUR ACROSS THE CENTRAL GULF OF MEXICO LATER TODAY...IN RESPONSE TO EASTWARD MOTION OF VORT MAX CURRENTLY SEEN IN WATER VAPOR ANIMATION ACROSS NORTHEAST MEXICO/DEEP SOUTH TEXAS. THIS WILL ALLOW THE WEAK STALLED FRONTAL BOUNDARY TO LIFT NORTHWARD TONIGHT...WITH INCREASING EASTERLIES IN THE LOW-LEVELS AND STRENGTHENING WARM/MOIST ADVECTION REGIME RESULTING IN A GOOD COVERAGE OF NOCTURNAL SHOWER ACTIVITY ALONG THE SOUTHEAST COAST. THE LATEST RUN OF THE GFS STILL SEEMS TO BE SUFFERING FROM CONVECTIVE FEEDBACK...AND IS LIKELY OVERLY AGGRESSIVE IN DEVELOPING A WELL-DEFINED SURFACE LOW AND TRACKING IT NORTHEASTWARD ACROSS CENTRAL FLORIDA ON WEDNESDAY. THE UKMET/ECMWF APPEAR MORE REALISTIC IN DEPICTING AN INVERTED SURFACE TROUGH SHIFTING SLOWLY EASTWARD ACROSS THE PENINSULA THROUGH THE DAY... AND FOCUSING WIDESPREAD SHOWERS AND ISOLATED THUNDERSTORMS ACROSS EASTERN HALF OF THE FORECAST AREA. IT APPEARS MORE LIKELY THAT A DEFINED SURFACE LOW MAY FORM ALONG THIS BOUNDARY IN THE ATLANTIC ON WEDNESDAY NIGHT/THURSDAY MORNING...ALLOWING LOW-LEVEL FLOW TO GRADUALLY SHIFT TO NORTH-NORTHWEST AS COLD FRONT BEGINS PUSHING INTO THE REGION. HOWEVER...WILL SPLIT DIFFERENCE IN MAV/MET POPS ALONG THE ATLANTIC COAST DURING THIS PERIOD...AS MODERATE ASCENT BETWEEN THE 300-310K ISENTROPES MAY ALLOW SHOWER ACTIVITY TO LINGER INTO THE EVENING...ESPECIALLY ACROSS THE FAR SOUTHEAST COAST. GENERALLY DRY WEATHER IS EXPECTED FROM THANKSGIVING THROUGH THE END OF THE EXTENDED FORECAST PERIOD...AS THE REGION WILL COME UNDER MORE OF AN INFLUENCE FROM CANADIAN AIR MASS WHICH WILL OVERTAKE MUCH OF THE EASTERN U.S. DURING THIS PERIOD. THE MAIN FORECAST CONCERN WILL BE TEMPERATURES...WITH FRIDAY AND SATURDAY MORNING STILL LOOKING TO BE THE COOLEST. LOW TEMPERATURES RANGING FROM THE LOWER/MID 40S NORTHWEST INTERIOR TO THE UPPER 50S/AROUND 60 SOUTHEAST COAST WILL BE POSSIBLE BOTH NIGHTS BEFORE EASTERLY FLOW AND A WARMING TREND BEGIN EARLY NEXT WEEK. MARINE... THERE ARE NO MARINE WEATHER CONCERNS TODAY OR TONIGHT...WITH EASTERLY WINDS EXPECTED TO INCREASE TO 10-15 KNOTS ACROSS ALL WATERS AS THE WEAK STALLED FRONTAL BOUNDARY ACROSS CENTRAL FLORIDA BEGINS TO LIFT NORTHWARD. A SLIGHTLY MORE COMPLICATED FORECAST EXISTS FROM WEDNESDAY INTO THURSDAY...AS EITHER A WEAK INVERTED TROUGH OR AREA OF SURFACE LOW PRESSURE IS EXPECTED TO MOVE ACROSS THE REGION FROM THE WEST. THIS SHOULD ALLOW WINDS TO SHIFT TO SOUTHWEST AND INCREASE DURING THE DAY ON WEDNESDAY...WITH 15-20 KNOT SPEEDS AND SCEC CONDITIONS POSSIBLE. WINDS WILL SHIFT TO NORTHWEST ON THANKSGIVING DAY...AS A STRONGER COLD FRONT BEGINS TO PUSH ACROSS THE REGION. SCEC CONDITIONS LIKELY FOR 15-20 KNOT NORTHWEST WINDS ON FRIDAY...WITH SCA POSSIBLE OVER THE WEEKEND IN THE GULF STREAM AS SEAS BUILD ABOVE 6 FEET. IMPROVING CONDITIONS ARE ANTICIPATED BY LATE WEEKEND...AS FLOW VEERS TO THE EAST. HOWEVER...A 1-3 FOOT NORTHEAST SWELL POISED TO ENTER THE ATLANTIC WATERS THIS WEEKEND WILL ALLOW FOR A CONTINUATION OF LOCALLY HIGH SEAS AND AN INCREASED THREAT FOR RIP CURRENTS. FIRE WEATHER... MINIMUM AFTERNOON RH VALUES IN THE 40-45 PERCENT RANGE CAN BE EXPECTED ACROSS THE NORTHWEST INTERIOR FIRE WEATHER ZONES ON FRIDAY...AND ACROSS MOST OF SOUTH FLORIDA ON SATURDAY...AS A MUCH DRIER AIR MASS MOVES INTO THE REGION FOLLOWING FRONTAL PASSAGE ON THANKSGIVING DAY. OTHERWISE...A GRADUAL MOISTENING TREND IS EXPECTED BY EARLY NEXT WEEK...AS WINDS VEER TO THE EAST. && .PRELIMINARY POINT TEMPS/POPS... WEST PALM BEACH 84 73 78 66 / 20 50 70 50 FORT LAUDERDALE 84 75 79 68 / 20 50 70 60 MIAMI 85 73 80 68 / 20 50 70 60 NAPLES 82 71 77 65 / 20 60 70 40 && .MFL WATCHES/WARNINGS/ADVISORIES... FL...NONE. AM...NONE. GM...NONE. && $$ LONG TERM...52/PS SHORT TERM/AVIATION...17/ERA