000 FXUS62 KMFL 041156 AFDMFL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MIAMI FL 756 AM EDT SAT JUL 4 2009 .AVIATION... MAINLY VFR CONDITIONS EXPECTED FOR ALL S. FL TERMINALS THROUGH THE MORNING HOURS. LIGHT SYNOPTIC SURFACE FLOW ACROSS THE REGION WILL ALLOW SEA BREEZES TO FORM ALONG WEST AND EAST COASTS...WITH VCSH POSSIBLE ALL TERMINALS THROUGH THE MORNING HOURS. BY EARLY AFTERNOON VCTS EXPECTED ALONG EAST COAST TERMINALS...WITH BRIEF PERIODS OF MVFR CONDITIONS POSSIBLE WITH ANY CONVECTION OCCURRING AT THE TERMINALS. LOW LEVEL FLOW EXPECTED TO BE LIGHT...WITH ANY THUNDERSTORMS EXPECTED TO BE SLOW MOVING. 60 && .PREV DISCUSSION... /ISSUED 436 AM EDT SAT JUL 4 2009/ DISCUSSION... GENERALLY QUIET CONDITIONS PREVAIL ACROSS MAINLAND SOUTH FLORIDA THIS MORNING...WITH PARTLY CLOUDY SKIES AND SEASONABLY WARM TEMPERATURES IN THE UPPER 70S. HOWEVER...CONVECTION IS BEGINNING TO INCREASE ACROSS THE OFFSHORE ATLANTIC WATERS BETWEEN PALM BEACH AND SETTLEMENT POINT...WHICH IS LIKELY INDICATIVE OF THE APPROACH OF A WEAK UPPER-LEVEL TROUGH EXTENDING FROM CENTRAL FLORIDA WESTWARD INTO THE EASTERN GULF OF MEXICO. MODELS ARE IN GOOD AGREEMENT THAT THIS UPPER TROUGH WILL DRIFT SLOWLY SOUTHEASTWARD ACROSS THE FORECAST AREA TODAY...IN RESPONSE TO BOTH AN EASTWARD EXPANSION OF SOUTHERN PLAINS MID-LEVEL RIDGE ACROSS THE NORTHERN GULF COAST...AS WELL AS A DEEPENING UPPER LOW SHIFTING EASTWARD FROM SOUTHERN QUEBEC ACROSS THE NORTHEASTERN STATES. VERY LIGHT STEERING LAYER FLOW AS DEPICTED IN POINT FORECAST SOUNDINGS FROM THE NAM/GFS SUGGEST THUNDERSTORMS DEVELOPING BY EARLY AFTERNOON ALONG INLAND MOVING GULF/ATLANTIC COAST SEA BREEZE BOUNDARIES... WITH VERY LITTLE OVERALL STORM MOTION AND ACTIVITY BECOMING CONCENTRATED ACROSS INTERIOR PORTIONS OF THE PENINSULA. WILL ADJUST POPS ACCORDINGLY...BASED ON THIS REASONING...AND PLACE LOWEST POPS ALONG THE IMMEDIATE COASTAL ZONES. SLIGHTLY STRONGER LARGE SCALE LIFT AND COOLER TEMPERATURES ALOFT PROGGED TO ACCOMPANY THE UPPER TROUGH MAY SUPPORT STRONG THUNDERSTORMS ONCE AGAIN THIS AFTERNOON...WITH SMALL HAIL/GUSTY WINDS POSSIBLE. ALTHOUGH MOST OF THE CONVECTIVE ACTIVITY SHOULD DISSIPATE BY DUSK...THERE IS THE POTENTIAL FOR REMNANT OUTFLOW BOUNDARIES TO INITIATE ADDITIONAL CONVECTION THROUGH MID/LATE EVENING...AND WITH UPPER TROUGH AXIS EXPECTED TO REMAIN IN PLACE OVER SOUTHEASTERN HALF OF THE AREA...WILL LEAVE HIGHEST EVENING POPS IN THIS REGION. MOST OF THE MODEL GUIDANCE INDICATES THAT THE UPPER TROUGH AXIS WILL GRADUALLY DISSIPATE IN PLACE ACROSS SOUTHEAST FLORIDA FROM SATURDAY NIGHT INTO SUNDAY...AS ANOTHER STRONG UPPER LOW DROPPING SOUTHEASTWARD ACROSS THE NORTHERN GREAT LAKES REGION FORCES A WESTWARD EXPANSION OF SUBTROPICAL RIDGE OVER THE ATLANTIC. HOWEVER...DESPITE A SLIGHTLY MORE UNFAVORABLE ENVIRONMENT ALOFT... ANOTHER ACTIVE DAY OF CONVECTION IS EXPECTED ACROSS THE INTERIOR AND EAST COAST ON SUNDAY...AS SURFACE LOW ASSOCIATED WITH MCS CURRENTLY MOVING ACROSS THE CENTRAL PLAINS DIVES SOUTHEASTWARD ACROSS THE CENTRAL APPALACHIANS AND INDUCES STRONGER SOUTHWESTERLY STEERING FLOW ONCE AGAIN. TEMPERATURES WILL REMAIN CONSISTENT THROUGH THE SHORT TERM PERIOD...WITH HIGHS GENERALLY IN THE LOWER TO MID 90S...AND LOWS GENERALLY IN THE MID TO UPPER 70S. GLOBAL MODELS CONTINUE TO INDICATE A STAGNANT PATTERN REMAINING IN PLACE THROUGH MUCH OF THE EXTENDED FORECAST PERIOD...AS A BROAD SPLIT FLOW BLOCK MATERIALIZES ACROSS THE WESTERN U.S. AND SUBTROPICAL RIDGE REMAINS ANCHORED ACROSS SOUTH FLORIDA. ALTHOUGH PWAT VALUES MAY GRADUALLY DECLINE OVER THE COURSE OF THE WEEK... PRIMARILY AFTERNOON/EARLY EVENING SHOWERS AND THUNDERSTORMS ARE EXPECTED EACH DAY...WITH PREVAILING SOUTHWEST STEERING FLOW FAVORING THE INTERIOR AND EAST COAST FOR THE HIGHEST CHANCES FOR PRECIPITATION. THIS IS ALREADY INDICATED IN THE CURRENT EXTENDED FORECAST AND WILL BE MAKING NO MAJOR CHANGES TO GRIDS IN THESE PERIODS. MARINE... THERE ARE NO MARINE WEATHER CONCERNS THIS FORECAST PERIOD...ASIDE FROM THOSE ASSOCIATED WITH POTENTIAL MORNING WATERSPOUT ACTIVITY OVER THE LOCAL ATLANTIC WATERS...AND LOCALLY HIGHER WINDS/WAVES ASSOCIATED WITH CONVECTION WHICH COULD OCCUR AT ALMOST ANY TIME. OTHERWISE...MARINERS CAN EXPECT PREVAILING SOUTHERLY WINDS THROUGH MUCH OF NEXT WEEK...WITH SPEEDS OF 10-15 KNOTS AT MOST ACROSS THE ATLANTIC WATERS/BISCAYNE BAY/LAKE OKEECHOBEE. THIS WILL RESULT IN PREVAILING SEAS OF 2-4 FEET FOR THE GULF STREAM...AND 1-2 FEET IN THE SOUTHEASTERN GULF WATERS. FIRE WEATHER... THERE ARE NO FIRE WEATHER CONCERNS THIS FORECAST PERIOD...WITH MINIMUM AFTERNOON RH VALUES EXPECTED TO REMAIN WELL ABOVE CRITICAL LEVELS. && .PRELIMINARY POINT TEMPS/POPS... WEST PALM BEACH 90 76 90 76 / 40 20 50 20 FORT LAUDERDALE 92 79 92 79 / 30 30 50 20 MIAMI 92 78 92 78 / 50 30 50 20 NAPLES 89 76 89 76 / 50 30 30 20 && .MFL WATCHES/WARNINGS/ADVISORIES... FL...NONE. AM...NONE. GM...NONE. && $$ LONG TERM...47/RHG SHORT TERM/AVIATION...60/BD