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000 FXUS62 KMFL 231841 AFDMFL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MIAMI FL 241 PM EDT TUE SEP 23 2008 .DISCUSSION... WATER VAPOR IMAGERY SHOWS A MOISTURE PLUME ACROSS SOUTH FLORIDA SLOWLY TRANSLATING TO THE SOUTH AS A TROUGH DEEPENS ALONG THE EASTERN CONUS COAST THIS AFTERNOON. LATEST RUC ANALYSIS SHOWS THE TROUGH IS IN THE PROCESS OF CLOSING OFF INTO A CLOSED/CUTOFF LOW JUST OFF THE CAROLINA COAST. A WEAK SURFACE LOW IS DEVELOPING OFFSHORE CAPE HATTERAS...WITH A STRONG SURFACE HIGH OVER WESTERN NEW YORK. THE STRONG GRADIENT BETWEEN THE TWO HAS GENERATED STRONG WINDS...AND MODERATE TO LARGE SWELLS AS FAR SOUTH AS OFF THE NE FLORIDA COAST ALREADY THIS AFTERNOON. LOCALLY...SCATTERED SHOWERS AND A FEW THUNDERSTORMS CONTINUE ACROSS THE CWA WITH MOVEMENT TO THE SOUTHWEST. MUCH OF THIS ACTIVITY WILL DIMINISH THIS EVENING WITH LOSS OF DAYTIME HEATING BUT SHOWERS COULD LINGER MUCH OF THE NIGHT ALONG THE EAST COAST METRO AREAS WITH INCREASING NE FLOW WHILE INTERIOR AND WEST COAST AREAS DRY OUT. BEYOND TONIGHT...THE UPPER TROUGH AXIS SWINGS THROUGH DISPLACING MOST DEEP-LAYER MOISTURE SOUTH OF THE FLORIDA PENINSULA ON NORTHERLY WINDS. MODELS HAVE BEEN VERY CONSISTENT IN SHOWING THIS ABUNDANCE OF DRY AIR MOVING SOUTH...AND WITH AN INCREASING SUBSIDENCE INVERSION AND MOSTLY WNW/NW FLOW CHANCES FOR RAIN WILL BE ALMOST NIL WEDNESDAY THROUGH FRIDAY ALTHOUGH WITH LINGERING NE FLOW SOME STRATOCU AND SHOWERS ARE POSSIBLE ACROSS EASTERN AREAS ON WEDNESDAY. THE CLOSED LOW WILL OPEN AND LIFT NORTHEAST TOWARDS SOUTHEASTERN CANADA BY THIS WEEKEND ALLOWING THE SUBTROPICAL RIDGE OVER THE ATLANTIC TO BUILD BACK ACROSS THE FLORIDA STRAITS. SOUTHERLY FLOW ON THE NORTH SIDE OF IT MAY ALLOW ABUNDANT DEEP-LAYER MOISTURE TO MOVE BACK NORTH ACROSS THE REGION...BUT ANY SHIFT OR DELAY IN THE RIDGE COULD CHANGE TIMING OF ANY MOISTURE/PRECIP INCREASE. THE DRIER AIRMASS MOVING IN WILL LEAD TO LOWER DEWPOINTS ESPECIALLY TOMORROW NIGHT THROUGH FRIDAY...WITH VALUES DROPPING INTO THE 60S MOST PLACES WITH GOOD MIXING FROM ABOVE EACH DAY...EXCEPT RIGHT ALONG THE IMMEDIATE EAST COAST AS ONSHORE FLOW KEEPS VALUES CLOSER TO 70. THE DRIEST AIR WILL BE ACROSS GLADES AND HENDRY COUNTIES WHERE 900MB DEWPOINTS ARE FORECAST TO BE QUIET LOW AND THIS MAY ALLOW SURFACE DEWPOINTS TO MIX OUT AS LOW AS 60F. TEMPERATURES WILL ALSO BE A FEW DEGREES COOLER THE NEXT FEW DAYS...MOST NOTICEABLY AT NIGHT. LOW TEMPS WILL RANGE FROM THE 60S ACROSS MUCH OF THE INTERIOR...COLDEST NORTHWEST...TO JUST ABOVE 70 ACROSS THE MIAMI AREA. SWELLS WILL INCREASE FROM THE NORTH TO NORTHEAST TONIGHT AND ARE ALREADY BEING REPORTED OFF THE NE FLORIDA COAST. SWELLS SHOULD PEAK AROUND 6FT ALONG THE PALM BEACH COUNTY COAST AND 3 TO 5FT ALONG THE MIAMI-DADE AND BROWARD COASTS LATE WEDNESDAY NIGHT AND THURSDAY WITH SOME HIGHER VALUES OFFSHORE. IF THESE SWELL HEIGHTS VERIFY...PERIODS OF AROUND 12S COULD LEAD TO 10FT BREAKERS ESPECIALLY ALONG THE PALM BEACH COAST DURING THAT TIME FRAME AND A HIGH SURF ADVISORY MAY BE NEEDED. && .MARINE... NORTHERLY WINDS WILL INCREASE TONIGHT AND WEDNESDAY TO NEAR OR JUST ABOVE EXERCISE CAUTION CRITERIA...AND THIS IS A LITTLE ABOVE GFS GUIDANCE BASED ON UPSTREAM OBS AND SURGES IN LOW-LEVEL WINDS JUST ABOVE THE SURFACE. SEAS WILL BUILD OVER 7FT IN RESPONSE TO THAT AND SMALL SWELL LATE TONIGHT...AND 8 TO 11FT LATE WEDNESDAY INTO THURSDAY AS SWELLS INCREASE TO AS MUCH AS 8FT OFFSHORE. && .FIRE WEATHER... LOWER DEWPOINTS EXPECTED LATE THIS WEEK WITH RH`S POSSIBLY NEARING 40 PERCENT ACROSS THE INTERIOR THURSDAY AND FRIDAY. && .PRELIMINARY POINT TEMPS/POPS... WEST PALM BEACH 74 86 73 86 / 20 20 20 10 FORT LAUDERDALE 75 86 75 87 / 30 20 20 10 MIAMI 76 86 76 86 / 30 20 20 10 NAPLES 72 88 72 87 / 20 10 10 10 && .MFL WATCHES/WARNINGS/ADVISORIES... FL...NONE. AM...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 5 AM WEDNESDAY TO 8 AM EDT FRIDAY FOR AMZ650-AMZ651-AMZ670-AMZ671. GM...NONE. && $$ PUBLIC/MARINE/FIRE WX...STRASSBERG SHORT TERM/AVIATION...GREGORIA