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