000
FXUS62 KMFL 201904
AFDMFL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
304 PM EDT SAT SEP 20 2008

.DISCUSSION...
WIDELY SCATTERED SHOWER ACTIVITY AFFECTING THE LOCAL ATLANTIC
WATERS THIS AFTERNOON SHOULD PERSIST FOR A FEW MORE HOURS...WITH
ISOLATED SHOWERS EXPECTED ACROSS THE REMAINDER OF THE FORECAST
AREA. THE LATEST WATER VAPOR ANIMATION INDICATES A FAIRLY BROAD
AREA OF DRY AIR ALOFT EMBEDDED WITHIN THE BASE OF A LOW-AMPLITUDE
SHORTWAVE TROUGH LOCATED JUST OFF THE EAST COAST OF FLORIDA. THIS
AIRMASS IS STILL IN PLACE ACROSS THE SOUTHEASTERN FLORIDA
PENINSULA AND ADJACENT PORTIONS OF THE ATLANTIC...AND WAS SAMPLED
VERY WELL IN THE 12Z KMFL RAOB...WITH PRECIPITABLE WATER SLIGHTLY
BELOW 1.5 INCHES.

MODELS AGREE THAT THIS MID-LEVEL SHORTWAVE TROUGH WILL GRADUALLY
SHEAR APART OVER THE NEXT 24 HOURS...WITH ITS REMNANTS EXPECTED
TO LIFT NORTHEASTWARD AROUND THE WESTERN PERIPHERY OF A
STRENGTHENING MID-TROPOSPHERIC ANTICYCLONE OVER THE CENTRAL NORTH
ATLANTIC. IN THE WAKE OF THIS FEATURE...A SUBSIDENT AIRMASS WILL
SPREAD ACROSS SOUTH FLORIDA...COURTESY OF CENTRAL ATLANTIC RIDGE
BUILDING OVERHEAD...AND THIS WILL RESULT IN A PERIOD OF SLIGHTLY
BELOW CLIMATOLOGICALLY NORMAL POPS...EXTENDING THROUGH MUCH OF THE
SHORT TERM PORTION OF THIS FORECAST. AN EAST TO NORTHEASTERLY
COMPONENT TO FLOW IN THE BOUNDARY LAYER WILL PERSIST THROUGHOUT
THE PERIOD...AND AT LEAST SCATTERED SHOWER ACTIVITY IS ANTICIPATED
ACROSS THE ATLANTIC WATERS. ASSUMING NO LAND BREEZE DEVELOPMENT...
IT SEEMS REASONABLE TO ASSUME THAT HIGHEST NOCTURNAL POPS WILL
OCCUR ALONG THE IMMEDIATE EAST COAST AND ADJACENT WATERS...WITH
ACTIVITY SPREADING INLAND DURING THE DAY. GUIDANCE FROM THE
NGM/NAM...AS WELL AS FROM THE VARIOUS GLOBAL MODELS INDICATE THAT
BACKGROUND FLOW WILL LIKELY BE LIGHT ENOUGH FOR THE FORMATION OF A
GULF COAST SEA BREEZE...AND WILL PLACE SLIGHTLY HIGHER AFTERNOON
POPS OVER THE WESTERN HALF OF THE PENINSULA. NO MAJOR CHANGES ARE
ANTICIPATED IN THE TEMPERATURE FORECAST...WITH A ROUGHLY 10 DEGREE
DIURNAL VARIATION EXPECTED ALONG THE EAST COAST...AND A SLIGHTLY
LARGER SPREAD ALONG THE WEST COAST.

MEDIUM RANGE GUIDANCE FROM BOTH THE GFS/ECMWF SUGGEST THAT A
TRANSITION TO A WETTER PATTERN WILL OCCUR JUST BEYOND THE END OF
THE SHORT TERM...AS A WEAK UPPER-LOW OVER THE MID-MISSISSIPPI
VALLEY REGION...WHICH IS CURRENTLY CUT OFF FROM THE POLAR BRANCH
OF THE WESTERLIES...BEGINS TO DRIFT EASTWARD IN RESPONSE TO
RIDGING ALOFT OVER THE SOUTHERN PLAINS. THIS FEATURE WILL BEGIN TO
INFLUENCE THE WEATHER ACROSS SOUTH FLORIDA BY MID-WEEK...WITH AN
INCREASE IN DIURNAL SHOWER/THUNDERSTORM ACTIVITY FOR THE EASTERN
HALF OF THE AREA...AS STEERING FLOW BACKS TO THE WEST/NORTHWEST.
THE LATEST GFS SOLUTION IS SLOWLY COMING INTO BETTER AGREEMENT
WITH THE ECMWF IN GRADUALLY DEEPENING THIS MID-LEVEL TROUGH INTO A
CUTOFF LOW AS IT DRIFTS OVER WARM OCEAN WATERS OFF THE COAST OF
THE CAROLINAS BY THE END OF THE WEEK...WITH THE POTENTIAL FOR
SEVERAL WEAK SURFACE LOWS TO SPIN UP OFF THE SOUTHEAST COAST OF
THE U.S. A PROLONGED PERIOD OF NORTHERLY FLOW WILL LIKELY BE THE
RESULT FOR SOUTH FLORIDA...AND THIS PATTERN WILL CERTAINLY HAVE
THE POTENTIAL TO BRING AT LEAST A BRIEF PERIOD OF SLIGHTLY
COOLER/DRIER AIR TO SOUTH FLORIDA NEXT WEEKEND...BUT IT IS FAR TOO
EARLY TO INDICATE SPECIFIC DETAILS IN THE FORECAST.

&&

.MARINE...
THERE ARE NO IMMINENT MARINE WEATHER CONCERNS...AS DATA FROM LOCAL
WEB CAMS SUGGESTS THAT LONG PERIOD NORTH/NORTHEAST SWELL IN THE
PALM BEACH WATERS IS LIKELY NOT MATERIALIZING AS EARLIER THOUGHT.
GIVEN THIS...AND EXPECTATIONS OF A WEAKER SURFACE LOW OFF THE
COAST OF NORTHEAST FLORIDA...HAVE DECIDED TO TRIM BACK SWELL
HEIGHT...BUT DID NOT REMOVE ENTIRELY. ANY SWELL WILL ENHANCE
COMBINED SEAS IN THE PALM BEACH WATERS...WITH 2-4 FOOT SEAS
POSSIBLE THROUGH THE END OF THE WEEKEND. OTHERWISE...EXPECT EAST
FLOW TO PERSIST THROUGH EARLY NEXT WEEK...WITH SPEEDS IN THE 10-15
KNOT RANGE OVER THE ATLANTIC WATERS/BISCAYNE BAY/LAKE OKEECHOBEE...
AND 5-10 KNOTS OVER THE LOCAL GULF WATERS. PERHAPS A GREATER
THREAT FOR LONG PERIOD SWELL WILL COME AT THE END OF THE WEEK...AS
A DEEPER CYCLONE MAY DEVELOP OFF THE COAST OF THE CAROLINAS.

&&

.FIRE WEATHER...
THERE ARE NO FIRE WEATHER CONCERNS THROUGHOUT THE FORECAST
PERIOD...AS MINIMUM AFTERNOON RH VALUES WILL REMAIN SUFFICIENTLY
HIGH.

&&

.PRELIMINARY POINT TEMPS/POPS...
WEST PALM BEACH  76  88  77  88 / 30 50 30 50
FORT LAUDERDALE  79  89  80  89 / 30 40 30 30
MIAMI            77  89  78  89 / 30 40 30 30
NAPLES           74  91  75  91 / 20 40 30 40

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
AM...NONE.
GM...NONE.

&&

$$

LONG TERM...70/DD
SHORT TERM/AVIATION...30/KOB