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000
FXUS62 KKEY 251503
AFDKEY

AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS
NATIONAL WEATHER SERVICE KEY WEST FL
1103 AM EDT SAT MAY 25 2013

.DISCUSSION...
A REVIEW OF MEAN SEA LEVEL PRESSURE ANALYSES OVER THE LAST 24 HOURS
SHOWS A LARGE-SCALE RIDGE BUILDING TOWARD THE SOUTH AND EAST OVER
THE GULF OF MEXICO AND FLORIDA PENINSULA. AS A RESULT...THE COL IN
THE PRESSURE FIELD WHICH WAS EVIDENT NEARBY BOTH YESTERDAY AND THE
DAY BEFORE HAS BEEN REPLACED BY ROUGHLY EAST-WEST ORIENTED ISOBARS
WHICH INCREASINGLY ARE PACKED CLOSER TOGETHER. THE SURFACE WIND
RESPONSE HAS LAGGED THE PRESSURE CHANGES. HOWEVER...WINDS ACROSS THE
FLORIDA KEYS SHIFTED OUT OF THE NORTHEAST OVERNIGHT...AND UPSTREAM
OBSERVATIONS HAVE SHOWN INCREASES IN WIND SPEED THIS MORNING. A WIND
SURGE BOUNDARY APPEARS TO BE ASSOCIATED WITH THE CONVERGENCE ZONE
AND BAND OF CLOUDINESS AND SHOWERS CURRENTLY EVIDENT IN
GEOSTATIONARY SATELLITE ANIMATIONS APPROACHING SOUTHEASTERN FLORIDA.
ONE OF THE SHOWERS AT THE LEADING EDGE OF THIS BAND WENT THROUGH THE
OCEAN REEF CLUB EARLIER.

AT PRESENT...MOSTLY SUNNY SKIES PREVAIL OVER MOST KEYS ISLAND
COMMUNITIES...WITH AIR TEMPERATURES RISING THROUGH THE 80S AFTER
MORNING LOWS IN THE MID-UPPER 70S. CURRENT DEWPOINTS ARE RIGHT AROUND
70F.

THE FIRST-PERIOD FORECAST CHALLENGES TODAY INCLUDE THE FOLLOWING...

1 - WILL A CUMULUS LINE FORM OVER OR NEAR THE LOWER FLORIDA KEYS IN A
FAVORABLE LOW-LEVEL WIND/SHEAR ORIENTATION BEFORE ONSET OF A EASTERLY
WIND SURGE AND INCREASED SHEAR THIS AFTERNOON?

2 - WILL SEA AND BAY BREEZES OVER SOUTHERN PENINSULAR FLORIDA BE
STRONG ENOUGH TO INITIATE THUNDERSTORMS WHICH THEN MOVE WESTWARD OVER
OUR SOUTHEASTERN GULF MARINE ZONES? AND...IF THIS HAPPENS...WILL
THERE BE ANY INTERACTION BETWEEN THE STORMS/OUTFLOW AND A LOWER KEYS
CUMULUS LINE/SHOWERS/OUTFLOW?

LIMITING FACTORS FOR CONVECTIVE RAINFALL INCLUDE...LIKE YESTERDAY...
VERY DRY AIR JUST ABOVE THE BOUNDARY LAYER AND SIGNIFICANT CONVECTIVE
INHIBITION BASED AT LOW ALTITUDES. UNLIKE YESTERDAY...ONSET OF AN
EASTERLY WIND SURGE LIKELY WILL IMPART SHEAR TO THE ENVIRONMENT WHICH
WILL EXACERBATE SIGNIFICANT DRY-AIR ENTRAINMENT.

EXISTING FORECASTS ARTICULATE THE APPROPRIATE LEVEL UNCERTAINTY AND
SHOW SLIGHTLY HIGHER RAIN CHANCES IN THE LOWER KEYS AND GULF REGIONS
WHERE MESOSCALE FORCING APPEARS TO BE MOST FAVORABLE FOR EVENTUAL
CONVECTIVE RAINFALL. SO...WE WILL ROLL WITH THE GOING FORECASTS...AND
UPDATE AS NECESSARY THIS AFTERNOON.
&&

.MARINE...
A NORTHEAST TO EAST WIND SURGE IS EXPECTED TO OVERSPREAD FLORIDA KEYS
COASTAL WATERS THIS AFTERNOON...AND SMALL CRAFT OPERATORS ARE URGED
TO EXERCISE CAUTION BEGINNING AROUND NOON. BREEZES SHOULD FRESHEN TO
A STEADY 20 KNOTS MOST AREAS TONIGHT...WHEN SMALL CRAFT ADVISORIES
LIKELY WILL BE REQUIRED FOR ALL ZONES. THIS WIND SURGE WILL USHER IN
A NEARLY WEEK-LONG PERIOD OF BREEZY CONDITIONS.
&&

.AVIATION...
THROUGH THIS AFTERNOON AND EARLY EVENING...VFR CONDITIONS ARE
EXPECTED TO PREVAIL AT BOTH THE KEY WEST AND MARATHON TERMINALS.
THERE IS A CHANCE OF SHOWERS OVER THE MIDDLE AND LOWER KEYS AFTER
NOON. EXPECT A LIGHT NORTH BREEZE EARLY THIS MORNING TO TURN MORE
TOWARDS THE EAST...AND INCREASE TO 10 TO 15 KNOTS WITH HIGHER
GUSTS DURING THE AFTERNOON.
&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
GM...NONE.
&&

$$

PUBLIC/MARINE.........KASPER
AVIATION/NOWCASTS.....DEVANAS
DATA COLLECTION.......MSB

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