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FXUS62 KKEY 160831
AFDKEY

AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS
NATIONAL WEATHER SERVICE KEY WEST FL
431 AM EDT WED APR 16 2014

.DISCUSSION...
CURRENT WEATHER SUMMARY -- A SURFACE ANALYSIS THIS MORNING SHOWS A
1027MB HIGH PRESSURE CELL CENTERED OVER THE OHIO VALLEY. THIS HIGH
CONTAINS A CONTINENTAL POLAR AIR MASS WHICH IS EVOLVING EASTWARD
BENEATH A PROGRESSIVE UPPER SHORT-WAVE RIDGE. A COLD FRONT ALONG THE
SOUTHERN FLANK OF THIS AIR MASS CURRENTLY IS DECELERATING AND RAPIDLY
WEAKENING AS IT APPROACHES THE FLORIDA KEYS...HAVING LOST ALL UPPER
SUPPORT AND MOST LOWER SUPPORT. THE APPROACHING FRONT IS FORCING JUST
ENOUGH LOW-LEVEL MOISTURE CONVERGENCE TO INITIATE ISOLATED TO
SCATTERED SHOWERS ACROSS PORTIONS OF THE SERVICE AREA THIS MORNING
WITHIN A MODERATELY UNSTABLE WARM SECTOR...WITH FAIRLY MOIST
CONDITIONS AT LEAST IN THE BOUNDARY LAYER. HOWEVER...BOTH CONVECTION
CELL COVERAGE AND INTENSITY ARE LIMITED OWING TO WEAK FORCING AND
DRY AIR AT LOW ALTITUDES. CURRENTLY...AIR TEMPERATURES REMAIN IN THE
UPPER 70S IN MOST ISLAND COMMUNITIES WHILE DEWPOINT TEMPERATURES ARE
IN THE LOWER 70S. GEOSTATIONARY SATELLITE INFRARED CHANNEL ANIMATIONS
SHOW THE DECELERATING AND DISINTEGRATING FRONTAL ZONE APPROACHING THE
FLORIDA KEYS...WITH MULTI-LAYERED CLOUD DECKS OVER THE EXTREME
SOUTHEASTERN GULF OF MEXICO...FLORIDA KEYS...AND STRAITS OF FLORIDA.
SURFACE WINDS HAVE ALREADY VEERED CONSIDERABLY...RANGING FROM
SOUTHWESTERLY OFF THE UPPER KEYS TO NORTHERLY OUT AT DRY TORTUGAS
NATIONAL PARK. STRONGEST WIND SPEEDS ARE WEST OF KEY WEST.

FORECAST HIGHLIGHTS -- SKIES PROBABLY WILL BE MOSTLY CLOUDY ACROSS
THE FLORIDA KEYS TODAY AS THE FRONTAL ZONE STALLS OVERHEAD. SCATTERED
SHOWER COVERAGE IS EXPECTED WITH A 12-HOUR MEASURABLE RAIN CHANCE OF
30 PERCENT. AN ISOLATED THUNDERSTORM OR TWO IS NOT OUT OF THE REALM
OF POSSIBILITY. HOWEVER...THE PROBABILITY IS TOO LOW FOR INCLUSION IN
THE FORECASTS. A FEW DEGREES WILL BE SHAVED OFF THE HIGH TEMPERATURES
FROM YESTERDAY...MAINLY DUE TO CLOUD COVER AND NOT ANY SIGNIFICANT
COLD THERMAL ADVECTION. THE GOVERNING HIGH PRESSURE CELL WILL SHIFT
QUICKLY EASTWARD...AND LOCAL BREEZES WILL TURN FROM NORTHWEST EARLY
THIS MORNING TO NORTHEAST BY AFTERNOON.

FOR TONIGHT THROUGH THURSDAY NIGHT -- THE LARGE-SCALE UPPER FLOW
PATTERN WILL REMAIN GENERALLY SPLIT AND PROGRESSIVE WITH A VERY
BROAD CYCLONIC FLOW REGIME OVER OLD MEXICO AND THE GULF BASIN. A
SURFACE HIGH PRESSURE CELL WILL WEDGE DOWN THE EASTERN SEABOARD TO
NORTH FLORIDA...WITH A MODERATE EASTERLY FLOW IN PLACE ACROSS THE
FLORIDA KEYS AND ADJACENT COASTAL WATERS. SUFFICIENT MOISTURE AND
WEAK INSTABILITY WILL SUPPORT SLIGHT SHOWER CHANCES. HOWEVER...
FORCING FOR ASCENT WILL BE A LIMITING FACTOR.

FRIDAY THROUGH SATURDAY -- THIS IS THE PART OF THE FORECAST WITH THE
MOST UNCERTAINTY...ESPECIALLY REGARDING WINDS...RAIN CHANCES...AND
THUNDER POTENTIAL. THE BROAD CYCLONIC FLOW REGIME ALOFT OVER OLD
MEXICO AND THE GULF BASIN WILL FAVOR SOME AMPLIFICATION OF SOUTHERN
STREAM IMPULSES...ONE OF WHICH HAS BEEN TARGETED BY MOST MODELS TO
INDUCE SOME DEGREE OF SURFACE WAVE DEVELOPMENT/CYCLOGENESIS FROM THE
EASTERN GULF TO WESTERN NORTH ATLANTIC OVER THE FRIDAY-SATURDAY TIME
FRAME. HOWEVER...SIGNIFICANT MODEL DIFFERENCES REMAIN REGARDING THIS
EVOLUTION...AND WE FAVOR SLIGHTLY THE NCEP GLOBAL MODEL OVER THE
EURO/UKMET SOLUTIONS. RAIN CHANCES REMAIN ELEVATED A BIT FOR
FRIDAY/FRIDAY NIGHT...WITH A VEERING SURFACE WIND. THUNDERSTORMS ARE
A POSSIBILITY...BUT CONFIDENCE IS TOO LOW FOR INCLUSION IN FORECASTS.

SUNDAY THROUGH TUESDAY -- MODERATE TO FRESH NORTHERLY BREEZES WILL
TURN NORTHEASTERLY DURING THE PERIOD...POWERED BY AN EASTWARD-
MIGRATING CONTINENTAL ANTICYCLONE OF MODERATE INTENSITY.
&&

.MARINE...
SMALL CRAFT SHOULD EXERCISE CAUTION OVER THE EXTREME SOUTHEASTERN
GULF OF MEXICO BEYOND FIVE FATHOMS...INCLUDING DRY TORTUGAS AND
REBECCA SHOAL CHANNEL...AS WELL AS THE LOWER STRAITS OF FLORIDA FROM
HALFMOON SHOAL WESTWARD. A WEAK FRONT WILL FALL APART OVER THE
STRAITS OF FLORIDA TODAY. A SPRAWLING HIGH PRESSURE CELL WILL EXTEND
FROM NEW ENGLAND TO THE GULF OF MEXICO TONIGHT THROUGH THURSDAY
NIGHT. A LOW PRESSURE AREA THEN WILL DEVELOP FROM THE NORTHEASTERN
GULF OF MEXICO TO THE ATLANTIC NORTH OF THE BAHAMAS FRIDAY THROUGH
SATURDAY. ANOTHER HIGH PRESSURE CELL WILL MOVE ACROSS THE EASTERN
UNITED SATURDAY NIGHT THROUGH SUNDAY NIGHT.
&&

.AVIATION...
OCCASIONAL MVFR CEILINGS FROM 1.5 KFT TO 2.5 KFT WILL BE POSSIBLE
THROUGH DAYBREAK...OTHERWISE VFR CONDITIONS WILL PREVAIL AT BOTH THE
KEY WEST AND MARATHON TERMINALS THROUGH THIS AFTERNOON. SURFACE
WINDS WILL BE NORTHWEST NEAR 10 KNOTS THROUGH THE MORNING...BECOMING
NORTHEAST THIS AFTERNOON. A FEW ISOLATED SHOWERS ARE POSSIBLE BEFORE
SUNRISE.
&&

.PRELIMINARY POINT TEMPS/POPS...
KEY WEST  82  75  83  76 / 30 20 20 20
MARATHON  82  75  85  76 / 30 20 20 20
&&

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

$$

PUBLIC/MARINE.........KASPER
AVIATION/NOWCASTS.....DEVANAS

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