Area Forecast Discussion
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000
FXUS62 KKEY 310902
AFDKEY

AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS
NATIONAL WEATHER SERVICE KEY WEST FL
502 AM EDT SUN AUG 31 2014

.DISCUSSION...
OBSERVATIONS/TRENDS -- FAST-MOVING SHOWERS AND THUNDERSTORMS...SOME
WITH VIGOROUS SQUALLS...HAVE BEEN MOVING WEST-NORTHWESTWARD ACROSS
THE SERVICE AREA ALL NIGHT...WITH SPEEDS OF MOVEMENT OCCASIONALLY
REACHING 30 KNOTS. THE MOST VIGOROUS SQUALLS AFFECTED THE AREA
BETWEEN BOOT KEY HARBOR AND SOMBRERO KEY LIGHTHOUSE BETWEEN 830 AND
900 PM SATURDAY EVENING. A WIND GUST OF 48 KNOTS WAS RECORDED ATOP
SOMBRERO KEY LIGHTHOUSE...WITH A GUST OF 52 KNOTS REPORTED OUT OF
MARATHON CITY MARINA. DOWNDRAFT VIGOR AND OUTFLOW INTENSITY CLEARLY
WERE AUGMENTED BY FAST CELL MOVEMENT...AND PROBABLY ENHANCED BY
EVAPORATIVE COOLING FROM DRY AIR ENTRAINED INTO DESCENDING
PRECIPITATION CORES. IN ANY CASE...CELL INTENSITIES AND COVERAGE HAVE
DECREASED GRADUALLY OVER THE LAST FOUR HOURS...PROBABLY WITH THE
ARRIVAL OF SLIGHTLY RICHER MOISTURE FROM THE SOUTHEAST.

ON THE LARGE SCALE...A TROPICAL WAVE IS MOVING WESTWARD ACROSS THE
YUCATAN PENINSULA WHILE A SPRAWLING SUBTROPICAL HIGH PRESSURE CELL
COVERS MOST OF THE WESTERN NORTH ATLANTIC...SOUTHEASTERN UNITED
STATES...AND EASTERN GULF OF MEXICO. FRESH EAST TO SOUTHEAST BREEZES
HAVE BEEN BLOWING PERSISTENTLY ACROSS MOST FLORIDA KEYS COASTAL
WATERS...WITH OCCASIONALLY STRONG BREEZES OVER THE WESTERN ZONES.
WINDS RECENTLY HAVE LULLED...BUT THIS SHOULD BE SHORT-LIVED BASED ON
OUR EARLY MORNING ANALYSIS.

CURRENTLY...AIR TEMPERATURES REMAIN IN THE MID 80S...WITH DEWPOINT
TEMPERATURES IN THE MID 70S. THE COMBINATION OF HEAT AND HUMIDITY
YIELDS HEAT INDICES IN THE MID 90S AT THIS EARLY HOUR. THE
TEMPERATURE AT MARATHON ACTUALLY DROPPED TO THE MID 70S IN RAIN
COOLED AIR. HOWEVER...THE TEMPERATURE QUICKLY REBOUNDED TO THE MID
80S WITH THE ONSET OF A EAST-SOUTHEAST BREEZE. NEARSHORE SEA SURFACE
TEMPERATURES ARE STILL IN THE 86-88F RANGE.

FORECASTS -- OUR BASIC PROGNOSTIC REASONING HAS CHANGED LITTLE OVER
THE LAST FEW FORECAST CYCLES. FAIRLY LOW RAIN CHANCES OVERALL SHOULD
PERSIST FOR THE NEXT TWO DAYS...ALTHOUGH SHOWERS AND THUNDERSTORMS
CERTAINLY WILL BE AROUND THE AREA EACH DAY AND NIGHT. AN UPPER-
TROPOSPHERIC COLD-CORE CYCLONE CURRENTLY DEVELOPING EAST OF THE
BAHAMAS WILL INTENSIFY AS IT MOVES GRADUALLY WESTWARD...AND THEN
LIKELY WEAKEN RAPIDLY AS IT APPROACHES THE FLORIDA KEYS WEDNESDAY OR
THURSDAY. THE INFLUENCE OF THIS SYSTEM ON LOCAL WEATHER REMAINS
UNCERTAIN DUE TO ITS PROBABLE WEAK AND PERHAPS SHALLOW FORCE FIELDS.
THESE TUTT-TYPE CELLS TEND TO HAVE LITTLE IMPACT ON SENSIBLE WEATHER
IF THEIR CYCLONIC FLOW FIELDS REMAIN ABOVE THE MIDTROPOSPHERE.
NEVERTHELESS...WE WILL MAINTAIN A SLIGHTLY ELEVATED RAIN CHANCE FOR
THE WEDNESDAY/THURSDAY TIME FRAME BECAUSE IT LOOKS AS THOUGH SOME
LOWER-TROPOSPHERIC REFLECTION MAY EXIST/DEVELOP ACCORDING TO LATEST
NWP GUIDANCE. GRADIENT FLOW WILL WEAKEN BELOW WHAT IT HAS BEEN...
ESPECIALLY BY MONDAY...WITH MODERATE EASTERLY BREEZES ANTICIPATED FOR
MOST OF THE WEEK THEREAFTER.
&&

.MARINE...
SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR THE LOWER STRAITS OF
FLORIDA AND THE EXTREME SOUTHEASTERN GULF OF MEXICO AROUND DRY
TORTUGAS. CAUTION HEADLINES REMAIN UP FOR REMAINING ZONES EXCEPT FOR
FLORIDA BAY. WINDS AND SEAS WILL BE LOCALLY HIGHER AND VARIABLE IN
AND NEAR SHOWERS AND THUNDERSTORMS.
&&

.AVIATION...
EXTREMELY BRIEF PERIODS OF MVFR TO IFR CONDITIONS ARE POSSIBLE...BUT
NOT LIKELY AT EITHER THE KEY WEST INTERNATIONAL OR MARATHON ISLAND
TERMINALS THROUGH 12Z DUE TO SHOWERS AND A FEW THUNDERSTORMS MOVING
WEST - NORTHWEST ACROSS THE AREA. SURFACE WINDS WILL BE OUT OF THE EAST
TO SOUTHEAST AROUND 10 KNOTS...WITH GUSTS AROUND 15 KNOTS OUTSIDE OF
ANY SHOWER ACTIVITY. WINDS WILL INCREASE TO NEAR 20 KNOTS QUICKLY
OFF THE DECK BUT WILL NOT REACH LOW LEVEL WIND SHEAR CRITERIA.
&&

.CLIMATE...
THE LOW TEMPERATURE AT KEY WEST YESTERDAY WAS 85F. THIS BREAKS THE
DAILY WARM MINIMUM TEMPERATURE RECORD OF 83F LAST OBSERVED IN 2004.
TEMPERATURE RECORDS AT KEY WEST DATE BACK TO 1872.
&&

.PRELIMINARY POINT TEMPS/POPS...
KEY WEST  90  84  90  83 / 20 20 30 30
MARATHON  92  84  92  83 / 20 20 30 30
&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
GM...SMALL CRAFT ADVISORY IN EFFECT FOR GMZ034...GMZ054...GMZ055...
     GMZ074...GMZ075.
&&

$$

PUBLIC/MARINE.........KASPER
AVIATION/NOWCASTS.....BWC

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