Area Forecast Discussion
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000
FXUS62 KKEY 050842
AFDKEY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KEY WEST FL
442 AM EDT WED AUG 5 2015

.DISCUSSION...
ANALYSIS OF REGIONAL UPPER-AIR DATA TRENDS OVER THE LAST 24 HOURS
REVEAL GEOPOTENTIAL HEIGHT RISES ACROSS THE FLORIDA PENINSULA AND
KEYS THANKS TO A FORTIFICATION OF THE WESTERN EXTENSION OF THE
ATLANTIC SUBTROPICAL ANTICYCLONE. A SUBTLE TROUGH IS STILL EVIDENT
FROM THE SOUTHEASTERN GULF OF MEXICO TO THE YUCATAN PENINSULA...PER
LOW-LEVEL STREAMLINE AND CYCLONIC VORTICITY ANALYSES. A SLIGHT
SOUTHEASTERLY WIND SURGE IS EVIDENT EAST OF THE TROUGH. IN
FACT...SOUTHEASTERLY FLOW HAS OVERSPREAD THE FLORIDA KEYS...WITH
ISOLATED SHOWERS AND THUNDERSTORMS PERIODICALLY DEVELOPING ALONG
TRANSIENT BOUNDARIES.

VARIOUS SATELLITE PRODUCTS IDENTIFY A FAIRLY WELL-IN-TACT SAHARAN
AIR LAYER PLUME CURRENTLY OVERSPREADING THE BAHAMAS AND EASTERN CUBA.
SOME RECENT SATELLITE-DERIVED SOUNDINGS WITHIN THE PLUME ENVIRONMENT
REVEAL VERY DRY AIR ALOFT...STEEP LOW- TO MID-TROPOSPHERIC LAPSE
RATES...AND STRONG LOW-ALTITUDE CONVECTIVE INHIBITION ENERGY. SUCH
THERMODYNAMIC CONDITIONS ARE CHARACTERISTIC OF SAHARAN AIR LAYER...
OR SAL..PLUMES IN THE WESTERN PORTIONS OF THE ATLANTIC BASIN.

CURRENTLY...AIR TEMPERATURES IN MOST KEYS ISLAND COMMUNITIES REMAIN
IN THE MID 80S...WITH DEWPOINT TEMPERATURES IN THE MID TO UPPER 70S.
HEAT INDICES AT THIS LATE/EARLY HOUR ARE STILL 92-95F.

FORECASTS -- TODAY -- BEST RAIN...THUNDERSTORM...AND WATERSPOUT
CHANCES WILL BE THIS MORNING AS THE APPROACHING SAL PLUME AND ITS
STEEP MID-LEVEL LAPSE RATES BRIEFLY OVERRIDE A BOUNDARY-LAYER WIND
SURGE ALONG A DEPARTING PRECIPITABLE WATER GRADIENT. THIS AFTERNOON
AND TONIGHT...SHOWER AND STORM COVERAGE SHOULD DROP RAPIDLY WITH A
STEADY BREEZE KEEPING VERY WARM AND HUMID CONDITIONS IN KEYS
COMMUNITIES ALL NIGHT.

THURSDAY AND THURSDAY NIGHT -- THE SAL PLUME...STILL IN TACT...
SHOULD BE PASSING NEARLY DIRECTLY OVERHEAD WITH MOSTLY
SUNNY/CLEAR/HAZY SKIES...AND RAIN-FREE CONDITIONS WITH HIGHS IN THE
LOW/MID 90S AND LOWS IN THE MID 80S.

FRIDAY-SUNDAY -- A SOUTHERN PLAINS DEEP LAYER MEAN ANTICYCLONE WILL
GROW AS THE ATLANTIC SUBTROPICAL ANTICYCLONE WANES...WHILE MID-
LATITUDE CYCLONIC VORTICITY INTRUSIONS REACH EQUATORWARD OVER NORTH
FLORIDA...BETWEEN THE TWO ANTICYCLONES. GRADUAL DEEPENING OF THE
MOIST LAYER ACROSS THE KEYS WILL OCCUR ALONG WITH A RETURN OF SHOWER
AND THUNDERSTORM CHANCES.

SUNDAY NIGHT-TUESDAY -- ESSENTIALLY A CLIMATOLOGICAL FORECAST WITH
DEEP BUT WEAK EASTERLY FLOW...WEAK LARGE-SCALE FORCING...AND TYPICAL
MOISTURE/POTENTIAL BUOYANCY VALUES.
&&

.MARINE...
A HIGH PRESSURE AREA WILL REMAIN CENTERED ACROSS THE FLORIDA
PENINSULA TODAY THROUGH SUNDAY. A SHORT-LIVED WIND SURGE WILL OCCUR
MAINLY OVER THE STRAITS OF FLORIDA TONIGHT...WITH WINDS WELL OFFSHORE
PEAKING AT A STEADY 15 KNOTS...WITH SEAS UP TO 4 FEET IN THE GULF
STREAM. OTHERWISE...MAINLY EAST WINDS WILL AVERAGE LESS THAN 15
KNOTS WITH SEAS 3 FEET OR LESS MOST AREAS.
&&

.AVIATION...
THROUGHOUT THE REMAINDER OF THE TAF PERIOD...VFR CONDITIONS WILL
PERSIST AT BOTH THE EYW AND MTH TERMINALS. SOME SHOWERS AND
THUNDERSTORMS MAY IMPACT THE TERMINALS BEFORE 05/17Z...BUT AT THIS
TIME CONFIDENCE IS TOO LOW TO INCLUDE IN THE TAFS. AMENDMENTS WILL
BE ISSUED AS NEEDED. &&

.PRELIMINARY POINT TEMPS/POPS...
KEY WEST  90  83  91  83 / 30 10 -  -
MARATHON  93  83  94  83 / 30 10 -  -
&&

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

$$

PUBLIC/MARINE.........KASPER
AVIATION/NOWCASTS.....VICKERY

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