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000
FXUS62 KKEY 200708
AFDKEY

AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS
NATIONAL WEATHER SERVICE KEY WEST FL
308 AM EDT THU JUN 20 2013

.DISCUSSION...
AN ANALYSIS OF SATELLITE-DERIVED TOTAL PRECIPITABLE WATER
MEASUREMENTS THIS MORNING REVEALS A RATHER SHARP MOISTURE GRADIENT
RUNNING APPROXIMATELY EAST-WEST ACROSS THE SERVICE AREA. ALONG AND
NORTH OF THIS GRADIENT IS WHERE CURRENT DOPPLER RADAR SCANS SHOW
ISOLATED SHOWERS AND THUNDERSTORMS. RAIN-FREE CONDITIONS EXIST SOUTH
OF THE GRADIENT. ON A LARGER SCALE...WE FIND A SYNOPTIC SITUATION NOT
ALL THAT UNUSUAL FOR LATE JUNE. A LARGE UPPER CYCLONE IS EVIDENT OVER
THE WESTERN NORTH ATLANTIC...WHILE AT LOWER LEVELS A WEAK TROPICAL
WAVE IS PASSING THROUGH PUERTO RICO...THE VIRGIN ISLANDS...AND
ADJACENT COASTAL WATERS. A PLUME OF RICH TROPICAL MOISTURE LIES EAST
OF THE WAVE AXIS...WHILE A VERY DRY PLUME OF SAHARAN ORIGIN COVERS
MUCH OF THE BAHAMAS AND CUBA. BOTH MOISTURE REGIMES WILL BE OF
INTEREST FOR LOCAL WEATHER DURING THE NEXT FEW DAYS.

BELOW-AVERAGE RAINFALL IS EXPECTED TODAY THROUGH FRIDAY AS VERY DRY
AIR ALOFT SUPPRESSES OR LIMITS SHOWER AND THUNDERSTORM DEVELOPMENT.
THE WEAK WAVE IN THE EASTERLIES CURRENTLY AFFECTING PUERTO RICO AND
THE VIRGIN ISLANDS IS LIKELY TO WEAKEN FURTHER AS IT DAMPENS IN A
CONTRACTING...DECELERATING EASTERLY CURRENT AND MOVES AWAY FROM AN
UPPER CYCLONE. HOWEVER...PORTIONS OF THE RICH TROPICAL MOISTURE PLUME
ASSOCIATED WITH THE WAVE ARE LIKELY TO APPROACH SOUTHERN FLORIDA
FRIDAY NIGHT OR SATURDAY...ENHANCING SHOWER AND THUNDERSTORM COVERAGE
OVER THE WEEKEND. RAINFALL PATTERNS WILL BE MODULATED BY LOCAL
MESOSCALE CIRCULATIONS.

NEXT WEEK...A LARGE-SCALE LOW/MID-LEVEL SUBTROPICAL RIDGE IS
EXPECTED TO BUILD NORTH OF THE REGION WITH A RESULTING DEEP EASTERLY
CURRENT ACROSS THE FLORIDA KEYS. LARGE-SCALE VERTICAL MOTION
CHARACTER WILL BE RANGE FROM WEAK SUBSIDENCE TO NEUTRAL...SO DAILY
RAINFALL CHANCES SHOULD BE CLOSE TO CLIMATOLOGY. A DEVELOPING UPPER
CYCLONE OVER THE EASTERN GULF OF MEXICO BY MID WEEK MAY OR MAY NOT
ELEVATE RAIN CHANCES LOCALLY DEPENDING ON THE DEGREE TO WHICH ANY
FORCING COUPLES WITH THE LOWER TROPOSPHERE. FOR NOW...CLIMATOLOGICAL
PRECIPITATION PROBABILITIES PREVAIL.
&&

.MARINE...
GENTLE TO MODERATE EAST-SOUTHEAST BREEZES WILL BECOME MODERATE TO
FRESH EASTERLY TONIGHT...WITH A PATTERN OF EVENING SURGES AND LATE
MORNING LULLS LIKELY THROUGH SATURDAY. THEREAFTER...A STEADY MODERATE
EASTERLY BREEZE IS EXPECTED FOR SEVERAL DAYS NEXT WEEK. SHOWER AND
THUNDERSTORM COVERAGE WILL BE HIGHEST FRIDAY NIGHT THROUGH SUNDAY.
&&

.AVIATION...
VFR CIGS/VIS AND EAST SOUTHEASTERLY SURFACE WINDS NEAR 10 KNOTS WILL
PREVAIL AT THE EYW AND MTH TERMINALS. UPSTREAM SATELLITE
OBSERVATIONS PORTRAY A DRY AND STABLE AIR MASS ATOP A WELL MIXED AND
MOIST BOUNDARY LAYER. THEREFORE...LOW CHANCES FOR PRECIPITATION
TODAY AND TONIGHT...WITH TEMPORARY MVFR CIGS POSSIBLE EARLY THIS
MORNING AND LATE TONIGHT.
&&

.CLIMATE...
JUNE 20TH...ON THIS DATE IN FLORIDA KEYS WEATHER HISTORY...IN
1983... A TORNADO CLASSIFIED AS F1 ON THE FUJITA SCALE PRODUCED
$2.5M IN DAMAGE NEAR LOWER SUGARLOAF KEY. ACCORDING TO
RECORDS...THERE WERE NO TROPICAL CYCLONES IN THE AREA. A TORNADO
WOULD BE CLASSIFIED AS F1 IF IT PRODUCED DAMAGE CONSISTENT WITH WIND
SPEEDS OF 73 TO 112 MPH.
&&

.PRELIMINARY POINT TEMPS/POPS...
KEY WEST  89  83  89  81 / 10 20 20 30
MARATHON  92  83  92  82 / 10 20 20 30
&&

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

$$

PUBLIC/MARINE/FIRE............KASPER
AVIATION/NOWCASTS/CLIMATE.....CLR

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