079  
FXUS62 KKEY 240914  
AFDKEY  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE KEY WEST FL  
514 AM EDT MON SEP 24 2018  
   
DISCUSSION
 
 
AN UPPER-LEVEL COMPOSITE ANALYSIS EARLY THIS MORNING REVEALS A  
DEEP LAYER MEAN ANTICYCLONE CENTERED OVER THE WESTERN NORTH  
ATLANTIC NEAR BERMUDA, WITH A RIDGE EXTENDING WEST ACROSS THE  
SOUTHEASTERN UNITED STATES. A DISORGANIZED VORTEX IS MOVING ALONG  
THE SOUTHERN FLANK OF THIS SYSTEM, ABOUT HALFWAY BETWEEN BERMUDA  
AND THE BAHAMAS. AN ASSOCIATED BROAD AREA OF LOW PRESSURE AT THE  
SURFACE HAS DISRUPTED THE GRADIENT FLOW ALONG THE SOUTHERN FLANK  
OF THE SURFACE ANTICYCLONE, WHICH HAS RESULTED IN LIGHT/GENTLE  
BREEZES ACROSS THE FLORIDA KEYS AND ADJACENT WATERS. THE  
MID/UPPER-LEVEL CYCLONE WHICH HAS BEEN DRIFTING WESTWARD ACROSS  
THE GULF OF MEXICO DURING THE LAST FEW DAYS HAS WEAKENED, AND  
CURRENTLY IS LOCATED OVER THE SOUTH-CENTRAL GULF OF MEXICO. TOTAL  
PRECIPITABLE WATER VALUES HAVE DECREASED DURING THE LAST 24 HOURS  
ACROSS THE SERVICE AREA, OWING TO ADVECTION OF DRIER AIR INTO THE  
LOWER AND MIDDLE TROPOSPHERE FROM THE EAST. THIS, IN TURN, HAS  
DECREASED COVERAGE OF SHOWERS AND THUNDERSTORMS.  
 
FORECASTS FOR TODAY THROUGH WEDNESDAY -- A DEEP LAYER MEAN  
ANTICYCLONE WILL PERSIST ACROSS THE WESTERN NORTH ATLANTIC, WHILE  
THE VORTEX ALONG ITS SOUTHERN FLANK MIGRATES WEST-NORTHWESTWARD,  
TOWARD THE SOUTH ATLANTIC BIGHT. LOCALLY, LARGE-SCALE VERTICAL  
MOTIONS WILL BE CHARACTERIZED BY EITHER NEUTRALITY OR WEAK  
SUBSIDENCE ATOP A SEASONABLY DEEP AND UNSTABLE MOIST LAYER.  
THEREFORE, MEASURABLE RAIN AND THUNDER CHANCES WILL BE NEAR  
CLIMATOLOGICAL VALUES, WHICH REPRESENTS NO CHANGE FROM THE  
PREVIOUS FORECAST CYCLE. AFTER WEDNESDAY, THE DEEP LAYER MEAN  
ANTICYCLONE WILL BUILD WESTWARD ACROSS THE SOUTHEASTERN UNITED  
STATES, WITH CORRESPONDING RISING MEAN SEA LEVEL PRESSURES  
BENEATH RESULTING IN INCREASING GRADIENT FLOW LOCALLY. MODERATE TO  
OCCASIONALLY FRESH EAST OR EAST-SOUTHEAST BREEZES LIKELY WILL  
DEVELOP BY THE WEEKEND.  

 
   
MARINE
 
 
NO WATCHES, WARNINGS, OR ADVISORIES ARE IN EFFECT FOR FLORIDA  
KEYS COASTAL WATERS ZONES. A RIDGE AXIS WILL EXTEND WEST-SOUTHWEST  
INTO THE SOUTHEASTERN UNITED STATES TODAY THROUGH TUESDAY.  
MEANWHILE, AN AREA OF LOW PRESSURE WILL ROTATE CLOCKWISE IN THE  
NORTHWESTERN ATLANTIC, LIFTING NORTHEAST ALONG THE EASTERN  
SEABOARD LATE TUESDAY. LIGHT TO GENTLE EAST TO SOUTHEAST BREEZES  
WILL PREVAIL ACROSS THE FLORIDA KEYS THROUGH MUCH OF THE FORECAST  
PERIOD, STRENGTHENING A BIT MID WEEK.  

 
   
AVIATION
 
 
06Z TAF DISCUSSION.  
 
VFR CONDITIONS EXPECTED TO PREVAIL AT EYW AND MTH TERMINALS  
GENERALLY THROUGH THE FORECAST PERIOD. WIDELY SCATTERED LIGHT TO  
MODERATE SHOWERS WILL BE POSSIBLE OFF AND ON THROUGH MUCH OF THE  
NIGHT INTO THE MORNING. WILL HAVE A VCSH AT BOTH TERMINALS, BUT  
STRONGER CONVECTION CHANCES REMAIN TOO LOW TO MENTION. OUTSIDE OF  
CONVECTION, WINDS WILL REMAIN EASTERLY NEAR 5 TO 10 KTS. 08/MNK  

 
   
CLIMATE
 
 
FOR SEPTEMBER 24TH, THE DAILY RECORD HIGH TEMPERATURE OF 92 DEGREES  
WAS LAST RECORDED IN 1989. IN 1894, THE DAILY RECORD COLD HIGH  
TEMPERATURE OF 78 DEGREES WAS RECORDED. THIS IS ALSO TIED FOR THE  
COLDEST HIGH TEMPERATURE EVER RECORDED IN SEPTEMBER. ALSO IN 1894  
ON THIS DATE, THE DAILY RECORD RAINFALL OF 5.83 INCHES WAS RECORDED.  
TEMPERATURE RECORDS AT KEY WEST DATE BACK TO 1872, AND PRECIPITATION  
RECORDS DATE BACK TO 1871. 08/MNK  

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
KEY WEST 90 80 90 81 / 30 30 30 30  
MARATHON 90 80 91 81 / 30 30 30 30  

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

 
 

 
 
PUBLIC/MARINE/FIRE...KASPER  
AVIATION/NOWCASTS....MNK  
 
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