033  
FXUS62 KKEY 200759  
AFDKEY  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE KEY WEST FL  
359 AM EDT WED SEP 20 2017  
ISSUED BY NATIONAL WEATHER SERVICE MELBOURNE FL  
 
   
DISCUSSION
 
 
   
CURRENT
 
A WEAK INVERTED SURFACE TROUGH EXTENDS NORTHEASTWARD  
FROM JUST WEST OF FLORIDA BAY ACROSS THE SOUTHERN PENINSULA TO  
NEAR WEST PALM BEACH EARLY THIS MORNING. A RATHER BAGGY PRESSURE  
PATTERN IS LEADING TO LIGHT/SOMEWHAT CHAOTIC WINDS. 3.9UM IR AND  
KBYX SHOW SOME CU STREAMERS WITH A FEW EMBEDDED SHOWERS ASSOCIATED  
WITH THE TROUGH, REMAINING NORTH OF THE LOCAL MARINE AREA. 00Z  
RAOBS SHOWED MEAN PWATS IN THE 1.7 TO 1.8" RANGE OVER THE KEYS AND  
SOUTH FLORIDA WITH SIGNIFICANT DRYING ABOVE 700MB. LOOKING ALOFT,  
NE MID-UPPER LEVEL FLOW CONTINUES BETWEEN A LARGE GOMEX RIDGE AND  
A DEFORMING MID-UPPER TROUGH EXTENDING FROM WEST-CENTRAL CUBA  
INTO THE WESTERN BAHAMAS.  
   
SHORT TERM (TODAY-FRIDAY NIGHT)
 
GLOBAL MODEL GUIDANCE IS IN  
DECENT AGREEMENT SHOWING INITIAL ADVECTION OF DRIER AIR TODAY,  
SLOWLY GIVE WAY TO INCREASING MOISTURE AND RAIN CHANCES THROUGH  
LATE WEEK (AND BEYOND). KEPT THE OVERALL INCREASING POP TREND  
FROM AROUND 20 PERCENT THURSDAY TO 40-50 PERCENT FRIDAY/FRIDAY  
NIGHT. TRADE FLOW GRADUALLY INCREASES THURSDAY, THEN BACKS AND  
FRESHENS A BIT MORE ON FRIDAY AS THE PERIPHERAL CIRCULATION OF  
MAJOR HURRICANE MARIA BEGINS TO EXERT A LITTLE MORE INFLUENCE  
LOCALLY. THE CENTER OF MARIA WILL MOVE NORTHWARD REMAINING EAST OF  
THE BAHAMAS, WHILE REACHING THE LATITUDE OF THE STRAITS BY MID  
DAY FRIDAY AND THEN THE SOUTHERN PENINSULA BY LATE FRIDAY NIGHT.  
MAXES AROUND 90-91F THE NEXT COUPLE DAYS WILL TAPER BACK BY A  
COUPLE DEGREES AS WINDS INCREASE. MINS 80-82F.  
 

 
   
LONG TERM (SATURDAY-TUESDAY)
 
FROM THIS WEEKEND INTO EARLY NEXT  
WEEK, THE OUTER/PERIPHERAL CIRCULATION OF MARIA WILL CONTINUE TO  
BE THE PRIMARY DRIVER OF THE LOCAL WIND/MOISTURE REGIME AS IT  
PASSES WELL EAST OF THE PENINSULA THIS WEEKEND, AND THEN CONTINUES  
NORTHWARD JUST OFFSHORE THE SE AND MID ATLANTIC SEABOARD EARLY  
NEXT WEEK. LINGERING MOISTURE INTO SATURDAY WILL STEADILY DECREASE  
AS WINDS DECREASE FROM SATURDAY EVENING ONWARD AS THEY BACK MORE  
NORTHERLY SUNDAY, THEN BECOME MORE OUT OF THE SE MONDAY-TUESDAY.  
INITIAL POPS 40-30 PERCENT SATURDAY-SATURDAY NIGHT TAPER BACK TO  
20 PERCENT FROM SUNDAY-TUESDAY. MAX TEMPS GENERALLY 88-90F WITH  
MINS AROUND 80-81F.  
 

 
   
MARINE
 
WITH THE WEAK PRESSURE GRADIENT IN PLACE, EXPECT LIGHT  
WINDS AROUND 5KT TODAY, THEN INCREASING OUT OF THE ENE 5-10KT  
TONIGHT. WINDS FRESHEN FURTHER TO AROUND 7-12KT THURSDAY-FRIDAY,  
SPEEDS COULD BRIEFLY APPROACH 15KT WELL OFFSHORE THE UPPER KEYS  
SATURDAY-SATURDAY DEPENDING ON LOCATION AND OUTER WIND FIELDS  
ASSOCIATED WITH MARIA, BEFORE WINDS BACK MORE NORTHERLY AND  
SLACKEN SOME BY SUNDAY.  
 

 
   
AVIATION
 
VFR. SE WINDS BELOW 10KT AFTER 14Z, THEN BACKING SOME  
WHILE DROPPING TO LESS THAN 5KT AFTER 02Z TONIGHT.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
KEY WEST 90 82 91 81 / - - 20 30  
MARATHON 91 82 91 81 / - - 20 30  
 

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

 
 

 
 
PUBLIC/MARINE/FIRE...CRISTALDI (MLB)  
AVIATION...COTTRILL (KEY)  
DATA COLLECTION...COTTRILL (KEY)  
 
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