908  
FXUS62 KKEY 190822  
AFDKEY  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE KEY WEST FL  
422 AM EDT FRI JUL 19 2019  
   
DISCUSSION
 
 
SCATTERED SHOWERS AND ISOLATED STORMS HAVE PROLIFERATED ACROSS THE  
STRAITS OF FLORIDA DURING THE LAST COUPLE OF HOURS, AND MORE  
RECENTLY ALONG THE UPPER KEYS AND EASTERN FLORIDA BAY, BUT AN  
EARLIER BOUT OF ACTIVITY ACROSS THE WATERS BETWEEN KEY WEST AND  
THE DRY TORTUGAS HAS NOW FADED. SOME SHOWERS AND STORMS HAVE MOVED  
ACROSS PARTS OF THE LOWER AND UPPER KEYS DURING THE NIGHT, WHILE  
OTHER PARTS OF THE ISLAND CHAIN HAVE REMAINED DRY. TEMPERATURES  
ALONG THE KEYS ARE HOVERING IN THE LOWER TO MID 80S, WHILE WINDS  
ON LAND ARE FROM THE EAST AROUND 10 MPH.  
 
SURFACE ANALYSIS DEPICTS THE BERMUDA HIGH EXTENDING FROM THE  
WESTERN ATLANTIC ACROSS THE FLORIDA PENINSULA AND THE NORTHERN  
GULF OF MEXICO, WITH THE KEYS LYING WITHIN MODERATE EASTERLY FLOW  
TO THE SOUTH OF THE RIDGE AXIS. ALOFT, LOWER/MID LEVEL RIDGING  
PREVAILS ACROSS THE REGION, BUT WATER VAPOR IMAGERY ALONG WITH  
CIMSS ANALYSIS SHOWS A WEAK UPPER LEVEL TUTT-TYPE FEATURE  
EXTENDING FROM NORTH OF THE BAHAMAS SOUTHWESTWARD TO WESTERN CUBA.  
THE 00Z KEY WEST SOUNDING FOUND A GENERALLY MOIST AND  
CONDITIONALLY UNSTABLE PROFILE, BUT SOME CONVECTIVE INHIBITION  
WAS PRESENT AT THAT TIME JUST ABOVE 900 MB. MEASURED PW WAS 1.83  
INCHES, WHICH IS NORMAL FOR THIS TIME OF YEAR. GOES TPW IMAGERY  
SHOWS A SLIGHTLY DRIER AIRMASS WITH ESTIMATED PW VALUES OF 1.5 TO  
1.7 INCHES LOCATED JUST TO THE E AND SE OF THE KEYS.  
 
FOR TODAY, THE BEST RAIN CHANCES WILL PROBABLY OCCUR DURING THE  
EARLY MORNING HOURS, AS IS OFTEN THE CASE WITH MODERATE ESE  
STEERING FLOW. WITH THIS FLOW REGIME LARGELY PREVENTING BOUNDARY  
INTERACTIONS, WOULD EXPECT SHOWER ACTIVITY TO DECREASE TO ISOLATED  
LATER THIS MORNING, DUE BOTH TO TYPICAL DIURNAL TRENDS AND A  
DRIER MID LEVEL AIRMASS EXPECTED TO MOVE IN FROM THE EAST.  
 
NOT MUCH CHANGE IS EXPECTED TONIGHT AND SATURDAY, WITH MODERATE  
ESE STEERING FLOW CONTINUING ALONG WITH NEAR NORMAL PW VALUES.  
BEST RAIN CHANCES WILL PROBABLY OCCUR DURING THE LATE NIGHT AND  
EARLY MORNING HOURS. FOR SATURDAY NIGHT THROUGH MONDAY, THE  
NORTHERN EDGE OF A WEAK TROPICAL WAVE MOVING THROUGH THE AREA  
SHOULD BRING DEEPER MOISTURE OVER THE KEYS, WITH PW VALUES AROUND  
2 INCHES AT TIMES. WE SHOULD ALSO BE ON THE WET SIDE OF A WEAK  
TUTT CELL IN THE GULF AT THAT TIME. HAVE NUDGED RAIN CHANCES  
UPWARD INTO THE 40-50 PERCENT RANGE, NOTING THAT THE LAST FEW  
RUNS OF THE GFS AND ECMWF ALSO BOTH SHOW ABOVE CLIMO POPS FOR  
THOSE TIME PERIODS.  
 
HEADING TOWARD THE MIDDLE OF NEXT WEEK, THE LATEST GUIDANCE  
REMAINS CONSISTENT IN DIGGING A RATHER STRONG MID-LATITUDE TROUGH  
FOR MIDSUMMER INTO THE EASTERN UNITED STATES, WHICH WOULD PUSH THE  
SUBTROPICAL RIDGE SOUTHWARD OVER OUR AREA. THIS WOULD RESULT IN A  
LIGHT WIND REGIME ACROSS THE KEYS, WHICH WOULD FAVOR DAYTIME  
ISLAND CLOUD LINES, ALONG WITH BOUNDARY INTERACTIONS AT ANY TIME.  
WITH GUIDANCE INDICATING THAT ADEQUATE MOISTURE AND INSTABILITY  
WILL BE AVAILABLE, HAVE NUDGED RAIN CHANCES UP A NOTCH TO 30  
PERCENT FOR MONDAY NIGHT THROUGH THURSDAY.  
 

 
   
MARINE
 
 
EASTERLY BREEZES HAVE SURGED INTO THE 10-15 KNOT RANGE ACROSS THE  
KEYS WATERS DURING THE NIGHT, AS SHOWN BY OBSERVATIONS FROM ALONG  
THE REEF AND IN THE GULF WATERS. ESE BREEZES SHOULD BACK OFF A  
FEW KNOTS DURING THE DAY, THEN INCREASE A FEW KNOTS AGAIN TONIGHT,  
PROBABLY MAXING OUT NEAR 15 KNOTS ACROSS THE STRAITS. THIS  
EASTERLY FLOW PATTERN WILL SLOWLY WEAKEN DURING THE WEEKEND, THEN  
BE REPLACED BY LIGHT WINDS DURING MUCH OF NEXT WEEK.  
 

 
   
AVIATION
 
 
VFR CONDITIONS WILL PREVAIL FOR BOTH TERMINALS. EXPECT SE WINDS NEAR  
10 KNOTS WITH FEW TO SCT CLOUDS AROUND FL025 THROUGHOUT THE PERIOD.  
SHOWERS COULD AFFECT TERMINALS WITH POSSIBLE BRIEF MVFR CEILINGS.  
REMNANT BOUNDARIES FROM EARLIER CONVECTION COULD INITIATE FURTHER  
CONVECTION THAT COULD MOVE OVER THE TERMINALS. CONFIDENCE IS TOO  
LOW FOR TIMING AND PLACEMENT AT THIS TIME TO INCLUDE IN THE  
FORECAST.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
KEY WEST 91 83 91 82 / 30 30 30 40  
MARATHON 93 83 93 82 / 30 30 30 40  
 

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

 
 

 
 
PUBLIC/MARINE/FIRE...JACOBSON  
AVIATION/NOWCASTS....CHESSER  
 
VISIT US ON THE WEB AT WEATHER.GOV/KEY  
 
FOLLOW US ON FACEBOOK AND TWITTER AT:  
WWW.FACEBOOK.COM/NWSKEYWEST  
WWW.TWITTER.COM/NWSKEYWEST  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab FL Page Main Text Page