566  
FXUS62 KKEY 161955  
AFDKEY  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE KEY WEST FL  
355 PM EDT MON SEP 16 2019  
   
DISCUSSION
 
IN THE MIDDLE AND UPPER LEVELS(700-200 MB), LATEST  
AVAILABLE SATELLITE IMAGERY OVERLAID WITH MODEL STREAMLINE  
ANALYSIS AS OF 300 PM, DEPICT LOWER AMPLITUDE AUTUMNAL TYPE  
TROUGHING ACROSS THE MIDWESTERN, NORTHEASTERN, AND MIDDLE ATLANTIC  
UNITED STATES. WELL TO THE SOUTH OF THAT, A REGIONAL SCALE WARM  
CORE MIDDLE AND UPPER ANTICYCLONE IS CENTERED OVER THE FLORIDA  
STRAITS. THIS SYSTEM ENCOMPASSES SOUTH FLORIDA AND THE FLORIDA  
KEYS, THE NORTHERN BAHAMAS, MUCH OF CUBA, THE SOUTHEASTERN GULF OF  
MEXICO. OF COURSE AT 1100 AM AND IN BETWIXT THESE AFOREMENTIONED  
FEATURES, EXISTS STRENGTHENING 978 MB HURRICANE HUMBERTO, WHICH  
WAS LOCATED IN THE WESTERN ATLANTIC NEAR 29.7N 77.3W MOVING  
EAST NORTHEAST AT 7 MPH AND WAS ABOUT 710 MILES WEST OF BERMUDA  
AT THAT TIME.  
 
AT THE SURFACE AND IN THE LOWER TO MIDDLE LEVELS, (SURFACE TO 700  
MB), LATEST AVAILABLE SURFACE AND MARINE OBSERVATIONS AND ANALYSIS  
AS OF 300 PM, DETAIL NEAR 1020 MB RIDGING CENTERED FROM MISSOURI  
EAST NORTHEAST TO CENTRAL VIRGINIA. WELL TO THE SOUTH OF THAT  
FEATURE, A MESOSCALE RIDGE WAS LOCATED OVER WESTERN CUBA. UPSTREAM  
OF THAT KEYS, THE NEXT TROPICAL WAVE OF SIGNIFICANCE WAS  
APPROACHING THE WINDWARD ISLANDS FROM THE TROPICAL ATLANTIC, YET  
UPSTREAM OF THAT FEATURE, AT 2 PM, A 1009 MB DISTURBANCE WAS  
BEING MONITORED BY NHC AND WAS LOCATED IN THE TROPICAL ATLANTIC  
AT ABOUT 40W AROUND 11N.  
   
CURRENTLY
 
AS OF 300 PM, SKIES ARE MOSTLY SUNNY ACROSS THE  
ISLANDS AND SURROUNDING WATERS, RADAR DETECTS A CLUSTER OF SHOWERS  
MOVING ACROSS THE UPPER FLORIDA KEYS AND SURROUNDING WATERS, WITH  
JUST A FEW SHOWERS INDICATED ACROSS PORTIONS OF THE FLORIDA  
STRAITS ALONG A CONFLUENT STREAMER/BOUNDARY PROPAGATING SOUTHEAST.  
TEMPERATURE ACROSS THE ISLANDS HAVE REACHED THE UPPER 80S TO  
AROUND 90, WITH DEWPOINTS IN THE UPPER 70S. C-MAN STATIONS ALONG  
THE FLORIDA REEF ARE RECORDING NORTHWEST WINDS AT 10 TO 15 KNOTS,  
AND LAND STATIONS RECORDING 10 TO 15 MPH OVER THE ISLANDS.  
   
SHORT TERM
 
TONIGHT THRU WEDNESDAY NIGHT, HURRICANE HUMBERTO  
WILL CONTINUE TO MOVE STEADILY AWAY FROM SOUTH FLORIDA AND THE  
FLORIDA KEYS. WE EXPECT GENTLE TO MODERATE NORTHWEST BREEZES THIS  
EVENING, BUT SLIGHTLY STRONGER ACROSS THE UPPER KEYS GIVEN  
TYPICAL LAND BREEZE CONVECTION. AFTER MIDNIGHT, WINDS WILL  
DIMINISH OUT OF THE NORTHWEST AND RAIN CHANCES WILL DROP FURTHER  
GIVEN MIDDLE LEVEL DRY AIR MOVING ACROSS. HAVE STARTED WITH A LOW  
CHANCE FOR SHOWERS THIS EVENING, 305, THEN BRING IT DOWN TO  
ISOLATED OVERNIGHT. THEREAFTER, LOCAL WINDS WILL VEER MORE TO THE  
NORTH DURING TUESDAY AS WEAK SURFACE RIDGING IS TO THE WEST OF THE  
KEYS, THEN BECOMES NORTHWEST OF THE KEYS TUESDAY NIGHT. VERY DRY  
AIR IN THE MIDDLE LEVELS WILL LIMIT CHANCES FOR SHOWERS AND  
STORMS. AS SUCH WE HAVE ISOLATED SHOWERS AND STORMS AT BEST FOR  
THOSE PERIODS, 10-20%. THEN DURING WEDNESDAY, NEAR 1030 MB  
AUTUMNAL HIGH PRESSURE OVER THE MIDWESTERN AND NE STATES WILL  
GRADUALLY OOZE SOUTHWARDS TO OVER FLORIDA AND THE KEYS. SLIGHT  
INCREASES IN MOISTURE WILL FAVOR A MORE LATE SUMMER MESOSCALE  
PATTERN AS LOCAL GENTLE WINDS WILL BECOME MORE NORTHEAST AND  
INCREASE LATER IN THE DAY, BECOMING MODERATE BY THE AFTERNOON AND  
EVENING. AS SUCH, WE ARE CARRYING 30% CHANCES FOR SHOWERS AND  
ISOLATED STORMS FOR WEDNESDAY AND WEDNESDAY NIGHT.  
 

 
   
LONG TERM
 
THURSDAY THRU MONDAY, THE AFOREMENTIONED PRE-  
AUTUMNAL LIKE HIGH PRESSURE WILL INTENSIFY ALONG THE EASTERN  
SEABOARD AND REMAIN STRONG THURSDAY THRU SATURDAY, REMAINING  
LOCKED IN PLACE FROM THE MIDDLE ATLANTIC STATES TO THE CAROLINAS  
THRU THE PERIOD. THRU THIS TIME, A SHARP MSLP GRADIENT AND  
TYPICALLY MOIST CONDITIONS BELOW 800 MB, WILL RESULT IN AMPLE NEAR  
SURFACE CONVERGENCE ALLOWING FOR THE DEVELOPMENT OF FAST MOVING  
SHOWERS AND ISOLATED STORMS, WITH MOST OF THE ACTIVITY OCCURRING  
LATE AT NIGHT AND IN THE MORNING HOURS. THE 12 HOUR CHANCES FOR  
SHOWERS WILL AVERAGE BETWEEN 30 AND 40%, WHICH IS TYPICAL AT THIS  
TIME IN THE WET SEASON. BREEZY CONDITIONS CAN BE EXPECTED FRIDAY  
THRU SATURDAY NIGHT, WITH WINDS DECREASING SUNDAY AND MONDAY.  
DAYTIME HIGH TEMPERATURES WILL REACH THE UPPER 80S WITH LOWS IN  
THE UPPER 70S. ONE ADDITIONAL NOTICEABLE CHANGE THAT WILL ALSO  
ACCOMPANY THE NEAR BREEZY TO BREEZY CONDITIONS WILL BE A SLIGHT  
DECREASE IN HUMIDITY, WITH SURFACE DEWPOINTS FALLING TO NEAR 70  
FOR AT LEAST THE THURSDAY THRU FRIDAY NIGHT PERIODS. HUMIDITY  
LEVELS RECOVER BY SUNDAY THRU MONDAY AND SURFACE WINDS DROP DOWN  
AGAIN WITH THE SURFACE RIDGE TO THE NORTH WEAKENING A BIT.  
 

 
   
MARINE
 
FOR TONIGHT THRU TUESDAY NIGHT, SEAS WILL REMAIN  
ELEVATED ACROSS THE EASTERN FLORIDA STRAITS OWING TO NEAR 6 FOOT  
LONG PERIOD SWELL STILL EMANATING FROM HURRICANE HUMBERTO. WINDS  
AND SEAS WILL BE BELOW SCEC OR SCA CATEGORIES ELSEWHERE ON THE  
WATERS, BUT WINDS AND SEAS WILL BEGINNING TO BUILD WED AND WED  
NIGHT, WITH SCEC LIKELY BY THURSDAY ON ALMOST ALL WATERS, WITH SCA  
POSSIBLE IN THE STRAITS, AND SMALL CRAFT ADVISORIES LIKELY FRIDAY  
THRU AT LEAST SATURDAY NIGHT ACROSS ALMOST ALL OF THE MARINE  
DISTRICT WITH THE EXCEPTION OF THE SHALLOWER FLORIDA BAY AND  
NEARSHORE GULF WATERS. WINDS AND SEAS WOULD SLOWLY LET DOWN FOR  
THE SECOND HALF OF THE WEEKEND.  
 

 
   
AVIATION
 
ISOLATED SHOWERS HAVE MOVE OFFSHORE ACROSS THE FLORIDA  
STRAITS AND AWAY FROM THE MIDDLE KEYS. SHOWER POTENTIAL WILL  
QUICKLY DIMINISH FOR THE REMAINED OF THE AFTERNOON AND INTO THIS  
EVENING. AS SUCH EXPECTING VFR CONDITIONS TO CONTINUE THROUGH THIS  
EVENING. WINDS HAVE ABRUPTLY SHIFTED TO THE WNW/NW ACROSS BOTH  
TERMINALS AND WILL CONTINUE THROUGH THE OVERNIGHT BEFORE SHIFTING  
MORE NORTHERLY TOWARDS DAWN TUESDAY.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
KEY WEST 82 89 81 89 / 30 10 10 30  
MARATHON 81 92 81 91 / 30 10 10 30  
 

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

 
 

 
 
PUBLIC/MARINE/FIRE...FUTTERMAN  
AVIATION/NOWCASTS....LIW  
DATA COLLECTION......KBL  
 
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