657  
FXUS62 KMFL 181319 AAA  
AFDMFL  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE MIAMI FL  
919 AM EDT FRI AUG 18 2017  
   
..STRONG THUNDERSTORMS POSSIBLE IN SOUTHWEST FLORIDA TODAY
 
 
   
UPDATE
 
 
DRIER AIR AHEAD OF AN APPROACHING DISTURBANCE IS SHOWING UP WELL  
IN THIS MORNING'S MFL SOUNDING, WITH PRECIPITABLE WATER VALUES OF  
1.46 INCHES. STILL BELIEVE THE CURRENT FORECAST TREND OF A DRIER  
DAY ALONG THE EAST COAST METRO WITH WARMER TEMPERATURES IS ON  
TRACK. CONCERN SHIFTS TO THE WEST WHERE THE MORNING TBW AND KEY  
SOUNDINGS MAY BE MORE REPRESENTATIVE. THE AVAILABLE SURFACE  
MOISTURE CONTINUES TO BE PRESENT THERE WITH MORE POSSIBLY PROVIDED  
BY THE ONSHORE FLOW OF THE GULF SEA BREEZE EXPECTED TO DEVELOP  
LATER THIS MORNING. COMBINE THE MOISTURE WITH PLENTIFUL  
INSTABILITY AIDED IN PART BY COOLER TEMPERATURES ALOFT AND VERY  
WARM SURFACE TEMPERATURES AND YOU COULD SEE A DAY WHERE ANY STRONG  
CONVECTION ALONG THE INTERIOR AND GULF COAST COULD REACH NEAR  
SEVERE THRESHOLDS. THE MFL SOUNDING CONFIRMS MODEL GUIDANCE HINTS  
AT STRONG DCAPE VALUES EXCEEDING 1000 J/KG WITH KEY EXCEEDING 1300  
J/KG OF DCAPE! WHILE COVERAGE THIS AFTERNOON MAY NOT BE AS  
WIDESPREAD AS A TYPICAL SUMMER DAY, THE STORMS THAT DEVELOP WILL  
HAVE THE POTENTIAL TO TAP A HEALTHY ENVIRONMENT FOR STRONG  
DOWNBURSTS. WILL ADD SOME ENHANCED WORDING TO THE GRIDDED FORECAST  
AND ZONE FORECASTS FOR GUSTY WINDS AND SMALL HAIL THAT MAY BE  
POSSIBLE WITH TODAY'S STORMS, ALONG WITH SIMILAR UPDATES TO THE  
HAZARDOUS WEATHER OUTLOOK. UPDATED ZONES WILL BE SENT SHORTLY.  
 

 
   
PREV DISCUSSION
 
/ISSUED 757 AM EDT FRI AUG 18 2017/  
 
AVIATION...  
A DRIER DAY IS EXPECTED TODAY, THOUGH APF AND SOME OF THE INLAND  
EAST COAST TERMINALS COULD SEE CONVECTION AROUND. SUB-VFR IS  
POSSIBLE AROUND STORMS, WHICH COULD PROMPT SHORT-FUSED AMENDMENTS.  
THINGS SHOULD QUIET DOWN FOR THE EVENING, THOUGH AN APPROACHING  
WAVE COULD BRING INCREASING RAIN CHANCES BEYOND THE TAF PERIOD.  
 
PREV DISCUSSION... /ISSUED 406 AM EDT FRI AUG 18 2017/  
 
DISCUSSION...  
 
TODAY AND TONIGHT: AN INTERESTING SYNOPTIC SETUP WILL BE IN PLACE  
ACROSS SOUTH FLORIDA TODAY. SATELLITE SHOWS A WELL DEFINED UPPER  
LEVEL LOW MOVING THROUGH THE CENTRAL/NW BAHAMAS AND EASTERN CUBA  
THIS MORNING. ENTRAINED WITHIN IN IT IS A CONSIDERABLE AMOUNT OF DRY  
AIR, A SAHARAN AIRMASS, THAT IS SUPPRESSING MOST CONVECTION DESPITE  
THE COLD MID LEVEL TEMPS OF -8 TO -9C.  
 
MODELS ARE SHOWING THAT THIS DRY AIR WILL BE THE DOMINANT FEATURE,  
HOLDING STORM CHANCES GENERALLY IN THE 30-50% RANGE DESPITE AN  
OTHERWISE FAVORABLE DYNAMIC PROFILE WITH MODERATELY STEEP LAPSE  
RATES AND A 40-50KT UPPER LEVEL JET AS THE LOW TRACKS WEST  
THROUGH THE FL STRAITS LATER TODAY. AS WITH THE PAST FEW DAYS WE  
SHOULD SEE STORMS GETTING GOING AROUND MIDDAY AS BOTH SEABREEZES  
DEVELOP AND MOVE INLAND, FOCUSING TOWARDS THE WESTERN INTERIOR  
LATER IN THE AFTERNOON AND EVENING. THE PRESENCE OF THE  
AFOREMENTIONED UPPER LEVEL FEATURES MAY HELP ENHANCE STORMS, WITH  
A FEW MORE STRONG STORMS WITH GUSTY WINDS LIKELY, ESPECIALLY WITH  
BOUNDARY COLLISIONS.  
 
WITH LIMITED CLOUD COVER AND STORM COVERAGE, TEMPERATURES WILL RISE  
WELL ABOVE NORMAL WITH HIGHS CLIMBING INTO THE LOW TO MID 90S. A  
FEW UPPER 90S ARE LIKELY FOR THE INTERIOR PORTIONS OF COLLIER INTO  
HENDRY COUNTIES. SEE THE CLIMATE SECTION BELOW FOR TODAY'S RECORD  
HIGHS.  
 
THIS WEEKEND: AN UNSETTLED AND STORMY WEEKEND LOOKS TO BE IN STORE  
FOR SOUTH FLORIDA. THE UPPER LEVEL LOW AND THE COLDEST MID LEVEL  
TEMPERATURES WILL MOVE INTO THE GULF SATURDAY MORNING, BUT THIS WILL  
PLACE A ROBUST SOUTHERLY UPPER LEVEL JET ACROSS THE REGION WITH  
SPEEDS IN THE 40-50KT RANGE. MOVING INTO THE REGION BEHIND THE UPPER  
LEVEL FEATURE WILL BE A TROPICAL WAVE (NOT ANY OF THE FEATURES  
CURRENTLY BEING MONITORED FOR DEVELOPMENT BY NHC), WITH ITS DEEPER  
TROPICAL MOISTURE SPREADING ACROSS THE AREA SATURDAY AFTERNOON  
AND SUNDAY.  
 
MODELS SHOW IT POTENTIALLY TAKING MOST OF SATURDAY MORNING FOR  
THE DEEPER MOISTURE TO ADVECT ACROSS THE REGION, WHICH MAY GIVE US  
A PERIOD OF MORNING SUNSHINE TO HELP DESTABILIZE THE ATMOSPHERE.  
WITH TEMPERATURES A LITTLE COOLER ALOFT, A FEW MORE STRONG STORMS  
MAY BE POSSIBLE.  
 
THE WAVE AXIS LOOKS TO CROSS THE REGION SATURDAY NIGHT, PUTTING US  
ON THE ASCENDING SIDE ON ON SUNDAY. WITH TEMPERATURES WARMING ALOFT  
AND THE DEEP TROPICAL AIRMASS IN PLACE, ACTIVITY ON SUNDAY WILL  
LIKELY BE MORE IN THE FORM OF RAIN WITH EMBEDDED THUNDERSTORMS.  
MODERATE EAST-SOUTHEAST FLOW, AROUND 15 KNOTS, MAY ALSO HELP ENHANCE  
CONVERGENCE AND RAINFALL ALONG THE EAST COAST, MAINLY EARLY IN THE  
DAY. HEAVY RAINFALL WILL BE A CONCERN BOTH DAYS, MOST LIKELY IN THE  
SATURDAY AFTERNOON TO MIDDAY SUNDAY TIMEFRAME. WPC HAS ALREADY  
HIGHLIGHTED MOST OF SOUTH FLORIDA FOR A SLIGHT RISK OF EXCESSIVE  
RAINFALL FOR 12Z SAT THROUGH 12Z SUNDAY.  
 
NEXT WEEK: MODEL FORECASTS FOR NEXT WEEK SUGGEST THE WET AND  
UNSETTLED PATTERN WILL CONTINUE THROUGH THE WEEK.  
 
UPPER LEVEL LOW AND TROPICAL WAVE WILL DEPART TO THE WEST ON MONDAY  
AS A STRONG UPPER LEVEL RIDGE BUILDS ACROSS NORTH FLORIDA/GA. RIDGE  
CENTER WILL MIGRATE WESTWARDS THROUGH MIDWEEK TO OUR NORTH, KEEPING  
SOUTH FLORIDA UNDER DEEP EAST-SOUTHEAST FLOW. MONDAY LOOKS TO BE THE  
DRIEST DAY OF THE WEEK WITH NEAR NORMAL STORM COVERAGE AS DRY AIR  
AND SUBSIDENCE MOVE IN BEHIND THE LOW/TROPICAL WAVE.  
 
THE EXACT DETAILS OF THE WEATHER TUESDAY THROUGH THURSDAY WILL HINGE  
ON THE EXACT DEVELOPMENT AND MOVEMENT OF THE TROPICAL DISTURBANCE  
CURRENTLY LOCATED ABOUT 1000 MILES EAST OF THE LEEWARD ISLANDS. AS  
OF 2 AM, NHC CURRENTLY GIVES THIS FEATURE A 70% CHANGE OF DEVELOPING  
INTO A TROPICAL CYCLONE IN 2 DAYS AND 5 DAYS RESPECTIVELY. IT IS  
EXPECTED THAT THIS FEATURE WILL CONTINUING MOVING NORTHWEST AND  
POTENTIALLY BE IN THE BAHAMAS AND SOUTH FLORIDA AS WE HEAD INTO MID  
NEXT WEEK.  
 
REGARDLESS OF DEVELOPMENT, AT THIS POINT SIGNS ARE POINTING TOWARDS  
ANOTHER PERIOD OF HEAVY RAINFALL ACROSS THE REGION FOR AT LEAST  
TUESDAY AND WEDNESDAY. WHICH, ESPECIALLY DEPENDING ON THIS WEEKEND'S  
RAINFALL, MAY RAISE FLOODING CONCERNS ACROSS THE AREA. ALL RESIDENTS  
AND VISITORS OR SOUTH FLORIDA NEED TO CONTINUE TO MONITOR THIS  
TROPICAL DISTURBANCE THROUGH THE WEEKEND.  
 
MARINE...EAST-SOUTHEAST WINDS WILL PREVAIL FOR THE WEEKEND AND  
THROUGH THE UPCOMING WEEK ACROSS THE LOCAL WATERS. THE MAIN CONCERN  
WILL BE WIND SPEEDS, WITH SEVERAL PASSING TROPICAL WAVES  
PERIODICALLY BUMPING UP SPEEDS TO CAUTIONARY LEVELS. RIGHT NOW,  
EXPECT OVERALL SPEEDS TO INCREASE TO AROUND 15 KNOTS, WITH 15-20KTS  
POSSIBLE WITH THE FIRST WAVE SATURDAY NIGHT INTO SUNDAY, AND AGAIN  
MONDAY NIGHT INTO TUESDAY. SEAS 2FT OR LESS TODAY, BUILDING TO 3-  
4FT, ESPECIALLY IN THE ATLANTIC BY SUNDAY.  
 
CONVECTION WILL REMAIN MORE ISOLATED OVER THE OPEN WATERS TODAY,  
FAVORING THE THE INTERIOR/LAKE OKEECHOBEE THIS AFTERNOON. EXPECT  
SCATTERED TO NUMEROUS STORMS OVER ALL THE WATERS FOR THE WEEKEND  
WITH THE FIRST TROPICAL WAVE.  
 
THE THREAT OF RIP CURRENT COULD INCREASE THIS WEEKEND ALONG THE  
EAST COAST BEACHES OF SOUTH FLORIDA, DUE TO THE INCREASE IN  
EASTERLY WIND FLOW.  
 
CLIMATE...HIGH TEMPERATURES TODAY MAY BE WITHIN A FEW DEGREES OF  
RECORD.  
 
FORECAST HIGHS RECORD HIGHS  
MIAMI 94 95 - 1995  
FORT LAUDERDALE 94 98 - 1921  
WEST PALM BEACH 95 96 - 1949  
NAPLES 94 97 - 2001  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
WEST PALM BEACH 95 81 91 80 / 20 10 60 60  
FORT LAUDERDALE 94 82 90 81 / 20 20 60 60  
MIAMI 94 81 90 80 / 20 20 70 60  
NAPLES 94 76 92 78 / 50 30 40 40  
 

 
   
MFL WATCHES/WARNINGS/ADVISORIES
 
 
FL...NONE.  
AM...NONE.  
GM...NONE.  
 

 
 
UPDATE...02/RAG  
 
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