303  
FXUS62 KMFL 250049  
AFDMFL  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MIAMI FL  
849 PM EDT THU SEP 24 2020  
   
UPDATE
 
 
A SWATH OF HIGHER MOISTURE IS INTACT OVER MOST OF THE ATLANTIC  
METROS/WATERS. SATELLITE DERIVED PRECIPITABLE WATER INDICES OF 2.5  
INS ARE READILY APPARENT, FURTHER SUPPORTED BY 2.33 INS ON THE 00Z  
SOUNDING. THE 00Z MFL SOUNDING ALSO INDICATES A VEERING WIND  
PROFILE, WITH EFFECTIVE BULK SHEAR OF 17 KTS AND SFC-3KM SRH OF 64  
M2/S2. THE UPTICK IN SHEAR/SRH IS LIKELY A RESULT OF A MID-LEVEL  
PERTURBATION TRANSVERSING THE REGION. GIVEN ENVIRONMENTAL  
INCREASES IN SHEAR AND MOISTURE, STORMS THAT DO DEVELOP WILL  
LIKELY BE VERY EFFICIENT RAIN PRODUCERS. THIS COULD POSE A  
FLOODING THREAT OVERNIGHT INTO TOMORROW MORNING, THOUGH THIS RISK  
WILL BE HIGHLY LOCALIZED. WATERSPOUT/FUNNEL-CLOUD DEVELOPMENT IN  
THE ATLANTIC/GULF WATERS IS ALSO A CONCERN TO MONITOR GIVEN A  
SLIGHTLY MORE FAVORABLE ENVIRONMENT. WILL HAVE TO MONITOR AREAS OF  
STRONG MOISTURE CONVERGENCE AND HIGH INSTABILITY, AS THESE  
REGIONS WILL BE AREAS TO WATCH TONIGHT INTO TOMORROW EVENING.  
 

 
   
PREV DISCUSSION
 
/ISSUED 741 PM EDT THU SEP 24 2020/  
   
.00Z AVIATION UPDATE
 
 
AVIATION...  
A FEW SCATTERED SHOWERS AND STORMS EXPECTED OVERNIGHT. MOSTLY VFR  
EXPECTED. THERE MAY BE SOME REDUCTIONS ON SATURDAY AS SHOWERS AND  
PERHAPS A STORM OR TWO CONTINUE TO DEVELOP AND MOVE INTO THE  
REGION. WINDS SHOULD REMAIN GENERALLY EAST OR SOUTHEASTERLY AROUND  
10 KNOTS OR SO.  
 
PREV DISCUSSION... /ISSUED 452 PM EDT THU SEP 24 2020/  
 
SHORT TERM (TODAY THROUGH FRIDAY)...  
ATLANTIC SURFACE HIGH PRESSURE, A MID-LEVEL TROUGH PUSHING ACROSS  
THE EASTERN UNITED STATES, AND A RETREATING WARM FRONT ARE THE MAIN  
FEATURES IN PLAY THROUGH FRIDAY ACROSS SOUTHERN FLORIDA. INCREASING  
MOISTURE AS THE WARM FRONT PUSHES NORTHWARD WILL ALLOW FOR EFFICIENT  
RAINFALL PROCESSES WHICH, EVEN WITH SHALLOW CONVECTION, COULD LEAD  
TO A CONCERN FOR FLOODING. THE WEATHER PREDICTION CENTER MAINTAINS  
PORTIONS OF COASTAL SOUTHWEST FLORIDA WITHIN A MARGINAL RISK OF  
EXCESSIVE RAINFALL FOR FRIDAY. THERE COULD BE A FEW ROUNDS OF  
CONVECTION INCLUDING ONE CURRENTLY UNDERWAY WHICH COULD LINGER  
THROUGH THE EVENING IN PART DUE TO THE DIURNAL MAXIMUM.  
 
NOT MANY CHANGES FROM THE PREVIOUS FORECAST PHILOSOPHY FOR THE  
PERIOD EXCEPT TO NOTE THAT THERE ARE SOME SLIGHT TIMING DIFFERENCES  
WITH AN OVERNIGHT WAVE OF RAINFALL POTENTIALLY FOCUSING MORE AROUND  
DAWN COMPARED TO THE EARLY MORNING HOURS. AS THE MORNING CONTINUES,  
THE ACTIVITY WILL OVERSPREAD THE AREA WITH AN AFTERNOON MAXIMUM FOR  
RAIN CHANCES OVER THE NORTHERN PORTIONS OF THE AREA. THE PATTERN IS  
CAPABLE OF SUPPORTING WIDESPREAD EFFICIENT RAINFALL PRODUCTION BUT  
ONE MITIGATING FACTOR IS THE RECENT DRY DAYS WHICH HAVE ALLOWED MANY  
AREAS TO DRAIN. ONE FACTOR TO WATCH IS THE HIGHER THAN NORMAL TIDES  
WHICH MAKE COASTAL DRAINAGE MORE DIFFICULT. ADDITIONALLY, ANY AREAS  
THAT RECEIVE RAINFALL TODAY COULD BE MORE LIKELY TO REACH SATURATION  
TONIGHT THROUGH TOMORROW.  
 
LONG TERM (SATURDAY THROUGH THURSDAY)...  
 
SATURDAY AND SUNDAY  
 
UPPER LEVEL RIDGING GRADUALLY BUILDS OVER THE REGION, WITH A 500 HPA  
HIGH CENTER LOCATED IN GULF WATERS OFFSHORE OF FLORIDA. WITH THE  
EASTERN PERIPHERY OF THE RIDGE OVER THE REGION. THIS SHOULD INDUCE  
MODEST SUBSIDENCE OVER THE REGION, HOWEVER LIKELY NOT ENOUGH TO  
ENTIRELY SUPPRESS CONVECTIVE DEVELOPMENT. BENEATH THE RIDGE,  
BOUNDARY LAYER WINDS ARE GENERALLY SOUTHERLY, WHICH MAY PIN THE  
ATLANTIC SEA-BREEZE NEAR THE ATLANTIC METROS. WITH GENERALLY LIGHT  
STEERING FLOW, LOCALIZED FLOODING COULD BE A CONCERN WHERE STORMS  
PROPAGATE SLOWLY AND/OR BACKBUILD.  
 
ON SUNDAY, THE UPPER RIDGE WEAKENS A BIT, AS NEAR-SURFACE FLOW  
BECOMES MORE EASTERLY. THIS SHOULD FAVOR THE DEVELOPMENT OF SHOWERS  
AND THUNDERSTORMS OVER THE ATLANTIC COAST/METROS IN THE MORNING,  
WITH A GRADUAL PROGRESSION TOWARDS THE INTERIOR/GULF COAST BY THE  
AFTERNOON/EVENING. ANY DEVELOPING ACTIVITY SHOULD BE FAIRLY QUICK-  
MOVING AND DEVOID OF ANY CONSIDERABLE HAZARDS, THOUGH TYPICAL GUSTY  
WINDS, FREQUENT LIGHTNING, AND HEAVY RAINFALL ARE ALL POSSIBLE.  
 
MONDAY THROUGH THURSDAY  
 
A SHORTWAVE TROUGH EMBEDDED IN THE 500 HPA FLOW TRANSVERSES THROUGH  
FLORIDA AROUND MONDAY/TUESDAY. A NOTICEABLE SHIFT IN THE NEAR-  
SURFACE WIND DIRECTION TRANSPIRES, WITH AN EASTERLY SHIFT TO MORE OF  
A SE COMPONENT. THE GREATEST STORM COVERAGE APPEARS TO BE DIRECTED  
OVER THE INTERIOR STILL, WITH POPS IN THE 50-60 RANGE, WITH  
AFTERNOON POPS IN THE 40-50S ACROSS MOST OF THE METRO REGION.  
 
BY MID-DAY TUESDAY, A DEEP, MORE VIGOROUS 500 HPA TROUGH DIGS  
SOUTHERLY INTO MOST OF THE FLORIDA. A DISTINCT SURFACE FRONT IS  
ATTENDANT WITH THIS FEATURE, THOUGH THE WPC FORECAST HAS THIS  
BOUNDARY JUST NORTH OF THE REGION, WITH AN NE/SW ORIENTATION JUST  
NORTH OF LAKE OKEECHOBEE. THIS WILL LIKELY PRECLUDE THE COOLER,  
DRIER AIR FROM REACHING PORTIONS OF SOUTH FLORIDA. OF LIKELY GREATER  
CONCERN FOR SOUTH FLORIDA IS A PRE-FRONTAL TROUGH AHEAD OF THIS  
SURFACE FRONT, WHICH MAY CORRESPOND WITH WIDESPREAD CONVECTIVE  
COVERAGE. WHETHER OR NOT THIS FEATURE AND CORRESPONDING HIGH  
MOISTURE CONVERGENCE BECOMES ORIENTED OVER THE ATLANTIC METRO REGION  
OR WATERS IS DIFFICULT TO DETERMINE, AS SUBTLE CHANGES IN THE  
SYNOPTIC PATTERN WILL DICTATE WHERE WIDESPREAD CONVECTIVE  
DEVELOPMENT MATERIALIZES. WITH THE PROXIMITY OF THIS DEEP TROUGH, A  
LOW-LEVEL MASS RESPONSE WILL ACT TO INCREASE THE BULK-SHEAR PROFILE  
AND LIKELY ADVECT A WARM, MOIST AIRMASS, AS FLOW VEERS WITH HEIGHT.  
THIS MAY ENHANCE STORM DEVELOPMENT IN SOME LOCATIONS, ESPECIALLY IF  
IT TIMES WELL WITH MESOSCALE FEATURES, THOUGH PRESENTLY IT IS TOO  
EARLY TO HONE IN STORM INTENSITY AND SPECIFIC LOCATION OF COVERAGE.  
REGARDLESS, PRECIPITATION CHANCES INCREASE WEDNESDAY AND THURSDAY  
ACROSS THE REGION, INDICATED BY 60-70 POPS IN THE OFFICIAL FORECAST.  
 
TEMPERATURES ARE FORECAST TO BE FAIRLY SEASONABLE, WITH HIGHS  
GENERALLY IN THE UPPER 80S/LOWER 90S. THE HIGHEST TEMPERATURES  
WILL LIKELY BE EXPERIENCED OVER THE INTERIOR, AND WHERE CLOUD  
COVER IS MINIMIZED. A SLIGHT DECREASE IN TEMPERATURES IS POSSIBLE  
MIDDLE TO LATE NEXT WEEK, PENDING THE ORIENTATION OF THE SURFACE  
COLD FRONT.  
 
MARINE...  
A WARM FRONT AND INCREASING MOISTURE SPREAD NORTHWARD ACROSS THE  
LOCAL WATERS. RAIN AND THUNDERSTORM CHANCES WILL GRADUALLY INCREASE  
FROM SOUTH TO NORTH ACROSS THE AREA, BRINGING LOCAL REDUCTIONS TO  
VISIBILITY, GUSTY WINDS, AND OCCASIONAL LIGHTNING. THE LARGE  
NORTHEASTERLY SWELL AFFECTING THE PALM BEACH WATERS SHOULD GRADUALLY  
SUBSIDE OVER THE NEXT DAY OR SO, ALLOWING FOR IMPROVING MARINE  
CONDITIONS.  
 
BEACH FORECAST...  
LARGE NORTHEASTERLY SWELL FROM POST-TROPICAL CYCLONE TEDDY AND  
BREEZY ONSHORE WINDS WILL MAINTAIN AN ELEVATED RIP CURRENT RISK FOR  
ALL ATLANTIC BEACHES THROUGH THE WEEK. HIGH SURF ALONG THE PALM  
BEACHES IS ALSO EXPECTED TO PERSIST THROUGH AT EARLY FRIDAY MORNING  
WHERE BEACH EROSION HAS ALSO BEEN A CONCERN. HIGHER THAN NORMAL  
TIDES COMBINED WITH BREEZY WINDS AND LARGE SWELL COULD LEAD TO  
CONTINUED MINOR COASTAL FLOODING NEAR TIMES OF HIGH TIDE, WITH  
CONDITIONS POTENTIALLY IMPROVING HEADING INTO THE WEEKEND.  

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
WEST PALM BEACH 88 77 88 76 / 30 50 70 50  
FORT LAUDERDALE 88 79 88 78 / 30 50 70 40  
MIAMI 88 78 89 78 / 40 60 70 40  
NAPLES 91 76 88 77 / 50 50 60 30  
 

 
   
MFL WATCHES/WARNINGS/ADVISORIES
 
 
FL...COASTAL FLOOD ADVISORY UNTIL 8 AM EDT FRIDAY FOR FLZ168-172-173.  
 
HIGH RIP CURRENT RISK THROUGH FRIDAY EVENING FOR FLZ168.  
 
HIGH SURF ADVISORY UNTIL 4 AM EDT FRIDAY FOR FLZ168.  
 
AM...SMALL CRAFT ADVISORY UNTIL 4 AM EDT FRIDAY FOR AMZ650-670.  
 
GM...NONE.  

 
 
UPDATE...09/BHATTI  
MARINE...02/RAG  
AVIATION...28/FRYE  
BEACH FORECAST...02/RAG  
 
SHORT TERM...02/RAG  
LONG TERM...09/BHATTI  
 
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