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000 FXUS62 KMFL 220539 AFDMFL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MIAMI FL 139 AM EDT MON SEP 22 2008 .AVIATION...MOSTLY VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD. A FEW SHOWERS CAN BE EXPECTED ALONG THE EAST COAST TONIGHT AND TOMORROW WITH MOST TSRA EXPECTED ALONG THE WEST COAST WITH THE SEA BREEZE. WINDS WILL GENERALLY REMAIN EASTERLY AT ALL EAST COAST SITES AND AT APF... EASTERLY IN THE AM BUT WESTERLY IN THE AFTERNOON AND EVENING WITH THE SEA BREEZE. /TINGLER && .PREV DISCUSSION... /ISSUED 913 PM EDT SUN SEP 21 2008/ UPDATE... THE EAST AND WEST COAST SEA BREEZES COLLIDED OVER THE WESTERN INTERIOR AREAS OF SOUTH FLORIDA LATE THIS AFTERNOON AND EARLY THIS EVENING...WITH SCATTERED SHOWERS AND THUNDERSTORMS DEVELOPING ALONG THE BOUNDARY. THE SHOWERS AND THUNDERSTORMS ARE SLOWLY DISSIPATING OVER WESTERN INTERIOR AREAS OF THE CWA THIS EVENING...AND SHOULD CONTINUE TO SLOWLY DISSIPATE THROUGH REST OF THE EVENING HOURS. SO WILL REMOVE THE POPS OVER THE INTERIOR AND WEST COAST METRO AREAS BY MIDNIGHT. THERE HAS ALSO BEEN A FEW SHOWERS DEVELOPING OVER THE EAST COAST ATLANTIC WATERS THIS EVENING. THESE SHOWERS SHOULD CONTINUE TO DEVELOP AND MOVE TO THE WEST INTO THE EAST COAST METRO AREAS BEFORE DISSIPATING...AS THE STEERING FLOW WILL REMAIN FROM THE EASTERLY DIRECTION AROUND HIGH PRESSURE OVER THE SOUTHEAST UNITED STATES. SO HAVE KEPT A 20 PERCENT POPS FOR THE EAST COAST METRO AREAS FOR THE OVERNIGHT HOURS. THE 00Z MIA SOUNDING ALSO SHOWED THAT THERE WAS STILL SOME DRY AIR IN THE LOWER TO MID LEVELS OF THE ATMOSPHERE. SO HAVE REMOVE THE THUNDER WORDING FOR THE EAST COAST METRO AREAS AND THE ATLANTIC WATERS FOR THE OVERNIGHT HOURS. THE 00Z MIA SOUNDING WAS ALSO SHOWING 10 TO 15 KNOTS BETWEEN 900 AND 1000 MB. THIS WIND SPEED SHOULD MIX DOWN TO THE ATLANTIC AND BISCAYNE BAY WATER SURFACE TONIGHT. SO HAVE INCREASE THE WIND SPEED UP A LITTLE BIT FOR THESE WATERS TONIGHT. REST OF THE FORECAST LOOKS GOOD AT THIS TIME AND NO OTHER CHANGES ARE PLAN. UPDATE...54/BNB AVIATION... /ISSUED 731 PM EDT SUN SEP 21 2008/ AVIATION...VFR CONDITIONS ARE EXPECTED OVER ALL TERMINALS OVERNIGHT. SHWRS/STORMS OVER INTERIOR SECTIONS ARE EXPECTED TO DISSIPATE BEFORE GETTING NEAR KAPF. DECIDED TO INDICATE VCSH OVER THE ERN TERMINALS THROUGH EARLY MORNING HOURS OF MONDAY BUT NOT SIGNIFICANT IMPACT EXPECTED. VCTS WILL BE INDICATED FOR KAPF AFT 18Z MON AS THE WEST COAST SEA BREEZE DEVELOPS. PREV DISCUSSION... /ISSUED 321 PM EDT SUN SEP 21 2008/ DISCUSSION... THE CURRENT WATER VAPOR SATELLITE ANIMATION CONTINUES TO INDICATE AN INCREASING TREND IN MID AND HIGH-LEVEL MOISTURE ACROSS SOUTH FLORIDA...WITH THIS CONFIRMED BY DATA FROM RECENT UPPER AIR OBSERVATIONS ACROSS THE AREA. THUS...DESPITE WEAK MID-LEVEL SUBSIDENCE PROVIDED BY RIDGE AXIS ALOFT...EXPECT AT LEAST WIDELY SCATTERED SHOWERS/THUNDERSTORMS TO DEVELOP ALONG COASTAL CONVERGENCE BOUNDARIES AND AFFECT MUCH OF THE CENTRAL/WESTERN PORTIONS OF THE FORECAST AREA THIS AFTERNOON. SHORT TERM MODEL SOLUTIONS INDICATE THAT MODERATE EASTERLY FLOW WILL PERSIST IN THE BOUNDARY LAYER OVERNIGHT...NECESSITATING SLIGHT CHANCE POPS OVER THE ATLANTIC WATERS AND ADJACENT PORTIONS OF THE MAINLAND. HOWEVER...SUBSIDENT EFFECTS OF MID-LEVEL RIDGE WILL LIKELY LIMIT COVERAGE COMPARED TO WHAT WAS SEEN SUNDAY MORNING...AS INDICATED BY RUC/WRF-NMM MODEL SOLUTIONS. THE GLOBAL MODELS UNANIMOUSLY SUGGEST THAT A LARGE MID- TROPOSPHERIC HIGH OVER THE CENTRAL NORTH ATLANTIC WILL WEAKEN AND SHIFT EASTWARD THROUGH THE REMAINDER OF THE SHORT TERM PERIOD...AS A POTENT VORT MAX TRANSLATES THROUGH BASE OF LONG WAVE TROUGH CURRENTLY POSITIONED OVER THE DAVIS STRAIT. THIS WILL SLOWLY ERODE THE RIDGE CENTERED ACROSS SOUTH FLORIDA ON MONDAY...AND THIS...WHEN COMBINED WITH GRADUALLY INCREASING DEEP- LAYER MOISTURE...SHOULD RESULT IN A SLIGHTLY GREATER COVERAGE OF AFTERNOON CONVECTION OVER THE MAINLAND. WILL STILL CARRY HIGHEST POPS ALONG THE CORRIDOR FROM WEST PALM BEACH SOUTHWESTWARD TO NAPLES...WITH LOWEST CHANCES ALONG THE IMMEDIATE SOUTHEAST COAST. EXPECT THE COVERAGE OF NOCTURNAL SHOWERS AND THUNDERSTORMS TO INCREASE OVER THE ATLANTIC WATERS ON MONDAY NIGHT...AS WELL. HOWEVER...THE HIGHEST CHANCES FOR RAIN WILL LIKELY COME ON TUESDAY...AS MODELS REMAIN VERY CONSISTENT IN FORECASTING A WEAK UPPER LOW CURRENTLY CENTERED OVER WESTERN ILLINOIS TO DRIFT EAST- SOUTHEASTWARD OVER THE NEXT 48 HOURS...IN RESPONSE TO RISING MID- LEVEL HEIGHTS OVER THE SOUTHERN PLAINS. THIS FEATURE IS PROGGED TO DRIFT SLOWLY SOUTHWARD OVER THE CAROLINAS ON TUESDAY...AND DEEPEN INTO A CUTOFF LOW...AS A BLOCKING SHORTWAVE RIDGE AXIS BUILDS ACROSS THE GREAT LAKES AND NORTHEAST U.S. AS THIS OCCURS...THE COMBINATION OF STRENGTHENING MID-LEVEL DIVERGENCE...STEEPENING LAPSE RATES...AND INCREASING DEEP-LAYER MOISTURE WILL LEAD TO A VERY FAVORABLE ENVIRONMENT FOR SHOWERS/THUNDERSTORMS TO DEVELOP. REGARDING TEMPERATURES...WILL MAINTAIN A PERSISTENCE FORECAST FOR THE NEXT 48 HOURS...AND COOL BOTH MAXIMUM/MINIMUM VALUES BY A 1-3 DEGREES ON TUESDAY/TUESDAY NIGHT...WITH EXPECTATIONS OF A HIGHER COVERAGE OF CLOUDS AND PRECIPITATION...AS WELL AS NORTHEAST FLOW OFF THE ATLANTIC. THE PRIMARY FEATURE OF INTEREST IN THE EXTENDED FORECAST WILL BE THE CUTOFF LOW...WHICH MODELS INDICATE WILL REMAIN LOCATED EITHER OVER COASTAL PORTIONS OF GEORGIA/S.C./N.C. OR JUST OFF SHORE THROUGH THE END OF THE WEEK. THE INFLUENCE OF THIS FEATURE ON THE WEATHER ACROSS SOUTH FLORIDA WILL BE DIRECTLY RELATED TO HOW DEEP THE SYSTEM BECOMES...AND HOW CLOSE IT ACTUALLY COMES TO THE LOCAL AREA. THE LATEST ECMWF MAINTAINS THE CORE OF THE CYCLONE OVER WATER...ALLOWING IT TO INITIALLY BECOME SIGNIFICANTLY DEEPER THAN THE GFS WOULD SUGGEST...AND DEEPENS THE SYSTEM EVEN FURTHER AS ENERGY FROM A POTENT MID-LATITUDE TROUGH BEGINS TO PHASE WITH IT LATE NEXT WEEKEND. AS A RESULT OF THIS...THE ECMWF ALSO INDICATES A MUCH DRIER PATTERN FOR SOUTH FLORIDA...AND WITH THIS AMOUNT OF UNCERTAINTY...WILL MAKE NO CHANGES TO THE EXTENDED FORECAST AT THIS TIME. MARINE... THERE ARE NO MARINE WEATHER CONCERNS THROUGH THE FIRST 24-36 HOURS OF THIS FORECAST...WITH EAST TO NORTHEAST WINDS EXPECTED TO REMAIN IN THE 10-15 KNOT RANGE OVER THE SOUTHERN LEG OF THE ATLANTIC WATERS...AND SLIGHTLY LOWER ACROSS THE REMAINDER OF THE COASTAL ZONES. A SMALL RESIDUAL SWELL IN THE PALM BEACH COUNTY WATERS WILL RESULT IN SLIGHTLY HIGHER COMBINED SEAS IN THIS REGION. MARINE WEATHER CONDITIONS ACROSS THE ATLANTIC WILL LIKELY DETERIORATE BY TUESDAY AFTERNOON...AS NORTHEAST FLOW INCREASES IN RESPONSE TO DEVELOPING LOW PRESSURE OFF THE COAST OF NORTH/CENTRAL FLORIDA. NORTH/NORTHEAST WINDS WILL LIKELY INCREASE INTO THE 15-20 KNOT RANGE...WITH SEAS IN THE GULF STREAM APPROACHING MARGINAL SCA CRITERIA. WINDS/SEAS ARE FORECAST TO RELAX LATER IN THE WEEK...BUT THE DEVELOPMENT OF A DEEPER CYCLONE OFF THE COAST OF THE CAROLINAS WILL GENERATE NORTH/NORTHEAST SWELL WHICH WILL AFFECT THE ATLANTIC WATERS BY NEXT WEEKEND. FIRE WEATHER... THERE ARE NO FIRE WEATHER CONCERNS THROUGHOUT THE FORECAST PERIOD...AS MINIMUM AFTERNOON RH VALUES WILL REMAIN SUFFICIENTLY HIGH. && .PRELIMINARY POINT TEMPS/POPS... WEST PALM BEACH 88 76 87 72 / 50 40 60 30 FORT LAUDERDALE 90 79 88 75 / 40 40 50 30 MIAMI 90 79 88 75 / 40 40 50 30 NAPLES 90 74 87 72 / 50 40 60 30 && .MFL WATCHES/WARNINGS/ADVISORIES... FL...NONE. AM...NONE. GM...NONE. && $$