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Show Area Forecast Discussion - Key West, FL (Florida Keys) Selection: |
| #535726 (Received by flhurricane at: 9:32 PM 20.Aug.2012) AFDKEY AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS NATIONAL WEATHER SERVICE KEY WEST FL 930 PM EDT MON AUG 20 2012 .DISCUSSION...IN THE MID AND UPPER LEVELS...(700-200 MB)...THE MAIN AXIS OF AN UNUSUALLY DEEP FULL LATITUDINAL TROUGH IS SITUATED FROM THE UPPER GREAT LAKES SOUTH SOUTHWESTWARD TO THE NORTHWESTERN GULF COAST. A DEEP MID TO UPPER RIDGE IS ORIENTED FROM NEAR 35 NORTH 50 WEST SOUTHWESTWARD TO ACROSS EXTREME SOUTH FLORIDA...WITH A UPPER LOW PRESSURE SYSTEM MOVING WESTWARD ACROSS THE SOUTHEASTERN BAHAMAS. A SURFACE FRONT IS UNUSUALLY FAR SOUTH AND PRESENTLY EXTENDS FROM THE CAROLINA PIEDMONT SOUTH SOUTHWEST TO ACROSS CENTRAL FLORIDA TO THE CENTRAL GULF OF MEXICO TO NEAR 90 WEST. THE FLORIDA KEYS REMAIN ON THE WESTERN EDGE OF WEAKENED ATLANTIC SURFACE RIDGING CENTERED AT 25 NORTH AND 60 WEST. THE 00Z EVENING SOUNDING ILLUSTRATED A TYPICALLY MOIST GENTLE TO MODERATE SOUTH TO SOUTHWEST FLOW FROM THE SURFACE TO 600 MB...WITH PWAT NEAR 1.82 INCHES. .CURRENTLY...AS OF 900 PM...SKIES ARE PARTLY CLOUDY ACROSS THE ISLANDS AND ADJOINING WATERS. TEMPERATURES ARE IN THE UPPER 80S WITH DEWPOINTS IN THE MIDDLE 70S ACROSS THE ISLAND CHAIN. RADAR DETECTS NO ECHOES IN THE ENTIRE MARINE KEYS SERVICE AREA ATTM...BUT IT DOES DETECT CLUSTERS OF SHOWERS AND THUNDERSTORMS ALONG THE CUBAN COAST EAST OF VARADERO...AND OTHER CLUSTERS TO THE WEST OF HAVANA OVER PINAR DEL RIO CUBA. BUT CAVEAT EMPTOR...THERE ARE AMPLE BOUNDARIES IN THE SERVICE AREA LURKING NEAR THE KEYS AND SURROUNDING WATERS .FORECAST...OVERNIGHT...EXPECT GRADUAL WEAKENING OF THE WESTERN SURFACE RIDGING AXIS...SO LIGHT TO GENTLE WINDS ON THE WATERS AND OVER THE KEYS WILL GRADUALLY BECOMING LIGHT AND VARIABLE. DESPITE NO ACTIVE ECHOES IN THE KEY WEST SERVICE AREA ATTM...AM RELUCTANT TO LOWER RAIN CHANCES TO LOWER THAN SLIGHT CHANCE...GIVEN AFOREMENTIONED SLOW MOVING BOUNDARIES. BOTH 18Z GFS AND NAM MODEL FORECAST SOUNDINGS ONLY ILLUSTRATE A SLIGHT STORM MOTION FROM THE SOUTH NEAR 5 KNOTS...BUT SUFFICIENT COLUMNAR PWAT REMAINING BETWEEN 1.75 AND 2.00 INCHES THROUGH 12Z. && .MARINE... LIGHT AND VARIABLE BREEZES WILL DEVELOP AGAIN ALONG THE WEAKENED WESTERN END OF THE ATLANTIC SURFACE RIDGE AXIS...WHICH WILL REMAIN POSITIONED NEAR THE FL KEYS. && .AVIATION...VFR CONDITIONS WILL PREVAIL AT BOTH THE KEY WEST AND MARATHON TERMINALS OVERNIGHT. SURFACE WINDS WILL BE SOUTH SOUTHEASTERLY BETWEEN 5 AND 10 KNOTS. .KEY WATCHES/WARNINGS/ADVISORIES... FL...NONE. GM...NONE. && $$ |
| #535669 (Received by flhurricane at: 3:05 PM 20.Aug.2012) AFDKEY AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS NATIONAL WEATHER SERVICE KEY WEST FL 300 PM EDT MON AUG 20 2012 .DISCUSSION... DEEP CUMULUS CONVECTION HAS BEEN COMPLETELY SUPPRESSED TODAY OVER THE FLORIDA KEYS AND ADJACENT COASTAL WATERS OWING TO A POCKET OF WARM... DRY AIR IN THE LOWER TROPOSPHERE. A GEOSTATIONARY SATELLITE- DERIVED SOUNDING NEAR SAND KEY AT 1800 UTC REVEALED A CAP AND SIGNIFICANT DRY AIR BELOW 700MB...DESPITE A CONSIDERABLE AMOUNT OF POTENTIAL BUOYANCY AND A VERY WARM/MOIST BOUNDARY LAYER. SOUTHERLY WINDS AROUND THE FLORIDA KEYS ARE HIGHER THAN EITHER MODELED OR FORECAST THIS AFTERNOON...ESPECIALLY WEST OF THE SEVEN MILE BRIDGE. THIS APPEARS TO HAVE OCCURRED AS THE RESULT OF A DEVELOPING CHANNEL OF HIGHER- VELOCITY FLOW STREAMING INTO A LOW PRESSURE TROUGH AND VIGOROUS SQUALL LINE OVER THE NORTHEASTERN GULF OF MEXICO. THESE CASES USUALLY ARE SHORT-LIVED...AND WE DO EXPECT A WEAK ATLANTIC RIDGE TO RETURN THIS EVENING...ALLOWING BREEZES TO SLACKEN ONCE AGAIN. TONIGHT AND TUESDAY -- THE BEST CHANCE FOR RAIN WILL BE OVERNIGHT AS CUBAN SEA-BREEZE SHOWERS AND THUNDERSTORMS MIGRATE OVER THE STRAITS OF FLORIDA...WITH SUBSEQUENT CONVECTION INITIATION ALONG NORTHWARD- MOVING OUTFLOW BOUNDARIES. TUESDAY NIGHT THROUGH THURSDAY -- A DEEP LAYER MEAN RIDGE AXIS WILL SHIFT NORTHWARD DURING THIS TIME FRAME...ALLOWING A LATE-SEASON SAHARAN AIR LAYER PLUME AND ASSOCIATED DRY AIR TO MIGRATE WEST- NORTHWESTWARD OVER THE FLORIDA KEYS AND ADJACENT COASTAL WATERS. RAIN AND THUNDER CHANCES ARE REDUCED FOR THIS PERIOD WITH THE DRIEST AIR AND SUNNIEST WEATHER EXPECTED DURING THE DAY WEDNESDAY. EASTERLY BREEZES SHOULD FRESHEN AS A SURFACE RIDGE AXIS MOVES NORTHWARD. FRIDAY THROUGH MONDAY -- THE DEEP LAYER MEAN ATLANTIC RIDGE IS EXPECTED TO WEAKEN SOME ALONG ITS WESTERN FLANK...ALTHOUGH THE DEGREE TO WHICH THIS HAPPENS AND THE TIMING IS STILL UNCERTAIN. THE EVOLUTION OF THE DEEP LAYER MEAN RIDGE DURING THIS TIME FRAME WILL HAVE CONSEQUENCES FOR ANY TROPICAL CYCLONIC CIRCULATIONS THAT MAY BE UPSTREAM OF THE FLORIDA KEYS OVER THE WEEKEND. ONE SUCH SYSTEM CURRENTLY LOCATED OVER THE TROPICAL ATLANTIC OCEAN 1000 MILES EAST OF THE LESSER ANTILLES HAS BEEN IDENTIFIED BY THE NATIONAL HURRICANE CENTER AS HAVING A HIGH PROBABILITY OF DEVELOPMENT INTO A TROPICAL CYCLONE. SHOULD SUCH DEVELOPMENT TAKE PLACE...LOCAL IMPACTS OR INFLUENCES...IF ANY...WOULD NOT OCCUR UNTIL THE SATURDAY-MONDAY TIME FRAME. && .MARINE... A SHORT-LIVED SOUTHERLY WIND SURGE SHOULD SUBSIDE LATE THIS AFTERNOON OR EARLY THIS EVENING...WITH LIGHT AND VARIABLE BREEZES DEVELOPING AGAIN ALONG A SURFACE RIDGE AXIS POSITIONED NEARLY OVER THE FLORIDA KEYS. WINDS AND SEAS WILL BE HIGHER IN AND NEAR SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS OVERNIGHT. FOR THE REST OF THE WEEK...EXPECT A GRADUAL BACKING OF THE WIND FROM SOUTHEAST TO EAST...AND A SLOWLY FRESHENING BREEZE. CAUTIONARY HEADLINES MAY BE REQUIRED FOR SMALL CRAFT BY SATURDAY. && .AVIATION... THROUGH 21/18Z...VFR CONDITIONS WILL PREVAIL AT KEY WEST INTERNATIONAL AND MARATHON TERMINALS THROUGH THE FORECAST PERIOD...WITH SOUTHERLY WINDS AVERAGING 5 TO 10 KNOTS. PRECIPITATION PROBABILITY REMAINS LOW FOR BOTH TERMINALS AND HAVE NOT BEEN MENTIONED. && .PRELIMINARY POINT TEMPS/POPS... KEY WEST 82 89 82 89 / 30 30 20 10 MARATHON 82 92 82 92 / 30 30 20 10 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...NONE. GM...NONE. && $$ |
| #535622 (Received by flhurricane at: 10:32 AM 20.Aug.2012) AFDKEY AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS NATIONAL WEATHER SERVICE KEY WEST FL 1025 AM EDT MON AUG 20 2012 .DISCUSSION... THE KEY WEST MORNING RAWINSONDE OBSERVATION REVEALED A POCKET OF DRY AIR AT THE SURFACE...WHICH APPARENTLY DEVELOPED OVERNIGHT OWING TO COMPENSATORY MESOSCALE SUBSIDENCE ADJACENT TO DEEP CUMULUS CONVECTION CELLS WHICH DEVELOPED ALL AROUND BUT NOT AT KEY WEST OVERNIGHT. THE LOCAL ATMOSPHERE STILL IS INHIBITING CUMULUS CONVECTION AT THIS HOUR AS EVIDENCED BY BOTH VISIBLE SATELLITE IMAGES AND A LOOK OUT THE WINDOW. MEAN LOWER-TROPOSPHERIC FLOW IS WEAK AND DIFLUENT ACROSS THE FLORIDA KEYS AND ADJACENT COASTAL WATERS...CONSISTENT WITH THE PREVALENCE OF A LARGE-SCALE RIDGE OVERHEAD. AIR TEMPERATURES IN KEYS ISLAND COMMUNITIES ARE RISING QUICKLY THROUGH THE MID 80S THIS MORNING...WITH DEWPOINTS RANGING FROM 70-75F. IF WE MODIFY THE MORNING RAWINSONDE DATA TO REMOVE THE ANOMALOUS LOW-LEVEL DRY POCKET AND ACCOUNT FOR DIURNAL HEATING...WE OBTAIN A VERY UNSTABLE STRATIFICATION WITH SOME SIGNIFICANT LOW-LEVEL CONVECTIVE INHIBITION ENERGY REMAINING. GIVEN THE EXPECTED FLOW IN THE LOWER TROPOSPHERE... SEVERAL MORE HOURS OF MOSTLY SUNNY AND RAIN-FREE ARE LIKELY. HOWEVER... BY EARLY-MID AFTERNOON...A FEW SHOWER LINES MAY POP UP OVER THE GULF WATERS NORTH OR NORTHEAST OF THE LOWER KEYS. CUBAN CONVECTION WILL BE VIGOROUS...BUT LATE-DEVELOPING. IN ADDITION...THE FOCUS FOR CUBAN CONVECTION WILL SHIFT EASTWARD FROM WHERE IT WAS YESTERDAY...SO SHOWERS AND STORMS MAY BE MORE LIKELY NEAR THE CAY SAL BANK AND THE STRAITS SOUTH OF THE MIDDLE AND UPPER KEYS TONIGHT. IN ANY EVENT...THE ONLY FORECAST ISSUE FOR THE FIRST PERIOD WILL BE WHETHER TO DROP RAIN CHANCES FURTHER FROM THE ALREADY-SLIGHT 20 PERCENT CURRENT FORECAST. && .MARINE... LIGHT SOUTH TO SOUTHWEST BREEZES...OCCASIONALLY VARIABLE IN DIRECTION...WILL PERSIST THIS AFTERNOON. A FEW SHOWERS WILL POP OVER THE GULF WATERS ADJACENT TO THE LOWER KEYS AFTER NOON...AND THUNDERSTORMS WILL ENTER THE STRAITS NEAR THE CAY SAL BANK BY DARK. && .AVIATION... THROUGH 21/18Z...VFR CONDITIONS WILL PREVAIL AT BOTH ISLAND TERMINALS THROUGH THE FORECAST PERIOD. SOUTHERLY WINDS AT BOTH TERMINALS WILL REMAIN NEAR 5 KNOTS. PRECIPITATION PROBABILITY REMAINS LOW FOR BOTH TERMINALS AND HAVE NOT BEEN MENTIONED. && .KEY WATCHES/WARNINGS/ADVISORIES... FL...NONE. GM...NONE. && $$ |
| #535553 (Received by flhurricane at: 3:17 AM 20.Aug.2012) AFDKEY AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS NATIONAL WEATHER SERVICE KEY WEST FL 305 AM EDT MON AUG 20 2012 .DISCUSSION... SCATTERED SHOWERS AND CLUSTERS OF THUNDERSTORMS HAVE BEEN LIFTING NORTHWARD SLOWLY IN THE ATLANTIC WATERS. AWAY FROM THESE STORMS...WINDS ARE LIGHT FROM THE SOUTH OR VARYING IN DIRECTION AT TIMES. SKIES ARE PARTLY CLOUDY AND TEMPERATURES ARE IN THE MIDDLE 80S ALONG THE ISLAND CHAIN AT THIS HOUR. A DEEP LAYERED RIDGE WILL REMAIN ALIGNED ACROSS SOUTH FLORIDA AND THE FLORIDA KEYS TODAY AND INTO TUESDAY. A RATHER DEEP BUT LIGHT SOUTHERLY STEERING FLOW WILL BE MAINTAINED...BEFORE THE SURFACE AXIS LIFTS NORTHWARD ACROSS THE FLORIDA PENINSULA. IN THE SHORT TERM...BUMPED OUR PROBABILITY OF MEASURABLE RAIN UP 10 PERCENT ACROSS THE ISLAND CHAIN. OBVIOUSLY...ONLY WEAK LOW LEVEL CONVERGENCE IS NECESSARY TO KICK OFF AT LEAST SCATTERED SHOWERS AND A FEW THUNDERSTORMS. WOULD NOT BE SURPRISED TO SEE A REPEAT IN SHOWERS AND A FEW THUNDERSTORMS LIFTING NORTHWARD FROM CUBA LATE TONIGHT AND THROUGH THE EARLY MORNING HOURS ON TUESDAY. A LONG WAVE TROUGH WILL REMAIN ENTRENCHED ACROSS THE EASTERN PORTION OF THE NATION THROUGH THE MIDDLE AND LATER PERIODS OF THE WEEK...AND A TUTT WILL BEGIN MEANDERING IN THE VICINITY OF THE BAHAMAS. HOWEVER...BY WEDNESDAY...LOWER LEVEL FLOW BACKS TO THE SOUTHEAST AND WE SHOULD SEE DRIER AIR BEGINNING TO FILTER ACROSS THE IMMEDIATE AREA. WILL KEEP A SLIGHT CHANCE POP ADVERTISED FOR WEDNESDAY THROUGH FRIDAY. BY THE WEEKEND...THERE IS THE POTENTIAL FOR MUCH DEEPER MOISTURE LIFTING CLOSE TO THE KEYS AND SOUTH FLORIDA FROM THE NORTHERN PORTION OF THE CARIBBEAN. THE LATEST FEW RUNS OF THE GFS HAS FAVORED A STRENGTHENED AND DEEP CYCLONIC CIRCULATION FOR OUR REGION...THE LATEST BEING STRONGER AND FASTER THAN THE PREVIOUS INTERMEDIATE RUN. THAT MODEL IS NOT RECEIVING MUCH SUPPORT FROM OTHER GLOBAL FORECASTS...BUT IT WILL BEAR WATCHING AS THE WEEK PROGRESSES. FOR NOW...WILL HANG ON TO A LOW CHANCE POP WITH WINDS MODERATING FROM THE EAST. && .MARINE... EXPECT LIGHT AND VARIABLE WINDS...AT TIMES FAVORING THE SOUTHERLY DIRECTION...OVER THE NEXT COUPLE OF PERIODS AWAY FROM SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS. SURFACE WINDS WILL BACK TO THE EAST/SOUTHEAST FOR THE MIDDLE PORTIONS OF THIS WEEK. THESE WINDS WILL MODERATE BY FRIDAY. FOR NOW...NO CAUTIONARY HEADLINES FOR SMALL CRAFT ARE EXPECTED IN ANY OF THE WATERS SURROUNDING THE FLORIDA KEYS THROUGH THE DURATION OF THE FORECAST. && .AVIATION... SHOWERS AND THUNDERSTORMS MAY CONTINUE TO THREATEN THE EYW TERMINAL THROUGH THE REMAINDER OF THE OVERNIGHT HOURS...THOUGH CURRENT INDICATIONS ARE THAT MTH SHOULD REMAIN RAIN FREE THROUGH 12Z. AFTER THIS OVERNIGHT BOUT OF RAIN. WINDS WILL REMAIN LIGHT AND VARIABLE AROUND THE KEYS...AND A CHANCE OF SHOWERS WILL PERSIST THROUGH THE REMAINDER OF THE DAY. OUTSIDE OF SHOWERS...VFR SHOULD PREVAIL. && .PRELIMINARY POINT TEMPS/POPS... KEY WEST 89 82 89 82 / 30 30 30 30 MARATHON 92 82 92 82 / 30 30 30 30 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...NONE. GM...NONE. && $$ |
