879
FXUS62 KKEY 190929
AFDKEY
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KEY WEST FL
429 AM EST THU DEC 19 2024
..NEW DISCUSSION, MARINE, AVIATION
DISCUSSION
ISSUED AT 430 AM EST THU DEC 19 2024
IT IS ANOTHER WARM AND STICKY NIGHT ACROSS THE FLORIDA KEYS.
HOWEVER, THERE ARE ALSO SOME ITEMS OF INTEREST TO POINT OUT
TONIGHT THAT WE DON'T SPEAK OF ALL TOO OFTEN. GOES 16 NIGHTTIME
MICROPHYSICS IMAGERY SHOWS A FOG BANK MEANDERING ACROSS THE
OFFSHORE GULF WATERS SOUTH TO THE WESTERN STRAITS OF FLORIDA. WHAT
IS EVEN MORE INTERESTING IS THIS FOG BANK STRETCHES NORTHWARD TO
THE BIG BEND AREA OF FLORIDA THUS ENCOMPASSING MUCH OF THE COASTAL
WATERS OFF THE WEST COAST OF FLORIDA. ON THE OTHER HAND, ACROSS
THE EASTERN STRAITS OF FLORIDA, KBYX RADAR HAS BEEN ACTIVE FOR
MUCH OF THE NIGHT WITH SCATTERED SHOWERS. MRMS DATA SHOWS
ESTIMATED 3 HOURLY RAINFALL AMOUNTS OF MOSTLY 0.1 TO 0.25 INCHES
BUT, WHERE THE ACTIVITY REMAINED THE MOST PERSISTENT, SOME
AMOUNTS WERE ESTIMATED TO BE BETWEEN A HALF TO ONE INCH. THE UPPER
KEYS GOT IN ON THE ACTION EARLIER IN THE NIGHT RESULTING IN
AMOUNTS OF 0.1 TO 0.3 INCHES WITH LOCALLY 0.3"+. A WEAK LOW
PRESSURE CENTER IS JUST OFF THE SPACE COAST OF FLORIDA EARLY THIS
MORNING WITH A HIGH PRESSURE SYSTEM MOVING EASTWARD ACROSS THE
MISSISSIPPI RIVER VALLEY. AS A RESULT, MARINE PLATFORMS AROUND THE
KEYS ARE OBSERVING MAINLY NORTH BREEZES OF 5 TO 10 KNOTS WITH
SAND KEY OBSERVING 10 TO 15 KNOTS. ISLAND CHAIN COMMUNITIES WERE
OBSERVING NORTH TO NORTHEAST BREEZES OF 5 TO 10 MPH. TEMPERATURES
ALONG THE ISLAND CHAIN ARE IN THE LOWER 70S WITH DEW POINTS IN
THE LOWER 70S.
FORECAST
THE MAIN FORECAST ISSUE FOR TODAY IS WHAT DOES THE FOG BANK OVER
THE OFFSHORE GULF WATERS AND WESTERN STRAITS OF FLORIDA DO? FOG
FORECASTING IS ALWAYS VERY TRICKY. SINCE WE HAVE HAD QUITE THE
COOL SNAPS THIS MONTH, THE WATER TO THE NORTH OF THE ISLAND CHAIN
IS COOL. WHEN WE SEND THE WARMER AND MORE HUMID AIR NORTH OVER
THE COOL WATER, IT CONDENSES AND LEADS TO FOG FORMATION. THERE
ARE A FEW DIFFERENT SOLUTIONS THAT CAN HAPPEN. ONE IS THE FOG
HOLDS ON THROUGH THE DAY AND STAYS WHERE IT CURRENTLY IS, OR IT
EXPANDS AND MOVES INTO THE ISLAND CHAIN COMMUNITIES, IN
PARTICULAR, THE LOWER KEYS, OR THE WINDS COME UP JUST ENOUGH TO
HELP MIX OUT THE FOG RESULTING IN A NICER DAY FOR THE CHAIN.
CURRENT THINKING IS THAT THE FOG WILL MOVE INTO AT LEAST THE LOWER
KEYS AT SOME POINT TODAY WHICH WOULD RESULT IN DENSE FOG
ADVISORIES IF IT DOES. HOW LONG IT STAYS REMAINS TO BE SEEN BUT IF
IT HAPPENS, IT APPEARS IT WOULD HAVE TO DO SO BEFORE THE EVENING
HOURS WHEN THE WEAK FRONT CURRENTLY ALONG THE NORTH GULF COAST
MOVES SOUTHEASTWARD AND THROUGH THE KEYS. THIS WILL PROMOTE
INCREASING WINDS WHICH WOULD HELP TO MIX OUT THE FOG.
THEN, AN POSITIVELY TILTED UPPER LEVEL TROUGH CURRENTLY ACROSS
THE NORTH GULF COAST AND NORTHERN FLORIDA IS EXPECTED TO BECOME
NEGATIVELY TILTED LATE TODAY. AT THE SURFACE, A WEAK FRONT IS
EXPECTED TO PRESS THROUGH THE KEYS AS A RESULT SOMETIME LATE TODAY
OR THIS EVENING. THIS WILL RESULT IN FRESHENING NORTHERLY BREEZES
ALONG WITH MUCH DRIER AIR MOVING IN BEHIND IT. ANOTHER MORE
POTENT UPPER LEVEL TROUGH WILL SWING ACROSS THE OHIO AND TENNESSEE
VALLEYS, AND THE NORTHEAST FRIDAY WHICH WILL SEND A SECONDARY
FRONT AT THE SURFACE THROUGH THE KEYS FURTHER DROPPING THE DEW
POINTS AND TEMPERATURES. TEMPERATURES ON SATURDAY ARE EXPECTED TO
BE IN THE UPPER 60S WITH OVERNIGHT LOWS IN THE UPPER 50S. DEW
POINTS WILL ALSO DROP INTO THE 50S PERHAPS EVEN THE MID TO UPPER
40S. WINTER WILL MAKE A RETURN! ALSO, PLENTY OF DRY AIR WILL BE IN
PLACE RESULTING IN A DRY FORECAST FRIDAY THROUGH SUNDAY NIGHT.
IN THE WAKE OF THE SECONDARY FRONT, A LARGE AND STRONG HIGH
PRESSURE BUILDS ACROSS THE EASTERN UNITED STATES OVER THE WEEKEND
INTO EARLY TO MID NEXT WEEK WITH MOST ENSEMBLE AND DETERMINISTIC
GUIDANCE ON BOARD WITH THIS SOLUTION. THIS WILL PROMOTE FRESHENING
NORTHEAST TO EAST BREEZES WITH ANOTHER POTENTIALLY LENGTHY BLOW
EXPECTED AS A HEALTHY PRESSURE GRADIENT DEVELOPS. INITIALLY,
MOISTURE IS EXPECTED TO REMAIN SCARCE, BUT THIS IS EXPECTED TO
RAPIDLY CHANGE AS MOISTURE QUICKLY INCREASES AT 850 MB. ANY
SHOWERS WILL YET AGAIN REMAIN SHALLOW AND QUICK MOVING IN THE
EASTERLIES PRODUCING MINOR RAINFALL AMOUNTS GENERALLY UNDER A
TENTH OF AN INCH. THIS MAY BE JUST ENOUGH TO CREATE A WET LEAD-UP
TO CHRISTMAS WITH THE WET REGIME AND WINDY CONDITIONS POTENTIALLY
CONTINUING INTO THE CHRISTMAS HOLIDAY.
MARINE
ISSUED AT 430 AM EST THU DEC 19 2024
A DENSE FOG ADVISORY IS IN EFFECT FOR THE OFFSHORE GULF WATERS
INCLUDING THE DRY TORTUGAS, THE WESTERN STRAITS OF FLORIDA, AND
NOW WESTERN HAWK CHANNEL, AND THE GULFSIDE WATERS SURROUNDING THE
LOWER KEYS THROUGH LATE THURSDAY MORNING.
FROM SYNOPSIS, WEAK HIGH PRESSURE REMAINS IN PLACE ACROSS THE
FLORIDA KEYS TODAY PROMOTING LIGHT TO GENTLE NORTH TO NORTHEAST
BREEZES. THE LIGHT TO GENTLE BREEZES AND A QUICK REDUCTION OF
TEMPERATURES OVER WARM WATER WILL ALLOW FOR DEVELOPMENT OF PATCHES
OF DENSE FOG ACROSS THE COASTAL WATERS OF THE FLORIDA KEYS
THROUGH LATE THIS MORNING, ESPECIALLY IN THE OUTER GULF WATERS AND
WESTERN STRAITS OF FLORIDA. A WEAK FRONT WILL THEN PRESS THROUGH
THE KEYS LATE TODAY OR THIS EVENING RESULTING IN FRESHENING
NORTHERLY BREEZES. A SECONDARY FRONT IS EXPECTED TO PRESS THROUGH
THE KEYS LATE FRIDAY REINFORCING THE PREVIOUS FRONT. IN THE WAKE
OF THE FRONT, STRONG HIGH PRESSURE BUILDS ACROSS THE EASTERN
UNITED STATES RESULTING IN A STRENGTHENING PRESSURE GRADIENT. THIS
PROMOTE FRESHENING NORTHEAST TO EAST BREEZES OVER THE WEEKEND
INTO EARLY NEXT WEEK.
AVIATION
(06Z TAFS)
ISSUED AT 430 AM EST THU DEC 19 2024
LOW CLOUDS AND FOG MAY IMPACT THE EYW TERMINAL WITH LIFR
CONDITIONS DURING THE MORNING HOURS, ALTHOUGH CONFIDENCE IN
OCCURRENCE AND TIMING REMAINS QUITE LOW. MTH IS MORE LIKELY TO SEE
MVFR CEILINGS, WITH FOG PROBABLY REMAINING WEST OF THAT TERMINAL.
THERE IS ALSO LOW CONFIDENCE ON THE TIMING FOR IMPROVEMENT AT
EYW, IF FOG AND/OR LOW STRATUS DOES REACH THE TERMINAL, WITH SOME
GUIDANCE INDICATING THAT LIFR/IFR CONDITIONS COULD LINGER WELL
INTO THE AFTERNOON. A DRIER AIRMASS IS EXPECTED TO FILTER INTO THE
AREA FROM THE NORTH THIS EVENING, WITH GREATER CONFIDENCE IN VFR
CONDITIONS BY THEN. SURFACE WINDS WILL REMAIN FROM THE NNE AT 5 TO
8 KNOTS THIS MORNING, BACKING SLIGHTLY TO THE NNW THIS AFTERNOON.
PRELIMINARY POINT TEMPS/POPS
KEY WEST 78 71 77 64 / 10 0 0 0
MARATHON 80 70 78 62 / 10 0 0 0
KEY WATCHES/WARNINGS/ADVISORIES
FL...NONE.
GM...DENSE FOG ADVISORY UNTIL 11 AM EST THIS MORNING FOR GMZ033>035-
044-054-055-074-075.
PUBLIC/MARINE/FIRE...MJV
AVIATION/NOWCASTS....JACOBSON
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