981
FXUS62 KKEY 130918
AFDKEY
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KEY WEST FL
518 AM EDT SAT SEP 13 2025
..NEW DISCUSSION, MARINE, AVIATION
DISCUSSION
ISSUED AT 430 AM EDT SAT SEP 13 2025
YET ANOTHER ACTIVE OVERNIGHT PERIOD FOR THE FLORIDA KEYS AND THE
ADJACENT COASTAL WATERS. AN EXTENSIVE OUTFLOW BOUNDARY IN THE
SOUTHEASTERN GULF NORTHWEST OF THE LOWER KEYS PROGRESSED
SOUTHEASTWARD, TRIGGERING A MESOSCALE CONVECTIVE SYSTEM (MCS) TO
RAPIDLY PUSH THROUGH THE MIDDLE AND UPPER KEYS. PERHAPS MOST
NOTABLY, MARATHON INTERNATIONAL AIRPORT MEASURED AN IMPRESSIVE
WIND GUST OF 47 KNOTS, ALONG WITH AROUND 1 INCH OF RAINFALL IN
LESS THAN ONE HOUR. THIS MCS HAS SINCE WANED IN THE SOUTHEASTERN
STRAITS OF FLORIDA. GOES NIGHTTIME MICROPHYSICS IMAGERY IS
DETECTING GENERALLY PARTLY CLOUDY SKIES ACROSS THE CWA. SAMPLED
TEMPERATURES ALONG THE ISLAND CHAIN ARE GENERALLY IN THE MID TO
UPPER 70S AT THIS EARLY SATURDAY MORNING HOUR.
CIMSS SATELLITE-DERIVED PRODUCTS HIGHLIGHT AN ABNORMALLY STRONG
UPPER-LEVEL TROUGH IN THE GULF, WITH ITS BASE NEARLY NUDGING THE
TIP OF THE YUCATAN PENINSULA. THE LONGITUDINAL PLACEMENT OF THE
TROUGH PLACES THE MAXIMUM UPPER-LEVEL DIVERGENCE IN THE VICINITY
OF THE BAHAMAS. AT THE SURFACE, A DIFFUSE FRONTAL BOUNDARY CAN BE
DISCERNED BY AVAILABLE SURFACE WIND OBSERVATIONS, WHICH HAVE
DEMONSTRATED A NOTICEABLE SHIFT TO NORTHEASTERLIES ACROSS THE
ISLAND CHAIN OVER THE PAST TWENTY FOUR HOURS, INDICATING THE
FRONTAL BOUNDARY LOCATED SOMEWHERE SOUTH OF THE KEYS. THE FRONTAL
BOUNDARY REMAINS WEAK, WITH DEWPOINTS SHOWING LITTLE CHANGE
FOLLOWING THE PASSAGE TODAY, STILL WELL IN THE LOWER TO MID 70S
ACROSS THE FLORIDA KEYS.
A VERY CHALLENGING FORECAST FOR THE BALANCE OF TODAY. WHILE THE
MIDDLE AND UPPER KEYS LIKELY USED UP MOST AVAILABLE CONVECTIVE
POTENTIAL ENERGY OVERNIGHT UNTIL RECHARGING CAN OCCUR, THE LOWER
KEYS ARE LIKELY UNTAPPED. WITH THE AFOREMENTIONED UPPER- LEVEL
DIVERGENCE LARGELY DISPLACED EASTWARD OF THE KEYS, THE DRIVING
FORCING FOR CONVECTIVE INITIATION WILL BE CHAOTIC MESOSCALE
BOUNDARY INTERACTIONS. GIVEN THE ACTIVE CONVECTION OVERNIGHT AND
THE LIKELY DORMANT PERIOD UNTIL RECHARGING CAN OCCUR, ELECTED TO
NUDGE MEASURABLE RAIN CHANCES DOWN CLOSER TO STATISTICAL GUIDANCE
(AROUND 60%). WITH THAT SAID, WISH TO EMPHASIZE THAT SHORT-TERM
FORECAST UNCERTAINTY IS UNUSUALLY HIGH.
CONFIDENCE IN THE FORECAST BEYOND TODAY REMAINS QUITE LOW. WHILE
THE UPPER-LEVEL TROUGH WILL SLOWLY LIFT NORTHEASTWARD, GLOBAL
ENSEMBLE NUMERICAL WEATHER PREDICTION (NWP) MEAN PRODUCTS SUGGEST
THE SURFACE BOUNDARY WILL CONTINUE TO FLIRT WITH THE KEYS THROUGH
THE WORK WEEK. AS THE SURFACE HIGH NORTH OF THE BOUNDARY
STRENGTHENS AND BUILDS SOUTHWARD, THE PRESSURE GRADIENT WILL
LIKELY INCREASE, SUPPORTING FRESHENING EASTERLY BREEZES. WHERE THE
MOISTURE GRADIENT ASSOCIATED WITH THE BOUNDARY ENDS UP IN
RELATION TO THE KEYS WILL DETERMINE MEASURABLE RAIN CHANCES.
CURRENT NWP PRODUCTS SUGGEST DRIER PERIODS MONDAY NIGHT INTO
TUESDAY, BEFORE A RETURN TO ELEVATED RAIN AND THUNDER CHANCES FOR
TUESDAY NIGHT AND BEYOND. TEMPERATURES WILL REMAIN SEASONABLY
WARM, WITH HIGHS IN THE UPPER 80S TO NEAR 90, AND LOWS IN THE
UPPER 70S TO NEAR 80.
MARINE
ISSUED AT 430 AM EDT SAT SEP 13 2025
CONVECTION OVER THE EASTERN STRAITS OF FLORIDA SOUTH OF THE
MIDDLE AND UPPER KEYS WILL WANE OVER THE NEXT COUPLE OF HOURS. A
LULL IN CONVECTION WILL COMMENCE, FOLLOWED BY ADDITIONAL
CONVECTIVE DEVELOPMENT EXPECTED BY LATE MORNING OR EARLY
AFTERNOON. ANY STRONGER STORM WILL BE CAPABLE OF PRODUCING
FREQUENT CLOUD TO SURFACE LIGHTNING STRIKES, LOCALLY STRONG WINDS,
AND CONFUSED SEAS.
FROM SYNOPSIS, A WEAK FRONTAL BOUNDARY WILL REMAIN IN THE
VICINITY OF THE FLORIDA KEYS COASTAL WATERS OVER THE NEXT SEVERAL
DAYS. WEAK UNDULATIONS OF THIS FEATURE, INTERACTING WITH HIGH
PRESSURE TO ITS IMMEDIATE NORTH, WILL RESULT IN A LOW CONFIDENCE
FORECAST FOR WINDS AND RAIN CHANCES. GENTLE TO MODERATE NORTHEAST
TO EAST BREEZES ARE EXPECTED TO BUILD IN BY TUESDAY OR WEDNESDAY,
AS THE AXIS OF THE HIGH PRESSURE FINALLY IS ABLE TO SPREAD DOWN
CLOSER TO THE KEYS MARINE ZONES.
AVIATION
(06Z TAFS)
ISSUED AT 430 AM EDT SAT SEP 13 2025
VFR CONDITIONS ARE EXPECTED TO PREVAIL AT BOTH TERMINALS THROUGH THE
MORNING HOURS, BUT RESIDUAL CLOUD COVER FROM OVERNIGHT CONVECTION
MAY LEAD TO INFREQUENT INSTANCES OF MVFR CIGS. ANOTHER ROUND OF
SHOWERS AND THUNDERSTORMS ARE EXPECTED IN THE GENERAL AREA BY THE
AFTERNOON, BUT THERE IS LOW CONFIDENCE WITH RESPECT TO WHETHER OR
NOT THIS ACTIVITY WILL EVEN REACH EITHER TERMINAL. OPTING TO
MAINTAIN AN EXTENDED PERIOD OF VCSH THIS MORNING AND AFTERNOON, AND
WILL REEVALUATE ONCE NEW CONVECTION INITIATES.
CLIMATE
IN 2024, THE DAILY RECORD WARM LOW TEMPERATURE OF 87F WAS RECORDED
IN KEY WEST. THIS ALSO RANKS AS THE WARMEST LOW TEMPERATURE EVER
RECORDED IN SEPTEMBER. TEMPERATURE RECORDS FOR KEY WEST DATE BACK TO
1872.
PRELIMINARY POINT TEMPS/POPS
KEY WEST 88 78 89 79 / 60 50 40 40
MARATHON 87 78 88 79 / 60 50 40 40
KEY WATCHES/WARNINGS/ADVISORIES
FL...NONE.
GM...NONE.
PUBLIC/MARINE/FIRE...BT
AVIATION/NOWCASTS....DP
DATA ACQUISITION.....DP
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