908
FXUS62 KKEY 190822
AFDKEY
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KEY WEST FL
422 AM EDT FRI JUL 19 2019
DISCUSSION
SCATTERED SHOWERS AND ISOLATED STORMS HAVE PROLIFERATED ACROSS THE
STRAITS OF FLORIDA DURING THE LAST COUPLE OF HOURS, AND MORE
RECENTLY ALONG THE UPPER KEYS AND EASTERN FLORIDA BAY, BUT AN
EARLIER BOUT OF ACTIVITY ACROSS THE WATERS BETWEEN KEY WEST AND
THE DRY TORTUGAS HAS NOW FADED. SOME SHOWERS AND STORMS HAVE MOVED
ACROSS PARTS OF THE LOWER AND UPPER KEYS DURING THE NIGHT, WHILE
OTHER PARTS OF THE ISLAND CHAIN HAVE REMAINED DRY. TEMPERATURES
ALONG THE KEYS ARE HOVERING IN THE LOWER TO MID 80S, WHILE WINDS
ON LAND ARE FROM THE EAST AROUND 10 MPH.
SURFACE ANALYSIS DEPICTS THE BERMUDA HIGH EXTENDING FROM THE
WESTERN ATLANTIC ACROSS THE FLORIDA PENINSULA AND THE NORTHERN
GULF OF MEXICO, WITH THE KEYS LYING WITHIN MODERATE EASTERLY FLOW
TO THE SOUTH OF THE RIDGE AXIS. ALOFT, LOWER/MID LEVEL RIDGING
PREVAILS ACROSS THE REGION, BUT WATER VAPOR IMAGERY ALONG WITH
CIMSS ANALYSIS SHOWS A WEAK UPPER LEVEL TUTT-TYPE FEATURE
EXTENDING FROM NORTH OF THE BAHAMAS SOUTHWESTWARD TO WESTERN CUBA.
THE 00Z KEY WEST SOUNDING FOUND A GENERALLY MOIST AND
CONDITIONALLY UNSTABLE PROFILE, BUT SOME CONVECTIVE INHIBITION
WAS PRESENT AT THAT TIME JUST ABOVE 900 MB. MEASURED PW WAS 1.83
INCHES, WHICH IS NORMAL FOR THIS TIME OF YEAR. GOES TPW IMAGERY
SHOWS A SLIGHTLY DRIER AIRMASS WITH ESTIMATED PW VALUES OF 1.5 TO
1.7 INCHES LOCATED JUST TO THE E AND SE OF THE KEYS.
FOR TODAY, THE BEST RAIN CHANCES WILL PROBABLY OCCUR DURING THE
EARLY MORNING HOURS, AS IS OFTEN THE CASE WITH MODERATE ESE
STEERING FLOW. WITH THIS FLOW REGIME LARGELY PREVENTING BOUNDARY
INTERACTIONS, WOULD EXPECT SHOWER ACTIVITY TO DECREASE TO ISOLATED
LATER THIS MORNING, DUE BOTH TO TYPICAL DIURNAL TRENDS AND A
DRIER MID LEVEL AIRMASS EXPECTED TO MOVE IN FROM THE EAST.
NOT MUCH CHANGE IS EXPECTED TONIGHT AND SATURDAY, WITH MODERATE
ESE STEERING FLOW CONTINUING ALONG WITH NEAR NORMAL PW VALUES.
BEST RAIN CHANCES WILL PROBABLY OCCUR DURING THE LATE NIGHT AND
EARLY MORNING HOURS. FOR SATURDAY NIGHT THROUGH MONDAY, THE
NORTHERN EDGE OF A WEAK TROPICAL WAVE MOVING THROUGH THE AREA
SHOULD BRING DEEPER MOISTURE OVER THE KEYS, WITH PW VALUES AROUND
2 INCHES AT TIMES. WE SHOULD ALSO BE ON THE WET SIDE OF A WEAK
TUTT CELL IN THE GULF AT THAT TIME. HAVE NUDGED RAIN CHANCES
UPWARD INTO THE 40-50 PERCENT RANGE, NOTING THAT THE LAST FEW
RUNS OF THE GFS AND ECMWF ALSO BOTH SHOW ABOVE CLIMO POPS FOR
THOSE TIME PERIODS.
HEADING TOWARD THE MIDDLE OF NEXT WEEK, THE LATEST GUIDANCE
REMAINS CONSISTENT IN DIGGING A RATHER STRONG MID-LATITUDE TROUGH
FOR MIDSUMMER INTO THE EASTERN UNITED STATES, WHICH WOULD PUSH THE
SUBTROPICAL RIDGE SOUTHWARD OVER OUR AREA. THIS WOULD RESULT IN A
LIGHT WIND REGIME ACROSS THE KEYS, WHICH WOULD FAVOR DAYTIME
ISLAND CLOUD LINES, ALONG WITH BOUNDARY INTERACTIONS AT ANY TIME.
WITH GUIDANCE INDICATING THAT ADEQUATE MOISTURE AND INSTABILITY
WILL BE AVAILABLE, HAVE NUDGED RAIN CHANCES UP A NOTCH TO 30
PERCENT FOR MONDAY NIGHT THROUGH THURSDAY.
MARINE
EASTERLY BREEZES HAVE SURGED INTO THE 10-15 KNOT RANGE ACROSS THE
KEYS WATERS DURING THE NIGHT, AS SHOWN BY OBSERVATIONS FROM ALONG
THE REEF AND IN THE GULF WATERS. ESE BREEZES SHOULD BACK OFF A
FEW KNOTS DURING THE DAY, THEN INCREASE A FEW KNOTS AGAIN TONIGHT,
PROBABLY MAXING OUT NEAR 15 KNOTS ACROSS THE STRAITS. THIS
EASTERLY FLOW PATTERN WILL SLOWLY WEAKEN DURING THE WEEKEND, THEN
BE REPLACED BY LIGHT WINDS DURING MUCH OF NEXT WEEK.
AVIATION
VFR CONDITIONS WILL PREVAIL FOR BOTH TERMINALS. EXPECT SE WINDS NEAR
10 KNOTS WITH FEW TO SCT CLOUDS AROUND FL025 THROUGHOUT THE PERIOD.
SHOWERS COULD AFFECT TERMINALS WITH POSSIBLE BRIEF MVFR CEILINGS.
REMNANT BOUNDARIES FROM EARLIER CONVECTION COULD INITIATE FURTHER
CONVECTION THAT COULD MOVE OVER THE TERMINALS. CONFIDENCE IS TOO
LOW FOR TIMING AND PLACEMENT AT THIS TIME TO INCLUDE IN THE
FORECAST.
PRELIMINARY POINT TEMPS/POPS
KEY WEST 91 83 91 82 / 30 30 30 40
MARATHON 93 83 93 82 / 30 30 30 40
KEY WATCHES/WARNINGS/ADVISORIES
FL...NONE.
GM...NONE.
PUBLIC/MARINE/FIRE...JACOBSON
AVIATION/NOWCASTS....CHESSER
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