NWS Keywest AFD

[TampaFl]

FXUS62 KEYW 170651
AFDEYW

FLORIDA KEYS AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KEY WEST FL
250 AM EDT MON MAY 17 2004

.DISCUSSION...
.OBSERVATIONS/TRENDS...

.FORECASTS...
PERSISTENCE WILL BE THE BEST FORECASTING METHOD FOR AT LEAST THE
NEXT THREE DAYS...AS THE SUBTROPICAL WARM ANTICYCLONE CONTINUES TO
DOMINATE THE LOW-LEVEL FLOW PATTERN.

UPPER-TROPOSPHERIC FLOW WILL EVOLVE INTO A MORE COMPLEX PATTERN OVER
THE GULF OF MEXICO BASIN DURING THE WEEK...AS A COLD-CORE CYCLONE
CUTS OFF ABOVE 700MB...AND MIGRATES/EVOLVES TOWARD THE SOUTH AND
EAST. HOWEVER...VERTICAL MOTION FIELDS WITH THIS SYSTEM APPEAR TO BE
WEAK IN THE NUMERICAL MODEL SOLUTIONS...AND POSITIONED PRIMARILY
WEST OF THE SERVICE AREA. IN ADDITION...LAYER PRECIPITABLE WATER
VALUES OVER SOUTH FLORIDA AND THE KEYS WILL LIKELY DROP FROM PRESENT
VALUES OF AROUND 1.5 IN...TO 1.1-1.2 IN FOR THE PERIOD MONDAY NIGHT-
THURSDAY...SINCE MEAN LOW/MID-TROPOSPHERIC FLOW WILL REMAIN EASTERLY
ACROSS OUR REGION...ALLOWING DRY MID-LEVEL AIR CURRENTLY RESIDING
OVER THE WESTERN NORTH ATLANTIC TO BE ADVECTED SOUTH AND WEST...
AROUND THE PERIPHERY OF THE SUBTROPICAL ANTICYCLONE. FRIDAY COULD BE
THE WETTEST DAY AS THE MID/UPPER CYCLONE GETS CLOSEST...BUT THIS IS
TOO FAR OUT INTO THE FUTURE TO MAKE ANY DETERMINISTIC STATEMENT OF
VALUE...GIVEN THE INCREASING UNCERTAINTY.

THE UPSHOT IS THAT A NEAR-PERSISTENCE/NEAR-CLIMATOLOGY FORECAST WILL
ENSUE. CONFIDENCE IS HIGH THAT WINDS WILL STAY NEAR PRESENT VALUES
THROUGH ABOUT THURSDAY...WITH ONLY MINOR/SHORT-LIVED PEAKS AND
LULLS. THE SUBTROPICAL ATLANTIC ANTICYCLONE WILL GRADUALLY WEAKEN
DURING THIS TIME. HOWEVER...IT WILL ALSO BE TRANSLATING SOUTHWARD...
WHICH SHOULD KEEP THE LOCAL PRESSURE GRADIENT NEAR CONSTANT. BY
FRIDAY...FORECAST CONFIDENCE DECREASES DUE TO:

A) UNCERTAINTY ASSOCIATED WITH STRENGTH AND POSITION OF ATLANTIC
RIDGE NORTH OF THE KEYS...
B) UNCERTAINTY ASSOCIATED WITH LOCATION AND MAGNITUDE OF MSLP FALLS
ACROSS WESTERN CARIBBEAN...
C) UNCERTAINTY ASSOCIATED WITH LOCATION AND STRENGTH OF UPPER COLD-
CORE CYCLONE OVER GULF...AND ASSOCIATED VERTICAL MOTION FIELDS.

Thoughts and comments welcomed.

Robert

[KatDaddy]

Excerpt:

LONG TERM...5H RIDGING REMAINS ELONGATED FROM OVER MEX AND THE GULF
COAST STATES IN THE LONG RANGE WHICH WILL MAINTAIN NIL POPS AND
ABOVE NORMAL TEMPS. ALTHOUGH JUNE 1ST IS STILL A COUPLE OF WEEKS
AWAY...BOTH THE GFS AND THE ECMWF ARE BOTH INITIALIZING ON AN AREA
OF CONV OFF OF NICARAGUA AND DEVELOP THIS FEATURE INTO A BROAD
SURFACE LOW LATER THIS WEEK AND MOVE IT OUT TO THE NE. AS INDICATED
IN THE LATEST PMDEPD...THIS AREA IS CLIMATOLOGICALLY FAVORED FOR
EARLY SEASON TROPICAL DEVELOPMENT.

[Brent]

Cool.

[Brett Adair]

Cool.

Yup....glad to see you joined Brent!

[Rainband]

This is from my forecast discussion
000
FXUS62 KTBW 170543
AFDTBW

WEST CENTRAL AND SOUTHWEST FLORIDA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY AREA - RUSKIN FL
145 AM EDT MON MAY 17 2004

.SHORT TERM (TODAY-WED)...PRECIP CHANCES ONLY TOUGH FORECAST
PARAMETER THRU MID WEEK. DIRTY UPPER RIDGE OVER THE REGION TODAY WITH
WSW UPPER FLOW ALOFT AS SEVERAL WEAK VORT MAXES ROTATE OVER THE
STATE. LATEST WV SAT IMAGERY SHOWING DRY AIR OVER THE WESTERN
ATLANTIC WITH MOISTURE FILLING INTO THAT REGION. MID AND SFC RIDGE
AXIS NORTH OF THE AREA FROM OFF CAPE HATTERAS INTO THE DEEP
SOUTH. MODELS INDICATE MID LEVEL EASTERLY FLOW TO BRING SOME OF THIS
DRY AIR OVER THE STATE WHILE THERE IS NO DOUBT THE DRY AIR IS OUT
THERE THE QUESTION IS WILL IT MAKE IT THE WEST FL. THE WETTER GFS
SOLUTION KEEPS IT S AND E OF OUR AREA WHILE THE DRIER ETA BRINGS IT
INTO OUR AREA. AND LOOKS LIKE THE WETTER SOLUTIONS VERIFIED BETTER
OVER THE LAST FEW DAYS. BOTH MODELS HOWEVER HAVE INCREASED THE POPS
FROM PREVIOUS RUNS. SO AM LEANING TOWARD THE HIGHER POPS MAINLY
ALONG WEST COAST SEA BREEZE N OF SARASOTA CO THIS AFTERNOON INTO THE
EVENING.

TUE...EXPECT MORE OF A WEST COAST SEABREEZE DEVELOPING IN THE
AFTERNOON HEATING AND HAVE INCREASED DIURNAL POPS ON TUE AS WELL WITH
MORE UPPER ENERGY IN PLACE.

WED...GFS TRIES TO WRAP MOISTURE AROUND MID LEVEL DRY SLOT AS SFC
RIDGE BEGINS TO SINK SOUTHWARD. WILL KEEP SLIGHT CHANCE POPS HERE
FOR NOW. TEMPS NEAR NORMAL THRU THE PERIOD.

.LONG TERM (WED NIGHT-SUN)...SFC RIDGING WILL CONTINUE OVER THE AREA
THRU THE PERIOD. THIS WILL KEEP ATMOSPHERE FAIRLY DRY...ESPECIALLY
FRI THRU SUN...AND ALLOW DAILY SEA BREEZES TO PUSH INLAND WITH
LITTLE SHOWER ACTIVITY FORMING ALONG THE BNDY. ONLY CHANGE DAY TO DAY
WILL BE LOCATION OF AN UPPER LEVEL CLOSED LOW...WHICH IS CURRENTLY A
S/W OVER CENTRAL TX. 00Z GFS HAS IT FURTHER E...OUT OVER THE S
CENTRAL GULF ON THU AND JUST W OF THE KEYS ON FRI...THAN PREVIOUS
RUN. THIS FEATURE WILL INCREASE UPPER LEVEL CLOUD COVER OVER THE
WEEKEND DOWN SOUTH. ALSO...MODEL GUIDANCE IS DEVELOPING A SPURIOUS
TROPICAL LOW OVER THE NW CARIBBEAN. THE EFFECT OF THIS LOW ON
GUIDANCE IS TO INCREASE WINDS OVER THE SRN ZONES. WILL DISCOUNT THIS
EFFECT...BUT CONTINUE TO MONITOR FOR ANY DEVELOPMENT.

WILL KEEP 20 POPS IN FOR THU TO MAINTAIN CONTINUITY WITH PREVIOUS
FORECAST...DESPITE LOWERING PW'S IN LATEST GUIDANCE. IF GUIDANCE
PERSISTS WITH TREND...THEN WILL DROP IN A FUTURE FORECAST.

&&

.MARINE...EASTERLY FLOW TO REMAIN IN PLACE AND WEAKEN BY WED. WINDS
AND SEAS SLIGHTLY HIGHER OVER SOUTHERN WATERS WITH TIGHTER
GRADIENT. AFTERNOON WEST COAST SEABREEZE TO BECOME STRONGER THRU THE
WEEK WITH CHANCES FOR PRECIP IN THE LATE AFTERNOONS AND EVENINGS.

&&

.FIRE WX...WITH DRIEST MID LEVEL AIR EXPECTED TO STAY TO OUR S AND
E MIN RH LEVELS EXPECTED TO BOTTOM OUT AROUND 40 PERCENT NEXT FEW
DAYS.

&&

.PRELIMINARY POINT TEMPS/POPS...
TPA 088 069 088 068 / 30 10 30 10
FMY 089 067 089 067 / 20 10 20 10
GIF 089 067 089 067 / 20 00 20 00
SRQ 088 066 088 067 / 30 10 30 10
BKV 090 063 090 063 / 30 10 30 10

&&

.TBW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

RD/RS