Area Forecast Discussion
Issued by NWS San Juan, PR

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000
FXCA62 TJSJ 160931
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
531 AM AST WED APR 16 2014

.SYNOPSIS...AT UPPER LEVELS...RIDGING AND NORTHWEST FLOW WILL DOMINATE THE
PATTERN THROUGH SATURDAY NIGHT. A VERY WEAK SHORT WAVE WILL GLIDE
BY ON SUNDAY.

AT MID LEVELS...HIGH PRESSURE REMAINS OVER THE WESTERN AND CENTRAL
CARIBBEAN WITH A WEAK RIDGE MOVING THROUGH ON SUNDAY...FOLLOWED BY
A WEAK SHORT WAVE TROUGH. FLOW BECOMES ZONAL DURING THE UP COMING
WEEK AS A MUCH SHARPER WAVE APPROACHES THE AREA.

AT LOWER LEVELS...HIGH PRESSURE IN THE CENTRAL ATLANTIC AND
MODERATE TO FRESH TRADE WINDS WILL CONTINUE THROUGH THE WEEKEND AS
THE HIGH DRIFTS EASTWARD. A TROUGH JUST OFF THE EASTERN COAST OF
THE UNITED STATES WEAKENS OVER THE WESTERN ATLANTIC DURING THE
WORK WEEK BUT RE-STRENGTHENS OVER THE WEEKEND...EDGING SLOWLY
TOWARD THE LOCAL AREA DURING THE UPCOMING WEEK AHEAD OF THE MID
LEVEL TROUGH. MOISTURE INCREASES TODAY AND TOMORROW...DIPS ON
FRIDAY...BUT RECOVERS ON SATURDAY AND SUNDAY TO INCREASE THROUGH
MUCH OF THE FOLLOWING WEEK. THUNDERSTORMS ARE MORE LIKELY TO
DEVELOP BEGINNING ON SUNDAY.

&&

.DISCUSSION...SCATTERED SHOWERS BROUGHT MINIMAL...BUT MEASURABLE
AMOUNTS OF RAIN TO AREAS OF THE NORTHEASTERN THIRD OF PUERTO RICO
AND SAINT CROIX. MOISTURE IS EXPECTED TO INCREASE A LITTLE TODAY
AND...WITH EASTERLY WINDS CONTINUING...ANOTHER ROUND OF SHOWERS IS
EXPECTED IN WESTERN PUERTO RICO. ALTHOUGH AMOUNTS WERE GENERALLY
LIGHT TO MODERATE...ADJUNTAS DID HAVE ONE REPORT OF ALMOST TWO
INCHES OF RAIN YESTERDAY AND SIMILAR AMOUNTS ARE EXPECTED TODAY
EVEN THOUGH THEY MAY NOT FALL IN THE SAME PLACES. MOISTURE
INCREASES ON THURSDAY AND RAIN CHANCES ARE EXPECTED TO INCREASE
AGAIN THEN. MOISTURE DIPS ON FRIDAY AND THE MODEL HAS BEEN
CONSISTENTLY BRINGING IN DRIER AIR FROM THE EAST NORTHEAST. FRIDAY
ALSO MARKS THE BEGINNING OF THE TRANSITION TO MORE SOUTHEASTERLY
LOW LEVEL FLOW WHICH WILL BE COMPLETE BY SUNDAY. THIS WILL BE THE
MECHANISM BY WHICH MUCH BETTER MOISTURE WILL BE BROUGHT IN. THE
GFS MODEL SOUNDING SHOWS THAT BY WEDNESDAY A VERY MOIST SOUNDING
WILL BE FOUND WITH FEW PORTIONS OF THE SOUNDING LESS THAN 70
PERCENT RELATIVE HUMIDITY. THIS TRANSITION BEGINNING SUNDAY WILL
USHER IN THE BEGINNING OF MORE ACTIVE CONVECTION AND EXPECT
THAT AT LEAST ISOLATED THUNDERSTORMS WILL BE ENCOUNTERED IN
INTERIOR PUERTO RICO SUNDAY THROUGH THURSDAY OF NEXT WEEK. THE
GALVEZ-DAVIDSON INDEX SUGGESTS THAT THUNDERSTORMS MAY ALSO BE
POSSIBLE ON SUNDAY AROUND THE U.S. VIRGIN ISLANDS. IT IS TOO EARLY
TO DETERMINE IF THIS HEIGHTENED ACTIVITY LEVEL WILL CONTRIBUTE TO
LOCAL FLOODING IN THE AREA...BUT DEVELOPMENT OF THIS NEWLY MOIST
PATTERN WILL BE MONITORED FOR THAT POSSIBILITY.

&&

.AVIATION...VFR CONDITIONS AT ALL TAF SITES THROUGH AT LEAST 16/15Z
WITH A FEW PASSING SHOWERS POSSIBLE IN AND AROUND TJSJ/TIST/TISX AND
TNCM/TKPK. AFT 16/15Z...SHOWERS WILL DEVELOP ONCE AGAIN ACROSS W PR
AND MAY AFFECT TJMZ RESULTING IN BRIEF MVFR CONDS AND MOUNTAIN
OBSCURATIONS. LLVL EAST WINDS OF 10-20 KT BELOW 10 KFT.

&&

.MARINE...MARINE CONDITIONS ARE BELOW EXERCISE CAUTION LEVELS AT
PRESENT...BUT CONDITIONS ARE EXPECTED TO BEGIN TO DETERIORATE ON
THURSDAY AS WINDS INCREASE. LATEST WAVE WATCH STILL SUGGESTS 7 TO
8 FOOT SEAS THURSDAY OR THURSDAY NIGHT...BUT HAS BACKED OFF
CONSIDERABLY ON THE WAVE DEVELOPMENT IN THE CARIBBEAN. SHOULD
LATER MODELS CONFIRM...THE FORECAST WILL NEED TO BE LOWERED. GFS
IS ALSO FORECASTING STRONGER WINDS THAN CURRENTLY EXPECTED AND
HENCE IS LIKELY TO ALSO BE FORECASTING EXAGGERATED SEAS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  86  75  85  75 /  30  50  50  50
STT  84  75  85  76 /  30  50  50  50

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
COASTAL WATERS...NONE.
&&

$$

13/12






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