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000
FXCA62 TJSJ 171546
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1146 AM AST FRI MAY 17 2013

.UPDATE...CLOUDINESS HAS INCREASED THIS MORNING ACROSS PUERTO
RICO. IN ADDITION...A FEW SHOWERS HAVE BRIEFLY AFFECTED PORTIONS
OF EASTERN AND NORTHERN PUERTO RICO AS WELL AS THE WATERS TO THE
SOUTH OF SAINT CROIX.

EVEN THOUGH AVAILABLE MOISTURE IS EXPECTED TO GRADUALLY DECREASE
THROUGH THE DAY...THE AVAILABLE MOISTURE WILL COMBINE WITH THE
LOCAL EFFECTS AND DIURNAL HEATING TO CAUSE SHOWERS AND POSSIBLY
EVEN THUNDERSTORMS ACROSS WESTERN PR.

NO CHANGES WERE MADE TO THE FORECAST PACKAGE AS EVERYTHING IS IN
ALIGNMENT WITH THE LATEST GUIDANCE AND OBSERVATIONS.

&&

.AVIATION...NO SIGNIFICANT CHANGES FROM THE PREVIOUS DISCUSSION.
VFR CONDITIONS EXPECTED WITH THE EXCEPTION OF THOSE AREAS IN THE
INTERIOR AND WESTERN SECTIONS OF PR WHERE SHRA/TSRA DEVELOPMENT IS
EXPECTED AFTER 17/16Z...CAUSING MOUNTAIN OBSCURATIONS AND POSSIBLE
MVFR/IFR CONDITIONS IN AND AROUND TJMZ AND TJBQ UNTIL 16/00Z.

&&

.MARINE...SEAS UP TO 5 FEET AND WINDS UP TO 17 KNOTS EXPECTED FOR
THE NEXT FEW DAYS.

&&

.PREV DISCUSSION... /ISSUED 558 AM AST FRI MAY 17 2013/

SYNOPSIS...BASE OF MID TO UPPER LEVEL TROUGH NOW ACROSS THE
NORTHERN LEEWARDS...AND EXTENDS INTO THE SOUTHEASTERN CARIBBEAN...
WITH WEAK UPPER RIDGE EXTENDING ACROSS THE MONA PASSAGE WITH ANOTHER
THIS WILL NOW PLACE THE REGION ON THE CONVERGENT SIDE OF THE UPPER
TROUGH AND SHOULD THEREFORE LIMITED WIDESPREAD CONVECTIVE DEVELOPMENT
TODAY. AT LOW LEVELS...SURFACE HIGH PRESSURE CENTERED ACROSS THE NORTH
CENTRAL ATLANTIC WILL SPREAD AND REESTABLISH ITSELF NORTH OF THE
REGION BY SATURDAY THEN GRADUALLY TIGHTEN THE LOCAL PRESSURE GRADIENT
ACROSS THE NORTH EAST CARIBBEAN. THIS WILL ALLOW FOR AN INCREASE IN
THE EASTERLY TRADE WINDS OVER THE WEEKEND AND INTO EARLY NEXT WEEK.

DISCUSSION...UPPER TROUGH WILL CONTINUE SHIFT EASTWARDS ACROSS THE
NORTHEAST CARIBBEAN WHILE WEAKENING. LOOKING FOR INCREASING SUBSIDENCE
CAP LATER THIS EVENING AND THROUGH SATURDAY. HOWEVER...THE PERSISTENT
AND GRADUALLY INCREASING EASTERLY TRADES WILL BRING SHALLOW PATCHES
OF LOW TO MID LEVEL MOISTURE ACROSS THE AREA FROM TIME TO TIME.
THEREFORE...EXPECT SUFFICIENT LOW LEVEL MOISTURE CONVERGENCE AND
DIURNAL EFFECTS TO ALLOW FOR AFTERNOON CONVECTIVE DEVELOPMENT IN
SOME AREAS ESPECIALLY ACROSS PARTS OF THE INTERIOR AND WEST SECTIONS
OF PUERTO RICO.

INTO THE WEEKEND...LOOKING FOR A GRADUAL DRYING TREND ACROSS THE
REGION AT LEAST UNTIL SATURDAY. THIS WILL BE FOLLOWED BY INCREASING
MOISTURE AND PWAT VALUES SUNDAY INTO THE EARLY PART OF NEXT WEEK...AS
ANOTHER SHORT WAVE TROUGH WILL APPROACH THE REGION FROM THE WEST
WHILE AN EASTERLY PERTURBATION IS FORECAST TO BRING AN INCREASE IN
TRADE WIND MOISTURE TO THE ISLANDS AND SURROUNDING WATERS. FOR NOW
BASED ON LATEST MODEL GUIDANCE...EXPECT BETTER CHANCE FOR ENHANCEMENT
OF EARLY MORNING AND AFTERNOON CONVECTION DURING THAT PERIOD. UNTIL
THEN...STILL EXPECT AFTERNOON SHOWERS TO DEVELOP WITH MAINLY ISOLATED
THUNDERSTORMS EACH DAY...ESPECIALLY IN ISOLATED AREAS OVER THE INTERIOR
SECTIONS OF PUERTO RICO...THEN DECREASING BY EARLY EVENING HOURS.

AVIATION...MOSTLY VFR CONDITIONS ARE EXPECTED AT ALL TAF SITES UNTIL
AROUND 17/16Z. MVFR OR EVEN IFR CONDITIONS ARE LIKELY BETWEEN
17/18Z-21Z ALONG THE CORDILLERA CENTRAL AND AROUND TJMZ IN AREAS OF
+SHRA/TSRA. MOUNTAINS WILL BE OBSCURED OVER WESTERN INTERIOR OF PR.
ELSEWHERE...VFR CONDITIONS ARE EXPECTED. TJSJ 17/00Z SOUNDING
INDICATED AN EASTERLY WIND FLOW UP TO 10 KNOTS ALL THE WAY FROM THE
SURFACE TO 20K FEET...BECOMING WESTERLY AND STRONGER ALOFT.

MARINE...SMALL CRAFT SHOULD EXERCISE CAUTION MAINLY ACROSS THE LOCAL
OFFSHORE WATERS...AS SEAS ARE EXPECTED TO REACH 6 FEET THROUGH THE
WEEKEND WITH INCREASING TRADE WINDS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  86  76  87  77 /  10   0  20  20
STT  86  76  88  78 /  10  10  20  30

&&

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

$$

25/23