AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
428 AM AST THU MAY 12 2011

.SYNOPSIS...BROAD LONGWAVE TROF ACROSS THE WRN ATLC WILL DEAMPLIFY
OVR THE NEXT FEW DAYS. SUBEQUATORIAL RIDGE ACROSS THE TROP ATLC WILL
BUILD WWD INTO THE CARIBBEAN MIDDLE OF NEXT WEEK.


&&

.DISCUSSION...LATEST WATER VAPOR IMAGERY SHOWS A SHORTWAVE TROUGH
ACROSS THE WINDWARD PASSAGE WITH AN ASSOCIATED 100-KT JET STREAK
EXTENDING FROM SOUTH OF HAITI TO THE NORTH OF PUNTA CANA IN THE
DOMINICAN REPUBLIC PER MOST RECENT ACARS PLOT. LATEST GUIDANCE SHOWS
THESE TWO FEATURES MOVING ACROSS PR/USVI LATE TODAY AND TONIGHT
SUPPORTING A PERIOD OF VERY ACTIVE WX LATER THIS AFTERNOON. WHILE
LIFT LOOKS PRETTY IMPRESSIVE TO GENERATE WIDESPREAD CONVECTION
LIMTING FACTORS FOR WIDESPREAD HEAVY RAINFALL ARE STORM MOTION
GREATER THAN 10 KT AND PW VALUES LESS THAN 2.0 INCHES. OF POTENTIALLY
GREATER CONCERN IS SUBSTANTIAL DIRECTIONAL SHEAR SEEN ON FCST
SOUNDINGS EARLY IN THE DAY WITH VEERING WIND PROFILES AS THE DAY
GOES ON. 0-3KM STORM REL HELICITIES ARE DECENT WITH SWEAT INDICES
UPWARDS OF 300 SUGGESTING A MARGINAL SEVERE THREAT WITH ANY
STORMS TODAY. CONVECTION SHOULD MOVE GENERALLY ENE AND AFFECT THE
NORTHEAST QUADRANT OF THE ISLAND.

CUTOFF LOW WELL NORTH OF THE AREA WILL CONTINUE TO DIVERT S/W
VORTICES ACROSS THE AREA OVR THE WEEKEND KEEPING UNSETTLED
CONDITIONS WITH AFTERNOON CONVECTION FOCUSING NORTH OF THE
CORDILLERA CENTRAL AND AFFECTING THE NORTH COAST OF PR.

UPPER FLOW DEAMPLIFIES EARLY NEXT WEEK WITH RIDGE BUILDING IN
FROM THE TROP ATLC MIDDLE OF NEXT WEEK. HOWEVER...MOISTURE AND
INSTABILITY LOOK MORE THAN ADEQUATE TO SUPPORT DAILY CONVECTION
WITH THE NW COAST THE MOST FAVORED LOCATION IN A SOUTHEAST
STEERING FLOW.


&&

.AVIATION...MVFR/IFR CONDITIONS LIKELY AT JSJ/IST LATER TODAY
WITH SMALL CHANCES AT ALL OTHER TERMINALS. JSJ AND JBQ WILL HAVE
THE BEST OF EXPERIENCING AFTERNOON TSRA OVER THE NEXT FIVE DAYS.


&&

.MARINE...SEAS HAVE BUILT UP TO 6 FEET IN NORTH SWELLS AT BUOY
41043. GUIDANCE SUGGESTS SEAS WILL BUILD QUICKLY ACROSS THE ATLC
COASTAL WATERS BY EVENING WITH 4-6 FT LIKELY ACROSS THE NEARSHORE
ATLC WATERS.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  87  73  84  74 /  70  50  70  20
STT  84  75  85  75 /  70  50  30  40

&&

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

$$