AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1100 AM AST MON APR 18 2011

.UPDATE...MOSTLY SUNNY TO PARTLY CLOUDY SKIES PREVAILED ACROSS
THE LOCAL AREA SO FAR THIS MORNING NO RAINFALL WAS OBSERVED OVER
LAND. HOWEVER...SATELLITE IMAGERY AND THE NATIONAL WEATHER SERVICE
DOPPLER WEATHER RADAR SHOWED A BAND OF LOW LEVEL CLOUDS WITH SOME
EMBEDDED SHOWERS...SLOWLY DRIFTING SOUTHWARDS ACROSS THE OFFSHORE
ATLANTIC WATERS. EXPECT THIS AREA OF CLOUDINESS TO EVENTUALLY
REACH PARTS OF THE NORTH COASTAL AREAS LATER THIS AFTERNOON...BUT
ASSOCIATED SHALLOW CONVECTION SHOULD DIMINISH AS IS REACHES THE
COAST.

LATEST TJSJ 12Z SOUNDING WAS SIGNIFICANTLY DRY WITH PWAT VALUES
NOW DOWN TO .87 INCHES...AND KI/LI -20 AND +1.5 RESPECTIVELY. THIS
ALONG WITH DRY AND SUBSIDENT UPPER LEVEL PATTERN...LOOK FOR MOSTLY
SUNNY SKIES WITH ONLY BRIEF AND SHORT DURATION SHOWER ACTIVITY IF
ANY AT ALL TODAY ACROSS THE ISLANDS. NO CHANGES MADE TO INHERITED
FORECAST PACKAGE AT THIS TIME.

&&

.AVIATION...VFR CONDS EXPECTED TO PREVAIL ACROSS LOCAL TAF SITES
NEXT 24 HOURS...WITH NO SIGNIFICANT OPERATIONAL WEATHER IMPACTS
ANTICIPATED OTHER THAN THAT PREVIOUSLY MENTIONED.

&&

.PREV DISCUSSION... /ISSUED 507 AM AST MON APR 18 2011/

SYNOPSIS...STRONG SURFACE HIGH PRESSURE ACROSS THE EASTERN ATLANTIC
WILL CONTINUE TO DOMINATE THE LOCAL REGION NEXT SEVERAL DAYS. AN
INVERTED TROUGH WILL SLOWLY MOVES NORTHWEST AND WILL MAINLY PASS
NORTH OF THE AREA.

DISCUSSION...LITTLE OR NO SHOWER ACTIVITY WAS OBSERVED OVERNIGHT
ACROSS PUERTO RICO AND THE U.S. VIRGIN ISLANDS. DRY CONDITIONS HAS
BEEN THE RULE FOR THE LAST 24 HOURS WITH ONLY LIGHT PASSING
SHOWERS NOTED MAINLY ACROSS THE NORTHERN PART OF THE ISLANDS.
THIS WEATHER IS IN RESPOND TO A HIGH PRESSURE SYSTEM LOCATED WELL
NORTHEAST OF THE REGION. THIS HIGH PRESSURE IS EXPECTED TO
MAINTAIN RELATIVELY DRY AND STABLE CONDITIONS THROUGH THE END OF
THE WEEK. HOWEVER...LATEST SATELLITE IMAGES SHOWS AN AREA OF
MOISTURE EAST OF THE LESSER ANTILLES. THIS AREA OF MOISTURE IS
ASSOCIATED WITH AN INVERTED TROUGH WHICH IS EXPECTED TO LINGER
ACROSS THE ATLANTIC...NORTHEAST OF PUERTO RICO DURING THE NEXT FEW
DAYS. THE PROXIMITY OF THIS SYSTEM WILL WEAKEN THE PRESSURE
GRADIENT WHICH WILL RESULT IN LIGHT WINDS ACROSS THE REGION.
THEREFORE...THE SEA BREEZE IS EXPECTED TO DEVELOP STRONGLY DURING
THE NEXT FEW DAYS. COMPUTER MODELS SUGGESTS...AS THIS TROUGH
MOVES SLOWLY TOWARD THE NORTHWEST...AN INCREASE IN MOISTURE CAN BE
EXPECTED MAINLY TUESDAY NIGHT INTO WEDNESDAY AS THIS FEATURE
APPROACH THE LOCAL REGION. THETA-E VALUES AS WELL AS PRECIPITABLE
WATER FORECASTS INCREASE TUESDAY THROUGH WEDNESDAY WITH THETA-E
VALUES REACHING A MAXIMA OF 330K AN PW VALUES RISING TO NEAR 1.5
INCHES. WITH THESE CONDITIONS...IN ADDITION TO STRONG SEA BREEZE
EXPECTED TO DEVELOP IN THE AFTERNOON...CHANCES FOR SHOWERS AND
POSSIBLE ISOLATED THUNDERSTORMS WILL BE HIGHER TUESDAY. BY
THURSDAY...A RETURN TO A MORE DRIER AND STABLE ATMOSPHERIC
CONDITIONS ARE EXPECTED...WHICH WILL LIMIT THE SHOWER DEVELOPMENT
ACROSS THE REGION.

AVIATION...VFR CONDITIONS WILL PREVAIL AT ALL TAF SITES THROUGH THE
NEXT 24 HOURS. NNE FLOW CONTINUES ACROSS THE AREA. AFT 18/17Z SHRA
AND A PSBL TSRA WILL DEVELOP JUST SOUTH OF THE CORDILLERA CENTRAL
ALONG THE SOUTH CENTRAL OR SOUTHWEST COASTAL REGION OF PUERTO RICO
WITH SOME MOUNTAIN OBSCURATIONS. VERY BRIEF MVFR CONDS WILL BE
PSBL AT TJPS TIL 18/21Z. WINDS ALOFT ARE NORTHERLY UP THROUGH 18
KFT.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  85  72  84  73 /  20  30  20  30
STT  85  74  84  74 /  10  20  20  30

&&

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

$$