AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
947 PM AST SUN APR 17 2011

.UPDATE...EXPECT CLEAR TO PARTLY CLOUDY SKIES ACROSS PUERTO RICO AND
THE U.S. VIRGIN ISLANDS DURING THE OVERNIGHT HOURS. A FEW ISOLATED
PASSING SHOWERS ARE EXPECTED...MAINLY OVER THE U.S. VIRGIN
ISLANDS...CULEBRA AND VIEQUES...THE NORTH SECTIONS OF PUERTO RICO
AND ACROSS THE COASTAL WATERS. SOME SHOWERS MAY HOWEVER BE ENHANCED
DURING THE AFTERNOONS DUE TO DIURNAL AND LOCAL TERRAIN EFFECTS...AS
WELL AS THE INFLUENCE OF THE MID TO UPPER LEVEL TROUGH AND
ASSOCIATED JET SEGMENT...WHICH IS FORECAST TO DIP SOUTHWARD ACROSS
THE REGION DURING THE LATTER PART OF THE WEEK. FORESEE NO MAJOR
INFLUX OF DEEP LAYERED TROPICAL MOISTURE ACROSS THE REGION AT THIS
TIME.

&&

.AVIATION...PREVAILING VFR CONDITIONS WILL CONTINUE ACROSS THE
LOCAL ISLANDS AND AT ALL TAF SITES DURING THE NEXT 24 HOURS.
HOWEVER...BRIEF MVFR CONDITIONS AND LOCAL MOUNTAIN OBSCURATIONS
ARE POSSIBLE IN ISOLATED PASSING SHOWERS.

&&

.PREV DISCUSSION... /ISSUED 241 PM AST SUN APR 17 2011/

SYNOPSIS...STRONG HIGH PRESSURE ANCHORED ACROSS THE NORTH CENTRAL
ATLANTIC AND PERSISTENT DEEP LAYER TROUGH EXTENDING ACROSS THE
LESSER ANTILLES AND INTO THE CENTRAL ATLANTIC WILL MAINTAIN LIGHT TO
MODERATE NORTH TO NORTHEAST LOW LEVEL WIND FLOW ACROSS THE REGION
THROUGH MUCH OF THE UPCOMING WEEK. THE MID TO UPPER LEVEL TROUGH
ACROSS THE CENTRAL ATLANTIC WILL SAG FURTHER SOUTHWARDS TO JUST
NORTH OF THE REGION AND BECOME SLIGHTLY MORE AMPLIFIED BY THE
LATTER PART OF THE WEEK. BY TUESDAY INTO WEDNESDAY...ABOVE
MENTIONED TROUGH WILL WEAKEN AND SHIFT FURTHER NORTH OF THE
LEEWARD ISLANDS ALLOWING THE GENERAL WIND FLOW TO BECOME MORE
EASTERLY BY THE END OF THE WORK WEEK.

DISCUSSION...MOSTLY DRY AIR AND FAIRLY STRONG SUBSIDENCE ACROSS THE
REGION TODAY LEAD TO OVERALL FAIR WEATHER CONDITIONS ACROSS THE
ISLANDS AND SURROUNDING WATERS. RETURN FLOW AROUND UPPER TROUGH
WHICH DIPS SOUTH OVER THE NORTHEAST CARIBBEAN HELP TO PROVIDE FAIRLY
STRONG SUBSIDENCE ACROSS THE LOCAL AREA AND SUPPRESSED AND SIGNIFICANT
SHOWER DEVELOPMENT.

LIGHT TO MODERATE TRADE WINDS EXPECTED TO PREVAIL ACROSS THE NORTHEAST
CARIBBEAN DUE TO THE LOOSE PRESSURE GRADIENT CREATED BETWEEN ATLANTIC
HIGH AND ELONGATED TROUGH EXTENDING ACROSS THE LESSER ANTILLES INTO
THE CENTRAL ATLANTIC. THESE LIGHT TO MODERATE TRADE WINDS WILL CONTINUE
THROUGH MOST OF THE UPCOMING WEEK. AS A RESULT...EXPECT A GENERAL TREND
OF PASSING LOW LEVEL CLOUD FRAGMENTS AND INTERVALS OF LATE EVENING AND
EARLY MORNING SHOWERS...WITH LIMITED AFTERNOON SHOWER ACTIVITY DURING
THE DAY. SOME SHOWERS MAY HOWEVER BE ENHANCED DUE TO DIURNAL AND
LOCAL TERRAIN EFFECTS...AS WELL AS THE INFLUENCE OF THE MID TO UPPER
LEVEL TROUGH AND ASSOCIATED JET SEGMENT...WHICH IS FORECAST TO DIP
SOUTHWARD ACROSS THE REGION DURING THE LATTER PART OF THE WEEK. FORESEE
NO MAJOR INFLUX OF DEEP LAYERED TROPICAL MOISTURE ACROSS THE REGION
AT THIS TIME...SO FOR NOW KEPT POPS AT 40 PERCENT OR LESS FOR MOST
OF THE UPCOMING WORK WEEK ACROSS THE ISLANDS.

A RETURN OF THE EASTERLY TRADES IS FORECAST BY THE END OF THE WEEK.
THIS PATTERN WILL CONTINUE INTO THE FOLLOWING WEEKEND AS THE PREVIOUSLY
MENTIONED TROUGH WHICH HAS BEEN LINGERING EAST OF THE AREA...EVENTUALLY
BECOMES FLATTENED BY A DEEP LAYERED AREA OF HIGH PRESSURE WHICH WILL
BUILD ACROSS THE WEST ATLANTIC. THIS WILL ALLOW FOR MORE EASTWARD PROPAGATION
OF TROPICAL MOISTURE ACROSS THE REGION....AND THUS INCREASE CHANCES
OR LOCAL SHOWER ACTIVITY.

AVIATION...VFR CONDS WILL PREVAIL ACROSS THE LOCAL FLYING AREA DURG
NEXT 24 HRS. NO SIGNIFICANT OPERATIONAL WEATHER IMPACTS IS FORECAST
AT THIS TIME.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  73  84  73  84 /  20  20  30  30
STT  74  85  75  85 /  10  10  30  30

&&

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

$$