Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 260920
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
520 AM AST MON JAN 26 2015

.SYNOPSIS...HIGH PRESSURE RIDGE IS DOMINATING THE LOCAL REGION.
A FAIRLY STRONG SUBSIDENCE CAP WILL MAINTAIN A FAIR WEATHER PATTERN
ACROSS THE LOCAL AREA TODAY. THEN...A POLAR TROUGH WILL MOVE OVER
THE WESTERN ATLANTIC LATER TODAY...FLATTENING/WEAKENING THE RIDGE
ALOFT. AT LOW LEVELS...PRE-FRONTAL TROUGH/SHEARLINE APPROACHING
FROM THE NORTHWEST WILL ALLOW WINDS TO VEER FROM THE SOUTHEAST
ON TUESDAY. THE AIR MASS ACROSS THE ISLANDS WILL DESTABILIZE EVEN
MORE ON THURSDAY AND FRIDAY AS A SHORT-WAVE TROUGH/PERTURBATION
ALOFT MOVES ACROSS THE SW NORTH ATLANTIC.

&&

.DISCUSSION...SATELLITE DERIVED PWAT ANALYSIS AS WELL AS LOCAL
SOUNDING HAVE SHOWED BELOW NORMAL MOISTURE OVER THE NORTHEAST
CARIBBEAN REGION TODAY. AS A RESULT...CLOUDS AND SHOWERS HAVE
BEEN MINIMAL ACROSS PUERTO RICO AND THE USVI OVERNIGHT. THIS DRY
AND STABLE PATTERN IS FORECAST TO PERSIST THROUGH TONIGHT. THEN...
DEEPER MOISTURE EMBEDDED IN THE TRADES WILL ADVENT OVER THE AREA
OVERNIGHT AND TUESDAY. SHOWER ACTIVITY ON TUESDAY MORNING WILL BE
MAINLY OVER THE CARIBBEAN WATERS AND THE SOUTH COASTAL SECTIONS OF
PUERTO RICO...FOLLOWING BY A ROUND OF AFTERNOON CONVECTION OVER
NORTH CENTRAL AND NORTHWEST PUERTO RICO. DRIER TRADE WINDS WILL
ADVECT OVER THE REGION ON WEDNESDAY...KEEPING THE PROBABILITY OF
SHOWERS AROUND 20 PERCENT.

THURSDAY AND FRIDAY...A SHORT-WAVE TROUGH MOVES ACROSS THE SW
ATLANTIC WILL BRING COLDER AIR ALOFT AND UNSTABLE CONDITIONS
LATER THIS WEEK. THE INFLOW OF MID-UPPER LEVEL ENERGY WILL LIKELY
ENHANCE THE CONVECTIVE DEVELOPMENT ACROSS THE FORECAST AREA. THE
BEST UPPER DYNAMICS ARE EXPECTED ON FRIDAY...WHERE A FEW
THUNDERSTORMS COULD DEVELOP IN AND AROUND THE LOCAL ISLANDS.
THERE IS STILL QUITE A BIT OF DISAGREEMENT IN THE GLOBAL MODELS
FOR THE WEEKEND AND EARLY NEXT WEEK. BUT IN GENERAL...MOISTURE
WILL DECREASE ACROSS THE AREA...FAVORING A RELATIVELY STABLE
PATTERN ACROSS THE NORTHEAST CARIBBEAN ISLANDS.

&&

.AVIATION...MOSTLY VFR CONDITIONS ARE EXPECTED AT ALL TAF SITES
WITH BRIEF SHOWERS POSSIBLE IN AND AROUND TISX...TIST AND TJSJ.
BRIEF MVFR CONDITIONS WILL REMAIN POSSIBLE BETWEEN 26/17Z AND
26/20Z AT TJMZ/TJBQ IN SHRA. ESE WINDS AT 10 TO 15 KNOTS WITH
SOME SEA BREEZE VARIATIONS AFT 26/15Z.

&&

.MARINE...SEAS WILL GENERALLY RANGE BETWEEN 2 AND 4 FEET WITH
OCCASIONAL SEAS OF 5 FEET ACROSS THE ATLANTIC WATERS MOST OF THE
WEEK. TWO PULSES OF NW SWELLS OF AROUND 4-5 FEET ARE EXPECTED
TONIGHT AND LATE WEDNESDAY INTO THURSDAY. SEAS ARE FORECAST TO
REMAIN BELOW THE ADVISORY CRITERIA ALL WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  86  74  87  74 /  20  20  40  20
STT  84  75  84  74 /  20  20  40  20

&&

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

$$

71/11




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