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000
FXCA62 TJSJ 250916
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
516 AM AST SAT MAY 25 2013

.SYNOPSIS...AT UPPER LEVELS...AN UPPER LEVEL TROUGH WILL PASS
THROUGH THE AREA LATE TODAY AND A LONG WAVE TROUGH AND LOW PRESSURE
WILL MOVE INTO THE WESTERN ATLANTIC EARLY NEXT WEEK. THIS TROUGH
WILL LEAVE LOW PRESSURE NEAR FLORIDA EARLY MID WEEK THAT WILL
PERSIST THROUGH SATURDAY.

AT MID LEVELS...A WEAK TROUGH PASSAGE WILL OCCUR OVER THE LOCAL
AREA TONIGHT...OTHERWISE A RIDGE WILL EXTEND FROM THE WESTERN
TROPICAL ATLANTIC ACROSS THE EASTERN CARIBBEAN THROUGH THE REST OF
THE WEEK.

AT LOWER LEVELS...LOW PRESSURE IN THE WESTERN ATLANTIC WILL MOVE
NORTH AND LEAVE THE MID LATITUDES LOCKED UNDER HIGH PRESSURE FROM
A STRONG NORTH CENTRAL ATLANTIC HIGH AND A WEAKER WESTERN ATLANTIC
HIGH CENTER. THESE HIGHS WILL KEEP EAST TO SOUTHEAST TRADE WIND
FLOW OVER THE AREA THROUGH THE END OF NEXT WEEK.

&&

.DISCUSSION...SHOWERS PERSISTED OVER THE ATLANTIC AND CARIBBEAN
WATERS OVERNIGHT WITH SOME SHOWERS MOVING THROUGH THE EASTERN HALF
OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS. OVER ONE HALF INCH
FELL AT THE AIRPORT IN SAN JUAN...WITH HIGHER AMOUNTS VERY
LOCALIZED ELSEWHERE AND JUST OFFSHORE. THE GFS MODEL SOLUTION HAS
PROVEN TO BE ERRATIC LATELY BUT AGAIN SHOWS MOISTURE INCREASING DURING
THE DAY WITH STABILITY DECREASING CONSIDERABLY OVER THE LAST 24
HOURS. LIFTED INDICES FALL BELOW MINUS SIX BETWEEN 25/12Z AND
26/00Z. A WEAK SHORT WAVE ROTATING AROUND A MUCH LARGER AND
DEEPER LONG WAVE CENTERED OVER EASTERN CANADA WILL PASS THROUGH
THE LOCAL AREA TODAY AND TONIGHT AND WILL AID IN THIS
DESTABILIZATION. THIS WILL CREATE AN ENVIRONMENT MORE FAVORABLE TO
SHOWERS AND THUNDERSTORMS WITH INCREASED RAINFALL AMOUNTS.
AMOUNTS OF 2 TO 4 INCHES ARE STILL EXPECTED ACROSS THE MAINLAND
TODAY AND TONIGHT WITH 1 TO 2 INCHES OVER THE ISLANDS TO THE EAST
POSSIBLE. THE HIGHEST AMOUNTS ARE AGAIN EXPECTED IN THE NORTHWEST
AND INTERIOR PORTIONS OF PUERTO RICO. THEREFORE WILL HOLD ONTO THE
FLASH FLOOD WATCH...BUT NOT EXTEND IT BEYOND 6 PM AST UNTIL IT IS
KNOWN HOW WELL THE GFS IS DEPICTING THE CURRENT CONDITIONS. THE
LATEST GFS RUN...25/00Z...PAINTS TODAY AS HAVING THE MOST FAVORABLE MOISTURE
AND VERTICAL MOTION...HOWEVER GOOD PRECIPITABLE WATER
VALUES...ABOVE 1.8 INCHES...PERSISTS THROUGH THE END OF NEXT WEEK
AND WILL CONTINUE TO KEEP THE LOCAL AREA UNDER MUCH ABOVE NORMAL
RAINFALL DESPITE THE FACT THAT UPPER LEVEL RIDGING MAY BE THE
DOMINANT FORCE AFTER MONDAY SINCE THE UPPER LEVEL LOW CUTS OFF TOO
FAR WEST TO PUSH THE HIGH FARTHER EAST TOWARD THE LEEWARD ISLANDS.

&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL ACROSS TJBQ...TJMZ AND TJPS UNTIL
AROUND 25/16Z. SHRA/VCTS ARE POSSIBLE ACROSS TIST...TISX...TNCM...TKPK
AND TJSJ DURING THE FCST PERIOD. AFTER 25/16Z MVFR TO BRIEF IFR
CONDITIONS ARE EXPECTED ACROSS MOST OF THE TERMINALS DUE TO
SHRA/TSRA DEVELOPING ACROSS THE FCST AREA...MTN OBSCURATIONS
ISLAND WIDE AND VARIABLE GUSTY WINDS ARE EXPECTED NEAR THE
SHRA/TSRA. WINDS WILL BE EAST TO SOUTHEAST AT 10 TO 15 KTS FROM
SFC UP TO 2 KFT.

&&

.MARINE...WINDS AND SEAS DECREASE ONLY SLIGHTLY DURING THE NEXT
FIVE DAYS AND SMALL CRAFT WILL NEED TO EXERCISE CAUTION ACROSS
MOST EXPOSED WATERS FOR THE FORESEEABLE FUTURE.

&&

.HYDROLOGY...CURRENTLY LOW LEVEL WIND FLOW IS EAST TO EAST
SOUTHEAST BUT...WITH EXTENSIVE CLOUD COVER...SEA BREEZE FORMATION
HAS BEEN WEAK. THIS WILL CAUSE WINDS CLOSER TO 850 MB AND ALSO MORE
SOUTHEASTERLY TO BE THE STEERING FOR THUNDERSTORM FORMATION AND
HENCE THE RISK OF EXCESSIVE RAINFALL. CURRENT INDICATIONS ARE THAT
SOME RIVERS IN THE NORTHWEST INCLUDING THE CULEBRINAS AND ALSO
POSSIBLY THE HORMIGUEROS FARTHER SOUTH WILL EXPERIENCE RAPID
RISES. CURRENT INDICATIONS SUGGEST THAT THEY WILL NOT FLOOD...BUT
OTHER SMALL STREAMS AND TRIBUTARIES MAY FLOOD WHERE THUNDERSTORMS
PERSIST FOR MORE THAN TWO OR THREE HOURS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  87  75  87  77 /  70  70  70  60
STT  85  77  86  78 /  60  70  70  70

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...FLASH FLOOD WATCH THROUGH THIS AFTERNOON FOR CENTRAL INTERIOR-
     CULEBRA-EASTERN INTERIOR-MAYAGUEZ AND VICINITY-NORTH
     CENTRAL-NORTHEAST-NORTHWEST-PONCE AND VICINITY-SAN JUAN AND
     VICINITY-SOUTHEAST-SOUTHWEST-VIEQUES-WESTERN INTERIOR.

VI...FLASH FLOOD WATCH THROUGH THIS AFTERNOON FOR ST CROIX-ST.
     THOMAS/ST. JOHN/ADJACENT ISLANDS.

COASTAL WATERS...NONE.

&&

$$

13/12