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061
FXCA62 TJSJ 010902
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
502 AM AST MON SEP 1 2014

.SYNOPSIS...AT UPPER LEVELS...LOW PRESSURE OVER THE BAHAMA ISLANDS
WILL MOVE WESTWARD TODAY THROUGH THURSDAY AND ALLOW A RIDGE OF
HIGH PRESSURE TO SHIFT TO THE U.S. VIRGIN ISLANDS AND PUERTO
RICO. ON THURSDAY...LOW PRESSURE OVER THE WEST CENTRAL ATLANTIC
WILL MOVE SOUTH AND EXPAND OVER THE LOCAL AREA CAUSING WINDS TO
BECOME WEST NORTHWEST AND GENERALLY MORE UNSTABLE CONDITIONS.
OVER THE WEEKEND AND INTO THE FOLLOWING WEEK...THIS LOW PRESSURE
MOVES SOUTHWEST BUT CONTINUES TO DOMINATE THE AREA.

AT MID LEVELS...LOW PRESSURE OVER THE BAHAMAS RETREATS TO THE WEST
DURING THE WEEK...WHILE HIGH PRESSURE TO THE NORTHEAST MOVES WEST
NORTHWEST TOWARD THE ATLANTIC SEA BOARD OF THE UNITED STATES. THIS
HOLDS THE AREA UNDER WEAK HIGH PRESSURE AND WEAK GRADIENTS. OVER
THE WEEKEND AND INTO THE FOLLOWING WEEK A TROUGH FORMS OVER THE
WINDWARD PASSAGE WITH WEAK SOUTHERLY FLOW OVER THE LOCAL AREA.

AT LOWER LEVELS...HIGH PRESSURE OVER THE WEST CENTRAL ATLANTIC
SAGS SOUTH AND WEAKENS CONSIDERABLY DURING THE WEEK WHILE LOW
PRESSURE REMAINS IN THE SOUTHWEST CARIBBEAN. HENCE MODERATE TO
FRESH EASTERLY TRADE WINDS WILL SHIFT TO EAST SOUTHEAST AND WEAKEN
AFTER THURSDAY. SEVERAL BANDS OF MOISTURE IN WEAK TROUGHS OR
WAVES WILL PASS THROUGH MONDAY...TUESDAY...LATE THURSDAY AND
FRIDAY AND AGAIN ON SUNDAY BRINGING SCATTERED TO NUMEROUS SHOWERS
AND SOME AREAS OF HEAVY RAIN.

&&

.DISCUSSION...SHOWERS INCREASED OVER THE LOCAL WATERS OVERNIGHT EXCEPT
IN THE SHADOWS OF PUERTO RICO...BUT DUE TO THEIR SIZE AND MOVEMENT
OF 17 KNOTS...ONLY MINOR ACCUMULATIONS WERE SEEN AND ONLY A FEW
PASSED OVER LAND. AS MENTIONED IN THE SYNOPSIS...SEVERAL BANDS OF
MOISTURE WILL MOVE THROUGH IN THE NEXT 48 HOURS. THE FIRST IS
RELATIVELY SMALL BUT WILL PASS OVER THE AREA INCREASING
PRECIPITABLE WATER VALUES TODAY. ARRIVING AFTER MOST OF THE
HEATING IS ACCOMPLISHED...THIS AREA OF MOISTURE COULD PRODUCE SOME
ACTIVE CONVECTION AND SIGNIFICANT AMOUNTS OF RAIN IN WESTERN
PUERTO RICO INCLUDING SOME LOCALIZED URBAN AND SMALL STREAM
FLOODING. AFTER AN INTERMISSION BETTER MOISTURE FOLLOWS ABOUT 24
HOURS BEHIND AND SHOWERS AND THUNDERSTORMS SHOULD INCREASE ON
TUESDAY. IN FACT THE GFS SHOWS PRECIPITABLE WATER VALUES EXCEEDING
2 INCHES ON TUESDAY AT 02/18Z. MOISTURE THEN ABATES UNTIL THURSDAY
NIGHT. SHOWERS SHOULD INCREASE OVERNIGHT THEN...AT LEAST ON THE
WINDWARD SIDE OF PUERTO RICO AND IN THE U.S. VIRGIN ISLANDS AND
BECOME HEAVY ON FRIDAY. AT THIS TIME MODEL SOLUTIONS SUGGEST THAT
RAINFALL ACCUMULATIONS SHOULD NOT EXCEED URBAN AND SMALL STREAM
FLOODING...ALTHOUGH GREATER AMOUNTS THAN TODAY AND TUESDAY ARE
EXPECTED FRIDAY AS THE TROPICAL WAVE TAKES ON MORE OF AN INVERTED
V SHAPE. ANOTHER BAND OF MOISTURE MOVES THROUGH ON SUNDAY MORNING.

ALTHOUGH THE GFS DOES SHOW TROPICAL CYCLONE FORMATION OUT OF LOW
PRESSURE OFF THE AFRICAN COAST FRIDAY SIMILAR TO THE FALSE ALARMS
OF LAST WEEK. IT MOVES IT NORTH OF 20 NORTH BEFORE 50 WEST BY THE
MIDDLE OF NEXT WEEK WHERE IT WILL NOT BE ABLE TO AFFECT PUERTO
RICO OR THE VIRGIN ISLANDS.

&&

.AVIATION...VFR CONDS AT LOCAL TAF SITES. VCSH AT TJSJ AND LOCAL
ISLANDS THRU MORNING HOURS. THEN IN THE AFTERNOON...SHRA POSSIBLE
WITH CHANCE OF TSRA FOR TJMZ AND VCTS FOR TJBQ TIL AROUND 01/22Z.
WNDS E-SE AT 10-15 KTS FM SFC TO FL200 ON LABOR DAY...WITH SEA
BREEZE VARIATIONS. MTN OBSCURATIONS EXPECTED AFT 01/16Z AREA WIDE...AND
AS EARLY AS 01/10Z OVER THE HIGHEST MTN TOPS OF EL YUNQUE.

&&

.MARINE...SEAS WILL INCREASE TO AS MUCH AS 5 FEET THROUGH
WEDNESDAY AND THEN RETURN TO 3 TO 4 FEET THEREAFTER. SMALL CRAFT
ADVISORIES ARE NOT EXPECTED UNTIL BEYOND AT LEAST NEXT MONDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  89  79  90  79 /  40  30  40  30
STT  88  79  89  80 /  30  30  40  40

&&

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

$$

02/12







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