Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 030927
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
527 AM AST FRI JUL 3 2015

.SYNOPSIS...AT UPPER LEVELS...A WEAK LOW WILL CONTINUE TO WOBBLE
JUST NORTH OF THE DOMINICAN REPUBLIC THROUGH TUESDAY. THEN IT WILL
SLOWLY DRIFT OVER TO FLORIDA BY SATURDAY. AS IT DOES SO LOW
PRESSURE TO THE NORTHEAST WILL SLOWLY DRIFT TO AROUND 20 DEGREES
NORTH NORTH OF PUERTO RICO TUESDAY THROUGH SATURDAY OF NEXT WEEK.

AT MID LEVELS...HIGH PRESSURE STRETCHING ACROSS THE SUB TROPICAL
ATLANTIC WILL BE DIVIDED IN HALF NEAR 45 WEST MID WEEK NEXT WEEK
BY A STRONG LOW PRESSURE EAST OF MAINE. MID LEVELS REMAIN QUITE
DRY.

AT LOWER LEVELS...HIGH PRESSURE CENTERED OVER THE CENTRAL ATLANTIC
CONTINUES THROUGH TUESDAY. ALTHOUGH PRESSURE GRADIENTS WEAKEN HIGH
PRESSURE REMAINS NORTH OF THE AREA THROUGH THE END OF NEXT WEEK. A
WEAK TROPICAL WAVE WILL MOVE THROUGH TONIGHT. A PATCH OF MOISTURE
WILL PASS JUST NORTH OF THE LOCAL AREA SUNDAY AND MONDAY FOLLOWED
BY ANOTHER TROPICAL WAVE TUESDAY INTO TUESDAY NIGHT.

&&

.DISCUSSION...SHOWERS FORMED AFTER MIDNIGHT AND STREAMED ACROSS
THE NORTHERN U.S. VIRGIN ISLANDS AND INTO EASTERN PUERTO RICO
AFTER MIDNIGHT. A FEW SHOWERS MADE IT AS FAR WEST AS CAROLINA.
AMOUNTS WERE VERY LIGHT OWING TO SIZE AND SPEED AT WHICH THEY WERE
MOVING...ABOUT 28 KNOTS. MODELS SUGGEST THAT MOISTURE WILL
INCREASE DURING THE DAY BUT THERE WAS NO CONSISTENCY IN WHERE THE
MODELS PLACED THE BEST PRECIPITATION OR HOW MUCH CHANCE WAS TO
OCCUR. SO BEST ESTIMATE WILL BE SCATTERED POPS FROM EL YUNQUE TO
WESTERN PUERTO RICO THOUGH AGAIN AMOUNTS WILL LIKELY BE LIGHT WITH
A SLIGHT CHANCE OF A THUNDERSTORM. MAIN PROBLEM WITH GENERATING
SHOWERS ARE THE DRY MID LEVELS THAT PERSIST...THE STRONG
WINDS...UP TO 31 KNOTS...IN AND NEAR A STRONG INVERSION AND
PRECIPITABLE WATER VALUES OF LESS THAN 1.5 INCHES AND SO WILL
CONSIDER EVEN THE CURRENT FORECAST OF AROUND 30 TO 40 PERCENT
CHANCE ACROSS THE INTERIOR OF PUERTO RICO RATHER GENEROUS AND
SHOWERS SHOULD END AROUND SUNSET IN THE INTERIOR AND WEST. ONLY
ISOLATED SHOWERS ARE EXPECTED IN THE U.S. VIRGIN ISLANDS...BUT
CHANCES THERE AND ON THE NORTHEAST AND EAST COAST OF PUERTO RICO
WILL IMPROVE OVERNIGHT AS MOISTURE FROM THE TROPICAL WAVE RIDING
ON THE FRESH TRADE WINDS RIDES BY. DRYING BEGINS LATE FRIDAY NIGHT
AND CONTINUES THROUGH THE WEEKEND WITH MOSTLY ISOLATED SHOWERS
EXPECTED IN THE USUAL DIURNAL PATTERN.

CURRENTLY MID LEVEL MOISTURE IMPROVES LITTLE NEXT WEEK AND HENCE
THE CHANCES FOR RAIN REMAIN...EVEN DURING THE WAVE ON TUESDAY...LESS
THAN USUAL. SAHARAN DUST WILL ALSO CONTINUE IN THE AREA. CURRENT
MODELS CONTINUE THIS PATTERN THROUGH NEXT WEEK AND INTO THE
FOLLOWING WEEK.

&&

.AVIATION...PASSING SHRA ARE EXPECTED TO MOVE FROM TIME TO TIME ACROSS
TJSJ/TIST/TISX/TNCM/TKPK DURING THE MORNING HRS. FOLLOWED BY
ISOLD/SCT SHRA AT TJBQ/TJMZ AFT 03/18Z. MTN OBSCURATIONS AND
+SHRA/SHRA CAN BE EXPECTED ACROSS THE INTERIOR AND WESTERN
SECTIONS OF PR SOME OF THEM CAN REACH THE WESTERN TAF SITES.
EASTERLY SURFACE WINDS AT 15 TO 25 KT WITH HIGHER GUSTS CAN BE
EXPECTED TODAY.

&&

.MARINE...SEAS IN THE OUTER WATERS WILL INCREASE UP TO 7 FEET OVER
THE WEEKEND AND THESE CONDITIONS WILL WORK THEIR WAY INTO THE
EASTERN TIP OF AMZ715 AND AMZ725 SOUTH OF ANEGADA ISLAND SUNDAY
MORNING. CONDITIONS WILL BEGIN TO SUBSIDE ON MONDAY. UNTIL THEN
SMALL CRAFT ADVISORIES ARE IN PLACE OR WILL GO UP IN ALL OUTER
WATERS AND PASSAGES.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  89  78  90  79 /  20  40  40  20
STT  90  79  89  78 /  20  30  30  20

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
AM...SMALL CRAFT ADVISORY UNTIL 6 PM AST SATURDAY FOR ANEGADA PASSAGE
     SOUTHWARD TO 17N-ATLC WATERS OF PUERTO RICO AND USVI FROM
     10NM TO 19.5N.

     SMALL CRAFT ADVISORY UNTIL 6 PM AST SATURDAY FOR CARIBBEAN
     WATERS OF PUERTO RICO FROM 10 NM TO 17N-MONA PASSAGE
     SOUTHWARD TO 17N.

&&

$$

27/12


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