Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 240301
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1101 PM AST SAT MAY 23 2015

.UPDATE...
AFTERNOON CONVECTION GAVE WAY TO A MOSTLY CLEAR NIGHT ACROSS THE
LOCAL ISLANDS...WITH ONLY A FEW LIGHT PASSING SHOWERS DETECTED BY
THE NWS DOPPLER RADAR OVER THE LOCAL WATERS. LATEST AEROSOL
GUIDANCE SUGGESTS THAT WE WILL CONTINUE TO HAVE A LIGHT
CONCENTRATIONS OF DUST DURING THE NEXT FEW DAYS. RELATIVELY DRY
CONDITIONS ARE EXPECTED ACROSS THE CWA...WITH NOCTURNAL TRADE WIND
PASSING SHOWERS ACROSS THE EASTERN SECTIONS OF PR...THE USVI AND
THEIR SURROUNDING WATERS OVERNIGHT AND INTO THE MORNING HOURS.
FOLLOWED BY AFTERNOON CONVECTION ACROSS WESTERN PUERTO RICO. ONLY
MINOR CHANGES WERE MADE TO THE FIRST TWO PERIOD OF THE INHERITED
FORECAST PACKAGE.

&&

.AVIATION...
MOSTLY VFR CONDITIONS SHOULD PREVAIL OVER ALL TAF SITES
OVERNIGHT. ISOLATED SHOWERS MAY OCCUR OVER IST, ISX AND JSJ
TONIGHT AND DURING THE EARLY MORNING HOURS ON SUNDAY...HOWEVER NO
SIGNIFICANT IMPACT IN OPERATIONS IS EXPECTED. SCT SHRA/TSRA OVER
THE INTERIOR AND WESTERN PR COULD BE EXPECTED FROM 17Z THRU AT
LEAST 22Z ON SUNDAY...CREATING MTN TOP OBSCD AND MVFR TO BRIEF IFR
CONDS MAINLY AT JMZ AND BQN. SEA BREEZE VARIATIONS AND EAST WINDS
WILL PREVAIL SUNDAY.

&&

.MARINE...
LOCAL BUOY NETWORK WERE INDICATING SEAS OF 5 FEET OR LESS...AND
WINDS BELOW 18 KNOTS. ON SUNDAY AFTERNOON...WINDS AND SEAS WILL
INCREASE...AND MARINERS SHOULD EXERCISE CAUTION MAINLY ACROSS THE
OFFSHORE WATERS AND LOCAL PASSAGES.

&&

.PREV DISCUSSION... /ISSUED 305 PM AST SAT MAY 23 2015/

SYNOPSIS...AT MID AND UPPER LEVELS...THE JET STREAM OVERHEAD AT
UPPER LEVELS...WILL MOVE EAST AND A WEAK TROUGH WILL PASS THROUGH
MONDAY AFTERNOON OR EVENING. LOW PRESSURE WILL CUT OFF OVER THE
WEST CENTRAL ATLANTIC ON MONDAY NIGHT AND MOVE TOWARD THE AREA
WHILE DEEPENING TUESDAY AND TUESDAY NIGHT. THIS LOW WILL FILL
SLOWLY WHILE MOVING WEST STILL ABOUT 825 MILES NORTH OF PUERTO
RICO BY FRIDAY. HIGH PRESSURE WILL RIDGE OVER THE EASTERN
CARIBBEAN OVER THE FOLLOWING WEEKEND.

AT LOWER LEVELS...HIGH PRESSURE OFF THE VIRGINIA COAST WILL MOVE
INTO THE WESTERN ATLANTIC AND TIGHTEN THE GRADIENTS OVER THE LOCAL
AREA. THIS WILL KEEP TRADE WIND FLOW ACTIVE THROUGH THE FIRST
HALF OF THE WEEK. A TROPICAL WAVE NEAR 31 WEST EARLIER TODAY WILL
MOVE INTO THE AREA ON WEDNESDAY WITH SOME INCREASED SHOWER
ACTIVITY. LOW PRESSURE WILL BE GENERATED BY THE APPROACH OF THE
WAVE AND THE UPPER LEVEL LOW...MAINLY ABOVE THE SURFACE NORTH OF
THE LOCAL AREA...AND WILL GENERATE A SWATH OF SOUTHERLY FLOW OVER
THE AREA BEGINNING ON THURSDAY. THIS WOULD PULL CONSIDERABLE
MOISTURE ACROSS THE AREA FRIDAY AND SATURDAY IF IT DEVELOPS IN
THIS MANNER.

DISCUSSION...MOISTURE CONTINUED TO DEVELOP OVER THE LOCAL AREA
AND SHOWERS AND THUNDERSTORMS DEVELOPED JUST AFTER NOON FROM
GUAYNABO TO DORADO WITH SOME LOCAL URBAN AND SMALL STREAM FLOODING
IN GUAYNABO MUNICIPALITY. THEN STRONG SHOWERS AND THUNDERSTORMS
FORMED OVER THE WESTERN CENTRAL INTERIOR AND COASTAL
SECTIONS...WITH A NUMBER OF AREAS OF HEAVY RAIN NEEDING AN URBAN
AND SMALL STREAM FLOOD ADVISORY. THESE AREAS OF RAIN SHOULD
DISSIPATE AFTER SUNSET OVER LAND LEAVING A FEW SHOWERS...AND
CONTINUE FOR A FEW HOURS MORE OVER THE WATERS TO THE WEST. MORE
MOISTURE WILL MOVE INTO THE LOCAL AREA TONIGHT AND BRING SCATTERED
SHOWERS TO THE LOCAL ATLANTIC WATERS AND EASTERN PUERTO RICO. SOME
SHOWERS ARE ALSO EXPECTED ACROSS THE U.S. VIRGIN ISLANDS
TONIGHT...BUT ACCUMULATIONS SHOULD BE SLIGHT. THIS GENERAL
PATTERN WILL CONTINUE THROUGH THE WEEK WITH ENHANCEMENTS
WEDNESDAY AND THURSDAY DUE TO THE PASSING TROPICAL WAVE. THEN ON
FRIDAY...ACCORDING TO THE CURRENT SOLUTION OF THE
GFS...SIGNIFICANTLY BETTER MOISTURE WITH PRECIPITABLE WATER VALUES
OVER 2 INCHES WILL MOVE INTO THE AREA ON SOUTHERLY FLOW BRINGING
MUCH BETTER CHANCES OF RAIN IN MUCH GREATER QUANTITIES THAN HAD
LATELY.

AVIATION...SCT SHRA/TSRA OVER THE INTERIOR AND WESTERN PR WILL
CONTINUE AT LEAST THRU 22Z...CREATING MTN TOP OBSCD AND MVFR TO
BRIEF IFR CONDS MAINLY AT JMZ. VFR ELSEWHERE. LAND/SEA BREEZE
VARIATIONS AND EAST WINDS WILL CONTINUE AT 10-20 KT BLO
FL100...LIGHT AND VARIABLE OVERNIGHT AT THE SFC.

MARINE...WINDS AND SEAS WILL INCREASE SLIGHTLY CAUSING THE
SPREAD OF EXERCISE CAUTION CONDITIONS OVER THE EXPOSED WATERS
SUNDAY. WINDS AND SEAS SHOULD ABATE MID WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  78  88  77  88 /  10  10  40  40
STT  78  88  78  86 /  20  20  40  40

&&

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

$$

08/27


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