Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 030151
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
951 PM AST MON MAY 2 2016

.UPDATE...SHOWERS AND ISOLATED THUNDERSTORMS WERE OBSERVED MANLY
ACROSS THE NW QUADRANT OF PR DURING THE LATE AFTERNOON HOURS AND
ACROSS EASTERN PR AND THE U.S. VIRGIN ISLANDS BY EARLY IN THE
EVENING. THE DOPPLER RADAR ESTIMATED BETWEEN 1-2 INCHES OF RAIN
WITH THE HEAVIEST SHOWERS. THIS PRODUCED LOCALIZED URBAN AND SMALL
STREAM FLOODING ACROSS THE AFFECTED AREAS. FOR THE REST OF THE
OVERNIGHT INTO THE EARLY MORNING HOURS...SHOWERS WITH POSSIBLE
THUNDERSTORMS CAN CONTINUE TO AFFECT THE USVI AND THE
SOUTH/SOUTHEASTERN SECTIONS OF PR. LATEST 03/00Z TJSJ UPPER AIR
SOUNDING INDICATED LOW LEVEL E-ESE WINDS AT 10-26 KTS. NO MAJOR
CHANGE FROM PREVIOUS FORECAST.


&&


.AVIATION UPDATE...BRIEF PERIODS OF MVFR CONDITIONS IN SHRA ARE
EXPECTED TO PREVAIL ACROSS THE LEEWARD TAF SITES AS WELL AS ACROSS
TIST...TISX AND TJSJ. MOSTLY VFR CONDITIONS WITH VCSH EXPECTED
ELSEWHERE ACROSS THE LOCAL FLYING AREA. FOR TOMORROW AFTERNOON
MOUNTAIN OBSC POSSIBLE ACROSS THE INTERIOR AND WESTERN PR. SURFACE
WINDS WILL CONTINUE FROM EAST-SOUTHEAST AT AROUND 10 KNOTS
INCREASING AFTER 03/13Z AT 10 TO 15 KNOTS.


&&

.MARINE UPDATE...BUOYS ACROSS PR AND THE USVI ARE INDICATING SEAS
BETWEEN 3 TO 4 FEET AND EAST-SOUTHEAST WINDS AT 10-15 KNOTS. SEAS
SHOULD CONTINUE BELOW SMALL CRAFT ADVISORY CRITERIA FOR THE NEXT 7
DAYS.


&&

.PREV DISCUSSION... /ISSUED /

SYNOPSIS...MID TO UPPER LEVEL TROUGH WILL CONTINUE TO SLOWLY
LIFT EASTWARD ACROSS LOCAL REGION THROUGH TUESDAY.IN THE LOW
LEVELS...SURFACE HIGH PRESSURE CENTERED ACROSS THE NORTH CENTRAL
ATLANTIC WILL MAINTAIN A  MOIST SOUTHEAST WIND FLOW ACROSS THE
REGION THROUGH AT LEAST WEDNESDAY. WINDS ARE TO THEN BECOME MORE
SOUTHERLY DURING THE LATTER PART OF THE WORK WEEK AS THE ATLANTIC
HIGH BUILDS AND SINKS SOUTHWARD ACROSS THE CENTRAL ATLANTIC. THE
OVERALL WEATHER PATTERN WILL MAINTAIN AN MOIST AND UNSTABLE
ENVIRONMENT THROUGH THE MIDDLE OF THE WEEK.

DISCUSSION...FAVORABLE AND UNSTABLE CONDITIONS WILL CONTINUE
TODAY THROUGH EARLY WEDNESDAY AS PREVIOUSLY MENTIONED. FOR TODAY
EXPECT MOST ACTIVE AREAS TO BE FOCUSED ACROSS THE NORTHERN HALF
AND AND NORTHWESTERN SECTIONS OF PUERTO RICO RICO AS WELL AS OVER
ISOLATED AREAS IN THE U.S. VIRGIN ISLANDS DURING THE REST OF THE
AFTERNOON AND INTO THE EVENING HOURS. DUE TO SATURATED SOILS AND
UNSTABLE CONDITIONS...MINOR FLOODING OF URBAN AREAS AS WELL AS
QUICK RISES IN WATER LEVELS OF SOME RIVERS...SMALL STREAMS...AND
GUTS WILL REMAIN POSSIBLE FOR THE REST OF THE DAY OVER MUCH OF OF
THE ISLANDS. FOR THE NEXT FEW DAYS...THE MOIST SOUTHEAST FLOW AND
UNSTABLE CONDITIONS ALOFT WILL BE THE DRIVING FORCE OF ENHANCED
CONVECTIVE DEVELOPMENT ACROSS THE ISLANDS AND COASTAL WATERS WITH
INCREASE POTENTIAL FOR MINOR FLOODING SITUATIONS.

BY WEDNESDAY...THE UPPER TROUGH IS TO FILL AND LIFT NORTHEAST AND
THE HIGH PRESSURE RIDGE IS FORECAST TO BUILD ALOFT ACROSS THE REGION
THROUGH THURSDAY.THIS CHANGE IN THE WEATHER PATTERN WILL LEAD TO A
DECREASE IN WIDESPREAD CONVECTION ACROSS THE ISLANDS. HOWEVER SUFFICIENT
LOW LEVEL MOISTURE CONVERGENCE COMBINED WITH LOCAL TERRAIN EFFECTS AND
DAYTIME HEATING WILL LEAD TO PERIODS OF SHOWER AND ISOLATED THUNDERSTORM
DEVELOPMENT MAINLY OVER PORTIONS THE CENTRAL AND NORTHWESTERN SECTIONS
OF PUERTO RICO. ISOLATED SHOWERS AND THUNDERSTORMS CAN BE EXPECTED ELSEWHERE.

BASED ON THE LATEST GFS MODEL GUIDANCE...THIS SHIFT IN THE WEATHER PATTERN
WILL BE SHORT LIVED AS A DEEP POLAR TROUGH WILL BECOME AMPLIFIED ACROSS
THE WESTERN ATLANTIC AND QUICKLY ERODE THE RIDGE BY LATE THURSDAY AND
IN TO THE UPCOMING WEEKEND. AS A RESULT A RETURN TO A MOIST AND UNSTABLE
WEATHER PATTERN IS AGAIN EXPECTED WITH GOOD POTENTIAL FOR PERIODS OF
STRONG CONVECTIVE DEVELOPMENT ACROSS THE COASTAL WATERS AND PORTIONS
OF THE INTERIOR AND NORTHERNHALF OF PUERTO RICO RICO. ALL IN ALL...THE
POTENTIAL FOR URBAN AND SMALL STREAM FLOODING WILL CONTINUE MOST OF
THE WEEK WITH THE STRONGEST ACTIVITY FOCUSED THE EAST AND SOUTHEAST
SECTIONS OF PUERTO RICO AND ON THE WINDWARD SIDE OF THE VIRGIN ISLANDS
DURING THE LATE EVENING AND EARLY MORNING HOURS. THE ACTIVITY IS TO
THEN SHIFT TO THE NORTH AND NORTHWESTERN SECTIONS OF PUERTO RICO DURING
THE AFTERNOON HOURS.

AVIATION...MOSTLY VFR COND WITH VCSH CAN BE EXPECTED ACROSS THE TAF
SITES. MOUNTAIN OBSC PSBL ACROSS THE INTERIOR AND WESTERN PR
UNTIL AROUND 02/22Z. THE SURFACE WINDS WILL CONTINUE FROM THE
SOUTH TO EAST-SOUTHEAST AT 10 TO 15 KNOTS WITH SEA BREEZE
VARIATIONS.

MARINE...OVERALL FAIRLY TRANQUIL SEAS EXPECTED OVERNIGHT .
HOWEVER...SHOWERS AND THUNDERSTORM DEVELOPMENT WILL CONTINUE
ACROSS THE LOCAL WATERS THROUGH TUESDAY. THIS WILL CONTINUE TO
CREATE HAZARDOUS MARINE CONDITIONS DUE TO LOCALLY HIGHER WAVES AND
WIND GUSTS NEAR THE STORMS. OTHERWISE...SEAS UP TO 5 FEET AND
WINDS UP TO 15 KNOTS ARE EXPECTED.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  74  87  75  88 /  30  30  20  20
STT  76  86  77  86 /  30  30  30  30

&&

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

$$

72/13



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