Area Forecast Discussion
Issued by NWS San Juan, PR

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000
FXCA62 TJSJ 281449
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1049 AM AST THU MAY 28 2015

.UPDATE...BRIEF PASSING SHOWERS WERE DETECTED ACROSS THE LAND
AREAS...HOWEVER MOST OF THE SHOWER ACTIVITY HAVE BEEN OBSERVED
OVER THE LOCAL WATERS THIS MORNING. MOSTLY SUNNY TO PARTLY CLOUDY
SKIES PREVAILED ACROSS THE LOCAL ISLANDS TODAY. AFTER 8 AM AST
CLOUDINESS STARTED TO INCREASE OVER THE SOUTHERN SLOPES OF THE
CORDILLERA CENTRAL OF PUERTO RICO...ST CROIX...ST THOMAS...
VIEQUES AND CULEBRA. THE FORECAST PACKAGE STILL THE SAME THAT WE
RECEIVED THIS MORNING.

A SIMILAR PATTERN IS EXPECTED FOR THIS AFTERNOON...BUT THIS TIME
DUE TO THE EAST-SOUTHEASTERLY WIND FLOW...MOST OF THE SHOWER AND
THUNDERSTORM ACTIVITY IS EXPECTED ACROSS THE INTERIOR...WEST AND
NORTHWESTERN SECTIONS OF PUERTO RICO.

MODEL GUIDANCE STILL SUGGESTING THE ARRIVAL OF AN INDUCED TROUGH
ASSOCIATED WITH AN UPPER LEVEL LOW...NORTHEAST OF PUERTO RICO...
BY FRIDAY. THEREFORE...SHOWER AND TSTORM ACTIVITY IS STILL LIKELY
OVER THE WEEKEND.


&&

.AVIATION...VFR CONDS EXPECTED TO PREVAIL DURING THE MORNING HRS WITH
VCSH DUE TO QUICK SHOWERS ACROSS THE LOCAL AREA. BETWEEN 28/17Z
AND 28/23Z...MVFR PSBL MAINLY ACROSS TJBQ AND TJMZ DUE TO
AFTERNOON CONVECTION AND MOUNTAIN OBSC ACROSS THE INTERIOR...WEST
AND NW QUADRANT OF PR. SFC WINDS FROM THE E-ESE AT 10 TO 15 KT
WITH HIGHER GUSTS AND SEA BREEZE VARIATIONS THROUGH 28/23Z...
FOLLOWED BY LIGHT SFC WINDS AT AROUND 5KT THEREAFTER.

&&

.MARINE...MARINERS CAN EXPECT TRANQUIL WEATHER CONDITIONS WITH
WINDS UP TO 15 KNOTS AND SEAS OF 5 FEET OR LESS. WEATHER
CONDITIONS ARE EXPECTED TO DETERIORATE DURING THE WEEKEND...STAY
TUNED FOR MORE INFO.

&&

.PREV DISCUSSION... /ISSUED 408 AM AST THU MAY 28 2015/

DISCUSSION...SOUTHERLY FLOW HAS ALREADY BEGUN ABOVE 850 MB ACROSS
THE EASTERN CARIBBEAN WHERE TROPICAL MOISTURE IS SURGING NORTHWEST.
THE FLOW WILL TURN MORE SOUTHEASTERLY BY TONIGHT WHICH WILL PUSH
THE HIGHEST MOISTURE MORE TOWARDS HISPANIOLA. ALL MODELS SHOW
PRECIPITABLE WATER OVER PR PAST 2 INCHES BY FRI MORNING...EXCEPT
THE NAM WHICH HOLDS OFF UNTIL LATE FRI NIGHT. BUT EVEN NAM SHOWS
GOOD RAINFALL AMOUNTS ON FRI AFTERNOON SO HAVE CONSERVATIVELY
PUSHED PROBABILITY OF RAINFALL INTO LIKELY CATEGORY FOR NORTHERN
PR WESTWARD FROM SAN JUAN FOR FRI AND SAT AFTERNOONS. GFS ALSO
SHOWS SOME 250 MB DIVERGENCE ON FRI WHICH COULD HELP DEVELOPMENT
BUT THE MODEL IS NOT VERY GOOD AT LOCATING THIS PARAMETER. THE
OTHER MAIN CAVEAT APPEARS TO BE THE AMOUNT OF HIGH CLOUDS WE MAY
HAVE WHICH WOULD REDUCE HEATING AND AFTERNOON CONVECTION. MODEL
SOUNDINGS SUGGEST PERSISTENT HIGH CLOUDS BUT IS LIKELY OVERDONE.
GFS SUGGESTS KEEPING PRECIPITABLE WATER IN THE VICINITY OF 2
INCHES ALMOST ALL OF NEXT WEEK AND COULD BE A GOOD WEEK FOR RAIN
ACROSS THE ISLANDS.

AVIATION...VFR CONDS EXPECTED AT ALL LOCAL TERMINALS THROUGH
28/17Z WITH VCSH DUE TO QUICK SHOWERS ACROSS THE LOCAL AREA. FROM
28/17Z TO 28/23Z...MVFR PSBL MAINLY ACROSS TJBQ AND TJMZ DUE TO
AFTERNOON CONVECTION ACROSS THE NW QUADRANT OF PR. SFC WINDS WILL
REMAIN LIGHT AT AROUND 5KT THROUGH 28/13Z...BECOMING E-ESE AT AROUND
10KT WITH SEA BREEZE VARIATIONS THEREAFTER.

MARINE...GENTLE TO MODERATE TRADES WILL CONTINUE THROUGH FRIDAY
BUT INCREASE A LITTLE INTO THE WEEKEND. SHOWERS AND THUNDERSTORMS
WILL ALSO INCREASE BEGINNING ON FRIDAY AS TROPICAL MOISTURE
ARRIVES FROM THE SOUTHEAST.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  89  78  89  76 /  20  20  60  50
STT  86  77  86  78 /  20  40  40  50

&&

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

$$

27/12


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