Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 270953
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
553 AM AST WED MAY 27 2015

.SYNOPSIS...UPPER TROUGH AND ASSOCIATED LOW WILL CONTINUE NORTH
OF LOCAL ISLANDS THROUGH FRIDAY. AN INDUCED SURFACE TROUGH NORTHEAST
OF AREA WILL PROMOTE A MODERATE EAST NORTHEAST TRADE WIND FLOW
THROUGH TODAY SURFACE HIGH PRESSURE OVER THE ATLANTIC WILL PREVAIL
FOR THE NEXT SEVERAL DAYS. TROPICAL MOISTURE IS EXPECTED TO
INCREASE BY THIS WEEKEND.


&&

.DISCUSSION...PASSING SHOWERS ONCE AGAIN AFFECTED THE LOCAL WATERS
AS WELL AS THE NORTH AND EASTERN SECTIONS OF PR AND THE USVI. THIS
AFTERNOON...SHOWERS AND THUNDERSTORMS ONCE AGAIN EXPECTED ACROSS
THE INTERIOR...WESTERN INTERIOR...AND SOUTHWESTERN PR...WITH A
SLIGHT CHANCE OF RAIN ELSEWHERE IN PR AND IN THE USVI. THIS IS A
TYPICAL PATTERN FOR THIS TIME OF YEAR AND IT IS ONCE AGAIN
EXPECTED ON THURSDAY. HOWEVER ON FRIDAY...TROPICAL MOISTURE IS
EXPECTED TO START INCREASING QUITE A BIT WITH PRECIPITABLE WATER
VALUES GETTING CLOSE TO 2 INCHES. IN COMBINATION WITH THE UPPER
TROUGH...THE INSTABILITY WILL ALSO INCREASE. THIS MAY LEAD TO
ENHANCED THUNDERSTORM ACTIVITY ACROSS THE LOCAL AREA STARTING ON
FRIDAY INTO SATURDAY.

LATEST GUIDANCE SUGGESTS THAT THE INSTABILITY WILL BE BETTER JUST
SOUTH OF THE LOCAL ISLANDS BUT INSTABILITY WILL STILL INCREASE
OVER THE ISLANDS. IN ADDITION...THE OVERALL MOISTURE AND THE
UPPER LEVEL DYNAMICS LOOK FAVORABLE FOR SHOWERS AND THUNDERSTORMS
OVER THE LOCAL ISLANDS. BASED ON THE 27/00Z RUN FROM THE GFS
MODEL...THE UPPER LEVEL DIVERGENCE WILL NOT BE THAT GOOD ON
FRIDAY...IN FACT IT SHOWS CONVERGENCE IN THE UPPER LEVELS ON
FRIDAY. HOWEVER...ON SATURDAY...THE MODEL SHOWS A SHARP INCREASE
UN UPPER LEVEL DIVERGENCE WITH CONVERGENCE AT THE SURFACE. THIS
MEANS THAT ALTHOUGH IT LOOKS RAINY ON FRIDAY WITH THE MOISTURE
ADVECTION AND THETA-E INCREASING...THE DAY WITH THE MOST
THUNDERSTORMS MAY ACTUALLY BE ON SATURDAY. THIS IS NOT TO SAY THAT
THERE WILL BE NO THUNDERSTORMS ON FRIDAY...IT JUST THAT THE LATEST
GUIDANCE SUGGESTS BETTER DYNAMICS ON SATURDAY FOR THUNDERSTORMS
OVER THE LOCAL ISLANDS COMPARED TO FRIDAY. SUNDAY LOOKS LIKE THERE
MAY STILL BE SOME THUNDERSTORM ACTIVITY BUT NOT AS MUCH AS
SATURDAY. STAY TUNED FOR THE LATEST ON THIS.

&&

.AVIATION...POSBL MVFR IN ISOLD/SCT SHRA THIS MORNING AND TONITE BUT
MOST TAF SITES WL NOT FALL BLW VFR. SCT TSRA THIS AFT INTERIOR AND
SW PR WI SOME OBSCD MTNS...AGAIN WI POSBL VFR AT TJMZ/TJPS. WIND BLW
FL100 ENE 12 KT EARLY TDY BCMG VRBL 12 KT OR LESS LATE TDY TO THU.

&&

.MARINE...SEAS MAINLY IN THE 2-4 FT RANGE TODAY AND LIKELY THROUGH
THE END OF THE WORKWEEK. WINDS WILL BE GENERALLY UP TO 15 KNOTS
THROUGH THE END OF THE WORKWEEK AS WELL. WINDS AND SEAS ARE
EXPECTED TO INCREASE SLIGHTLY DURING THE WEEKEND.


&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  86  76  88  78 /  40  20  20  20
STT  87  77  87  77 /  40  20  20  30

&&

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

$$

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