Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 271930
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
330 PM AST WED MAY 27 2015

.SYNOPSIS...AT UPPER LEVELS...LOW PRESSURE ALONG 60 NORTH EAST OF
FLORIDA WILL MOVE NORTHWARD AND REJOIN THE FLOW. THE SUB TROPICAL
JET WILL PULL NORTH OVER THE AREA THURSDAY NIGHT AND FRIDAY THEN HIGH
PRESSURE WILL BUILD OVER THE EASTERN CARIBBEAN OVER THE WEEKEND.
THIS RIDGE WILL SHIFT SLOWLY TOWARD THE WINDWARD PASSAGE DURING
THE UPCOMING WEEK.

AT MID LEVELS...LOW PRESSURE NORTHEAST OF PUERTO RICO WILL PULL
NORTH AND WEAKEN OVER THE WEEKEND THEN HIGH PRESSURE WILL FILL IN
OVER THE EASTERN CARIBBEAN. VERY DRY MID LEVELS WILL GIVE WAY TO A
LARGE AREA OF MOISTURE ON FRIDAY. THIS MOISTURE WILL WEAKEN ON
TUESDAY BUT WILL NOT GET VERY FAR AWAY.

AT LOWER LEVELS...ALTHOUGH HIGH PRESSURE DOMINATES THE CENTRAL
ATLANTIC...VERY WEAK LOWS AND WEAK GRADIENTS ARE FOUND JUST NORTH
AND NORTHEAST OF THE FORECAST AREA. THESE WILL SHIFT WEST AND
FLOW WILL CONTINUE FROM THE SOUTHEAST. TROUGHINESS TO THE WEST AND
THE SOUTHEAST FLOW WILL CONTINUE THROUGH THE UPCOMING WEEK.

&&

.DISCUSSION...SHOWERS FORMED MID MORNING AROUND THE U.S. VIRGIN
ISLANDS AND OVER EASTERN PUERTO RICO...BUT HEAVY SHOWERS ERUPTED
QUICKLY JUST AFTER NOON OVER PUERTO RICO...BEING FUELED BY
INTENSE HEATING UNDER THE PREVIOUS SUNNY SKIES. THESE SHOWERS
CONTINUE TO PRODUCE HEAVY RAIN IN THE CENTRAL PORTION OF THE
ISLAND.

THE GFS CONTINUES TO SHOW RELATIVELY DRY AIR OVER THE AREA UNTIL
FRIDAY MORNING THEN MOISTURE INCREASES SHARPLY. ALTHOUGH THE
MOISTURE COLUMN FORECAST FOR THE WEEKEND IS NOT QUITE AS DEEP AS
WAS PREVIOUSLY FORECAST EARLIER THIS WEEK...VALUES STILL HOLD
BETWEEN 1.9 AND 2.1 INCHES OVER THE AREA THROUGH THE WEEKEND AND
INTO MONDAY. THEREFORE THE POSSIBILITIES FOR HEAVY RAIN AND
FLOODING INCREASE. A HYDROLOGICAL OUTLOOK HAS BEEN ISSUED WITH
MORE DETAILS. THE GFS CONTINUES TO SHOW THE BEST BANDS OF
PRECIPITATION STRETCHING FROM SOUTH OF PUERTO RICO NORTHEAST
ACROSS THE U.S. VIRGIN ISLANDS AND SOME OF THE HEAVIEST RAINS MAY
FALL THERE AND IN THE CORDILLERA CENTRAL DUE TO OROGRAPHIC ACTION.

MOISTURE LEVELS WILL CONTINUE MUCH HIGHER NEXT WEEK THAN THIS
PAST WEEK...BUT THE MIDDLE OF THE WEEK SHOULD NOT BE AS WET AS
THIS WEEKEND.

&&

.AVIATION...VFR CONDS EXPECTED FOR MOST OF THE TERMINALS EXCEPT
TJMZ AND TJPS WHERE AFTERNOON CONVECTION MAY PRODUCE BRIEF
MVFR/IFR CONDS THRU 22Z. MOUNTAIN OBSCURATIONS AND MVFR/IFR CONDS
ARE LIKELY ACROSS THE CORDILLERA CENTRAL THROUGH THIS EVENING..
WINDS BELOW 3K FT WILL PREVAIL FROM THE NE AT AROUND 10
KT...VEERING TO THE SE AFTER 28/06Z.

&&

.MARINE...A SWELL OF 8 SECONDS PERIOD...UNDETECTED BY THE
MODELS...MOVED INTO THE ATLANTIC WATERS AND THE WATERS NORTH OF
THE FORECAST AREA RAISING SEAS NEARLY 2 FEET...NEVERTHELESS SEAS
WILL NOT EXCEED 5 FEET THIS WEEK OR WEEKEND SINCE WINDS ARE GENTLE
TO MODERATE. SOME GUSTY WINDS MAY BE ENCOUNTERED IN THUNDERSTORMS
OVER THE WEEKEND.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  75  90  76  89 /  20  20  20  40
STT  74  85  78  87 /  20  20  40  40

&&

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

$$

11/12



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