Area Forecast Discussion
Issued by NWS San Juan, PR

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000
FXCA62 TJSJ 210726
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
326 AM AST SUN SEP 21 2014

.DISCUSSION...NUMEROUS SHOWERS/THUNDERSTORMS MOVING THROUGH SOUTH
MONA PASSAGE ARE RIDING JUST AHEAD OF A 850 MB SPEED MAXIMUM
WHICH WILL CLEAR WEST OF THE PASSAGE THIS MORNING NEAR OR SOON
AFTER 12Z. ISOLATED/SCATTERED CONVECTION CONTINUES BEHIND IN
HIGH TOTAL PRECIPITABLE WATER IN EXCESS OF 2 INCHES AS SHOWN BY
SSMI AND MIMIC-TPW IMAGES. 00Z GFS HAS A NICE HANDLE ON THE
DISTRIBUTION OF THIS MOISTURE AND SUGGESTS A HIGH NORTH TO SOUTH
MOISTURE GRADIENT OVER PR/USVI AND EXTENDING TO NORTHERN LEEWARD
ISLANDS TODAY. WRF AND NAM TAKE PRECIPITATION ACROSS EASTERN PR
AND NORTH OF THE ISLAND THIS MORNING WHILE GFS KEEPS IT FARTHER
SOUTH...STILL OVER PR. SIGNIFICANT CONVECTION OVER PR THIS MORNING
SEEMS HIGHLY UNLIKELY GIVEN THE POSITION OF THE 850 MB FLOW...A
CURRENTLY COOL ISLAND AND RELATIVE LACK OF CURRENT UPSTREAM
ACTIVITY.

WIND FLOW SHOULD NOT BE A SIGNIFICANT FACTOR AT ANY LEVEL IN
CONVECTIVE DEVELOPMENT TODAY OR NEXT SEVERAL DAYS...INSTEAD
DEPENDENT MORE ON HOW MUCH SOLAR HEATING OCCURS AND WHERE SEA
BREEZES SET UP. HIGH CLOUDS FROM THUNDERSTORMS OVER CARIBBEAN
COASTAL WATERS ARE SPREADING BUT MOST OF THIS WILL DISSIPATE AND
MOVE WEST BEFORE MUCH SUNSHINE OCCURS. GFS SHOWS 2+ INCHES OF
PRECIPITABLE WATER AT 18Z TODAY OVER WEST AND SOUTH PR...EXPECT
MOST AFTERNOON CONVECTIVE DEVELOPMENT TODAY OVER WEST PR WHERE THE
BEST HEATING WILL OCCUR AND RESULTANT SEA BREEZES FOCUS.

MOISTURE DECREASES SOMEWHAT ON MON BUT REBOUNDS IMMEDIATELY
FOLLOWING ARRIVAL OF A TROPICAL WAVE ON MON NIGHT. GFS SHOWS
PRECIPITABLE WATER PERSISTENTLY NEAR 2 INCHES FROM TUE-THU.
CONVECTION AGAIN HIGHLY DEPENDENT ON SUNSHINE.

&&

.AVIATION...SHRA ACTIVITY WILL CONTINUE WITH ISOLATED TSRA TOPS TO
FL400-450 MAINLY OVER THE LOCAL CARIBBEAN WATERS. AFTER 21/16Z AREAS
OF MVFR OR EVEN IFR CONDITIONS IN SHRA/TSRA WILL DEVELOP OVER
WESTERN AND CENTRAL PUERTO RICO WITH MOUNTAIN OBSCURATIONS.
OTHERWISE VFR CONDITIONS EXPECTED. LLVL WINDS ELY UP TO 20 KT WITH
LAND/SEA BREEZE VARIATIONS.

&&

.MARINE...MINOR SWELL IS MOVING WESTWARD NORTHEAST OF LEEWARD
ISLANDS. BUOY 41044 IS CURRENTLY RECORDING 5 FT SEAS AND ABOUT A
FOOT HIGHER THAN MODELS CURRENTLY SHOW. THESE SEAS WILL PASS
NORTH OF PR ON MON AND MAINLY NORTH OF 20N. MAINTAINING 4 FT IN
COASTAL WATERS GOOD.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  88  79  89  79 /  20  30  30  20
STT  89  79  89  79 /  40  40  40  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
COASTAL WATERS...NONE.
&&

$$

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