#15634 Postby cycloneye » Mon Mar 24, 2014 5:36 am
Good morning. Dry weather will prevail today in PR and VI.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
537 AM AST MON MAR 24 2014
.SYNOPSIS...AT UPPER LEVELS...A WEAK RIDGE CROSSES THROUGH THE
AREA LATE TODAY AND FORMS EAST OF THE AREA TUESDAY AND WEDNESDAY.
THEN RIDGING RE-BUILDS OVER THE WESTERN CARIBBEAN CAUSING FLOW TO
TURN MORE NORTHWESTERLY LATER IN THE WEEK. THIS RIDGE MOVES
THROUGH LATE SUNDAY NIGHT NEXT WEEK.
AT MID LEVELS...HIGH PRESSURE IN THE WESTERN CARIBBEAN MOVES
ACROSS THE AREA AND TO THE NORTHEAST TODAY THROUGH THURSDAY THEN
RETURNS TO THE WESTERN CARIBBEAN OVER THE WEEKEND BEFORE A CUT-OFF
LOW FORMS IN THE WINDWARD PASSAGE EARLY NEXT MONTH.
AT LOWER LEVELS...HIGH PRESSURE RETREATS TO THE NORTHEAST
ATLANTIC AND A FRONT EXTENDING OFF A LOW NORTH OF PUERTO RICO
BETWEEN 30 AND 40 NORTH WEAKENS AS IT SAGS TOWARD THE LOCAL AREA.
A SHEARLINE MOVES INTO THE NORTHERN ATLANTIC WATERS OF THE
FORECAST AREA TODAY AHEAD OF THIS FRONT. ON TUESDAY A LOW STRENGTHENS
EXPLOSIVELY ALONG THE EASTERN SEABOARD OF THE UNITED STATES AND
MOVES RAPIDLY NORTHEAST WEDNESDAY CAUSING GRADIENTS TO WEAKEN
JUST NORTH OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS. HIGH
PRESSURE ENTERING THE WESTERN ATLANTIC ON THURSDAY WILL CAUSE
LOCAL TRADE WINDS TO RE-STRENGTHEN THURSDAY AND FRIDAY. THIS HIGH
WILL DOMINATE THE CENTRAL ATLANTIC BY SATURDAY. LOW LEVEL FLOW
BECOMES SOUTHEASTERLY EARLY NEXT WEEK.
&&
.DISCUSSION...RADAR SHOWED ANOTHER DRY NIGHT OVER LAND WITH ONLY
ONE OR TWO MINOR SHOWERS OVER THE SOUTHEAST PORTION OF OUR
CARIBBEAN WATERS. A WEAK SHEARLINE IS EXPECTED TO MOVE INTO THE
LOCAL OUTER ATLANTIC WATERS TODAY...BRINGING VARIABLE WINDS...BUT
THESE WINDS ARE AGAIN FROM THE SOUTHEAST TOMORROW WHEN RIDGING
RETURNS TO THE ATLANTIC JUST NORTH OF THE FORECAST AREA. THIS
SHEAR LINE IS EXPECTED TO BRING SOME BRIEF RELIEF TO THE VERY WARM
TEMPERATURES EXPERIENCED IN THE GREATER SAN JUAN METROPOLITAN AREA
TODAY...BUT TEMPERATURES MAY INCREASE A LITTLE AGAIN TOMORROW. THE
NAM5 SHOWED LIKELY SHOWERS OVER THE CORDILLERA CENTRAL THIS
AFTERNOON. THE WRF SHOWS SHOWERS SPREADING OVER MUCH OF WESTERN
PUERTO RICO THEN AS WELL. HOWEVER LITTLE MOISTURE HAS COME IN TO
FUEL THESE SHOWERS AND THEREFORE HAVE KEPT COVERAGE IN THE AREA TO
ISOLATED...BUT EXPECT A LITTLE MORE ACTIVITY THAN YESTERDAY WITH
ONLY LIGHT ACCUMULATIONS IN BRIEF HEAVY SHOWERS WHERE THEY FORM.
FLOW BECOMES MORE EASTERLY DURING THE WEEK...AND...AS IT DOES...
PRECIPITABLE WATER VALUES IN THE GFS SOLUTION CLIMB STEADILY OVER
THE FORECAST AREA BETWEEN THE MINIMUM EXPECTED TUESDAY...OF JUST
ABOVE 1 INCH...TO A PEAK OF ALMOST 1.7 INCHES ON TUESDAY OF NEXT
WEEK. THIS INCREASE WILL BRING IN PATCHES OF MOISTURE BEGINNING
TUESDAY NIGHT AND CONTINUING INTO NEXT WEEK. AGAIN IT IS THE GFS
THAT SHOWS A GRADUAL DEEPENING OF THE MOIST LAYER BREAKING FIRST
THROUGH 850 MB EARLY THIS WEEK AND THEN THROUGH 700 MB NEXT WEEK.
EXTENDED OUTLOOK...NEXT WEEK THE GFS IS SHOWING A STRONG TROUGH
DEEPENING AS IT CROSSES OVER FLORIDA SENDING THE SUB TROPICAL JET
OVER THE LOCAL AREA AND INCREASING DIVERGENCE ALOFT BY MID WEEK. THE
ECMWF SHOWS THE TROUGH BUT DOES NOT DEEPEN OR FORM LOW PRESSURE
OVER THE GREATER ANTILLES QUITE AS MUCH AS THE GFS. AS IS
CLIMATOLOGICALLY SEASONAL FOR THE BEGINNING OF APRIL THE GFS IS
SIGNALING THE END OF THE DRIEST WEATHER FOR PUERTO RICO AND THE
U.S. VIRGIN ISLANDS WITH THE STRONG DEVELOPMENT OF THIS TROUGH AND
THE ACCOMPANYING TURN OF FLOW AT 700 MB FROM THE NORTH TO FLOW
WITH A SOUTHERN COMPONENT NEXT WEEK. THIS WOULD BRING MORE
MOISTURE OUT OF THE MOISTURE-RICH ENVIRONMENT OF SOUTH AMERICA
NEXT WEEK THAT WOULD CAUSE A SHARP INCREASE IN SHOWER ACTIVITY
OVER THE AREA. IT IS POSSIBLE THAT THE SOLUTION OF THE GFS IS SOME
WHAT EXAGGERATED...BUT WOULD EXPECT AT LEAST MODEST MOISTURE
INCREASES NEXT WEEK IN THE LONGER RANGE FORECAST WITH A
POSSIBILITY OF A SIGNIFICANT CHANGE IN THE PATTERN AT THAT TIME.
&&
.AVIATION...VFR CONDITIONS ACROSS THE LOCAL TERMINALS DURING THE
FCST PD. SFC WINDS MAINLY FROM THE SE AT 5-10 KTS WITH SEA BREEZE
VARIATIONS. WINDS LESS THAN 10 KTS BELOW 8 KFT...BCMG FROM THE W TO NW
AND INCREASING TO 15 TO 20 KTS LATER IN THE AFTERNOON. SOME
SHALLOW CONVECTION IS EXPECTED ALONG THE CORDILLERA CENTRAL AND
WESTERN PUERTO RICO AND SOME MOUNTAIN OBSCURATIONS ARE EXPECTED
AFTER 24/17Z.
&&
.MARINE...WITH WINDS ONLY MODERATE AND LITTLE SWELL AT THE MOMENT
SEAS WILL REMAIN BELOW 6 FEET THROUGH WEDNESDAY. SIGNIFICANT SWELL
FROM A VERY STRONG LOW FORECAST TO FORM OFF THE EASTERN SEA BOARD
OF THE UNITED STATES WEDNESDAY IS STILL EXPECTED LATE THURSDAY
AND INTO FRIDAY WITH SMALL CRAFT ADVISORIES LIKELY IN THE ATLANTIC
WATERS THEN.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 89 74 90 74 / 0 10 10 10
STT 85 76 85 75 / 0 10 10 20
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