#16666 Postby cycloneye » Sat Dec 06, 2014 7:31 am
Pardon the inconvencience for being late as I was without internet this morning.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
518 AM AST SAT DEC 6 2014
.SYNOPSIS...AT UPPER LEVELS...AN 85 KNOT JET CROSSED OVER THE AREA
LAST NIGHT AND A WEAK TROUGH WILL FOLLOW IT EARLY THIS MORNING.
NEVERTHELESS LITTLE DYNAMICS ARE SEEN WITH THESE FEATURES. A WEAK
TROUGH WILL ALSO PASS THROUGH THE AREA SUNDAY AFTERNOON. WEST
NORTHWEST FLOW WILL CONTINUE THROUGH MID WEEK AND WINDS WILL PICK
UP AS A SLIGHTLY ANTI CYCLONIC JET MOVES OVER THE AREA FROM THE
SOUTH MID WEEK NEXT WEEK. FLOW WILL TURN SLIGHTLY SOUTHWEST UNDER
THIS JET BY THURSDAY.
AT MID LEVELS...LOW PRESSURE NORTHEAST OF SAN JUAN AT 60 WEST WILL
DEEPEN SLIGHTLY OVER THE WEEKEND BEFORE BEING ABSORBED INTO A LONG
WAVE TROUGH SUNDAY. GRADIENTS WILL WEAKEN IN THE NORTHWEST FLOW
OVER THE AREA AFTER A MID-LATITUDE SHORT WAVE TROUGH PASSES BY ON
MONDAY FOLLOWED BY A SHIFT TO SOUTHWEST FLOW AS A LARGE LOW
ROTATES THROUGH THE NORTHEASTERN UNITED STATES. AFTER WHICH HIGH
PRESSURE WILL DOMINATE THE CARIBBEAN THROUGH THE END OF NEXT WEEK
UNTIL A SECOND LARGE LOW PRESSURE MOVES INTO THE WESTERN ATLANTIC
SATURDAY OF NEXT WEEK. MID LEVELS WILL BE MOSTLY DRY THROUGH THE
NEXT 10 DAYS.
AT LOWER LEVELS...A WEAK INVERTED TROUGH WILL DEEPEN THROUGH
SATURDAY NIGHT BEFORE MOVING NORTHEAST EARLY NEXT WEEK. FLOW
BECOMES EASTERLY NEXT WEEK AS VERY WEAK HIGH PRESSURE SETTLES JUST
NORTH OF THE AREA MID WEEK AND FLOW PERSISTS FROM THE CENTRAL
ATLANTIC.
&&
.DISCUSSION...SMALL SHOWERS PAINTED LIGHT TRAILS OVERNIGHT OF THE
MOST MINIMAL MEASURABLE RAINFALL AMOUNTS IN NORTHERLY FLOW
GENERATED BY THE LOW FORMING 640 MILES NORTHEAST OF PUNTA CANA IN
THE DOMINICAN REPUBLIC. SHOWERS COVERED ABOUT 10 TO 20 PERCENT OF
THE NORTHERN QUARTER OF PUERTO RICO AND THE NORTHERN U.S. VIRGIN
ISLANDS. THE GFS CONTINUES TO BE MUCH DRIER THAN PREVIOUS RUNS AND
ALMOST ANY PREVIOUS PERIOD THIS YEAR WITH PRECIPITABLE WATER
VALUES FALLING BELOW 0.90 INCHES ON BOTH MONDAY NIGHT AND EARLY
WEDNESDAY MORNING. ALSO NOTE THAT LITTLE OR NO DIVERGENCE OCCURS
AT THE 250 MB LEVEL AND SOME DOWNWARD MOTION IS ALSO
INDICATED...THEREFORE...HAVE LOWERED POPS OVER MANY AREAS DURING
THIS PERIOD AND DURING THE WEAK RECOVERY OF THURSDAY AND FRIDAY
MORNING. EVEN DURING A SUPPOSEDLY WET PERIOD FORECAST FOR THE
SUNDAY AFTER NEXT THE GFS ONLY HAS PRECIPITABLE WATER VALUES
REACHING 1.7 INCHES. IN COMPARISON WITH THE SOUNDERS AND THE LAST
RADIOSONDE AT 06/00Z MODEL VALUES ARE ABOUT .15-.25 INCHES TOO
LOW... BUT EVEN THIS MAY NOT BE ENOUGH TO CREATE MORE THAN A 10 TO
20 PERCENT CHANCE OF SHOWERS OVER THE WEEKEND AND THE FIRST PART
OF NEXT WEEK. WITH THE CURRENT SEVERE DRY BIAS OF THE GFS TOWARD
THE LATTER END OF ITS FORECAST THE LAST SEVERAL MONTHS... AND NO
VALUES EXCEEDING 19 PERCENT IN THE MEXJSJ THIS WEEK I MUST ALSO
NOTE THAT CONFIDENCE OF SO FEW SHOWERS FOR THIS WEEK IN DECEMBER
IS ONLY MEDIUM. HOWEVER EXPECT BETTER SHOWER ACTIVITY LATE NEXT
WEEK INTO THE WEEKEND AS MOISTURE COMES IN FROM THE CENTRAL
ATLANTIC.
&&
.AVIATION...VFR CONDITIONS EXPECTED FOR THE NEXT 24 HOURS. ONLY
-SHRA EMBEDDED ON NORTHERLY FLOW OVER THE ATLANTIC WATERS COULD
REACH PARTS OF THE NORTHERN TERMINALS OF PR AND THE USVI. THE 06/00Z
TJSJ UPPER AIR SOUNDING INDICATED LOW LEVEL N-NW WINDS AT 4-12
KT...BCMG NW-W AT FL150 AND ABOVE WITH 20-30 KT AND HIGHER WINDS.
&&
.MARINE...MULTIPLE VIGOROUS HIGHS AND LOWS TRANSITING THE
ATLANTIC WILL KEEP SEAS FAIRLY AGITATED WITH SWELL GROUPS COMING
IN FROM THE NORTH NORTHWEST AND THE NORTHEAST MONDAY THROUGH THURSDAY.
THEREFORE AM KEEPING THE 7 FOOT SEAS IN THE NORTHERN ATLANTIC
WATERS. SPECTRAL MODEL SUGGESTS SEAS UP TO 10 FEET BEGINNING
WEDNESDAY. WILL UPDATE FORECAST WHEN WAVE GENERATION CAN BE
CONFIRMED SINCE THERE IS SOME UNCERTAINTY WITH REGARD TO WIND
STRENGTH IN THE CRITICAL FETCH AREAS.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 85 76 83 74 / 20 20 0 10
STT 86 76 84 77 / 20 20 10 10
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