Post by cycloneye on May 9, 2016 4:00:25 GMT -6
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
540 AM AST MON MAY 9 2016
.SYNOPSIS...AT UPPER LEVELS...A TROUGH WILL SHARPEN OVER THE
WINDWARD PASSAGE AND BRIEFLY FORM A CUT-OFF LOW KEEPING THE LOCAL
AREA UNDER THE EXIT JET OF THE LOW TOMORROW. THE TROUGH WILL MOVE
OVER HISPANIOLA MID WEEK AND ACROSS PUERTO RICO THURSDAY NIGHT IN
A MUCH WEAKENED FORM. A SHORT WAVE TROUGH WILL CROSS THROUGH THE
AREA VERY RAPIDLY ON SUNDAY WITH MORE UNSETTLED WEATHER.
AT MID LEVELS...A WEAK TROUGH WILL HOVER JUST WEST OF THE AREA IN
THE GENERALLY HIGH PRESSURE OF THE TROPICAL ATLANTIC AND THE
CARIBBEAN. MID LEVELS ARE MODESTLY MOIST...BUT PATCHES OF VERY
MOIST AIR TRAVEL THROUGH AS PLUMES OF MOISTURE MOVE THROUGH THE
AREA.
AT LOWER LEVELS...HIGH PRESSURE DOMINATES THE SUB TROPICAL
ATLANTIC...BUT FLOW BECOMES MORE SOUTHEASTERLY LATE THIS WEEK AS
HIGH PRESSURE BUILDS AGAIN OVER THE EAST CENTRAL ATLANTIC. PATCHES
OF DRIER AIR PASS THROUGH WEDNESDAY...THURSDAY AND FRIDAY...BUT
MOISTURE RETURNS OVER THE WEEKEND. A BOUNDARY OVER THE U.S. VIRGIN
ISLANDS WILL MOVE BACK OVER PUERTO RICO TODAY BRINGING AN INCREASE
IN SHOWERS AND THUNDERSTORMS.
&&
.DISCUSSION...SHOWERS DEVELOPED OVERNIGHT OVER THE CARIBBEAN AND
ATLANTIC WATERS AROUND SAINT THOMAS...SAINT JOHN...CULEBRA AND
VIEQUES. SOME LEFT UP TO 2 INCHES OVER THE LOCAL WATERS. CULEBRA
DID RECEIVE A SIGNIFICANT SHOWER OVERNIGHT. BY 5 AM AST A FEW TOPS
WERE SEEN AS HIGH AS 40 KFT. ALL INDICATIONS ARE THAT THE BOUNDARY
TO CROSS THE AREA WILL INCREASE IN STRENGTH AND THAT MORE SHOWERS
AND THUNDERSTORMS THAN SEEN YESTERDAY AFTERNOON WILL DEVELOP OVER
THE LOCAL WATERS AND INTERIOR PUERTO RICO TODAY. THE UPPER LEVEL TROUGH
TO THE WEST WILL HOLD SOUTHWEST FLOW OF UP TO 60 KNOTS OVER THE
AREA TODAY WITH SOME AREAS OF DIVERGENCE MOVING OVER THE ISLAND
THIS AFTERNOON. THE BEST DIVERGENCE ALOFT IS NORTHEAST OF PUERTO
RICO IN THE NORTHEAST CORNER OF THE FORECAST AREA AND WELL BEYOND
HOWEVER. SURFACE WINDS TODAY WILL SHIFT FROM ALMOST NORTHEAST TO
EAST SOUTHEAST...BUT CLOUD COVER SHOULD PRECLUDE MAXIMUM
TEMPERATURES AS HIGH AS MOS WAS GIVING PUERTO RICO. BROUGHT SAN
JUAN DOWN FROM 88 TO 85 AS ONLY 82 OCCURRED YESTERDAY AND CLOUDY
SKIES ARE EXPECTED AGAIN TODAY. SINCE 1000-850 MB THICKNESS VALUES
DROP 8 METERS BETWEEN 09/00Z AND 10/06Z IT IS NOT CLEAR WHY MOS
WANTS TO BRING TEMPERATURES UP 6 DEGREES TODAY. MOISTURE DROPS
DURING THE DAY ON TUESDAY...BUT INCREASES AGAIN ON
WEDNESDAY...WITH ANOTHER MINIMUM ON THURSDAY NIGHT. MOISTURE
INCREASES AGAIN OVER THE WEEKEND AND PRESENT INDICATION BRING
SUPPORTING DYNAMICS OVER THE AREA FOR MORE SHOWERS AND
THUNDERSTORMS. THE GFS SHOWS GOOD DYNAMICS THIS TUESDAY THROUGH
THURSDAY IN ALTERNATING CYCLES. SO THIS SHOULD PROVE TO BE A
MOSTLY CLOUDY WEEK WITH SHOWERS AND A FEW THUNDERSTORMS. PRESENTLY
EXPECT SOME URBAN AND SMALL STREAM FLOODING TODAY AND POSSIBLY
TUESDAY AND THURSDAY AND OVER THE WEEKEND AND INTO THE FOLLOWING
MONDAY.
&&
.AVIATION...MOSTLY VFR CONDS ARE EXPECTED ACROSS THE TERMINALS TIL
AROUND 09/15Z. HOWEVER...SHRA/TSRA WILL CONTINUE TO DEVELOP OVER
THE WATERS AND AFFECT THE TERMINALS FROM EASTERN PR TO THE LEEWARD
ISLANDS THRU 09/15Z. THEN...AREAS OF MVFR IN CIGS AND VSBYS WITH
WIDESPREAD MTN OBSCURATIONS ARE EXPECTED THROUGH 10/00Z. LIGHT
AND VARIABLE WINDS WILL BECOME ENE 5 TO 15 KT...SWITCHING TO ESE
AFT 09/18Z.
&&
.MARINE...WINDS AND SEAS INCREASE TODAY AND TUESDAY. CURRENT
EXPECTATION IS THAT SEAS WILL REMAIN BELOW 7 FEET INSIDE THE
FORECAST AREA...BUT BUOY 41043 WILL LIKELY SEE 7 FEET BY TUESDAY.
SEAS DIMINISH AFTER TUESDAY.
&&
.PRELIMINARY POINT TEMPS/POPS...
SJU 85 75 86 76 / 60 50 50 10
STT 86 77 87 77 / 60 60 60 20