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000
FXPQ60 PGUM 190647
AFDPQ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
447 PM CHST SUN MAY 19 2013

.SYNOPSIS...
A SUB-TROPICAL RIDGE STRETCHES UN-SEASONALLY SOUTHWESTWARD FROM
NORTHEAST OF WAKE ISLAND THRU THE MARIANAS ALL THE WAY TO THE
CENTRAL PHILIPPINES. AT THE UPPER LEVELS...THE MARIANAS ARE
LOCATED IN AN AREA OF SUBSIDENCE SANDWICHED BETWEEN A HIGH
CENTERED NEAR THE NORTHERN CNMI AND A TROUGH JUST SOUTH OF GUAM.
LATEST SOUNDING INDICATES DRY AIR ASSOCIATED WITH THIS AREA OF
SUBSIDENCE HAS REACHED DOWN TO 850 MB.

&&

.DISCUSSION...
THE SUB-TROPICAL RIDGE AT THE SURFACE WILL COUPLE WITH DRY AIR
ALOFT TO PROLONG DRIER THAN NORMAL CONDITIONS THRU MONDAY NIGHT.
A FRONTAL BOUNDARY CURVES SOUTHWESTWARD FROM A LOW PRESSURE
SYSTEM CENTERED EAST OF NORTHERN JAPAN TO ANOTHER LOW PRESSURE
SYSTEM CENTERED NEAR IWO TO ISLAND. AS THESE FEATURES TRACK
EASTWARD... THEY WILL GRADUALLY WEAKEN THE SUB-TROPICAL RIDGE OVER
THE NEXT FEW DAYS. THIS SHOULD ALLOW A MORE MOIST TRADE-WIND FLOW
TO RETURN AND PROMOTE AN ISOLATED SHOWERS REGIME BY MIDWEEK.

&&

.MARINE...
SWELL GENERATED BY A DISTANT TRADE SURGE NEAR THE DATE LINE WILL
CAUSE SEA HEIGHTS TO SLOWLY RISE. COMBINED SEAS OF 2 TO 4 FEET ON
MONDAY ARE GOING TO RISE AND REACH 3 TO 5 FEET BY MIDWEEK.

&&

.EASTERN MICRONESIA...
VISIBLE SATELLITE INDICATES A BAND OF TRADE-WIND CONVECTION IS
ALIGNED ACROSS ALL OF EASTERN MICRONESIA BETWEEN 2N AND 8N. A
SURGE IN THE TRADES IS PROVIDING ADDITIONAL LOW-LEVEL CONVERGENCE
FOR CONVECTION SOUTH OF KWAJALEIN AND MAJURO AND FARTHER EASTWARD
THROUGH THE MARSHALLS TOWARD THE DATE LINE. WATER VAPOR LOOP
SHOWS A DIGGING MID TO UPPER-LEVEL TROUGH TO THE NORTH OF ALL THE
FORECAST POINTS BETWEEN 10N AND 20N. THIS FEATURE IS PROVIDING
SOME FAVORABLE DYNAMICS FOR CONVECTION NOW...BUT AS IT LOSES
LATITUDE IT COULD END UP SHEARING THE TOPS FROM TRADE-WIND
CONVECTION ON THE POLEWARD SIDE OF 5N.

FORECAST INVOLVED NO SIGNIFICANT CHANGES AND CLOSELY FOLLOWS
PERSISTENCE. MODEL GUIDANCE STILL SHOWS LITTLE DISPLACEMENT IN
THE TRADE-WIND CONVECTION OVER EASTERN MICRONESIA DURING THE NEXT
5 DAYS. STILL EXPECT TRADE-WIND SURGE TO FUEL CONVECTION OVER
MAJURO AND KOSRAE DURING THE NEXT COUPLE OF DAYS...BUT GFS TIME-
HEIGHT CROSS SECTION SUGGESTS SCATTERED SHOWERS COULD BE CURTAILED
BY TUESDAY NIGHT OVER MAJURO AS SHEAR AND SUBSIDENCE MOVE OVERHEAD.
WILL CHOOSE TO MONITOR SATELLITE TRENDS FOR NOW AND LEAVE ANY
CHANGES TO THE MAJURO FORECAST TO FUTURE SHIFTS. POHNPEI FORECAST
REMAINS UNCHANGED AS STRONG RIDGING TO THE NORTH KEEPS THE DEEPEST
TRADE-WIND CONVECTION JUST TO THE SOUTH THROUGH THE FORECAST
PERIOD.

GRAPHIC WAVE WATCH MODEL GUIDANCE SUGGESTS A TRADE-WIND SURGE
COULD CAUSE SEAS ACROSS EASTERN MICRONESIA TO BUILD DURING THE
SECOND HALF OF THIS WEEK. TABULAR GUIDANCE IS NOT NEARLY AS
AGGRESSIVE IN BUILDING TRADE-WIND ENERGY..SO LEFT SEAS FORECAST
UNCHANGED.

&&

.WESTERN MICRONESIA...
CHUUK FORECAST CLOSELY FOLLOWS PERSISTENCE. WEATHER PATTERN FOR
CHUUK CLOSELY RESEMBLES THAT FOR POHNPEI. EXPECT ZONE OF TRADE-
WIND CONVERGENCE TO REMAIN TO THE SOUTH THROUGH DAY 5. FORECAST
FOR YAP AND KOROR REVOLVES AROUND THE FUTURE TRACK AND EVOLUTION
OF A TRADE-WIND DISTURBANCE CENTERED ALMOST EXACTLY HALFWAY
BETWEEN CHUUK AND YAP. THIS SYSTEM HAS BECOME BETTER ORGANIZED
DURING THE PAST 12 HOURS AND MAY HAVE DEVELOPED A WEAK MID-LEVEL
CENTER. AT THE SURFACE...ONLY AN INVERTED TROUGH CAN BE DISCERNED
IN THE LATEST ASCAT IMAGERY. A SMALL TUTT CELL WAS CENTERED TO
THE NORTH OF YAP NEAR 14N...BUT IT APPEARS TO BE OF LITTLE
INFLUENCE TO WEATHER OVER YAP AND KOROR. PROXIMITY OF TRADE-WIND
DISTURBANCE TO YAP ARGUES FOR INCLUSION IN THE FORECAST. GFS
INITIALIZES/HANDLES THIS SYSTEM THE BEST...SO RELIED ON GFS SHORT
TERM SOLUTION FOR YAP AND KOROR FORECASTS. ADDED SCATTERED
SHOWERS TO YAP FORECAST FOR TOMORROW AFTERNOON UNTIL DAWN ON
TUESDAY. DUE TO UNCERTAINTY IN THE LONGEVITY OF THE TRADE-WIND
DISTURBANCE...MERELY ADDED SLIGHT CHANCE THUNDER TO THE KOROR
FORECAST FOR TUESDAY AND TUESDAY NIGHT. ZONE OF TRADE- WIND
CONVERGENCE OVER EASTERN MICRONESIA COULD PROPAGATE FAR ENOUGH TO
THE WEST TO AFFECT KOROR BY THE END OF THE WEEK.

OTHERWISE...A BENIGN MARINE PATTERN IS EXPECTED TO REMAIN IN PLACE
ACROSS WESTERN MICRONESIA WITH SEAS RANGING BETWEEN 2 AND 4 FEET
DURING THE NEXT SEVERAL DAYS.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...NONE.
MARIANAS WATERS...NONE.
&&

$$

CHAN/MCELROY