Area Forecast Discussion
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FXPQ60 PGUM 210803
AFDPQ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
603 PM CHST SUN SEP 21 2014

.MARIANAS SYNOPSIS...
RADAR SHOWS ISOLATED SHOWERS AND THUNDERSTORMS ACROSS THE COVERAGE
AREA. SATELLITE SHOWS PATCHY AREAS OF DEEP CONVECTION ACROSS THE
REGION WITH A MORE SIGNIFICANT AREA OF CONVECTION NORTH OF CHUUK
CENTERED NEAR 11N151E. ASCAT ANALYSIS INDICATES VERY SHARP TROUGHING
NORTH OF CHUUK CENTERED NEAR 12N152E...WHILE A WEAK CIRCULATION IS
EAST OF KOROR NEAR 7N137E. VAD GRADIENT WINDS ARE NE 5 TO 10 KT.
BUOYS SHOW COMBINED SEAS RANGING FROM 3 TO 5 FEET FROM WEST...AND
NORTHEAST TO EAST.

&&

.DISCUSSION...
ISLAND CONVECTION CAUSED LOCALLY HEAVY RAIN OVER THE UPPER SIGUA
RIVER TODAY AND ISOLATED THUNDERSTORMS SLID INTO THE SAIPAN MARINE
ZONE FROM NORTHEAST. THIS UNSTABLE AIRMASS WILL PERSIST WHILE AN
ACTIVE MONSOON TROUGH STARTS TO AFFECT THE MARIANAS IN THE COMING
DAYS. BOTH THE GFS AND ECMWF ARE VERY SIMILAR AND INDICATE THAT A
MONSOON TROUGH FORMING SE OF GUAM ALONG 12N WILL SPAWN A MONSOON
CIRCULATION NORTH OF CHUUK THAT WILL FURTHER DEVELOP AND MOVE TOWARD
THE NORTHERN MARIANA ISLANDS AS THE WEEK PROGRESSES.

&&

.MARINE...
MARINE CONDITIONS WILL DETERIORATE BY THURSDAY OR FRIDAY AS THE
NEARBY MONSOON TROUGH BECOMES MORE ACTIVE. A MONSOON CIRCULATION
WILL LIKELY FORM SE OF GUAM AND MOVE TOWARD THE NORTHERN MARIANAS.
WAVE GRIDS WERE ADJUSTED TO MATCH BUOY REPORTS AND WW3 GUIDANCE.
WIND GRIDS WERE REFRESHED WITH LATEST GFS DATA WHICH IS TONED-DOWN
SLIGHTLY FROM YESTERDAYS MODEL WINDS.

&&

.EASTERN MICRONESIA...
AN UNSETTLED WEATHER PATTERN WILL PERSIST AT CHUUK...POHNPEI AND
MAJURO TONIGHT. WEAK RIDGING WILL KEEP FAIR WEATHER IN PLACE AT
KOSRAE THROUGH MONDAY. A MONSOON TROUGH CURVES EASTWARD ALONG 10N TO
JUST NORTHEAST OF MAJURO. A WEAK CIRCULATION IS STILL SEEN WITHIN
THE TROUGH NORTH OF POHNPEI AND CHUUK. SATELLITE ANIMATION SHOWS
SCATTERED SHOWERS MAINLY NORTH OF ALL LOCATIONS...AND NORTHEAST OF
MAJURO. MODELS GENERALLY SHOW THE CIRCULATION NORTH OF POHNPEI AND
CHUUK SLOWLY DEVELOPING AS IT SLOWLY LIFTS NORTH THE NEXT FEW DAYS.
MODELS CONFINE MUCH OF THE MOISTURE TO NEAR THE CIRCULATION WITH
DRIER WEATHER BUILDING IN ACROSS EASTERN MICRONESIA BY MIDWEEK.
UNSETTLED WEATHER MAY LINGER THROUGH THE END OF THE WEEK AT POHNPEI
AND KOSRAE DUE TO WEAK CONVERGENCE SOUTH OF THE CIRCULATION. WEAK
TROUGHING TOWARDS THE END OF THE WEEK COULD BRING MORE SHOWERS TO
MAJURO THURSDAY AND FRIDAY.

&&

.WESTERN MICRONESIA...
CHUUK DISCUSSION IS INCLUDED IN THE EASTERN MICRONESIA DISCUSSION
ABOVE DUE TO SIMILAR SYNOPTIC REASONING.

WEATHER AT KOROR AND YAP WILL BE FAIRLY BENIGN THIS WEEK. A WEAK
CIRCULATION GENERATING SHOWERS AND THUNDERSTORMS AT YAP THIS MORNING
AND KOROR THIS AFTERNOON WILL PASS OVER OR JUST NORTH OF KOROR
TONIGHT. WEATHER HAS CLEARED OUT OF YAP ALREADY THIS AFTERNOON...AND
THE SAME WILL HAPPEN AT KOROR TONIGHT. MODELS SHOW WINDS BECOMING
SOUTHWEST AT KOROR AND YAP AFTER THE CIRCULATION LIFTS NORTH TONIGHT
AND MONDAY. SOUTHWEST FLOW IS EXPECTED THROUGH THE REMAINDER OF THE
WEEK WITH THE MONSOON TROUGH SITUATED JUST TO THE NORTH AND A
DEVELOPING CIRCULATION NORTH OF CHUUK. CONVERGENCE WITHIN THE
MONSOON FLOW WILL PRODUCE ISOLATED SHOWERS AND THUNDERSTORMS THE
NEXT SEVERAL DAYS.

&&

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

$$

SIMPSON/M. AYDLETT







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