668
FXPQ50 PGUM 191940
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
540 AM CHST SUN SEP 20 2026
MARIANAS UPDATE
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL LIKELY CONTINUE
THROUGH MUCH OF THE WEEK. HI-RES GUIDANCE SHOWS SOME LOCALLY HEAVY
RAINFALL WILL BE POSSIBLE TONIGHT, ESPECIALLY FOR GUAM AND SAIPAN.
LIGHT AND VARIABLE WINDS ARE EXPECTED TODAY AND WILL BECOME LIGHT TO
GENTLE SOUTH TO SOUTHEAST BY LATE MONDAY. COMBINED SEAS OF 4 TO 6 FT
WILL CONTINUE TODAY AND DROP A FOOT OR SO THROUGH MIDWEEK.
OTHERWISE, A MODERATE RISK OF RIP CURRENTS WILL CONTINUE ALONG ALL
REEFS THROUGH AT LEAST MONDAY.
EASTERN MICRONESIA UPDATE
A WEAK, LOW PRESSURE SYSTEM IS LOCATED NORTH OF KWAJALEIN THIS
MORNING WITH MONSOONAL INFLOW PERSISTING ACROSS PORTIONS OF EASTERN
MICRONESIA. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL BE
POSSIBLE AT ALL FORECAST POINTS INTO EARLY THIS WEEK. GENTLE TO
MODERATE WEST WINDS WILL CONTINUE INTO MONDAY AT POHNPEI AND KOSRAE
WITH WINDS EASING TO LIGHT TO GENTLE BY TUESDAY AS THE LOW PRESSURE
SYSTEM LIFTS NORTHWARD. SOUTHWEST TO WEST WINDS WILL INCREASE AT
MAJURO STARTING TODAY TO GENTLE TO MODERATE AND CONTINUE INTO EARLY
THIS WEEK AS THE AFOREMENTIONED LOW PRESSURE SYSTEM LIFTS NORTHWARD.
COMBINED SEAS OF 4 TO 6 FEET WILL CONTINUE THROUGH EARLY THIS WEEK AT
ALL FORECAST POINTS.
WESTERN MICRONESIA UPDATE
WET AND UNSETTLED WEATHER IS EXPECTED AT YAP THROUGH EARLY THIS WEEK
WITH LOCALLY HEAVY RAINFALL POSSIBLE WITH STRONGER SHOWERS AND
THUNDERSTORMS. MOSTLY SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
ARE EXPECTED AT CHUUK AND PALAU. LIGHT TO MODERATE WEST TO SOUTHWEST
WINDS WILL CONTINUE TODAY AND BEGIN TO EASE SLIGHTLY TONIGHT,
BECOMING MOSTLY LIGHT TO GENTLE BY MONDAY NIGHT. COMBINED SEAS OF 5
TO 7 FEET WILL CONTINUE THROUGH EARLY THIS WEEK AT ALL FORECAST
POINTS, THOUGH LOCALLY CHOPPY SEAS WILL BE POSSIBLE AT YAP NEAR
STRONGER SHOWERS AND THUNDERSTORMS.
PREV DISCUSSION
/ISSUED 605 PM CHST SAT SEP 19 2026/
MARIANAS SYNOPSIS...
SOME ISLAND CONVECTION HAS TRIED TO DEVELOP ALONG THE EASTERN
COASTLINE OF GUAM AND SAIPAN, AND ALONG THE NORTHERN TIP OF ROTA.
HOWEVER, MOST OF THE ASSOCIATED SHOWERS WITH IT REMAIN OFF SHORE.
THESE SHOWERS WILL DIMINISH BY SUNSET, WITH LIGHT AND VARIABLE WINDS
CONTINUING OVERNIGHT. LOOKING AHEAD, AN UNSETTLED PATTERN WILL
CONTINUE THROUGH THE WEEKEND AND INTO NEXT WEEK.
DISCUSSION...
DEEP SOUTHWESTERLY FLOW REMAINS ENTRENCHED ACROSS THE MARIANAS THIS
AFTERNOON, WITH VISIBLE IMAGERY AND DOPPLER RADAR SHOWING JUST
ISOLATED SHOWERS CROSSING THE REGION. SATELLITE IMAGERY DOES SHOW
SOME NEW CONVECTION TRYING TO DEVELOP TO OUR SOUTHWEST, AND TIME
HEIGHTS SO MOISTENING OF THE COLUMN WITH INCREASING OMEGA (LIFT)
DEVELOPING AFTER MIDNIGHT (MORE SO 2 AM). THUS, WILL TREND THE
FORECAST IN THAT DIRECTION (HOLDING OFF THE BETTER RAINFALL POTENTIAL
UNTIL LATER TONIGHT). OTHERWISE, THE INHERITED FORECAST REMAINS IN
GOOD SHAPE WITH THE MAIN CHANGES BEING TO INCREASE RAINFALL POTENTIAL
FOR THE MIDDLE TO LATTER PORTION OF NEXT WEEK, AS A TROPICAL
DISTURBANCE POTENTIALLY TRIES TO FORM TO OUR SOUTH OR SOUTHWEST.
MARINE...
WINDS HAVE SUBSIDED INTO THE LIGHT TO GENTLE RANGE AND THIS WILL
CONTINUE INTO THE FIRST HALF OF NEXT WEEK. AS TYPHOON DUJUAN
CONTINUES TO MOVE AWAY FROM THE REGION, A NORTHWESTERLY SWELL FROM IT
WILL CONTINUE TO SUBSIDE. OVERALL, LOOK FOR SEAS OF 5 TO 6 FEET TO
DROP A FOOT OR SO BY THE MIDDLE OF NEXT WEEK.
EASTERN MICRONESIA...
A WEAK LOW PRESSURE IS SITUATED NORTH OF KWAJALEIN AND BRINGING
GENTLE TO MODERATE WESTERLIES ACROSS POHNPEI AND KOSRAE AND LIGHT
SOUTHWESTERLIES OVER MAJURO. THIS MONSOONAL FLOW IS ALLOWING FOR A
WEDGE OF MOISTURE TO STRETCH FROM NEAR POHNPEI TO KOSRAE, BRINGING
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS TO THE ISLANDS FOR AT
LEAST THE NEXT TWO DAYS. THIS MOIST AIR IS EXPECTED TO SHIFT SLOWLY
NORTH, BRINGING THE POTENTIAL FOR HEAVY RAINFALL OVER POHNPEI SUNDAY
NIGHT DUE TO INCREASED CONVERGENCE. BY EARLY NEXT WEEK, KOSRAE MAY
MOVE OUT OF THE MOIST MONSOONAL FLOW AND ENTER A DRIER PERIOD WITH
ONLY ISOLATED SHOWERS. MAJURO WILL SEE A SLOW PROGRESSION OF WEAK
TROUGHS MOVING THROUGH THE AREA THIS WEEK, BRINGING PERIODS OF
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS AND JUST ISOLATED
SHOWERS. FOR THE MARINE CONDITIONS, SEAS OF 5 TO 6 FEET WILL PERSIST
FOR KOSRAE AND POHNPEI DUE TO A MIX OF SWELLS. SEAS OF AROUND 4 FEET
FOR MAJURO MAY INCREASE TO 5 TO 6 FEET BY MONDAY.
WESTERN MICRONESIA...
SATELLITE IMAGERY SHOWS WIDELY SCATTERED SHOWERS ACROSS YAP AND
CHUUK AND ISOLATED SHOWERS ACROSS PALAU. ALTIMETRY SHOWS COMBINED
SEAS BETWEEN 5 AND 7 FEET ACROSS THE REGION.
OVERALL, THE ONLY ADJUSTMENTS TO THE FORECAST THIS AFTERNOON WERE
FOR YAP. THE FORECAST REMAINED MAINLY UNCHANGED FOR PALAU AND CHUUK.
FOR PALAU, TONIGHT LOOKS TO BE THE END OF THE DRIER LULL AS
SCATTERED SHOWERS ARE EXPECTED TOMORROW, WITH INCREASING COVERAGE
OVER THE COMING DAYS. THE BEST CHANCE OF RAIN LOOKS TO BE TUESDAY
AND TUESDAY NIGHT. GUIDANCE SHOWS A TIGHT GRADIENT JUST NORTH OF
PALAU WITH KAYANGEL POTENTIALLY SEEING HEAVY RAIN ON TUESDAY. TRENDS
WILL NEED TO BE MONITORED OVER THE COMING DAYS TO SEE IF SOUTHWARD
SHIFTS IN THE HEAVIER RAINFALL OCCUR.
CHUUK LOOKS TO REMAIN ON THE SOUTHEASTERN FRINGE OF THE MONSOON
TROUGH, KEEPING THEM IN A REGION OF SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS THROUGH WEDNESDAY. BOTH THE GFS AND ECMWF SHOW A
DEVELOPING DISTURBANCE NEAR THE MARIANAS LATE THIS WEEK. THIS COULD
KEEP CHUUK OUT OF THE CONVERGENT SURFACE FLOW NECESSARY FOR SHOWERS
AND THUNDERSTORMS TOWARDS THE END OF THE WEEK.
THE MAIN CHANGE AT YAP WAS A SLIGHT DECREASE IN SHOWERS AND
THUNDERSTORMS LATE THIS WEEKEND AND INTO NEXT WEEK. POPS WERE
SLIGHTLY DECREASED FROM WIDESPREAD (80%+) OR NUMEROUS (60-70%).
GUIDANCE HAS BACKED OFF SOME WITH THE HEAVY RAIN EVENT OVER YAP, BUT
STILL SHOWS THE POTENTIAL FOR LOCALLY HEAVY RAINFALL. THE BEST
POTENTIAL IS SUNDAY NIGHT THROUGH TUESDAY FOR YAP.
MARINE CONDITIONS WILL GENERALLY BE BENIGN THROUGH MUCH OF THE WEEK.
THE CAVEAT IS AT YAP WHERE HEAVY SHOWERS COULD LEAD TO CHOPPY SEAS
AT TIMES. OTHERWISE, SEAS WILL GENERALLY BE BETWEEN 5 AND 7 FEET AND
SLOWLY FALLING THROUGH THE FORECAST PERIOD.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: WHISNANT
MARIANAS: DOLL
EAST MICRONESIA: OGLE
WEST MICRONESIA: WILLIAMS
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