677
FXPQ50 PGUM 121823
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
423 AM CHST SAT SEP 13 2025
MARIANAS UPDATE
THE MARIANAS REMAINED A LITTLE BIT DRIER THIS MORNING THAN EXPECTED,
THOUGH THIS IS EXPECTED TO CHANGE THROUGH THE DAY. THERE IS A WEAK
TROUGH APPROACHING THE ISLANDS THAT IS EXPECTED TO INCREASE SHOWERS
TO LOW-END SCATTERED LATER THIS MORNING OR EARLY AFTERNOON. ISOLATED
THUNDERSTORMS ARE EXPECTED THROUGH THE DAY. NO OTHER CHANGES WERE
MADE TO THE FORECAST.
EASTERN MICRONESIA UPDATE
A WEAK INTER-TROPICAL CONVERGENCE ZONE (ITCZ) IS SEEN ON THE LATEST
ASCAT ANALYSIS OVER MAJURO, EXTENDING EAST TO BEYOND THE DATE LINE.
THIS FEATURE IS BRINGING IN THE EXPECTED SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS TO THE ATOLL THIS MORNING. THIS WEAK ITCZ
LOOKS TO DRIFT WEST OVER THE NEXT COUPLE OF DAYS. A DRY TRADE-WIND
PATTERN LOOKS TO CONTINUE FOR KOSRAE THROUGH TODAY, AND AT POHNPEI
THROUGH TONIGHT. THE INCREASED CONVERGENCE FROM MAJURO IS THEN
EXPECTED TO INCREASE CONVECTION OVER KOSRAE TONIGHT AND POHNPEI
SUNDAY. THE REST OF THE FORECAST REMAINS UNCHANGED.
WESTERN MICRONESIA UPDATE
ONLY ONE MAJOR CHANGE TO THE INHERITED FORECAST FOR WESTERN
MICRONESIA. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS MOVED INTO
YAP THIS MORNING, WITH ADDITIONAL SHOWERS SEEN TO THE WEST,
APPROACHING THE ISLAND. OTHERWISE, THE FORECAST REMAINS UNCHANGED.
THE WEAK SURFACE RIDGE CURRENTLY OVER PALAU WILL KEEP MOVING WEST AND
WEAKENING OVER THE NEXT COUPLE OF DAYS, ALLOWING INCREASED SHOWERS TO
MOVE IN THIS AFTERNOON. FOR CHUUK, DRY CONDITIONS ARE CURRENTLY OVER
WENO, WITH A TROUGH BETWEEN WENO AND POHNPEI BRINGING INCREASED
SHOWERS TO THE REGION BY THIS AFTERNOON.
PREV DISCUSSION
/ISSUED 601 PM CHST FRI SEP 12 2025/
MARIANAS SYNOPSIS...
A BROAD TROUGH IS SLOWLY MOVING THROUGH THE REGION. SATELLITE IMAGERY
SHOWS PATCHY SHOWERS OVER GUAM AND ROTA, WITH SHOWERS AND
THUNDERSTORMS INCREASING NEAR TINIAN AND SAIPAN, ESPECIALLY NORTHEAST
OF COASTAL WATERS. BUOY AND ALTIMETRY DATA SHOWS COMBINED SEAS
BETWEEN 2 TO 4 FEET.
DISCUSSION...
AS A BROAD TRADE-WIND TROUGH SLOWLY MOVES WESTWARD THROUGH THE
MARIANAS, SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED
TO CONTINUE THROUGH AT LEAST SATURDAY. AFTERWARDS, LATEST MODEL
GUIDANCE CONTINUES TO SHOW A MIXTURE OF ISOLATED AND SCATTERED
SHOWERS THROUGH THE MIDDLE OF NEXT WEEK DUE TO PASSING SURFACE
TROUGHS AND WEAK CONVERGENCE IN THE TRADE-WIND PATTERN. ONE TROUGH IN
PARTICULAR MAY FURTHER DEVELOP AS IT NEARS THE MARIANAS AND AS IT
PUSHES OFF TO THE WEST OF THE ISLANDS AROUND TUESDAY NIGHT,
POTENTIALLY BRINGING ANOTHER PERIOD OF SCATTERED SHOWERS AROUND THE
MIDDLE OF NEXT WEEK.
MARINE/SURF...
BENIGN MARINE CONDITIONS CONTINUE THROUGH THE MIDDLE OF NEXT WEEK
WITH LIGHT TO GENTLE TRADE WINDS AND COMBINED SEAS OF 2 TO 4 FEET
EXPECTED. NORTHEASTERLY SWELL DIMINISHES OVER THE WEEKEND, WITH
EASTERLY TRADE SWELL CONTINUING THROUGH NEXT WEEK. THERE WILL BE A
LOW RISK OF RIP CURRENTS ALONG ALL REEFS THROUGH SATURDAY NIGHT, THEN
A MODERATE RIP RISK MAY RETURN ALONG EAST-FACING REEFS AS EASTERLY
TRADE SWELL BECOMES THE PRIMARY SWELL SUNDAY.
EASTERN MICRONESIA...
THE MAIN FEATURE OF INTEREST IS A SURFACE TROUGH THAT DEVELOPED
YESTERDAY AND HAS STRENGTHENED SINCE THEN. THIS WAS NOT EXPECTED AND
AS A RESULT OF ITS STRENGTHENING, THE TROUGH ALLOWED SUFFICIENT
MOISTURE TO POOL ALONG THE TROUGH WHERE CONVERGENCE WAS MAXIMIZED.
THIS RESULTED IN A MORNING FORECAST UPDATE TO INCREASE SHOWER
COVERAGE TO SCATTERED AT POHNPEI, WHICH WE EXTENDED INTO TONIGHT AS
THE TROUGH IS STILL DIRECTLY OVERHEAD WITH LITTLE MOVEMENT. THE REAL
QUESTION IS WILL THIS FEATURE REMAIN QUASI-STATIONARY IN ITS WEST-
SOUTHWEST TO EAST-NORTHEAST FASHION ANOTHER 24 HOURS? IF IT CAN, THEN
A LEADING AREA OF SURFACE CONVERGENCE A LITTLE EAST OF MAJURO COULD
CATCH UP TO THIS BOUNDARY BY THEN, PERHAPS ALLOWING FOR ITCZ
GENESIS/RENEWED DEVELOPMENT. SHOULD THIS NOT OCCUR, AT THE VERY
LEAST THE AREA OF CONVERGENCE EAST OF MAJURO WILL AT LEAST BRING
BRIEFLY-INCREASED RAINFALL POTENTIAL TO PORTIONS OF EASTERN
MICRONESIA THROUGH THE WEEKEND.
OTHERWISE, MARINERS CAN EXPECT MAINLY LIGHT TO GENTLE WINDS, BUT THEY
MAY BRIEFLY INCREASE INTO THE GENTLE TO MODERATE RANGE THIS WEEKEND
AS CONVECTION WITH THE MAJURO DISTURBANCE MOVES THROUGH THE REGION.
SEAS OF 3 TO 5 FEET WILL ALSO INCREASE INTO THE 4 TO 6 FOOT RANGE BY
EARLY NEXT WEEK.
WESTERN MICRONESIA...
A FAIRLY DRY AND LIGHT WIND PATTERN EXTENDS ACROSS PALAU, YAP AND
CHUUK, WITH SOUTHEAST TO SOUTH WINDS OVER YAP AND SOUTH TO SOUTHWEST
WINDS OVER PALAU, DRIVEN BY A WEAK CIRCULATION WEST OF 130E AND A
SURFACE TROUGH EXTENDING SLIGHTLY INTO THE REGION, NORTH OF PALAU.
FURTHER EAST, A WEAK RIDGE OF HIGH PRESSURE IS DEVELOPING ACROSS YAP
STATE AND SOUTH OF THE MARIANAS, CAUSING THE TRADE-WINDS OVER CHUUK
TO BE LIGHT. ANY SHOWERS IN THE REGION ARE CURRENTLY ASSOCIATED WITH
WEAK CONVERGENCE JUST ALONG 10N, NORTH OF YAP, AND A TRADE-WIND
TROUGH WELL EAST OF CHUUK, NEAR POHNPEI. FOR PALAU AND YAP, SINCE
WINDS ARE EXPECTED TO REMAIN LIGHT OVER THE NEXT FEW DAYS, THERE WILL
BE THE POTENTIAL FOR ISLAND-EFFECT SHOWERS AND THUNDERSTORMS DURING
THE LATE MORNING AND AFTERNOON HOURS, ESPECIALLY FOR PALAU WHERE
SOUTH TO SOUTHWEST WINDS WILL FAVOR DEVELOPMENT OVER THE LARGER
ISLAND OF BABELDAOB. ALSO, AS THE SURFACE TROUGH SHIFTS WEST-
NORTHWEST, MODELS SHOW SOME WEAK CONVERGENT FLOW DEVELOPING NEAR
PALAU AND YAP, WHICH MAY PRODUCE SOME PERIODS OF SCATTERED SHOWERS
THIS WEEKEND UNLESS THE RIDGE SHIFTS OVER THE ISLANDS. THEN EARLY
NEXT WEEK, A WEAK DISTURBANCE TO PASS THROUGH THE MARIANAS AND THEN
NORTH OF PALAU AND YAP, WHICH WILL LIKELY BE THE NEXT MAIN POTENTIAL
FOR SHOWERS AND THUNDERSTORMS IN THE AREA. FOR CHUUK, AS THE TROUGH
NEAR POHNPEI SHIFTS WESTWARD, THE POTENTIAL FOR SHOWERS WILL
INCREASING THROUGH THE DAY SATURDAY AND CONTINUE INTO SUNDAY.
OTHERWISE A FAIRLY QUIET TRADE-WIND PATTERN IS EXPECTED INTO NEXT
WEEK, WITH ANY SHOWERS AND THUNDERSTORMS ASSOCIATED WITH PASSING
TRADE-WIND TROUGHS.
COMBINED SEAS OF 3 TO 5 FEET ARE EXPECTED TO CONTINUE ACROSS THE
REGION WITH LIGHT TO GENTLE WINDS OVER THE NEXT FEW DAYS. WINDS MAY
BECOME MODERATE AT CHUUK EARLY NEXT WEEK AS THE TRADE-WIND PATTERN
STRENGTHENS SLIGHTLY.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: KLEESCHULTE
MARIANAS: CRUZ
EAST MICRONESIA: DOLL
WEST MICRONESIA: SCHANK
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