023
FXPQ50 PGUM 041904
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
504 AM CHST FRI SEP 5 2025
MARIANAS UPDATE
PARTLY CLOUDY SKIES AND SPOTTY SHOWERS ARE FOUND ACROSS GUAM, ROTA,
TINIAN AND SAIPAN THIS MORNING. THUNDERSTORMS ARE FOUND NORTH OF
SAIPAN, AND A LARGE CLUSTER OF SHOWERS AND THUNDERSTORMS ARE PRESENT
SOUTHEAST OF GUAM. COMBINED SEAS ACROSS THE MARIANAS ARE HOLDING
STEADY AROUND 3 FEET.
THE TROPICAL UPPER-TROPOSPHERIC TROUGH (TUTT) REMAINS IN THE REGION,
STRETCHED ACROSS THE NORTHERN CNMI. THE TUTT ALONG WITH A PASSING
SURFACE TROUGH WILL KEEP A MIX OF SUN, SHOWERS, AND ISOLATED
THUNDERSTORMS IN THE FORECAST THE NEXT FEW DAYS. PASSING SHOWERS
COULD BE LOCALLY HEAVY AT TIMES, COURTESY OF THE TUTT TO THE NORTH.
LITTLE CHANGE EXPECTED OVER THE COASTAL WATERS, BUT A LONGER-PERIOD
NORTH SWELL COULD BUILD IN NEXT WEEK.
EASTERN MICRONESIA UPDATE
THE INHERITED THURSDAY AFTERNOON FORECAST IS HOLDING STEADY FOR THE
REGION WITH SHOWERS AND THUNDERSTORMS TAPERING ACROSS KOSRAE AND
PUSHING THROUGH POHNPEI THIS MORNING. THE SURFACE TROUGH OVER POHNPEI
WILL CONTINUE WESTWARD WITH RELATIVELY FAIR WEATHER ACROSS THE
MARSHALLS BUILDING WESTWARD ACROSS THE EASTERN FSM FOR THE WEEKEND.
THE ITCZ COULD BRING MORE SHOWERS TO THE REGION NEXT WEEK. EXPECTED
MODERATE TRADES AND COMBINED SEAS OF 4 TO 6 FT TO CONTINUE THROUGH
THE WEEKEND.
WESTERN MICRONESIA UPDATE
ONLY SMALL CHANGES WERE MADE TO THE YAP FORECAST FOR TODAY TO INCREASE
SHOWERS AND THUNDERSTORMS FOR YAP TODAY. A SURFACE TROUGH NEAR THE
MARIANAS WILL PUSH WESTWARD THROUGH YAP TODAY BRINGING THOSE SHOWERS
AND THUNDERSTORMS. FARTHER EAST, FAIR WEATHER AT CHUUK WILL GIVE WAY
TO CLOUDS AND MORE SHOWERS THIS MORNING AS A SURFACE TROUGH NEAR
POHNPEI APPROACHES.
PREV DISCUSSION
/ISSUED 716 PM CHST THU SEP 4 2025/
MARIANAS SYNOPSIS...
RADAR AND SATELLITE IMAGERY SHOW A CLUSTER OF SHOWERS AND
THUNDERSTORMS EXTENDING ACROSS NORTHWESTERN GUAM WATERS AND
SOUTHWESTERN ROTA WATERS. RITIDIAN AND IPAN BUOYS INDICATE SEAS
AROUND 3 FEET.
DISCUSSION...
PASSING TRADE-WIND TROUGHS AS WELL AS SOME SUPPORT FROM THE TROPICAL
UPPER-TROPOSPHERIC TROUGH (TUTT) TO THE NORTH, ARE EXPECTED TO
GENERATE SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE
REGION THROUGH AT LEAST SUNDAY. THEN A MIXTURE OF ISOLATED TO
SCATTERED SHOWERS ARE EXPECTED STARTING SUNDAY NIGHT. MODEL GUIDANCE
SHOWS AN EMBEDDED TUTT CELL MAY MOVE ACROSS THE NORTHERN CNMI NEXT
WEEK, POSSIBLY INCREASING THUNDERSTORM POTENTIAL ONCE AGAIN.
MARINE/SURF...
LIGHT TO MODERATE WINDS WILL PERSIST THROUGH TONIGHT, THEN BECOMING
LIGHT TO GENTLE THROUGH MONDAY. RITIDIAN BUOY SHOWS COMBINED SEAS
AROUND 3 FEET AND A MIXTURE OR PRIMARY TRADE SWELL AND LIGHT NORTH
SWELL. WAVE MODELS HINT THAT SWELLS MAY SUBSIDE SLIGHTLY OVER THE
WEEKEND, BRINGING THE SEAS DOWN TO BETWEEN 2 AND 3 FEET. THEN,
ANOTHER PULSE OF NORTH SWELL MAY ARRIVE AROUND TUESDAY. CURRENTLY,
GFS WAVE MODEL IS AN OUTLIER AND IS SUGGESTING A SIGNIFICANT NORTH
SWELL, BUT HAVE KEPT IT AT AROUND 2 FEET AND 13 SECONDS UNTIL THERE
IS MORE MODEL CONSENSUS IN COMING DAYS.
EASTERN MICRONESIA...
SATELLITE IMAGERY THIS AFTERNOON SHOWS SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS, ASSOCIATED WITH A FRAGMENTED INTERTROPICAL
CONVERGENCE ZONE, EXTENDING ACROSS SOUTHERN POHNPEI STATE, THROUGH
KOSRAE, AND INTO THE MARSHALL ISLANDS WHERE SHOWERS ARE MAINLY NEAR
AND NORTH OF MAJURO. AS THE ITCZ SHIFTS WESTWARD OVERNIGHT, THE
SCATTERED SHOWERS NEAR MAJURO WILL PULL AWAY TO THE WEST, AND THE
POTENTIAL FOR ISOLATED THUNDERSTORMS IS ALSO EXPECTED TO DECREASE AS
RECENT LOOPS OF THE TPW SATELLITE IMAGERY SHOW DRIER AIR, WITH
PRECIPITAL WATER (PWAT) VALUES AROUND 1.8 TO 2.0 INCHES, MOVING
CLOSER TO MAJURO AND REPLACING THE MOISTER AIR WITH VALUES AROUND 2.3
INCHES. SHOWERS ARE ALSO EXPECTED TO DECREASE AT KOSRAE EARLY FRIDAY
MORNING BUT THE POTENTIAL FOR THUNDERSTORMS WILL LINGER DUE THE
MOIST AIR WITH PWATS AROUND 2.3 INCHES. AS THE SCATTERED SHOWERS NEAR
KOSRAE MOVE WEST-NORTHWEST, THEY ARE EXPECTED TO LIFT INTO POHNPEI
LATER TONIGHT AND INTO FRIDAY. THE FRAGMENTED ITCZ IS EXPECTED TO THEN
WEAKEN AND BECOME MORE OF A SURFACE TROUGH WEST OF POHNPEI AS
CONVERGENCE ALONG THE FEATURE WEAKENS. THIS WILL LEAD TO DRIER WEATHER
ACROSS POHNPEI AND KOSRAE FRIDAY NIGHT THROUGH SATURDAY NIGHT.
MEANWHILE, MODELS SHOW THE PORTION OF ITCZ IN THE CENTRAL PACIFIC
BUILDING WESTWARD AND CROSSING THE DATE LINE THIS WEEKEND. THIS IS
EXPECTED TO BRING SCATTERED SHOWERS TO MAJURO SATURDAY, AND TO
POHNPEI AND KOSRAE AROUND SUNDAY. THE ECMWF SHOWS THE NEW ITCZ
REMAINING COHERENT INTO TUESDAY, KEEPING A WETTER PATTERN ACROSS THE
REGION, BUT THE GFS SUGGESTS THIS ITCZ WILL ALSO FRAGMENT LEADING TO
MORE VARIABLE WEATHER ACROSS THE REGION. FOR NOW THE FORECAST FOR
NEXT WEEK FOLLOWS THE OVERALL BLEND OF MODEL GUIDANCE, SUPPORTING A
PERIOD WETTER WEATHER BUT WINDS REMAINING GENTLE TO MODERATE.
BUOY AND ALTIMETRY DATA SHOW SEAS ARE 4 TO 6 FEET ACROSS THE REGION,
WITH GENTLE TO MODERATE TRADE WINDS ACCORDING TO SATELLITE
SCATTEROMETER DATA. SEAS AND AND SWELL ARE NOT EXPECTED TO CHANGE
THROUGH THE WEEKEND AND WINDS REMAIN MOSTLY GENTLE TO MODERATE ACROSS
THE REGION. THE GFS WAVE IS STARTING TO SUGGEST A NORTH SWELL WILL
ENTER THE REGION BY THE MIDDLE OF NEXT WEEK, BUT THIS WILL LARGELY
DEPEND ON IF A SYSTEM DEVELOPS AND STRENGTHENS EAST OF JAPAN OVER
THE NEXT FEW DAYS.
WESTERN MICRONESIA...
A DRIER TRADE-WIND REGIME IS EXPECTED TO CONTINUE ACROSS THE REGION
OVERNIGHT, FOLLOWED BY A LEADING EDGE OF AN ITCZ THAT WILL BRING
PATCHY SHOWERS AND SOME THUNDERSTORMS TO CHUUK DURING THE WEEKEND.
THE ITCZ FRAGMENT IS EXPECTED TO WEAKEN SLIGHTLY AND REMAIN LARGELY
SOUTH OF PALAU AND YAP, BRINGING ONLY LOW-END SCATTERED SHOWERS TO
THE AREA BY EARLY NEXT WEEK.
COMBINED SEAS OF 3 TO 4 FEET ARE EXPECTED ACROSS MUCH OF WESTERN
MICRONESIA THROUGH THE WEEKEND AND THE FIRST HALF OF NEXT WEEK,
CONSISTING PRIMARILY OF A BACKGROUND TRADE SWELL.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: AYDLETT
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