206
FXPQ50 PGUM 132001
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
601 AM CHST SUN SEP 14 2025
MARIANAS UPDATE
SATELLITE IMAGERY SHOWS PARTLY SUNNY SKIES (SAME AS LOW-END MOSTLY
CLOUDY) WITH ISOLATED SHOWERS OVER THE MARIANAS WATERS. HOWEVER, JUST
TO THE EAST ARE SCATTERED SHOWERS MOVING TOWARD US, ALONG WITH
ISOLATED THUNDERSTORMS. THEREFORE, THE FORECAST ALREADY OUT THERE,
WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS, LOOKED GOOD AND
DID NOT NEED ANY CHANGES.
EASTERN MICRONESIA UPDATE
FORECAST WAS IN GOOD SHAPE OVERALL. ONLY MINOR TWEAK WAS TO INCREASE
THE CLOUDINESS AT MAJURO. THIS MADE THEM PARTLY SUNNY WITH ISOLATED
SHOWERS, VERSUS PARTLY CLOUDY. NO OTHER CHANGES WERE NEEDED, STILL
EXPECTING SHOWERS TO INCREASE AT POHNPEI AND TO BE LOW-END SCATTERED
AT KOSRAE.
WESTERN MICRONESIA UPDATE
FORECAST WAS ALSO IN GOOD SHAPE OVERALL HERE. ONLY MINOR TWEAK WAS
SIMILAR TO EASTERN MICRONESIA, INCREASED THE CLOUDS AT YAP, SO THEY
ARE NOW PARTLY SUNNY WITH ISOLATED SHOWERS VERSUS PARTLY CLOUDY. LEFT
CHUUK AND KOROR ALONE WITH PARTLY SUNNY AND SCATTERED SHOWERS FOR
TODAY. THE SCATTERED SHOWERS WILL BE LOW-END AT KOROR, BUT A FAIRLY
VIGOROUS LINE IS APPROACHING CHUUK. WE MAY NEED TO WATCH THEM FOR
ADDING THUNDERSTORMS IF THE ACTIVITY ON THAT LINE STARTS TO INCREASE.
PREV DISCUSSION
/ISSUED 545 PM CHST SAT SEP 13 2025/
MARIANAS SYNOPSIS...
SATELLITE IMAGERY SHOWS PARTLY CLOUDY TO MOSTLY CLOUDY SKIES, WHILE
RADAR IMAGERY SHOWER ISOLATED SHOWERS WITHIN THE MARIANAS AND
ADJACENT COASTAL WATERS. JUST OUTSIDE THE WATERS SHOWERS ARE
INCREASES AND MOVING WESTWARD TOWARDS GUAM AND ROTA'S COASTAL WATERS.
ALTIMETRY SHOWS COMBINED SEAS OF 2 TO 4 FEET AND RITIDIAN AND IPAN
BUOYS SHOW AROUND 3 FEET.
DISCUSSION...
THROUGH THE BEGINNING OF NEXT WEEK, PASSING SURFACE TROUGHS WILL BE
INTERACTING WITH A TROPICAL UPPER-TROPOSPHERIC TROUGH (TUTT) BRANCH.
THIS COMBINATION IS EXPECTED TO PRODUCE SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS FOR THE REGION. HOWEVER, THESE SHOWERS ARE NOT
EXPECTED TO DROP THE TEMPERATURE DOWN ENOUGH TO RULE OUT ISLAND
ENHANCEMENT IN THE AFTERNOON. THIS MEANS, ISLAND-EFFECT SHOWERS AND
THUNDERSTORMS ARE POSSIBLE ONCE DAYTIME HEATING BECOMES MAXIMIZED.
MODEL GUIDANCE SUGGESTS, NEAR THE MIDDLE OF THE WEEK THIS WET PATTERN
SHOULD BECOME A BIT DRIER, AND WEATHER MAY BECOME MORE PLEASANT.
MARINE...
BENIGN MARINE CONDITIONS CONTINUE THROUGH THE MIDDLE OF NEXT WEEK
WITH COMBINED SEAS AROUND 2 TO 4 FEET EXPECTED. NORTHEASTERLY SWELL
WILL DIMINISH OVER THE WEEKEND, WITH EASTERLY TRADE SWELL CONTINUING
THROUGH NEXT WEEK. WINDS ARE EXPECTED TO BE LIGHT TO MODERATE AND
WILL BECOME LIGHT TO GENTLE AROUND THE BEGINNING OF NEXT WEEK. THERE
WILL BE A MODERATE RISK OF RIP CURRENTS ALONG EAST FACING REEFS AND
LOW RISK ON ALL OTHER REEFS THROUGH SUNDAY NIGHT. THEN, A LOW RIP
RISK MAY RETURN ALONG EAST-FACING REEFS AROUND MONDAY OR TUESDAY
BECAUSE THE PRIMARY EAST SWELL IS EXPECTED TO DECREASE. THERE WILL
ALSO BE A MODERATE RISK OF LIGHTNING THROUGH THE MIDDLE OF NEXT WEEK.
EASTERN MICRONESIA...
A BROAD SURFACE TROUGH AT THE LEADING EDGE OF THE INTERTROPICAL
CONVERGENCE ZONE (ITCZ) IS GENERATING SCATTERED SHOWERS ACROSS
KOSRAE AND STRETCHES FARTHER NORTHEAST ACROSS MAJURO AND THE NORTHERN
MARSHALLS. SCATTEROMETRY DATA SHOWS LIGHT TO GENTLE TRADES WITH
MAINLY MODERATE WINDS TO THE SOUTHEAST OF THE AXIS, OVER KIRIBATI.
THIS TROUGH IS EXPECTED TO GRADUALLY MOVE WESTWARD, MAINTAINING
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS THROUGH SUNDAY EVENING
FOR KOSRAE, AND BRINGING AN UPTICK IN SHOWERS FOR POHNPEI SUNDAY
AFTERNOON THROUGH MONDAY. SCATTERED SHOWERS OVER MAJURO THIS
AFTERNOON ARE EXPECTED TO TREND BACK DOWN TO ISOLATED SUNDAY, THEN
THE ITCZ PATTERN MAY BEGIN TO BUILD BACK IN MONDAY AND FURTHER
EXTEND INTO KOSRAE AND POHNPEI AROUND THE MIDDLE OF THIS UPCOMING
WEEK.
BUOY AND ALTIMETRY REVEAL 3 TO 5 FOOT COMBINED SEAS ACROSS THE
REGION, COMPRISED MOSTLY OF EAST TO SOUTHEASTERLY SWELL. THERE IS
WEAKER, LONG-PERIOD SWELL EMANATING FROM THE SOUTHERN HEMISPHERE OVER
THE NEXT SEVERAL DAYS, BUT MAGNITUDES ARE NOT SIGNIFICANT ENOUGH TO
IMPACT SEAS OR SURF AT THIS TIME. OVERALL, BENIGN MARINE CONDITIONS
CONTINUE, WITH LIGHT TO GENTLE WINDS INCREASING SLIGHTLY TO LIGHT TO
MODERATE ON SUNDAY.
WESTERN MICRONESIA...
A COUPLE OF SURFACE TROUGHS, ONE NORTH OF YAP AND THE OTHER NORTH OF
CHUUK LAGOON, ARE GENERATING SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS THIS EVENING. SHOWERS ALONG THE TROUGH NORTH OF YAP
BUILT INTO YAP PROPER EARLIER TODAY AND ARE CURRENTLY ON THE DOWN
TREND OVER THE ISLAND. HOWEVER, CONVERGENT FLOW TO THE EAST IS
STARTING TO TRIGGER NEW SHOWERS NEAR ULITHI AND FAIS SO ADDITIONAL
SHOWERS AND POTENTIALLY SOME ISOLATED THUNDERSTORMS ARE EXPECTED
TONIGHT. THE SHOWERS ASSOCIATED WITH THE TROUGH NORTH OF CHUUK LAGOON
HAVE REMAINED NORTH OF WENO, BUT SATELLITE IMAGERY IS STARTING TO
SHOW SOME CUMULUS CLOUDS DEVELOPING TO EAST, ALONG WEAK CONVERGENT
FLOW EXTENDING FROM THE TROUGH. IF THIS AREA OF CUMULUS CONTINUES TO
DEVELOP INTO SHOWERS AND SHIFT WESTWARD, FOLLOWING THE SURFACE
TROUGH, THEN SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS SHOULD
MOVE INTO CHUUK LAGOON LATER TONIGHT. AT PALAU, LIGHT WINDS DID LEAD
TO SOME ISLAND-EFFECT SHOWERS OVER THE THE LARGER ISLAND OF BABELDAOB
DURING THE AFTERNOON HOURS, BUT IT LOOKS LIKE MOST OF THESE SHOWERS
WERE SHORT-LIVED DUE TO OUTFLOW GENERATED BY THE SAME SHOWERS,
HELPING TO PREVENT THUNDERSTORMS FROM DEVELOPING. AS THE SUN SETS,
THE POTENTIAL FOR ISLAND-EFFECT CONVECTION WILL DIMINISH AS HEATING
FROM THE SUN DECREASES. TO THE SOUTHEAST OF PALAU, THERE IS A VERY
LOOSE CLUSTER OF SHOWERS ARE DEVELOPING ALONG A WEAK CONVERGENT
BOUNDARY GENERATED BY LIGHT SOUTH TO SOUTHWEST FLOW MEETING LIGHT
SOUTHEAST FLOW. MODELS SHOW THIS AREA OF CONVERGENCE LIFTING WEST
NORTHWEST, POTENTIALLY GENERATING SOME SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS AT PALAU LATER TONIGHT AND INTO SUNDAY.
FOR PALAU AND YAP, THE LONG-TERM FORECAST REMAINS MOSTLY UNCHANGED.
BESIDES FOR THE POTENTIAL FOR ISLAND-EFFECT DUE TO LIGHT WINDS DURING
THE LATE MORNING TO AFTERNOON HOURS, AN OVERALL DRIER PATTERN WILL
CONTINUE INTO THE BEGINNING OF THE UPCOMING WEEK. THEN, THE NEXT
DISTURBANCE WILL APPROACH PALAU AND YAP AROUND THE MIDDLE OF THE WEEK,
AFTER PASSING NEAR THE MARIANAS, BRINGING THE NEXT MAIN POTENTIAL
FOR SHOWERS AND THUNDERSTORMS. FOR CHUUK, AS THE INTERTROPICAL
CONVERGENCE ZONE (ITCZ) DEVELOPS IN EASTERN MICRONESIA, MODELS
SUPPORT THE OVERALL POTENTIAL FOR SHOWERS AND THUNDERSTORMS TO
INCREASE AROUND MONDAY NIGHT OR TUESDAY AS THE ITCZ LIFTS WEST-
NORTHWEST INTO CHUUK WHILE ALSO INCREASING WINDS SLIGHTLY TO MODERATE
(~15 KT) AT TIMES. OTHERWISE, FOR SUNDAY AND MONDAY, EXPECT A
MIXTURE OF SUNSHINE AND SHOWERS WITH LIGHT TO GENTLE WINDS AS WEAK
TRADE-WIND TROUGHS PASS THROUGH REGION.
ALTIMETRY DATA SHOWS SEAS ARE AROUND 2 TO 3 FEET AROUND PALAU AND YAP
AND UP TO 4 FEET AROUND CHUUK. WINDS ARE STILL FAIRLY LIGHT ACROSS
THE REGION WITH THE PRIMARY SWELL BEING EAST-NORTHEAST. MARINE
CONDITIONS ARE NOT EXPECTED TO CHANGE MUCH AT PALAU AND YAP OVER THE
NEXT FEW DAYS BESIDES FOR WINDS BECOMING MORE SOUTHEAST TO EAST THIS
UPCOMING WEEK. SEAS MAY BUILD SLIGHTLY AT CHUUK AROUND TUESDAY AS
WINDS INCREASE SLIGHTLY AS THE ITCZ SHIFTS INTO CHUUK FROM EASTERN
MICRONESIA.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: STANKO
MARIANAS: BOWSHER
EAST MICRONESIA: CRUZ
WEST MICRONESIA: SCHANK
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