900
FXPQ50 PGUM 071918
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
518 AM CHST MON SEP 8 2025
MARIANAS UPDATE
SATELLITE SHOWS PARTLY CLOUDY SKIES WITH ISOLATED SHOWERS MOVING IN,
AND SCATTERED SHOWERS WITH ISOLATED THUNDERSTORMS DEPARTING. THIS WAS
A REASONABLY GOOD MATCH FOR CURRENT GRIDS, SO NO CHANGES WERE MADE.
EASTERN MICRONESIA UPDATE
ONLY SLIGHT CHANGES WERE NEEDED. DIMINISHED THE SHOWERS AT KOSRAE AS
THEY HAVE A CLEARER PATCH THERE FOR A BIT. OTHERWISE THE FORECAST WAS
IN FINE SHAPE.
WESTERN MICRONESIA UPDATE
NO CHANGES NEEDED FOR THE WESTERN MICRONESIA FORECAST. TRADE-WIND
TROUGHS WILL ROLL THROUGH WITH BOUTS OF HIGHER SHOWER AND SUN,
MIXED TOGETHER. THIS WAS WELL COVERED, ESPECIALLY FOR TODAY.
PREV DISCUSSION
/ISSUED 548 PM CHST SUN SEP 7 2025/
MARIANAS SYNOPSIS...
SATELLITE IMAGERY SHOWS PARTLY CLOUDY SKIES, WHILE RADAR SHOWS A FEW
ISOLATED SHOWERS OVER THE REGION. ALTIMETRY SHOWS 2 TO 3 FEET TO THE
WEST OF THE MARIANAS, WHILE THE RITIDIAN BUOY SHOWS ALMOST 3 FOOT
SEA HEIGHTS.
DISCUSSION...
MOSTLY PLEASANT WEATHER IS IN STORE FOR THE MARIANAS, ISOLATED
SHOWERS ARE EXPECTED THROUGH THE FORECAST PERIOD. ISLAND INDUCED
THUNDERSTORMS ARE POSSIBLE FOR MONDAY. A WEAK TROUGH IS ANTICIPATED
TO GRADUALLY MOVE INTO THE REGION AROUND THE MIDDLE OF THE WEEK.
PROBABILITY OF PRECIPITATION (POPS) ARE EXPECTED TO HOVER AROUND THE
20 TO 30 PERCENT RANGE. SHOWERS MAY LINGER THROUGH THE REST OF THE
WEEK.
MARINE...
LIGHT TO GENTLE TRADE WINDS WILL PREVAIL ACROSS THE REGION THROUGH
WEDNESDAY, THEN BECOME GENTLE TO MODERATE. COMBINED SEAS OF AROUND 3
FEET WILL GRADUALLY BUILD UP TO AROUND 5 FEET BY TUESDAY NIGHT. THIS
WILL BE DUE PRIMARILY TO TRADE AND NORTHERLY SWELLS, ALONG WITH
LOCALIZED WIND WAVES, STRENGTHENING AROUND MIDWEEK. SURF ALONG ALL
REEFS ARE CURRENTLY BELOW 5 FEET. THE RISK OF RIP CURRENTS IS LOW ON
ALL REEFS. SURF MAY BUILD AROUND THE MIDDLE OF THE WEEK AND ALLOW
THE RISK OF RIP CURRENTS TO INCREASE TO MODERATE ALONG EAST FACING
REEFS. A MODERATE RISK OF LIGHTNING WILL REMAIN THROUGH MONDAY, THEN
BECOME MODERATE AGAIN AROUND WEDNESDAY.
EASTERN MICRONESIA...
THE DRY TRADE-WIND PATTERN HAS ERODED ACROSS EASTERN MICRONESIA THIS
AFTERNOON. THIS IS DUE TO A WEAK INTER-TROPICAL CONVERGENCE ZONE
(ITCZ) OVER THE AREA COMBINED WITH STRONG UPPER-LEVEL DIVERGENCE AND
A COUPLE OF WEAK TRADE-WIND TROUGHS MOVING THROUGH. THE FIRST OF THE
TROUGHS IS NOW EAST OF POHNPEI WITH INCREASING CONVECTION SEEN
MOVING OVER THE ISLAND. POPS WERE INCREASED TO THE 50% RANGE FOR
TONIGHT AS THE TROUGH MOVES THROUGH. FOR KOSRAE, SHOWER COVERAGE
LOOKS TO REMAIN LOWER, THOUGH POPS WERE INCREASED TO COVER LOW-END
SCATTERED SHOWERS (30%) THROUGH MONDAY. MONDAY EVENING IS THE TIME
FRAME WHEN THE ITCZ LOOKS TO BECOME MOST ACTIVE. SINCE THE LOCATION
OF THE ITCZ HAS BECOME MORE OBVIOUS, DECIDED TO GO AHEAD AND INCREASE
SHOWERS TO NUMEROUS ACROSS POHNPEI AND KOSRAE MONDAY NIGHT INTO
TUESDAY. HOWEVER, HEAVY RAINFALL IS NOT EXPECTED AT THIS TIME. FOR
MAJURO, THE BULK OF THE CONVECTION LOOKS TO REMAIN SOUTH OF THE
ATOLL, SO KEPT SHOWERS SCATTERED THROUGH THE FORECAST PERIOD.
ISOLATED THUNDERSTORMS ARE ALSO EXPECTED AT ALL THREE FORECAST POINTS
THROUGH TUESDAY NIGHT FOR KOSRAE AND THROUGH WEDNESDAY FOR POHNPEI
AND MAJURO. BY MIDWEEK, THE ITCZ LOOKS TO LIFT NORTHWARD, ALLOWING A
DRIER PATTERN TO MOVE INTO KOSRAE WEDNESDAY AND INTO POHNPEI AND
MAJURO THURSDAY.
NO MAJOR CHANGES TO THE MARINE FORECAST. COMBINED SEAS OF 5 FEET OR
LESS AND LIGHT TO GENTLE TRADE WINDS ARE EXPECTED TO CONTINUE THROUGH
THE WEEK.
WESTERN MICRONESIA...
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE MOVING INTO PALAU
THIS EVENING AS A BROAD AND WEAK SURFACE TROUGH PASSES NEARBY. THIS
TROUGH HAS SHIFTED SLIGHTLY FURTHER SOUTH THEN PREVIOUSLY EXPECTED SO
SHOWERS ARE ISOLATED AT YAP, BUT CONVERGENT FLOW NORTH OF THE TROUGH
IS STARTING TO PRODUCE SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
JUST NORTH 10N, FROM 138E TO 143E, PASSING NEAR ULITHI. MODEL
GUIDANCE SHOWS THIS AREA OF SHOWERS EXPANDING INTO YAP LATER TONIGHT
AS THE AREA OF CONVERGENCE STRENGTHS. MODELS THEN SHOW THE AREA OF
CONVERGENCE WEAKENING MONDAY MORNING AND THEN BRIEFLY REBUILDING
MONDAY NIGHT AS THE SURFACE TROUGH MOVES WEST OF THE ISLANDS AND THEN
STARTS TO LIFT NORTHWEST. AS THE TROUGH MOVES AWAY, A LIGHT TO
GENTLE TRADE-WIND WILL CONTINUE ACROSS PALAU AND YAP, WITH A SLIGHT
DECREASE IN THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS OVERALL
THROUGH TUESDAY NIGHT. HOWEVER, SINCE WINDS WILL BE ON THE LIGHTER
SIDE, THERE IS THE POTENTIAL FOR ISLAND-EFFECT SHOWERS AND
THUNDERSTORMS DURING THE LATE MORNING TO AFTERNOON HOURS, ESPECIALLY
AT PALAU, AS SHOWERS START TO DEVELOP OVER THE ISLAND AND THEN ARE
PUSHED INTO THE WESTERN COASTAL WATERS, SO KEPT THE POTENTIAL FOR
SHOWERS AROUND 20% TO 30%. STARTING WEDNESDAY, AN ITCZ FRAGMENT, OR
A TROUGH BREAKING OFF OF THE ITCZ IN EASTERN MICRONESIA, IS EXPECTED
TO MOVE INTO YAP AND PALAU, INCREASING THE POTENTIAL SHOWERS AND
THUNDERSTORMS THROUGH FRIDAY TO AROUND 30% TO 40%.
AT CHUUK, SATELLITE IMAGERY SHOWS PARTLY CLOUDY SKIES AND ISOLATED
SHOWERS ACROSS MOST OF THE STATE. A TROUGH, ALONG THE LEADING EDGE OF
OF THE ITCZ IN EASTERN MICRONESIA IS EXPECTED TO DRIFT WESTWARD
OVERNIGHT. MODELS GUIDANCE SUGGEST THE POTENTIAL FOR SHOWERS WILL
INCREASE SLIGHTLY FROM 20% TO 30% AFTER MIDNIGHT, BUT THE MAIN
POTENTIAL FOR SHOWERS AND THUNDERSTORMS WILL BE MONDAY THROUGH
TUESDAY, WITH THE POTENTIAL OF SHOWERS INCREASING TO 40% TO 50% FOR
THAT TIME PERIOD AS THE ITCZ EXTENDS INTO CHUUK STATE FROM POHNPEI.
THOUGH WINDS ARE EXPECTED TO BE LIGHT TO GENTLE FOR MOST OF THE WEEK,
GUSTY WINDS MAY BE POSSIBLE NEAR SHOWERS. AROUND WEDNESDAY, THE ITCZ
IS EXPECTED TO LIFT NORTHWARD, THIS WILL DECREASE THE POTENTIAL FOR
SHOWERS TO AROUND 30% ACROSS CHUUK STATE TROUGH FRIDAY.
ALTIMETRY DATA SHOWS BENIGN SEAS OF 2 TO 3 FEET NEAR YAP AND PALAU
AND 3 TO 4 FEET NEAR CHUUK. COMBINED SEAS ARE EXPECTED TO INCREASE TO
3 TO 5 FEET AROUND THE MIDDLE OF THE WEEK WHEN A PULSE OF NORTHERLY
SWELL MOVES THROUGH THE REGION.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: STANKO
MARIANAS: BOWSHER
EAST MICRONESIA: KLEESCHULTE
WEST MICRONESIA: SCHANK
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page