243
FXPQ50 PGUM 101938
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
538 AM CHST MON AUG 11 2025
MARIANAS UPDATE
MADE VERY LITTLE CHANGES TO THE FORECAST OVERNIGHT. THE UPPER-LEVEL
DIVERGENCE ASSOCIATED WITH THE TUTT (TROPICAL UPPER TROPOSPHERIC
TROUGH) PRODUCED SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS
THE MARIANAS EARLIER IN THE NIGHT, BUT THE CORE OF SHOWERS AND
THUNDERSTORMS HAS SHIFTED EASTWARD, TOWARDS THE CENTER OF THE TUTT
EARLY THIS MORNING, GIVING A RESPITE FROM THE CONVECTION. GIVEN THE
PROXIMITY OF THE TUTT AND ITS EXPECTED SHIFT TO THE WEST-SOUTHWEST,
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED TODAY. ALSO
WINDS ARE EXPECTED TO REMAIN LIGHT THE NEXT FEW DAYS SO FOR GUAM,
ISLAND CONVECTION WILL BE POSSIBLE DURING THE AFTERNOONS OF TUESDAY
AND WEDNESDAY, AND COULD OCCUR AGAIN ON THURSDAY. OTHERWISE, A DRY
TRADE-WIND PATTERN IS EXPECTED TUESDAY NIGHT THROUGH THE WEEKEND.
SEA CONDITIONS REMAIN BENIGN WITH COMBINED SEAS OF 3 TO 5 FEET. SEAS
WILL SLOWLY SUBSIDE, DROPPING TO BETWEEN 2 AND 3 FEET BY THURSDAY.
LIGHT TO GENTLE WINDS WILL CONTINUE THROUGH THE WEEK. AN UPPER-LEVEL
TROUGH WILL PRODUCE ISOLATED THUNDERSTORMS THROUGH TUESDAY,
POTENTIALLY INTO TUESDAY NIGHT.
TROPICAL SYSTEMS UPDATE
TROPICAL STORM PODUL (16W) WAS CENTERED WELL SOUTHWEST OF IWO TO
NEAR 22N135E. PODUL IS MOVING WEST ACROSS THE PHILIPPINE SEA AT 14
MPH. PODUL IS EXPECTED TO MAINTAIN THIS COURSE AND FORWARD SPEED.
MAX WINDS ARE AT 60 MPH. PODUL IS STILL EXPECTED TO SLOWLY
STRENGTHEN, THOUGH IT IS NOT EXPECTED TO BECOME A TYPHOON UNTIL
TUESDAY. FOR MORE INFORMATION ON PODUL, PLEASE REFER TO BULLETINS
FROM THE JOINT TYPHOON WARNING CENTER UNDER WMO HEADER WTPN32 PGTW
AND FROM THE NATIONAL WEATHER SERVICE UNDER WMO HEADER WTPQ32 PGUM.
EASTERN MICRONESIA UPDATE
THE FRAGMENTED INTERTROPICAL CONVERGENCE ZONE (ITCZ) LOOKS TO BE
REPLACED BY A BROAD, EAST-WEST ORIENTED SURFACE TROUGH ACROSS THE
REGION, ACCORDING TO THE WIND FIELD PRESENTED ON THE LATEST
SCATTEROMETER DATA. THERE WERE TWO MAIN CHANGES TO THE FORECAST THIS
MORNING. ONE WAS TO DELAY SCATTERED SHOWERS AT KOSRAE TO THIS
AFTERNOON AS CONVECTION AND CLOUD COVER AS DECREASED OVER THE ISLAND
OVERNIGHT, BUT THERE IS CONVERGENT FLOW NEAR THE MARSHALL ISLANDS
THAT HAS BEEN SHIFTING WESTWARD AND AT ITS CURRENT SPEED SHOULD
REACH KOSRAE THIS AFTERNOON. MAJURO IS CURRENTLY ON THE EASTERN EDGE
OF THE CONVERGENT FLOW THAT EXTENDS NORTHEAST TO SOUTHWEST ACROSS
THE MARSHALL ISLANDS AND IS SLOWLY DRIFTING WESTWARD. SATELLITE
IMAGERY SHOWS VERY LITTLE TO THE EAST OF MAJURO, SO EXPECT SHOWERS TO
BECOME ISOLATED THIS AFTERNOON AS THE CONVERGENT FLOW PULLS AWAY,
BUT KEPT ISOLATED THUNDERSTORMS IN THE FORECAST. SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS ARE EXPECTED AT POHNPEI THROUGH THE DAY.
MODELS SHOW THIS SURFACE TROUGH WEAKENING TONIGHT AND FAVOR A
SLIGHTLY DRIER PATTERN TONIGHT THROUGH WEDNESDAY, THEN THE ITCZ AND
SHOWERS MAY START TO REBUILD STARTING NEAR MAJURO LATE THIS WEEK.
MARINE CONDITIONS LOOK TO REMAIN BENIGN THROUGH THE WEEK. COMBINED
SEAS OF 3 TO 5 FEET NEAR POHNPEI AND KOSRAE AND UP TO 6 FEET NEAR
MAJURO ARE EXPECTED OVER THE NEXT SEVERAL DAYS, WITH WINDS REMAINING
LIGHT TO GENTLE.
WESTERN MICRONESIA UPDATE
PALAU AND YAP ARE STILL WITHIN THE CONVERGENT, LIGHT TO GENTLE SOUTH
TO SOUTHWEST FLOW THAT CONTINUES TO PRODUCE LOW-END SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS ACROSS BOTH LOCATIONS. THIS
PATTERN FOR PALAU AND YAP IS EXPECTED TO CONTINUE FOR THE NEXT FEW
DAYS, AND WE WILL CONTINUE TO MONITOR THE POTENTIAL THAT POPS MAY
NEED TO BE INCREASED TO HIGH-END (50%) TO NUMEROUS (60%-70%), BUT THE
GFS AND ECMWF ARE STARTING TO DIFFER ON THE POTENTIAL AND TIMING
THAT THE CONVERGENT FLOW WILL STRENGTHEN OVER PALAU AND YAP THROUGH
WEDNESDAY. CHUUK IS CURRENTLY IN A LULL OF DRIER WEATHER BUT A
SURFACE TROUGH NEAR POHNPEI MAY NUDGE IT WAY INTO CHUUK LATER TODAY,
TRIGGERING SOME SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS THIS
AFTERNOON. SHOWERS WILL THEN DECREASE AGAIN TONIGHT AND WILL REMAIN
ON THE DRIER SIDE, OUTSIDE OF A TRADE-WIND TROUGH THAT LOOKS TO MOVE
IN WEDNESDAY OR WEDNESDAY NIGHT, BEFORE THE ITCZ DEVELOPS LATE THIS
WEEK.
LITTLE TO NO CHANGE WAS MADE WITH THE MARINE FORECAST. BENIGN
COMBINED SEAS OF 2 TO 4 FEET LOOK TO PREVAIL THROUGH THE FORECAST
PERIOD. WINDS ARE EXPECTED TO REMAIN LIGHT TO GENTLE WHILE BECOMING
VARIABLE AT TIMES.
PREV DISCUSSION
/ISSUED 510 PM CHST SUN AUG 10 2025/
MARIANAS SYNOPSIS...
LATEST SATELLITE AND RADAR SHOWS MOSTLY CLOUDY SKIES WITH SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE CNMI. MOSTLY CLOUDY
SKIES WITH ISOLATED SHOWERS ARE SEEN OVER GUAM. BUOYS SHOW SEAS
BETWEEN 2 AND 4 FEET, WHILE ALTIMETRY SHOWS SEAS OF 3 TO 5 FEET OVER
THE EASTERN WATERS.
DISCUSSION...
UPPER-LEVEL DIVERGENCE ASSOCIATED WITH THE TUTT (TROPICAL UPPER
TROPOSPHERIC TROUGH) MOVED OVER THE MARIANAS, BRINGING SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS TO THE CNMI TODAY AND TONIGHT.
THIS CONVECTION IS EXPECTED TO SPREAD SOUTH AS THE TUTT DRIFTS WEST-
SOUTHWEST THROUGH THE NEXT COUPLE OF DAYS. SCATTERED SHOWERS LOOK TO
CONTINUE FOR THE CNMI THROUGH MONDAY AFTERNOON AND SHOULD SPREAD
SOUTH OVER GUAM BY MONDAY MORNING. THE TUTT WILL SLOWLY MOVE THROUGH
THE REGION, ALLOWING SHOWERS TO DECREASE TO ISOLATED MONDAY NIGHT,
THOUGH THUNDERSTORMS WILL REMAIN A POSSIBILITY THROUGH TUESDAY. FOR
GUAM, LIGHT AND VARIABLE WINDS TUESDAY AND WEDNESDAY WILL BRING
RESULT IN ISLAND CONVECTION DURING THE AFTERNOON ON BOTH DAYS, AND
COULD OCCUR AGAIN ON THURSDAY. OTHERWISE, A DRY TRADE-WIND PATTERN
IS EXPECTED TUESDAY NIGHT THROUGH THE WEEKEND.
MARINE...
LIGHT TO GENTLE WINDS ARE EXPECTED THROUGH NEXT WEEK. COMBINED SEAS
OF 3 TO 5 FEET WILL SLOWLY SUBSIDE, DROPPING TO BETWEEN 2 AND 3 FEET
BY THURSDAY. AN UPPER-LEVEL LOW WILL PRODUCE ISOLATED THUNDERSTORMS
THROUGH TUESDAY.
TROPICAL SYSTEMS...
AT 1:00 PM, TROPICAL STORM PODUL (16W) WAS CENTERED SOUTH-SOUTHWEST
OF IWO TO NEAR 22N138E. PODUL IS MOVING WEST ACROSS THE PHILIPPINE
SEA AT 16 MPH. PODUL IS EXPECTED TO MAINTAIN THIS COURSE WITH A
DECREASE IN FORWARD SPEED. MAXIMUM SUSTAINED WINDS ARE 65 MPH. PODUL
IS STILL EXPECTED TO SLOWLY STRENGTHEN, THOUGH IT IS NOT EXPECTED TO
BECOME A TYPHOON UNTIL MONDAY NIGHT OR TUESDAY. FOR MORE INFORMATION
ON PODUL, PLEASE REFER TO BULLETINS FROM THE JOINT TYPHOON WARNING
CENTER UNDER WMO HEADER WTPN32 PGTW AND FROM THE NATIONAL WEATHER
SERVICE UNDER WMO HEADER WTPQ32 PGUM.
EASTERN MICRONESIA...
AN ACTIVE, BUT FRAGMENTED INTERTROPICAL CONVERGENCE ZONE (ITCZ)
STRETCHES ACROSS THE REGION. THE BULK OF CONVECTION IS FOCUSED AROUND
A BROAD TRADE-WIND TROUGH WITHIN THE OVERALL ITCZ PATTERN, EXTENDING
THROUGH MUCH OF KOSRAE STATE TO THE NORTHERN MARSHALLS. NUMEROUS
SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED FOR KOSRAE THROUGH
TONIGHT, MEANWHILE MAJURO IS SLIGHTLY EAST OF THE TROUGH AXIS,
ALTHOUGH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE STILL
EXPECTED, WITH BOTH LOCATIONS SEEING OCCASIONAL GUSTS TO 20 KT NEAR
HEAVIER SHOWERS THROUGH TONIGHT. PATCHIER SHOWERS ARE SEEN AHEAD OF
THIS FEATURE, NEAR POHNPEI THIS AFTERNOON AND SIMILAR CONDITIONS ARE
EXPECTED IN THE COMING DAYS AS THE ITCZ IS EXPECTED TO SHIFT NORTH
AND BECOME MORE FRAGMENTED. DUE TO THIS, ALL FORECAST LOCATIONS MAY
EXPECT A LULL IN THE OVERALL WEATHER PATTERN AFTER MONDAY, THEN ITCZ
SHOWERS MAY START TO REBUILD STARTING NEAR MAJURO LATE WEEK.
MARINE CONDITIONS LOOK TO REMAIN BENIGN THROUGH THE WEEKEND.
COMBINED SEAS OF 3 TO 5 FEET NEAR POHNPEI AND KOSRAE AND UP TO 6 FEET
NEAR MAJURO ARE EXPECTED OVER THE NEXT SEVERAL DAYS. CHOPPY SEAS AND
OCCASIONAL GUSTS TO 20 KT ARE POSSIBLE ACROSS KOSRAE AND MAJURO
WATERS THROUGH TONIGHT.
WESTERN MICRONESIA...
SATELLITE OBSERVATIONS SHOW SCATTERED SHOWERS ACROSS PALAU AND CHUUK
AND ISOLATED SHOWERS ACROSS YAP. ALTIMETRY AND BUOY DATA SHOW
COMBINED SEAS BETWEEN 2 TO 4 FEET.
OVERALL, LITTLE CHANGE IN THOUGHT FROM THE LAST COUPLE OF FORECASTS.
GUIDANCE HAS BACKED OFF SLIGHTLY FROM HIGHER POPS THIS WEEK, BUT
SCATTERED SHOWERS ARE STILL EXPECTED THROUGH MUCH OF THE PERIOD FOR
PALAU AND YAP AND LESS SO AFTER MONDAY FOR CHUUK. BOTH THE GFS AND
ECMWF SHOW THE GREATEST SURFACE CONVERGENCE OVER PALAU AND YAP DURING
THE MONDAY NIGHT AND TUESDAY PERIODS. THIS IS WHEN A POTENTIAL
INCREASE IN POPS TO HIGH-END SCATTERED (50%) TO NUMEROUS (60-70%) MAY
BEEN NEEDED WITH UPCOMING FORECAST CYCLES. FOR CHUUK, A LULL LOOKS TO
DEVELOP LATER THIS WEEK WITH ISOLATED SHOWERS OUTSIDE OF A TRADE-WIND
TROUGH THAT LOOKS TO MOVE IN WEDNESDAY OR WEDNESDAY NIGHT. AS WE HEAD
INTO NEXT WEEKEND, THE PATTERN ACROSS WESTERN MICRONESIA LOOKS TO
SHAKE UP AS A STRENGTHENING ITCZ MOVES INTO THE REGION.
LITTLE TO NO CHANGE WAS MADE WITH THE MARINE FORECAST. BENIGN
COMBINED SEAS OF 2 TO 4 FEET LOOK TO PREVAIL THROUGH THE FORECAST
PERIOD. WINDS ARE EXPECTED TO REMAIN LIGHT TO GENTLE WHILE VARIABLE
AT TIMES.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST/WEST MICRONESIA UPDATE: SCHANK
MARIANAS: KLEESCHULTE
EAST MICRONESIA: CRUZ
WEST MICRONESIA: WILLIAMS
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