786
FXPQ50 PGUM 232103
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
ISSUED BY NATIONAL WEATHER SERVICE HONOLULU HI
703 AM CHST TUE JUN 24 2025
MARIANAS UPDATE
FAIRLY QUIET CONDITIONS PERSIST ACROSS THE LOWER MARIANAS WITH
SATELLITE IMAGERY SHOWING SHALLOW CUMULUS CLOUDS AND ISOLATED SHOWERS
MOVING ALONG A GENTLE ESE FLOW. TS SEPAT (02W) CONTINUES TO PULL AWAY
FROM THE REGION AS IT APPROACHES 30N. WIDESPREAD SHOWERS AND
THUNDERSTORMS PERSIST WEST OF THE MARIANAS BETWEEN 135E AND 142E FROM
THE COMBINATION OF A WET SW FLOW AND VERY FAVORABLE CONDITIONS ALOFT,
INCLUDING A TUTT CIRCULATION NEAR 23N137E. THIS WEEK'S FORECAST STILL
TRENDS WET IN THE LONG TERM AS A DISTURBANCE POTENTIALLY TAKES SHAPE
LATE IN THE WEEK AND A SOUTHWEST MONSOON EXTENDS OVER THE MARIANAS
INTO EARLY NEXT WEEK. SEAS WILL REMAIN FAIRLY BENIGN THE NEXT FEW
DAYS, BUT WILL INCREASE 2-3 FEET OVER THE WEEKEND AS WINDS INCREASE
IN TANDEM WITH THE DISTURBANCE.
TROPICAL SYSTEMS
COMPUTER MODELS CONTINUE TO POINT TO THE POSSIBILITY OF A TROPICAL
DISTURBANCE TO FORM NEAR THE MARIANAS. FOR THE PAST COUPLE OF DAYS,
MODELS HAVE BEEN SPLIT EITHER TO THE WEST OR TO THE EAST OF THE
MARIANA ISLAND CHAIN. THE GFS, IN ADDITION TO BEING THE MOST
AGGRESSIVE IN RATE OF DEVELOPMENT, HAS STRONGLY FAVORED THE EASTERN
SIDE OF THE ISLANDS FOR GENESIS. HOWEVER, RECENT RUNS OF THE GEFS
HAVE SHOWN SOME WESTWARD SPREAD IN THE POTENTIAL DEVELOPMENT AREA.
WHILE ITS STILL TOO SOON TO STATE ANY CERTAINTY, ONE THING TO WATCH FOR
IN THE NEXT 24-36 HOURS WILL BE FOR A PUSH OF WESTERLY WINDS FROM
THE YAP AREA TO THE SOUTHEAST OF GUAM BY TONIGHT OR EARLY WED. THAT
WOULD LEND MORE SUPPORT TO GFS GUIDANCE. HOWEVER THINGS SHAPE UP LATE
THIS WEEK, THE COMMON OUTCOME AMONG MODELS IS FOR A MUCH WETTER
PATTERN IN THE MARIANAS. FOR THAT REASON, A HYDROLOGIC OUTLOOK WAS
ISSUED YESTERDAY.
EASTERN MICRONESIA UPDATE
A LARGE AREA OF SHOWERS AND THUNDERSTORMS IS FINALLY PUSHING TO
THE WEST OF THE MARSHALLS AND IS CURRENTLY ATOP KOSRAE STATE AND
CLOSING IN ON POHNPEI. ORIGINALLY ALIGNED MORE EAST-WEST, THE
CONVECTIVE FEATURE IS TILTED WNW-ESE ALONG THE CONVERGENCE BOUNDARY
OF MODERATE EASTERLY TRADES ENCROACHING ON GENTLE SOUTHEASTERLY FLOW
ACROSS CHUUK STATE. PASSING SHOWERS AND THUNDERSTORMS ARE STILL
ANTICIPATED TO BRING STRONGER GUSTS OF 20-25 KT ON OCCASION. SEAS
WILL BE BENIGN, MOSTLY EAST SWELL WITH KOSRAE AND POHNPEI SEEING
SOUTHEASTERLY SWELL MOVING IN BY WEDNESDAY.
WESTERN MICRONESIA UPDATE
REGIONAL WEATHER WILL BE QUITE CHANGEABLE AS A SOUTHWESTERLY MONSOON
PATTERN TRIES TO ESTABLISH ITSELF OVER YAP AND PALAU THE NEXT FEW
DAYS. CURRENTLY WITH A SOUTH TO SOUTHWEST FLOW OVERHEAD, MODELS SHOW
WINDS WEAKENING AND BECOMING VARIABLE FOR THE MIDWEEK TIME FRAME
UNTIL A BROADER DISTURBANCE NEAR THE MARIANAS MATERIALIZES LATER IN
THE WEEK AND HELPS TO REINFORCE THE SOUTHWEST MONSOON. SEAS FOR YAP
AND PALAU WILL STILL RANGE AROUND 4-5 FT, BUT WILL BE A MIX OF SMALL
EAST AND SOUTH OR SOUTHWEST SWELL FOR THE WEEK. SOUTHWEST SWELL AND
WINDS ARE ANTICIPATED TO INCREASE OVER THE WEEKEND.
CHUUK WILL SEE SHOWERS AND THUNDERSTORMS MOVING IN FROM THE EAST
LATER TODAY THAT COULD LINGER INTO MIDWEEK WITH A PERSISTENT
SOUTHEAST FLOW. LATE WEEK WEATHER REMAINS MORE UNCERTAIN WITH A LIGHT
AND VARIABLE WIND AND CONVECTION JUST TO THE EAST THAT MODELS SHOW
STAYING IN PLACE WITH LITTLE WESTWARD ADVANCEMENT.
PREV DISCUSSION
/ISSUED 547 PM CHST MON JUN 23 2025/
MARIANAS SYNOPSIS...
PARTLY CLOUDY SKIES WITH ISOLATED SHOWERS AND GENTLE TO MODERATE T
TRADE WINDS PREVAIL ACROSS THE MARIANAS THIS AFTERNOON. BUOYS SHOW
SEAS BETWEEN 2 AND 3 FEET.
DISCUSSION...
THE MARIANAS REMAIN FAIRLY DRY THIS AFTERNOON, WITH ONLY ISOLATED
SHOWERS SEEN ACROSS THE REGION. HOWEVER, THE ATMOSPHERE REMAINS
FAIRLY UNSTABLE ACROSS THE ISLANDS, MAINTAINING A RISK OF ISOLATED
THUNDERSTORMS THROUGH TUESDAY. BEGINNING TUESDAY NIGHT, INCREASING
MOISTURE WILL BEGIN TO STREAM INTO THE AREA FROM THE SOUTHWEST AS TS
SEPAT DRIFTS NORTH-NORTHWEST. AT THE SAME TIME WEAK SURFACE TROUGHS
WILL ALSO APPROACH THE ISLANDS. THIS WILL RESULT IN INCREASING
CONVECTION ACROSS THE MARIANAS FOR THE NEXT COUPLE OF DAYS. LATER IN
THE WEEK IS WHEN THINGS LOOK LIKE THEY COULD GET INTERESTING. LATEST
GUIDANCE SHOWS A TROUGH MOVING INTO THE MARIANAS FROM CHUUK STATE
AROUND THURSDAY. MODELS VARY A BIT ON EXACTLY WHAT THIS TROUGH WILL
DO AS IT APPROACHES, HOWEVER, THEY DO AGREE THAT AT LEAST A WEAK
CIRCULATION WILL DEVELOP OVER THE MARIANAS. THE GFS, AS IS COMMON, IS
THE MOST AGGRESSIVE WITH THE CIRCULATION, WHILE THE ECMWF SHOWS A
WEAKER CIRCULATION A LITTLE FARTHER WEST. WHAT LOOKS LIKELY AT THIS
POINT IS THAT THERE WILL BE AN INCREASE IN RAINFALL POTENTIAL, WITH
HEAVY RAIN EXPECTED FRIDAY INTO THE WEEKEND. THIS SITUATION WILL BE
MONITORED CLOSELY OVER THE NEXT FEW OF DAYS FOR ANY CHANGES OR
INDICATIONS THAT A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE. AS OF
NOW, A VERY WET AND UNSETTLED PATTERN LOOKS LIKELY INTO THE BEGINNING
OF NEXT WEEK.
MARINE...
OTHER THAN THUNDERSTORMS AND THE POTENTIAL FOR HEAVY RAINFALL LATER
IN THE WEEK, MARINE CONDITIONS LOOK TO REMAIN FAIRLY BENIGN.
COMBINED SEAS OF 2 TO 4 FEET WILL CONTINUE THROUGH TUESDAY, THEN
BEGIN TO SLOWLY BUILD TUESDAY NIGHT. SEAS ARE EXPECTED TO REACH 6
FEET BY THE WEEKEND. MOSTLY GENTLE WINDS ARE EXPECTED TO BEGIN TO
INCREASE AROUND THE MIDDLE OF THE WEEK AND SWING AROUND TO A
SOUTHERLY DIRECTION AS A WEAK DISTURBANCE DEVELOPS NEAR THE MARIANAS.
WINDS COULD BECOME MODERATE TO FRESH BY THE WEEKEND.
HYDROLOGY...
A TROPICAL DISTURBANCE COULD BRING HEAVY RAIN TO THE MARIANAS FROM
THURSDAY EVENING THROUGH SUNDAY. LATEST MODEL GUIDANCE SHOWS A
SURFACE TROUGH WITHIN CHUUK STATE THAT IS EXPECTED TO MOVE NORTHWEST
OVER THE NEXT COUPLE OF DAYS. THIS TROUGH IS EXPECTED TO DEVELOP INTO
A WEAK CIRCULATION THURSDAY OR FRIDAY NEAR THE MARIANAS. MODELS
DIFFER ON LOCATION AND STRENGTH OF THIS CIRCULATION, HOWEVER, THEY DO
AGREE THAT HEAVY RAINFALL IS LIKELY AS EARLY AS THURSDAY, BUT MOST
LIKELY FRIDAY THROUGH THE WEEKEND.
THERE IS A POTENTIAL FOR GUAM AND THE CNMI TO SEE RAINFALL AMOUNTS
VARYING FROM 5 TO 10 INCHES BY SUNDAY, THOUGH LOCALLY HEAVIER AMOUNTS
ARE POSSIBLE. THIS RAINFALL IS EXPECTED TO PRODUCE MINOR FLOODING
ACROSS THE ISLANDS, WITH FLASH FLOODING POSSIBLE IN THE AREAS OF
HEAVIER RAINFALL.
RESIDENTS IN THE MARIANAS NEED TO CLOSELY MONITOR THIS DEVELOPING
SITUATION AS WATCHES, ADVISORIES AND WARNINGS COULD BE ISSUED LATER.
EASTERN MICRONESIA...
AN ACTIVE SECTOR OF THE INTERTROPICAL CONVERGENCE ZONE (ITCZ) IS
PRODUCING SIGNIFICANT SHOWERS AND THUNDERSTORMS OVER KOSRAE, WHICH
ARE MOVING INTO POHNPEI WATERS OVERNIGHT. THE SURFACE TO MID-LEVEL
VORTICITY FEATURE MENTIONED YESTERDAY HAS MOVED INTO WESTERN
MICRONESIA, WHICH IS THEN EXPECTED TO BE THE CULPRIT BEHIND A
TROPICAL DISTURBANCE DEVELOPING NEAR THE MARIANAS DURING THE WEEKEND.
MEANWHILE, THE ACTIVE SECTOR OF THE ITCZ WILL CONTINUE TO MOVE
DOWNSTREAM TO THE WEST, KEEPING CONDITIONS GUSTY AND WET AT POHNPEI
AND KOSRAE FOR A GOOD WHILE. AT MAJURO, CONDITIONS HAVE IMPROVED
CONSIDERABLY, WITH ISOLATED TO LOW-END SCATTERED SHOWERS EXPECTED
THROUGH AT LEAST MIDWEEK.
COMBINED SEAS OF 4 TO 5 FEET AT POHNPEI AND KOSRAE WILL REMAIN AS
SUCH FOR MUCH OF THE FORECAST PERIOD, AS EASTERLY SWELL SLOWLY
DIMINISHES AND A SOUTHEASTERLY SWELL STRENGTHENS. COMBINED SEAS OF 4
TO 6 FEET NEAR MAJURO ARE EXPECTED TO INCREASE ANOTHER 2 FEET BY
THURSDAY, AS TRADE SWELL AND LOCALIZED WIND WAVES STRENGTHEN.
WESTERN MICRONESIA...
A MONSOON TROUGH EXTENDS SOUTHEAST INTO THE REGION AT AROUND 9N130E,
PASSING OVER THE REPUBLIC OF PALAU NEAR KOROR BEFORE ENDING AROUND
6N137E. THE REGION IS CONVECTIVELY QUIET ALONG THE MONSOON TROUGH
AXIS THIS AFTERNOON, WITH PARTLY CLOUDY SKIES AND ISOLATED SHOWERS
SEEN ACROSS MUCH OF THE AREA. NORTH OF THE TROUGH AXIS, SCATTERED
SHOWERS ARE DEVELOPING OVER AND NORTH OF YAP PROPER IN A REGION OF
CONVERGENT SOUTHERLIES, ENHANCED BY DIVERGENT FLOW ALOFT. THE
DEVELOPING CONVERGENCE BOUNDARY EXTENDS SOUTH-SOUTHEAST FROM AROUND
13N138E, PASSING JUST EAST OF YAP PROPER, THEN CONTINUING NEAR
SOROL, EAURIPIK, AND IFALIK IN YAP STATE WHERE A TRADE-WIND TROUGH IS
RUNNING INTO IT. MODEL GUIDANCE HAS SCATTERED TO NUMEROUS SHOWERS
BUILDING ALONG THIS CONVERGENCE BOUNDARY AND SHIFTING WEST ACROSS YAP
PROPER TONIGHT AND TOMORROW, BRINGING LOCALLY HEAVY RAINFALL AND
ISOLATED THUNDER AT TIMES. A QUIETER PATTERN MAY SET UP FOR PALAU AND
YAP WEDNESDAY THROUGH THE LATTER HALF OF THE WEEK AS THE MONSOON
TROUGH SHIFTS NORTH. HOWEVER, THE WEATHER PATTERN AND POSITIONING OF
THE MONSOON TROUGH WILL PARTIALLY DEPEND ON THE DEVELOPMENT AND
MOVEMENT OF A YET-TO-FORM TROPICAL DISTURBANCE, WHICH LOOKS TO BUILD
NEAR THE MARIANAS IN THE LATTER HALF OF THE WEEK ACCORDING TO LATEST
MODEL GUIDANCE.
TO THE EAST, SCATTERED SHOWERS ARE SEEN OVER CHUUK LAGOON WITH
NUMEROUS SHOWERS JUST TO THE SOUTH, WITHIN A FRAGMENTED ITCZ THAT
EXTENDS EASTWARD OVER POHNPEI AND KOSRAE. THE PROXIMITY OF THE ITCZ
AND ASSOCIATED DISTURBANCES WILL MAINTAIN SCATTERED SHOWERS IN THE
AREA THROUGHOUT MUCH OF THE WEEK, WITH NUMEROUS LOCALLY HEAVY
SHOWERS POSSIBLE AT TIMES, PARTICULARLY TUESDAY ONWARD. A MORE ROBUST
DISTURBANCE LOOKS TO DEVELOP JUST NORTHWEST OF CHUUK AROUND TUESDAY
NIGHT AND WEDNESDAY BEFORE SHIFTING NORTH OVER THE MARIANAS BY THE
END OF THE WEEK.
THERE WAS LITTLE CHANGE TO THE MARINE FORECAST, AND BENIGN SEA
CONDITIONS CONTINUE. BABELDAOB BUOY AND SOFAR DRIFTING BUOY DATA SHOW
2 TO 4 FOOT SEAS NEAR PALAU AND YAP THIS AFTERNOON. SEAS MAY INCREASE
NEAR PALAU BY A FOOT OR SO OVER THE NEXT DAY AS A PULSE OF SOUTH TO
SOUTHWEST WAVE ENERGY MOVES INTO THE REGION, A MIX OF WIND WAVES AND
SWELL WITH PERIODS AVERAGING 6 TO 7 SECONDS, SEEN IN LATEST GFSWAVE
AND ECMWFWAVE MODEL GUIDANCE. COMBINED SEAS NEAR PALAU WILL RELAX TO
AROUND 2 TO 3 FEET BY MIDWEEK AND REMAIN THERE THROUGH THE REST OF
THE WEEK. SEAS WILL REMAIN IN THE 3 TO 4 FOOT RANGE FOR CHUUK THROUGH
THE WEEK AS LIGHT TO GENTLE WINDS PERSIST ACROSS THE REGION, BECOMING
LIGHT AND VARIABLE AT TIMES.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS UPDATE: W. AYDLETT
EAST/WEST MICRONESIA UPDATE: W. AYDLETT
TROPICAL: W. AYDLETT
MARIANAS: KLEESCHULTE
EAST MICRONESIA: MONTVILA
WEST MICRONESIA: DECOU
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