681  
FXPQ50 PGUM 290650  
AFDGUM  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TIYAN GU  
450 PM CHST SUN JUN 29 2025  
   
MARIANAS SYNOPSIS  
 
SATELLITE SHOWS MOSTLY CLOUDY SKIES WITH SCATTERED SHOWERS OVER GUAM  
AND ROTA, WITH PARTLY CLOUDY SKIES AND ISOLATED SHOWERS OVER TINIAN  
AND SAIPAN. LIGHT TO GENTLE SOUTHEAST TO SOUTH WINDS PREVAIL ACROSS  
THE MARIANAS. BUOYS SHOW SEAS BETWEEN 2 AND 4 FEET WHILE ALTIMETRY  
SHOWS SEAS BETWEEN 3 AND 5 FEET.  
 
 
   
DISCUSSION  
 
SHOWERS HAVE DECREASED ACROSS THE MARIANAS TODAY. HOWEVER, THIS IS  
EXPECTED TO BE SHORT-LIVED. INVEST 99W REMAINS TO THE NORTHEAST OF  
THE MARIANAS, DRIFTING SLOWLY NORTH-NORTHEAST, WITH INVEST 98W SEEN  
WELL WEST OF THE MARIANAS. AS 99W DRIFTS NORTHWARD, IT WILL ALLOW AN  
OVERALL WET, UNSETTLED, MONSOON PATTERN TO MOVE ACROSS THE MARIANAS.  
LATEST MODEL GUIDANCE CONTINUES TO INDICATE THAT A WEAK MONSOON SURGE  
WILL ALSO PUSH INTO THE REGION, WITH A TROPICAL UPPER TROPOSPHERIC  
TROUGH (TUTT) REMAINING TO THE NORTH, PROVIDING A BROAD AREA OF  
DIVERGENCE TO AID IN THE GENERATION OF SHOWERS AND THUNDERSTORMS  
ACROSS THE MARIANAS. THE ISLANDS LOOK TO REMAIN UNDER THE INFLUENCE  
OF THE MONSOON FLOW, TUTT AND MONSOON SURGE THROUGH AT LEAST TUESDAY,  
MAINTAINING NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS, THOUGH THE  
HEAVIER SHOWERS ARE ONLY EXPECTED THROUGH MONDAY NIGHT. MONSOONAL  
FLOW LOOKS TO CONTINUE A BIT LONGER, MAINTAINING SOUTH TO SOUTHWEST  
FLOW INTO THE WEEKEND. THIS WILL KEEP AN OVERALL UNSETTLED PATTERN  
OVER THE ISLANDS FOR THE NEXT SEVERAL DAYS, THOUGH SHOWER COVERAGE IS  
EXPECTED TO DECREASE TO SCATTERED TUESDAY NIGHT, WITH POPS  
(PROBABILITY OF PRECIPITATION) DROPPING TO AROUND 30 PERCENT THROUGH  
SUNDAY.  
 
 
   
MARINE  
 
NOT MUCH OF A CHANGE IN THE MARINE FORECAST. SEAS OF 3 TO 5 FEET  
TONIGHT LOOK TO INCREASE 1 TO 2 FEET OVER THE NEXT COUPLE OF DAYS AS  
A SOUTHWEST MONSOON SWELL MOVES INTO THE AREA WHILE THE TRADE-WIND  
SWELL REMAINS UNCHANGED. SEAS ARE EXPECTED TO BE AROUND 4 TO 6 FEET  
THROUGH MIDWEEK, THEN SUBSIDE A BIT AS THE MONSOON SWELL SUBSIDES.  
LIGHT TO GENTLE WINDS TONIGHT LOOK TO BECOME GENTLE TO MODERATE  
MONDAY AND REMAIN AT THOSE LEVELS THROUGH THE WEEK. WINDS COULD  
BECOME OCCASIONALLY FRESH AS THE MONSOON SURGE MOVES THROUGH THE  
REGION. THE RIP CURRENT RISK WILL REMAIN MODERATE ALONG EAST FACING  
REEFS FOR THE NEXT SEVERAL DAYS. AS THE MONSOON SWELL INCREASES  
TUESDAY, THE RIP RISK IS EXPECTED TO BECOME MODERATE FOR A DAY OR SO  
ALONG WEST FACING REEFS.  
 
 
   
HYDROLOGY  
 
A FLASH FLOOD WATCH REMAINS IN EFFECT FOR GUAM AND ROTA. ALTHOUGH  
SHOWERS REMAIN LIMITED THIS AFTERNOON, THEY ARE EXPECTED TO INCREASE  
THROUGH THE EVENING, WITH NUMEROUS SHOWERS EXPECTED NEAR MIDNIGHT.  
LOCALLY HEAVY SHOWERS CAPABLE OF PRODUCING FLASH FLOODING ARE  
POSSIBLE. THE INCREASED SHOWERS ARE EXPECTED TO SPREAD NORTH THROUGH  
THE NIGHT, WITH NUMEROUS SHOWERS FOR TINIAN AND SAIPAN. BASED ON  
POSSIBLE RAINFALL AMOUNTS, THIS WATCH COULD BE REISSUED TO INCLUDE  
TINIAN AND SAIPAN, IF CONDITIONS WARRANT.  
 
 
   
TROPICAL SYSTEMS  
 
THERE ARE TWO DISTURBANCES FOUND ALONG THE MONSOON TROUGH. THE  
FIRST ONE IS JOINT TYPHOON WARNING CENTER'S (JTWC) INVEST 98W, SEEN  
AS AN EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), CENTERED NEAR  
15.1N 136.6E. 98W IS SLOWLY MOVING WEST-NORTHWEST OVER THE  
PHILIPPINE SEA WITH LITTLE CHANGE IN INTENSITY. THIS IS EXPECTED TO  
CONTINUE FOR THE NEXT COUPLE OF DAYS, WITH VERY LOW PROBABILITY OF  
DEVELOPMENT.  
 
THE SECOND DISTURBANCE IS JTWC'S INVEST 99W, CENTERED AT 16.6N  
148.5E. THIS FEATURE IS INTERACTING WITH DIVERGENCE SEEN SOUTHEAST  
OF A TUTT CELL CENTERED NEAR 20N150E. 99W IS SLOWLY DRIFTING NORTH-  
NORTHWEST. LITTLE DEVELOPMENT IS EXPECTED WITH 99W AS IT CONTINUES TO  
SLOWLY DRIFT NORTHWARD OVER THE COMING DAYS.  
 
THE MAIN AFFECT THAT THE TWO DISTURBANCES WILL HAVE ACROSS THE  
REGION IS TO HELP INCREASE MONSOON FLOW ACROSS THE MARIANAS OVER  
THE NEXT COUPLE OF DAYS. BOTH INVEST 98W AND 99W WILL BE MONITORED  
CLOSELY OVER THE NEXT FEW DAYS FOR ANY INDICATION OF DEVELOPMENT.  
 
 
   
EASTERN MICRONESIA  
 
A BROAD SURFACE TROUGH EMBEDDED WITHIN A GENERALLY MODERATE TO FRESH  
TRADES WILL BE THE PRIMARY WEATHER MAKER ACROSS EASTERN MICRONESIA  
FOR THE NEXT SEVERAL DAYS. PATCHY SHOWERS WILL MAKE THEIR WAY ACROSS  
MAJURO MONDAY, FOLLOWED BY KOSRAE TUESDAY, AND THE POHNPEI AROUND  
MIDWEEK, WITH PERIODS OF A DRIER CYCLE IN BETWEEN AT ALL THREE  
FORECAST LOCATIONS. WHILE SHOWER COVERAGE IS EXPECTED TO REMAIN  
LOWER-END NEAR MAJURO, THE LEADING EDGE OF SAID TROUGH HAS BEEN  
PRODUCING OUTFLOW BOUNDARIES MEASURED TO 30 KNOTS USING SATELLITE  
ANALYSIS TOOLS, SO SOME LINES OF SHOWERS MAY CARRY MUCH MORE  
SIGNIFICANT GUSTS OVERNIGHT AND MONDAY. OTHERWISE, LARGELY MODERATE  
TO FRESH TRADES EXPECTED DURING THE TROUGH PASSAGE, AND GENTLE TO  
MODERATE TRADES ELSEWHERE FOR MUCH OF THE WEEK.  
 
COMBINED SEAS OF 3 TO 5 FEET NEAR POHNPEI AND KOSRAE, ARE EXPECTED TO  
INCREASE AN ADDITIONAL 2 FEET AROUND MIDWEEK AS SWELL AND LOCALIZED  
WIND WAVES INCREASE, BEFORE TAPERING DOWN ONCE AGAIN BEFORE THE NEXT  
WEEKEND. COMBINED SEAS OF 5 TO 7 FEET NEAR MAJURO, WILL MOMENTARILY  
INCREASE ANOTHER FOOT TUESDAY, BEFORE DROPPING BACK DOWN TO BETWEEN 5  
AND 7 FEET FOR THE REST OF THE FORECAST PERIOD.  
 
 
   
WESTERN MICRONESIA  
 
A SOUTHWESTERLY MONSOON PATTERN WILL CONTINUE TO BRING HEAVIER  
SHOWERS AND THUNDERSTORMS TO PALAU OVERNIGHT AND TO YAP MONDAY,  
ALONG WITH GUSTIER WINDS NEAR THESE HEAVIER SHOWERS. AS VARIOUS  
MONSOON DISTURBANCES MOVE NORTHWARD AND SHIFT THE MONSOON TROUGH  
ALONG WITH IT, A RIDGE WILL FORM ALONG THE EASTERN SIDE OF SAID  
TROUGH, ALLOWING CONDITIONS TO IMPROVE SIGNIFICANTLY WITH ONLY  
ISOLATED SHOWERS EXPECTED AT PALAU AND YAP BEGINNING TUESDAY.  
MEANWHILE AT CHUUK, LOCALLY DIFFUSIVE FLOW INDUCED BY THE MONSOON  
TROUGH AND EMBEDDED DISTURBANCES, IS ALLOWING A DRIER REGIME TO ENSUE  
THROUGH AT LEAST MIDWEEK, FOLLOWED BY A RETURN OF PATCHY SHOWERS  
THEREAFTER.  
 
COMBINED SEAS OF 4 TO 6 FEET ARE EXPECTED TO TAPER DOWN A FOOT OR TWO  
AT ALL THREE FORECAST LOCATIONS IN THE SECOND HALF OF THE WEEK, AS  
VARIOUS SWELLS AND LOCALIZED WIND WAVES DIMINISH.  
 
 
   
GUM WATCHES/WARNINGS/ADVISORIES  
 
GU...FLOOD WATCH THROUGH LATE TONIGHT FOR GUZ001.  
 
MP...FLOOD WATCH THROUGH LATE TONIGHT FOR MPZ001.  
 
MARIANAS WATERS...NONE.  
 
 
 
 
MARIANAS/HYDROLOGY/TROPICAL: KLEESCHULTE  
EAST/WEST MICRONESIA: MONTVILA  
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