259  
FXPQ50 PGUM 210743 AAA  
AFDGUM  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE TIYAN GU  
543 PM CHST TUE OCT 21 2025  
 
UPDATED TO ADD COMPLETED WESTERN MICRONESIA SECTION.  
   
MARIANAS SYNOPSIS
 
 
GENTLE TO MODERATE SOUTHEASTERLIES PREVAIL ACROSS THE REGION.  
SATELLITE IMAGERY AND DOPPLER RADAR INDICATE A LINE OF SHOWERS  
APPROACHING GUAM'S SOUTHEASTERN SHORES. BUOYS AND ALTIMETRY SHOW SEAS  
ARE BETWEEN 5 AND 6 FEET.  
 

 
   
DISCUSSION
 
 
AS THE AFOREMENTIONED LINE OF SHOWERS MAKES ITS WAY ACROSS GUAM AND  
ROTA, A THUNDERSTORM OR TWO IS LIKELY TO DEVELOP DURING PASSAGE.  
SHOWERS ARE EXPECTED TO REMAIN SCATTERED, BUT WILL BE HEAVY AT  
TIMES, BRINGING OCCASIONALLY STRONG GUSTS IN THE NEXT FEW HOURS.  
PATCHY SHOWERS AND SOME THUNDERSTORMS ARE EXPECTED THROUGH WEDNESDAY,  
BEFORE TAPERING DOWN SLOWLY THEREAFTER AS THIS SURFACE TROUGH EXITS  
TO THE WEST AND ALLOWS A DRIER TRADE-WIND REGIME TO ENSUE FOR THE  
REST OF THE WEEK.  
 

 
   
MARINE
 
 
A LINE OF SHOWERS COMING IN FROM THE SOUTHEAST MAY BRING  
OCCASIONALLY STRONG WINDS DURING PASSAGE IN THE EARLY EVENING HOURS.  
COMBINED SEAS OF 4 TO 6 FEET, COMPRISED OF A DOMINANT TRADE SWELL  
AND DIMINISHING NORTHERLY SWELL, MAY DROP A FOOT OR TWO IN THE SECOND  
HALF OF THE WEEK WHEN ALL INCOMING SWELLS WEAKEN. A MODERATE RISK OF  
RIP CURRENTS IS EXPECTED ALONG NORTH AND EAST FACING REEFS OF THE  
MARIANAS FOR AT LEAST THE NEXT FEW DAYS, BEFORE POTENTIALLY BECOMING  
LOW ALONG NORTH FACING REEFS LATER ONCE THE AFOREMENTIONED NORTHERLY  
SWELL DIMINISHES.  
 

 
   
EASTERN MICRONESIA
 
 
EASTERN MICRONESIA WILL BE DOMINATED BY AN INTER TROPICAL CONVERGENCE  
ZONE FOR THE NEXT SEVERAL DAYS. POHNPEI AND MAJURO WILL BE CLOSE TO  
THE CENTER, AND WILL THEREFORE SEE SCATTERED SHOWERS OR MORE FOR THE  
ENTIRE PERIOD. KOSRAE WILL BE AT THE SOUTHERN EDGE, AND AS THE ITCZ  
UNDULATES, WILL MOVE INTO AND OUT OF THE CORE, AND PERHAPS EVEN LEAVE  
THE ITCZ AT TIMES. THE MOST LIKELY TIMES FOR KOSRAE TO EMERGE FROM  
UNDER THE ITCZ ARE TONIGHT, WEDNESDAY, AND THURSDAY. AS IT  
STRENGTHENS FRIDAY THROUGH SUNDAY, IT LOOKS LIKE KOSRAE WILL BE IN  
THE THICK OF IT AS WELL.  
 
COMBINED SEAS ARE 4 TO 6 FEET WITH A FEW 7 FOOTERS EARLY. THIS RAISED  
THE POSSIBILITY OF A HIGH SURF ADVISORY AT KOSRAE. WHEN WE CHECKED  
THE BUOY THOUGH, THE PEAK PERIOD THERE IS 6 SECONDS, WHICH MEANS IT  
IS MOSTLY WIND WAVES AND HAVE VERY LITTLE POTENTIAL FOR SHOALING,  
WHICH IS WHAT INCREASES SURF HEIGHT ABOVE THE SEA HEIGHT. THE SMALL  
CRAFT ADVISORY AT MAJURO IS OUT MAINLY FOR THE POTENTIAL FOR GUSTS UP  
TO 30 KNOTS IN HEAVIER SHOWERS. WINDS WILL DIMINISH SLIGHTLY AFTER  
TONIGHT, WHICH WILL REDUCE THAT POTENTIAL ENOUGH TO DROP THE  
ADVISORY. FOR NOW, ASCAT SHOWS WINDS OF 20 KNOTS JUST EAST OF THEM,  
WITH WINDS OF 25 KNOTS A BIT FURTHER EAST, WHICH COULD ADVECT INTO  
THEIR WATERS.  
 

 
   
WESTERN MICRONESIA
 
 
SCATTERED SHOWERS AND ISOLATED THUNDESTORMS EXTEND ACROSS PALAU AND  
YAP STATE AND UP TOWARDS THE MARIANAS, ALONG A TROUGH EXTENDING FROM  
A WEAK CIRCULATION NEAR THE PHILIPPINES. SCATTERED SHOWERS AND  
ISOLATED THUNDERSTORMS CONTINUE ACROSS CHUUK STATE, DRIVEN BY THE  
ACTIVE TRADE-WIND PATTERN AND ITCZ EXTENDING ACROSS EASTERN  
MICRONESIA. SCATTEROMETER DATA SHOWS POCKETS OF 20-25 KT (~22-30 MPH)  
WINDS ACROSS THE REGION, DRIVEN BY CONVECTIVE GUSTS GENERATED BY  
HEAVIER SHOWERS AND THUNDERSTORMS. AS THE THE TROUGH ACROSS PALAU AND  
YAP SHIFTS WESTWARD, AND THE ACTIVE TRADE-WIND PATTERN SPREADS  
ACROSS THE REGION, A FAIRLY WET PATTERN IS EXPECTED ACROSS THE ENTIRE  
REGION THROUGH AT LEAST THE END OF THE WEEK. THE GFS CONTINUES TO  
SUPPORT PERIODS OF STRONGER WINDS AROUND CHUUK WEDNESDAY NIGHT INTO  
THURSDAY, AND AROUND FRIDAY AND FRIDAY NIGHT FOR PALAU AND YAP, AS A  
EMBEDDED SURFACE TROUGH MOVES THROUGH THE ACTIVE TRADE-WIND PATTERN.  
CURRENTLY, THIS POTENTIAL FOR STRONGER WINDS LOOKS TO REMAIN BELOW  
THE 22 KT THRESHOLD FOR HAZARDOUS WINDS FOR SMALL CRAFT WITH SEAS  
EXPECTED TO REMAIN HAZARDOUS LEVELS ON 10 FEET.  
 
ALTIMETRY DATA SHOWS SEAS ARE AROUND 3 TO 5 FEET ACROSS PALAU AND  
YAP, AND 5 TO 7 FEET ACROSS CHUUK, WHERE AN ELEVATED NORTHEAST TO  
EAST SWELL IS BEING GENERATED BY THE TRADE-WIND PATTERN. CHUUK  
WILL SEE AN INCREASE IN WINDS AROUND WEDNESDAY NIGHT INTO THURSDAY,  
AS A TROUGH MOVES THROUGH, ALONG WITH A VERY SUBTLE UPTICK IN THE  
NORTHERLY SWELL. THIS SHOULD INCREASE SEAS ABOUT A FOOT ACROSS CHUUK.  
SUSTAINED WINDS ARE EXPECTED TO LIGHT TO GENTLE FOR PALAU AND YAP  
OVER THE NEXT COUPLE OF DAYS, BUT ARE EXPECTED TO INCREASE AROUND  
FRIDAY AS A TROUGH MOVES THROUGH THE AREA.  
 

 
   
GUM WATCHES/WARNINGS/ADVISORIES
 
 
GU...NONE.  
MP...NONE.  
MARIANAS WATERS...NONE.  

 
 

 
 
MARIANAS: MONTVILA  
EAST MICRONESIA: STANKO  
WEST MICRONESIA: SCHANK  
 
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