492
FXPQ50 PGUM 212014
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
614 AM CHST MON DEC 22 2025
MARIANAS UPDATE
RADAR AND SATELLITE IMAGERY SHOW SCATTERED SHOWERS EAST OF THE
MARIANAS ARE STARTING TO ENTER THE COASTAL WATERS THIS MORNING AND
WILL BE MOVING ACROSS THE ISLANDS LATER THIS MORNING. WINDS ARE
MODERATE TO FRESH, WITH ALTIMETRY AND BUOY DATA SHOWING SEAS ARE
AROUND 8 TO 10 FEET. THESE SEAS ARE BEING SUPPORTED ELEVATED
NORTHEAST SWELL THAT WAS GENERATED BY THE SURGE IN THE TRADE WINDS
SOUTH OF A HIGH PRESSURE SYSTEM MOVING ACROSS THE MID-LATITUDES, AND
ARE GENERATING HAZARDOUS SURF AND A HIGH RISK OF RIP CURRENTS ALONG
NORTH AND EAST FACING REEFS. HAS THE TRADE SURGE CONTINUES TO WEAKEN,
THE NORTHEAST SWELL WILL SLOWLY SUBSIDE. HAZARDOUS SURF ALONG EAST
FACING REEFS MAY END TONIGHT, WHILE HAZARDOUS SURF ALONG NORTH
FACING REEFS AND A HIGH RISK OF RIP CURRENTS ALONG NORTH AND EAST
FACING REEFS COULD BE EXTEND THROUGH AT LEAST TUESDAY IF THE
NORTHEAST SWELL DECREASES SLOWER THAN EXPECTED. LOOKING TOWARDS
CHRISTMAS, A SEASONAL TRADE-WIND PATTERN IS EXPECTED ACROSS THE
MARIANAS, BUT A COLD FRONT WILL BE PUSHING OFF OF JAPAN AND INTO THE
PACIFIC. DEPENDING HOW FAR SOUTH THE FRONT MOVES AS IT DISSIPATES,
THE MARIANAS COULD SEE A SLIGHT INCREASE IN WINDS, SHOWERS, AND SEAS
LATER THIS WEEK.
EASTERN MICRONESIA UPDATE
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE DEVELOPING AROUND
AND INTO POHNPEI THIS MORNING, ALONG THE NORTHERN EDGE OF A MORE
ROBUST TROUGH STARTING TO MOVE TOWARDS CHUUK. SCATTEROMETER ANALYSIS
SHOWS A WEAK BAND OF CONVERGENCE ACROSS KOSRAE AND MAJURO, PART OF A
DECAYING TROUGH. SO FAR SHOWERS HAVE BEEN SPOTTY TO LOW-END SCATTERED
ACROSS KOSRAE AND MAJURO, AND AS THE TROUGH NEAR POHNPEI CONTINUES
WESTWARD, SHOWERS WILL DECREASE AT POHNPEI. ISOLATED TO LOW-END
SCATTERED SHOWERS ACROSS THE REGION OVER THE NEXT FEW DAYS, WITH THE
POTENTIAL FOR THUNDERSTORMS OR HEAVY RAINFALL BEING VERY LOW DUE TO
THE LACK OF ANY MAJOR SURFACE FEATURES.
ALTIMETRY AND BUOY DATA SHOWS SEAS ARE BETWEEN 6 AND 8 FEET ACROSS
THE REGION. A LONG-PERIOD NORTH TO NORTH-NORTHEAST SWELL IS STILL
BEING DETECTED BY BUOY NEAR POHNPEI AND IS EXPECTED TO CONTINUE
THROUGH TUESDAY, KEEPING THE HIGH SURF ADVISORY FOR 9 FOOT SURF
ALONG NORTH FACING REEFS OF POHNPEI AND KOSRAE IN EFFECT. IF THE SURF
WILL REMAIN HAZARDOUS BEYOND TUESDAY IS STILL POSSIBLE, BUT STARTING
TO NOTICE THE GFS DECREASES THE LONG- PERIOD SWELL FASTER THAN THE
ECMWF, SUGGESTING THE ECMWF IS COMBINING THE THE NORTH TO NORTH-
NORTHEAST SWELL, WITH THE BACKGROUND NORTHEAST SWELL. THIS WOULD
INFLATE THE SURF FORECAST UPWARD FOR LONGER THAN WHAT WOULD ACTUALLY
OCCUR. WITH LIMITED SURF OBSERVATIONS IN THE REGION, POHNPEI BUOY
AND ANY DRIFTING BUOYS IN THE REGION WILL BE THE BEST SOURCES FOR
OBSERVATIONAL DATA TO COMPARE WITH THE MODELS TO PROVIDE UPDATES TO
THE FORECAST.
WESTERN MICRONESIA UPDATE
THE SATELLITE IMAGERY SOWS SHOWS PARTLY CLOUDY SKIES WITH SPOTTY
SHOWERS OVER YAP AND CHUUK. THERE IS A ROBUST TROUGH TO THE
SOUTHEAST OF CHUUK WHICH IS GENERATING SCATTERED TO NUMEROUS SHOWERS
AND ISOLATED THUNDERSTORM OUTSIDE OF THE COASTAL WATERS. WHILE THE
BULK OF THE HEAVY SHOWERS ARE EXPECTED TO REMAIN SOUTH OF WENO, AS
THE TROUGH PASSES TO THE SOUTH, SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS ARE EXPECTED TO DEVELOP TONIGHT. MOSTLY CLOUDY SKIES
WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS DEVELOPED NEAR
PALAU EARLY THIS MORNING BUT HAVE BEEN DECREASING FOR THE PAST COUPLE
OF HOURS AND SHOULD MOVE OUT BY THIS AFTERNOON. ALTIMETRY SHOWS SEAS
OF 5 TO 7 FEET FOR PALAU AND YAP, WITH 5 TO 8 FEET NEAR AND
NORTHEAST OF CHUUK.
DRY CONDITIONS THEN LOOK TO RETURN TO CHUUK AROUND MIDWEEK. FOR YAP
AND PALAU, THE TROUGHS MOVING THROUGH CHUUK LOOK TO APPROACH THE
REGION LATER IN THE WEEK, BRINGING AN INCREASE IN SHOWERS AND A
SLIGHT CHANCE OF THUNDERSTORMS TO THE AREA THURSDAY INTO FRIDAY.
THE MARINE FORECAST WAS LARGELY LEFT UNCHANGED OVERNIGHT. A BUILDING
NORTHEAST TRADE-WIND SWELL LOOKS TO MOVE INTO THE REGION TONIGHT.
FOR NOW, SEAS AND SURF LOOK TO REMAIN BELOW HAZARDOUS LEVELS AT PALAU
AND YAP, HOWEVER, A SLIGHT INCREASE IN THE EXPECTED NORTHEAST SWELL
COULD CHANGE THIS. HIGHER SEAS ARE EXPECTED TO MOVE INTO CHUUK THIS
EVENING.THE TRADE SWELL LOOKS TO BE IN THE 6 TO 8 FOOT RANGE,
RESULTING IN HAZARDOUS SURF CONDITIONS ALONG NORTH FACING REEFS.
THEREFORE, A HIGH SURF ADVISORY WILL GO INTO EFFECT THIS AFTERNOON
AND CONTINUE INTO THURSDAY. SEAS OF UP TO 10 FEET REMAIN A
POSSIBILITY FOR CHUUK FOR TUESDAY AND TUESDAY NIGHT, BUT LATEST MODEL
DATA HAS DECREASED THAT POTENTIAL SLIGHTLY. ALTIMETRY AND DRIFTING
BUOYS WILL BE MONITORED CLOSELY TO DETERMINE IF SEAS ARE WILL BECOME
HAZARDOUS AT CHUUK. GENTLE TO MODERATE WINDS ARE EXPECTED AT CHUUK
THROUGH THE WEEK. FOR YAP AND PALAU, GENTLE TO MODERATE WINDS WILL
BECOME LIGHT TO GENTLE BY MIDWEEK.
PREV DISCUSSION
/ISSUED 626 PM CHST SUN DEC 21 2025/
MARIANAS SYNOPSIS...
THERE IS A SMALL CRAFT ADVISORY (SCA), A HIGH SURF ADVISORY (HSA)
AND A HIGH RISK OF RIP CURRENTS (HRRC) STATEMENT IN EFFECT.
SATELLITE IMAGERY SHOWS PARTLY CLOUDY SKIES, WHILE RADAR IMAGERY
SHOWS ONLY ISOLATED SHOWERS OUTSIDE OF GUAM'S SOUTHERN WATERS.
ALTIMETRY SHOWS 10 TO 11 FOOT SEAS JUST EAST OF THE ISLANDS. BUOY
DATA SHOWS HEIGHTS OF 8 TO 11 FEET.
DISCUSSION...
A MOSTLY PLEASANT TRANSITION SEASON WEATHER PATTERN HAS SET UP OVER
THE REGION. WINDS WILL BE THE MAIN CONCERN OVER THE NEXT SEVERAL
DAYS. WINDS ARE EXPECTED TO BE 15 TO 20 MPH. MONDAY, THERE IS A BIT
OF SPEED CONVERGENCE THAT MAY BRING SOME SHOWERS TO GUAM. OVERALL A
DRY, BUT WINDIER, WEATHER PATTERN IS IN STORE FOR THE ISLANDS.
MARINE/SURF...
THIS IS WHERE THE MAIN CONCERNS ARE AT. SEAS ARE EXPECTED TO REMAIN
ELEVATED AND MAY REACH UP TO 12 FEET OVER THE NEXT FEW DAYS. WINDS
ARE EXPECTED TO BE MODERATE TO STRONG. SURF ALONG NORTH AND EAST
FACING REEFS WILL ALSO BE ELEVATED AND SURF ALONG THESE REEFS MAY
REACH UP TO 13 FEET. EAST FACING REEFS ARE SLIGHTLY DELAYED BY ABOUT
12 HOURS OR SO. REGARDLESS, WHETHER YOU ARE A BOATER, SURFER OR BEACH
GOER, THE SEAS AND SURF ARE NOT EXPECTED TO BE KIND FOR THE NEXT
SEVERAL DAYS.
EASTERN MICRONESIA...
THE MAIN FEATURE TO WATCH THE NEXT FEW DAYS IS THE NORTHERLY SWELL.
AS STATED IN THE ADDITIONAL DETAILS OF THE HIGH SURF ADVISORY ISSUED
EARLIER THIS MORNING, SURF DID SUBSIDE BELOW THE 9 FOOT THRESHOLD
FOR NORTH-FACING REEFS AT KOSRAE. HOWEVER, A NEW NORTHERLY SWELL WILL
ARRIVE SOMETIME DURING THE LATTER HALF OF MONDAY. SEEING THAT THIS
WAS WITHIN 12 TO 18 HOURS OF THE AFTERNOON FORECAST PACKAGE ISSUANCE
AND IN COORDINATION WITH THE PREVIOUS SHIFT'S MESSAGING, WE OPTED TO
KEEP THE ADVISORY GOING AT KOSRAE. MEANWHILE, THE POHNPEI BUOY
OBSERVATION SHOWS SEAS NEAR 8 FEET, NORTHEAST SWELL NEAR 6 FEET,
WITH A PERIOD OF 13 SECONDS, WHICH EQUATES TO A SURF OF 9 FEET. THIS
ADVISORY IS CURRENTLY SET TO EXPIRE AT 3 PM TUESDAY, BUT THIS MAY
NEED TO BE EXTENDED AS THE MODEL GUIDANCE CONTINUES TO SHOW HAZARDOUS
CONDITIONS POTENTIALLY CONTINUING THROUGH THURSDAY, POSSIBLY LONGER.
OTHERWISE, A SLOW-MOVING TROUGH STRETCHES FROM KOSRAE TO MAJURO, WITH
AN AREA OF STRONGER SURFACE CONVERGENCE NOTED BETWEEN POHNPEI AND
KOSRAE. THIS CONVERGENCE AND THE TROUGH IS ALLOWING FOR WIDELY-
SCATTERED SHOWERS TO DEVELOP NEAR BOTH OF THOSE LOCATIONS, WHILE
REMAINING MORE ISOLATED NEAR MAJURO. WE'LL KEEP AN EYE ON MAJURO
THOUGH FOR ANY POTENTIAL INCREASE IN SHOWER COVERAGE GIVEN THE
BOUNDARY IS IN YOUR NORTHWESTERN COASTAL WATERS, CLOSE ENOUGH TO
STILL ACT AS A FOCUS FOR CONVECTIVE DEVELOPMENT.
LOOKING AHEAD, PRECIPITATION-WISE, THE GFS GDI FORECASTS ARE RATHER
PALTRY WITH UPSTREAM SATELLITE IMAGERY NOT SHOWING MUCH CONVECTION
ASSOCIATED WITH AN UPSTREAM AREA OF CONVERGENCE LOCATED NEAR 170W.
IT REMAINS TO BE SEEN IF TROUGH GENESIS WILL TAKE PLACE, ALLOWING
MOISTURE TO POOL ALONG IT. SHOULD THIS OCCUR, CONVECTIVE COVERAGE
WOULD INCREASE AS IT HEADS WEST ACROSS THE DATE LINE AND INTO EASTERN
MICRONESIA. WE'VE SEEN THIS SCENARIO PLAY OUT LIKE THAT A FEW TIMES
OVER THE LAST FEW MONTHS, BUT, MORE OFTEN THAN NOT IT ISN'T AS ROBUST
OR WIDESPREAD AS THE MODELS SHOW. THUS, LATER FORECASTS MAY NEED TO
TREND DOWN RAINFALL POTENTIAL FOR THE LATTER HALF OF THE WEEK.
WESTERN MICRONESIA...
THE LATEST SATELLITE DATA SHOWS PARTLY CLOUDY SKIES WITH SPOTTY
SHOWERS OVER YAP AND CHUUK. MOSTLY CLOUDY SKIES WITH SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS ARE FOUND OVER PALAU. ALTIMETRY
SHOWS SEAS OF 5 TO 7 FEET FOR PALAU AND YAP, WITH 5 TO 8 FEET NEAR
AND NORTHEAST OF CHUUK.
AN OVERALL DRY PATTERN IS IN PLACE ACROSS WESTERN MICRONESIA. THE
ONLY EXCEPTION IS OVER PALAU. AT PALAU, LOW-END SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS REMAIN OVER THE REPUBLIC THIS AFTERNOON.
HOWEVER, THIS CONVECTION IS DRIFTING NORTHWEST, WITH THE DRIER
PATTERN MOVING INTO PALAU LATER THIS EVENING. FOR CHUUK, INCREASING
SHOWERS LOOK TO MOVE INTO THE AREA MONDAY AFTERNOON OR EVENING AS A
COUPLE OF WEAK TRADE-WIND TROUGHS APPROACH. THE TROUGHS WILL BRING
POPS (PROBABILITY OF PRECIPITATION) OF 30 TO 40% TO WENO THROUGH
TUESDAY NIGHT. DRY CONDITIONS THEN LOOK TO RETURN TO CHUUK AROUND
MIDWEEK. FOR YAP AND PALAU, THE TROUGHS MOVING THROUGH CHUUK LOOK TO
APPROACH THE REGION LATER IN THE WEEK, BRINGING AN INCREASE IN
SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS TO THE AREA THURSDAY
INTO FRIDAY.
THE MARINE FORECAST REMAINS RELATIVELY UNCHANGED. A BUILDING
NORTHEAST TRADE-WIND SWELL LOOKS TO MOVE INTO THE REGION BEGINNING
MONDAY NIGHT. FOR NOW, SEAS AND SURF LOOK TO REMAIN BELOW HAZARDOUS
LEVELS AT PALAU AND YAP, HOWEVER, A SLIGHT INCREASE IN THE EXPECTED
NORTHEAST SWELL COULD CHANGE THIS. HIGHER SEAS ARE EXPECTED TO MOVE
INTO CHUUK MONDAY AFTERNOON OR EVENING. THE TRADE SWELL LOOKS TO BE
IN THE 6 TO 8 FOOT RANGE, RESULTING IN HAZARDOUS SURF CONDITIONS
ALONG NORTH FACING REEFS. THEREFORE, A HIGH SURF ADVISORY WAS ISSUED
FOR NORTH FACING REEFS OF CHUUK BEGINNING MONDAY AFTERNOON. SEAS OF
UP TO 10 FEET REMAIN A POSSIBILITY FOR CHUUK FOR TUESDAY AND TUESDAY
NIGHT. THEREFORE, A SMALL CRAFT ADVISORY IS A POSSIBILITY AS EARLY AS
TUESDAY MORNING. GENTLE TO MODERATE WINDS ARE EXPECTED AT CHUUK
THROUGH THE WEEK. FOR YAP AND PALAU, GENTLE TO MODERATE WINDS WILL
BECOME LIGHT TO GENTLE BY MIDWEEK.
GUM WATCHES/WARNINGS/ADVISORIES
GU...HIGH RIP CURRENT RISK THROUGH LATE TONIGHT FOR GUZ001.
HIGH SURF ADVISORY UNTIL 4 AM CHST TUESDAY FOR GUZ001.
MP...HIGH RIP CURRENT RISK THROUGH LATE TONIGHT FOR MPZ001>003.
HIGH SURF ADVISORY UNTIL 4 AM CHST TUESDAY FOR MPZ001>003.
MARIANAS WATERS...SMALL CRAFT ADVISORY UNTIL 5 AM CHST TUESDAY FOR PMZ151>154.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: SCHANK
MARIANAS: BOWSHER
EAST MICRONESIA: DOLL/KLEESCHULTE
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