410
FXPQ50 PGUM 232021
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
621 AM CHST WED DEC 24 2025
MARIANAS UPDATE
THE FORECAST FOR THE CNMI LOOKED PRETTY GOOD OVERALL, SO NO CHANGES
WERE NEEDED OVERALL THERE. HAD TO UPGRADE THE FORECAST FOR GUAM
THOUGH TO WIDESPREAD SHOWERS. THE KBDI FOR TODAY IS 84. MOST LIKELY
THE KBDI FOR CHRISTMAS DAY WILL BE 0. AT LEAST THE FORESTRY FOLKS
WILL VIEW THAT AS A WELCOME CHRISTMAS GIFT.
MARINE
SEAS ARE SLOWLY DIMINISHING, AND THIS ALLOWED SURF TO DECREASE, AND
THE RISK OF RIP CURRENTS SLIPPED TO MODERATE. THE RESPITE COULD BE
SHORT LIVED AS ANOTHER PUSH OF SWELL IS PREDICTED IN THE MODELS. IT
LOOKS LESS ROBUST THAN THIS ONE THOUGH, SO HOPEFULLY NOT QUITE AS
LONG LIVED.
HYDROLOGY
COLLIDING BOUNDARIES AND A MID-LATITUDE TROUGH CONSPIRED TOGETHER TO
CREATE WIDESPREAD SHOWERS OVER GUAM, SOME OF WHICH ENDED UP BEING
LOCALLY HEAVY. THIS WAS PARTICULARLY A PROBLEM IN SOUTHERN GUAM WHERE
THE DRAINAGE SYSTEM CANNOT HANDLE AS MUCH. WE ENDED UP ISSUING A
FLOOD ADVISORY FOR THE ENTIRE ISLAND AND A WARNING FOR CENTRAL AND
SOUTHERN GUAM. SUBSTANTIAL FLOODING HAS BEEN REPORTED IN MERIZO
ESPECIALLY. WE'RE CANCELING THE WARNING NOW SINCE THE HEAVIEST
SHOWERS HAVE MOVED OFF TO THE SOUTH. WITH ALL THIS ANTECEDENT
RAINFALL, ANY FUTURE RAINFALL WILL ALL BECOME RUNOFF, SO WE'RE
LEAVING THE ADVISORY IN EFFECT FOR A LITTLE WHILE AT LEAST.
EASTERN MICRONESIA UPDATE
THE WEATHER FORECAST WAS IN FINE SHAPE, WITH THE ONLY FEATURE NEARBY
BEING A SHEAR LINE THAT IS GETTING AWFULLY LONG IN THE TOOTH. HAD TO
ADJUST THE MARINE GRIDS THOUGH, AS ALTIMETRY AND BUOY DATA INDICATED
THE MODELS WERE ABOUT 2 FEET LOW. GRADUALLY BLENDED TOWARD THE
MODELS BY ADDING 2 FEET TODAY AND 1 FOOT TONIGHT, THEN LEAVING THE
REST UNCHANGED. ALSO EXTENDED THE HIGH SURF ADVISORY BY 12 HOURS TO
BE CONSISTENT WITH THE NOW INCREASED WAVE HEIGHTS.
WESTERN MICRONESIA UPDATE
EVERYTHING WAS IN FINE SHAPE WITH THE INHERITED FORECAST IN WESTERN
MICRONESIA, SO NO CHANGES WERE MADE. CHUUK IS CATCHING A FEW SHOWERS
FROM THE SHEAR LINE, WHILE YAP AND KOROR, PALAU ARE BETWEEN FEATURES,
SO THE WEATHER IS FAIRLY DRY. THE LONGER EFFECTIVE PERIOD FOR THE
HIGH SURF ADVISORY AT CHUUK LOOKED REALLY GOOD AS IT MATCHED BETTER
WITH THE NEWLY EXTENDED ADVISORY FOR POHNPEI AND KOSRAE.
PREV DISCUSSION
/ISSUED 646 PM CHST TUE DEC 23 2025/
MARIANAS SYNOPSIS...
THERE REMAINS A HIGH SURF ADVISORY AND A HIGH RISK OF RIP CURRENTS
STATEMENT IN EFFECT.
SATELLITE IMAGERY SHOWS MOSTLY CLOUDY TO CLOUDY SKIES, WHILE RADAR
IMAGERY SHOW SCATTERED SHOWERS OVER THE MARIANAS AND THEIR WATERS.
ALTIMETRY SHOWS COMBINED SEAS OF 8 TO 9 FEET AND BUOY DATA SHOWS SEA
HEIGHTS OF 7 TO 8 FEET.
DISCUSSION...
ANOTHER WET AND GUSTY DAY TODAY. AS OF 4 PM CHST, 1.11 INCHES OF RAIN
HAS FALLEN SINCE MIDNIGHT. THESE SHOWERS ARE PRODUCED BY CONVERGENCE
ALONG THE BACKSIDE OF THE TROUGH THAT PASSED YESTERDAY WITH SUPPORT
FROM AN UPPER-LEVEL TROUGH. THIS MIXTURE OF FEATURES HAS BEEN
PRODUCING WIDESPREAD SHOWERS AND SCATTERED THUNDERSTORMS JUST
WEST OUTSIDE THE COASTAL WATERS, WITH SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS BACK-BUILDING NEAR THE ISLANDS THIS EVENING. THESE
FEATURES ARE EXPECTED TO MAINTAIN SHOWERS NEARBY OVER THE NEXT DAY
OR SO, POTENTIALLY BRINGING WETTER CONDITIONS FOR CHRISTMAS EVE.
THEN, A RIDGE IS EXPECTED TO MOVE IN OVER THE MARIANAS FOR CHRISTMAS
DAY, BRINGING RELATIVELY DRIER WEATHER FOR THE REST OF THE WEEK.
MARINE/SURF...
THE SMALL CRAFT ADVISORY HAS EXPIRED. THE STRONG MID-LATITUDE HIGH
PRESSURE SYSTEM CONTINUES TO MOVE EASTWARD ACROSS THE PACIFIC AND
ALLOWING THE TRADE WINDS AND TRADE SWELL IN THE REGION TO DIMINISH.
SEAS OF 7 TO 9 FEET ARE EXPECTED TO SLOWLY SUBSIDE AS THE NORTHEAST
SWELL DECREASES. THIS DECREASE MAY BE SHORT LIVED AS ANOTHER
SIGNIFICANT PULSE OF NORTHEAST SWELL IS ANTICIPATED TO MOVE THROUGH
THE REGION LATER THIS WEEK. SURF AND RISK OF RIP CURRENTS ARE
EXPECTED TO FALL BELOW HAZARDOUS LEVELS AS EARLY AS WEDNESDAY
MORNING. THERE WILL BE A MODERATE RISK OF LIGHTNING THROUGH WEDNESDAY
FOR GUAM. NEAR THE END OF THE WEEK, ANOTHER PULSE OF NORTHEAST SWELL
IS ANTICIPATED TO MOVE THROUGH THE AREA. THIS MAY PRODUCE HIGHER
SURF.
EASTERN MICRONESIA...
THE TAIL-END OF A BROAD MID-LATITUDE LOW PRESSURE FRONTAL SYSTEM
CONTINUES TO WEAKEN. A BAND OF PATCHY CLOUDS AND SHOWERS IS DRAPED
ACROSS THE NORTHERN RMI AND PASSES NORTH OF KOSRAE AND POHNPEI. CIMSS
MIMIC TPW PRODUCT SHOWS A RELATIVELY DRIER AIRMASS TO THE SOUTH OF
THE FEATURE, INDICATING PRECIPITABLE WATER AMOUNTS OF 1.20-1.60
INCHES OVER KOSRAE AND MAJURO. FAIRLY QUIET WEATHER IS EXPECTED OVER
THE NEXT FEW DAYS, THEN THE INTERTROPICAL CONVERGENCE ZONE (ITCZ)
LOOKS TO BUILD BACK IN OVER THE DATE LINE LATE WEEK, INCREASING
SHOWERS AT MAJURO BY FRIDAY AND AT KOSRAE OVER THE WEEKEND.
ALTIMETRY AND BUOY DATA SHOWED HAZARDOUS SEAS OF 8 TO 10 FEET TODAY.
POHNPEI BUOY STILL SHOWS ELEVATED SEAS THIS AFTERNOON, BUT IS
SLIGHTLY BELOW HAZARDOUS LEVELS, AT 8 TO 9 FEET. AS THIS PULSE OF
NORTHERLY SWELL GRADUALLY SUBSIDES TONIGHT AND WEDNESDAY, SEAS
DECREASE BACK DOWN TO 6 TO 8 FEET. THE HIGH SURF ADVISORY ALONG
NORTH-FACING REEFS WAS EXTENDED ANOTHER 12 HOURS, NOW EXPIRING
WEDNESDAY AFTERNOON. ANOTHER PULSE OF NORTHERLY SWELL ARRIVES LATE
WEEK AND OVER THE WEEKEND, POSSIBLY PUSHING SURF ALONG NORTH FACING
SURF AND COMBINED SEAS UP TO HAZARDOUS LEVELS ONCE AGAIN.
WESTERN MICRONESIA...
A FAIRLY DRY TRADE-WIND REGIME PREVAILS ACROSS FAR WESTERN
MICRONESIA, WITH SATELLITE THIS AFTERNOON SHOWING JUST ISOLATED
SHOWERS ACROSS MUCH OF THE REGION. A BROAD TRADE-WIND TROUGH,
CURRENTLY CENTERED JUST NORTHEAST OF YAP PROPER, IS EXPECTED TO
PROPAGATE WESTWARD ACROSS THE PHILIPPINE SEA OVER THE NEXT DAY OR SO,
WITH THE SOUTHERN EXTENT MOVING OVER YAP. MODEL GUIDANCE POINTS TO A
FAIRLY DRY PATTERN CONTINUING FOR YAP AS MOST OF THE SHOWERS AND
THUNDERSTORMS REMAIN FURTHER NORTH, WHERE UPPER-LEVEL SUPPORT IS
MORE FAVORABLE. SHOWERS INCREASE FROM WEDNESDAY NIGHT ONWARD AS A
SEPARATE TRADE-WIND TROUGH, MOVING WEST ACROSS YAP STATE, GRADUALLY
PROGRESSES THROUGH THE AREA. SHOWERS WILL REMAIN AT LEAST SCATTERED
FOR PALAU AND YAP THROUGH THE WEEKEND, POSSIBLY BECOMING NUMEROUS
FOR YAP AT TIMES TOWARD THE END OF THE WEEK.
FOR CHUUK, THE TRADE-WIND TROUGH THAT WAS EXPECTED TO BRING HEAVIER
SHOWERS THROUGH THE AREA IS MOVING AWAY WELL TO THE WEST OF COASTAL
WATERS, NOW CENTERED NEAR SATAWAL. DRIER CONDITIONS FOLLOW
IMMEDIATELY IN ITS WAKE, BUT AN UPTICK IN SHOWERS IS EXPECTED
OVERNIGHT DUE TO WEAKLY CONVERGENT TRADES BEHIND THE EXITING TROUGH,
AS THE NEXT TRADE-WIND TROUGH APPROACHES FROM THE EAST NEAR POHNPEI.
SCATTERED SHOWERS ARE EXPECTED THROUGH THE NEXT FEW DAYS AS WEAK
PASSING TROUGHS IN THE AREA INTERACT WITH THE REMNANTS OF A SHEARLINE
FRAGMENT NEARBY, WITH A PEAK AROUND THURSDAY. DRIER CONDITIONS LOOK
TO PREVAIL THIS WEEKEND, BEFORE A POSSIBLE TRADE-WIND DISTURBANCE
INCREASES SHOWERS EARLY NEXT WEEK.
SATELLITE ALTIMETRY FROM THIS MORNING CONTINUED TO SHOW ELEVATED
SEAS ACROSS THE REGION, WITH CHUUK LOCATED ROUGHLY ALONG AN AREA
OF 9 TO 10 FOOT COMBINED SEAS, AFTER THE NORTH-NORTHEAST SWELL
REACHED PEAK INTENSITY. SEAS ARE EXPECTED TO DIMINISH TO AROUND 6 TO
8 FEET THROUGH TONIGHT AS THE PULSE OF ELEVATED SWELL SUBSIDES,
REMAINING IN THIS RANGE FOR MUCH OF THE WEEK BEFORE ANOTHER PULSE OF
ELEVATED NORTH-NORTHEAST SWELL ENTERS THE REGION AROUND SATURDAY.
THE NEXT PULSE OF SWELL IS EXPECTED TO BE A BIT WEAKER OVER CHUUK
WATERS WITH MORE OF THE SWELL ENERGY FOCUSED FURTHER EAST, BUT WILL
BE CLOSELY MONITORED FOR POTENTIAL SURF AND SMALL CRAFT HAZARDS THIS
WEEKEND. THE HIGH SURF ADVISORY REMAINS IN EFFECT UNTIL 5 PM CHST
THURSDAY, WHEN THE NORTHEAST SWELL AND ASSOCIATED SURF ARE EXPECTED
TO DIMINISH BELOW HAZARDOUS LEVELS FOR CHUUK. FOR PALAU AND YAP,
ALTIMETRY REVEALS COMBINED SEAS AROUND 6 TO 8 FEET, AND SEAS AND SURF
LOOK TO REMAIN BELOW HAZARDOUS LEVELS, HOWEVER, A SLIGHT INCREASE IN
THE EXPECTED NORTHEAST SWELL COULD CHANGE THIS. GENTLE TO MODERATE
WINDS ARE EXPECTED AT CHUUK THROUGH THE WEEK. FOR YAP AND PALAU,
WINDS LOOK TO REMAIN MOSTLY LIGHT TO GENTLE.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: AYDLETT
MARIANAS/EAST AND WEST MICRONESIA UPDATE: STANKO
MARIANAS: BOWSHER
EAST MICRONESIA: CRUZ
WEST MICRONESIA: DECOU
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