829
FXPQ50 PGUM 242017
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
617 AM CHST THU DEC 25 2025
MARIANAS UPDATE
SHRUNK THE AREA OF THUNDERSTORMS TO A PERCENTAGE WHERE THE FORMATTER
JUST GLOSSED OVER IT, AND IT ISN'T MENTIONED. THE CONVECTION HAS
STRATIFIED AND THEY ARE NOW UNLIKELY. OVERALL VERY LITTLE CHANGE FROM
THE FORECAST OF YESTERDAY THOUGH. THE RAIN OF THE PAST FEW DAYS DID
KNOCK THE KBDI DOWN TO 0, WHICH WILL HELP THE FIRE WEATHER SITUATION,
SO AT LEAST ONE GOOD EFFECT CAME OUT OF IT.
MARINE
DID GO AHEAD AND REDO ALL OF THE WAVEHEIGHT GRIDS. THERE WERE SOME
THAT HAD STRANGE INTERFERENCE PATTERNS THAT WHILE PRETTY, WEREN'T
PHYSICAL. THOSE ARE GONE NOW, SO THE FIGURES REPRESENT THE ACTUAL
WAVEHEIGHTS EXPECTED. IN THE EXTENDED, THE WAVE HEIGHTS ARE A BIT
LOWER AROUND THE BEGINNING OF THE YEAR. THEY ALSO NEVER REACH 10 FEET
IN THE NEWEST MODEL RUN, SO THE NEW SWELL PULSES JUST AREN'T REACHING
THE SAME LEVEL THAT THE FIRST ONE DID.
EASTERN MICRONESIA UPDATE
RAISED THE POP'S FROM 20 TO 30 EACH AT POHNPEI AND KOSRAE. THE SHEAR
LINE IS PRESSING HARD ON BOTH ISLANDS, WITH COPIOUS CLOUDS AND
DOUBTLESS SOME SHOWERS, PROBABLY ENOUGH TO COUNT AS SCATTERED.
WESTERN MICRONESIA UPDATE
THE ONLY CHANGE FROM LAST NIGHT'S FORECAST WAS TO LOWER THE POP'S
FROM 40 TO 20 FOR YAP. THE CLOUDS HAVE ENDED UP HIGH AND THIN THERE,
MOSTLY CIRRUS. CHUUK WILL HAVE SOME SCATTERED SHOWERS IN THE AREA,
AND KOROR, PALAU WAS ALREADY FORECAST TO BE HIGH AND DRY, SO THESE
LOCATIONS WERE FINE AS THEY WERE.
PREV DISCUSSION
/ISSUED 616 PM CHST WED DEC 24 2025/
MARIANAS SYNOPSIS...
SATELLITE IMAGERY SHOWS MOSTLY CLOUDY TO CLOUDY SKIES, WHILE RADAR
IMAGERY SHOW ISOLATED SHOWERS OVER THE MARIANAS AND COASTAL WATERS.
ALTIMETRY SHOWS COMBINED SEAS OF 6 TO 8 FEET AND BUOY DATA SHOWS SEA
HEIGHTS OF 6 TO 7 FEET.
DISCUSSION...
A TRADE-WIND TROUGH AND AN UPPER-LEVEL TROUGH ARE PRODUCING
WIDESPREAD SHOWERS AND ISOLATED THUNDERSTORMS TO THE WEST OF THE
MARIANAS. THESE FEATURES ARE ALSO PRODUCING SHOWERS THAT ARE
GRADUALLY BACK BUILDING TOWARDS THE ISLANDS. SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS WERE PUT INTO THE FORECAST TO REFLECT THIS FOR
TONIGHT. TIME-HEIGHTS AND MODEL DATA SHOW A GRADUAL DRYING OUT OF OF
THE REGION'S MIDDLE AND UPPER LAYERS, AND THIS DRIER AIR WILL HELP
TO INHIBIT DEEP CONVECTION OVER THE AREA FOR CHRISTMAS AND THE NEXT
SEVERAL DAYS.
MARINE...
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 FURTHER DIMINISH. ALTIMETRY SUGGESTS THERE IS
A STRONGER PULSE FROM THE NORTH SWELL TO THE EAST OF THE ISLANDS
THAT IS PASSING OUTSIDE THE COASTAL WATERS, BUT THIS LOOKS TO BE A
NEAR MISS. HOWEVER, SEAS WITHIN THE COASTAL WATERS ARE EXPECTED TO
BE AROUND 6 TO 8 FEET AND ARE EXPECTED TO REMAIN FAIRLY STEADY
THROUGH THE WEEKEND. THEN, THEY BEGIN TO DECREASE AROUND THE
BEGINNING OF NEXT WEEK.
HYDROLOGY...
SO FAR TODAY, 1.13 INCHES OF RAIN HAVE FALLEN AT THE AIRPORT, WITH
HIGHER AMOUNTS OVER SOUTHERN PORTIONS OF THE ISLAND. LATEST CIMMS
MIMIC MODELS SUGGEST A LOWER PRECIPITABLE WATER (PWAT) OF ABOUT 1.8
INCHES. SCATTERED SHOWERS ARE POSSIBLE TONIGHT DEPENDING ON HOW FAR
THE FEATURES, TALKED ABOUT IN THE DISCUSSION, BACK BUILD.
EASTERN MICRONESIA...
VISIBLE SATELLITE IMAGERY SHOWS PATCHY CLOUDS AND SHOWERS OVER THE
MAIN FORECAST LOCATIONS THIS AFTERNOON. SOME ARE REMNANTS OF AN OLD
SHEAR LINE, WHILE WEATHER NEAR KOSRAE AND MAJURO LOOK TO BE FROM WEAK
CONVERGENCE IN THE EAST TO NORTHEAST TRADES. OVERALL, FAIRLY QUIET
WEATHER IS EXPECTED OVER THE NEXT FEW DAYS, THEN LATEST MODEL
GUIDANCE SHOWS AN INTERTROPICAL CONVERGENCE ZONE (ITCZ) ATTEMPTING
TO BUILD BACK IN, MAINLY OVER THE SOUTHERN HALF OF THE REGION.
OVERALL SHOWER COVERAGE LOOKS A BIT UNORGANIZED, WITH EMBEDDED
TROUGHS SPREADING SHOWERS NORTH OVER THE FORECAST LOCATIONS, OVER THE
WEEKEND AND EARLY NEXT WEEK.
ALTIMETRY AND BUOY DATA SHOWED HAZARDOUS SEAS OF 7 TO 9 FEET NEAR
POHNPEI AND 6 TO 8 FEET NEAR KOSRAE AND MAJURO. A LONGER-PERIOD NORTH
SWELL AND NORTHEAST TRADE SWELL CONTINUE TO SUPPORT HAZARDOUS SURF
ALONG NORTH-FACING REEFS THROUGH AT LEAST TONIGHT. SEAS AND SURF ARE
EXPECTED TO SUBSIDE ANOTHER FOOT OR TWO THURSDAY, HOWEVER ANOTHER
PULSE OF NORTHERLY SWELL ARRIVES LATE WEEK AND OVER THE WEEKEND,
PUSHING COMBINED SEAS BACK UP TO 7 TO 9 FEET, POSSIBLY UP TO
HAZARDOUS LEVELS OF 10 FEET FOR POHNPEI. DEPENDING ON THE BUOY DATA
AT POHNPEI OVERNIGHT, THE HIGH SURF ADVISORY MAY BE ALLOWED TO EXPIRE
EARLY THURSDAY MORNING. HOWEVER, IF ANOTHER EXTENSION IS WARRANTED,
THE TIMING OF THE NEXT PULSE OF NORTH SWELL MAY KEEP PROLONG THIS
ADVISORY THROUGH THE WEEKEND. LIGHT TO MODERATE TRADES CONTINUE,
INCREASING TO GENTLE TO FRESH NEAR POHNPEI AND MAJURO OVER THE
WEEKEND.
WESTERN MICRONESIA...
A FEW TRADE-WIND TROUGHS, STEMMING FROM A WEAK BUFFER CIRCULATION
NEAR EQ140E, HAVE BEEN PRODUCING NUMEROUS SHOWERS AND ISOLATED
THUNDERSTORMS TO THE SOUTH OF THE MAIN ISLANDS OF YAP AND PALAU.
SWATHS OF UPPER-LEVEL CLOUDS ASSOCIATED WITH THIS CONVECTION HAVE
BEEN STREAMING OVERHEAD, BUT OVERALL, SHOWERS HAVE BEEN LIGHT AND
ISOLATED OVER YAP AND PALAU COASTAL WATERS. SHOWERS WILL INCREASE
LATE OVERNIGHT NEAR YAP AS ONE OF THE AFOREMENTIONED TROUGHS,
CURRENTLY CENTERED BETWEEN SOROL AND EAURIPIK IN YAP STATE, SHIFTS
WEST-NORTHWEST INTO THE AREA. THIS TROUGH LOOKS TO BUILD OVER THE
AREA AROUND THURSDAY NIGHT AS IT MERGES WITH ANOTHER DISTURBANCE, ALSO
CONNECTED WITH THE BUFFER CIRCULATION FURTHER SOUTH, MAINTAINING AT
LEAST SCATTERED SHOWERS FOR YAP AND PALAU INTO THE WEEKEND WITH A
PEAK AROUND FRIDAY. THE NEXT DISTURBANCE LOOKS TO MOVE INTO THE
REGION EARLY NEXT WEEK, BEFORE A DRIER TRADE-WIND REGIME MOVES IN
AROUND MIDWEEK. CHUUK WILL EXPERIENCE A MORE UNEVENTFUL PATTERN, BUT
WILL SEE PERIODS OF A LEAST LOW-END SCATTERED SHOWERS (30 PERCENT
CHANCE) INTO THE WEEKEND DUE TO WEAK TRADE-WIND CONVERGENCE AS THE
PATCHY REMNANTS OF A SHEARLINE FRAGMENT LINGER NEARBY. A DRIER
PATTERN RESUMES FOR CHUUK EARLY NEXT WEEK.
SATELLITE ALTIMETRY SHOWS COMBINED SEAS AROUND 6 TO 8 FEET ACROSS THE
REGION, COMPRISED MAINLY OF THE BACKGROUND TRADE SWELL, LIGHT WIND
WAVES, AND A DIMINISHING PULSE OF NORTH-NORTHEAST SWELL THAT MOVED
THROUGH THE REGION EARLY THIS WEEK. ANOTHER PULSE OF ELEVATED NORTH-
NORTHEAST SWELL ENTERS THE REGION AROUND SATURDAY, INCREASING SEAS
MAINLY FOR CHUUK AS MORE OF THE SWELL ENERGY IS FOCUSED FURTHER EAST.
THIS 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. GENTLE TO
MODERATE WINDS ARE EXPECTED AT CHUUK THROUGH THE WEEKEND. FOR YAP
AND PALAU, WINDS LOOK TO REMAIN MOSTLY LIGHT TO GENTLE, BECOMING
GENTLE TO MODERATE FOR YAP THIS WEEKEND.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: STANKO
MARIANAS/HYDROLOGY: BOWSHER
EAST MICRONESIA: CRUZ
WEST MICRONESIA: DECOU
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