752
FXPQ50 PGUM 241931
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
531 AM CHST SUN JAN 25 2026
MARIANAS UPDATE
THE LEADING EDGE OF THE STATIONARY FRONT HAS SLIPPED SOUTHWARD TO
JUST NORTH OF THE SAIPAN WATERS. THE INHERITED GRIDS COVERED THIS, SO
NO CHANGES WERE NEEDED ON THE OVERNIGHT SHIFT. SOUTHWEST WINDS WILL
GRADUALLY LIGHTEN, BECOME VARIABLE, THEN CHANGE TO NORTHEAST AS THE
FRONT MOVES CLOSER. THE NORTHEAST WINDS WILL THEN START INCREASING.
MARINE
COMBINED SEAS OF 8 TO 11 FEET WILL DOMINATE THROUGH TUESDAY. THIS WAS
WELL HANDLED BY THE PREVIOUS GRIDS, SO NO CHANGES WERE NEEDED
OVERNIGHT. WINDS BEHIND THE STATIONARY FRONT ARE RESPONSIBLE FOR
THESE WAVES AND OTHER WEATHER.
EASTERN MICRONESIA UPDATE
EASTERN MICRONESIA IS PRETTY QUIET AT THIS TIME. THAT WAS COVERED
WELL IN THE INHERITED GRIDS, SO THERE WAS NO NEED FOR ANY CHANGES. A
TROUGH IS MOVING THROUGH POHNPEI SOON, BUT THEY'RE AT THE WEAK
(NORTH) END AND IT SEEMS TO BE WEAKENING FURTHER, SO IT LIKELY WON'T
AMOUNT TO MUCH. SIMILAR FOR KOSRAE, AND MAJURO HAS A BIG CLEAR AREA
UPSTREAM.
WESTERN MICRONESIA UPDATE
CHUUK AND YAP HAVE SUBSTANTIAL CLEAR AREAS UPSTREAM. THE INHERITED
FORECAST COVERED THAT WELL FOR THEM, SO NO CHANGES WERE NEEDED. THE
SHEAR LINE THAT CONTINUES FROM THE STATIONARY FRONT RUNS ONLY 100 TO
150 MILES WEST OF KOROR, PALAU. IT IS NOT EXPECTED TO REACH THEM, BUT
IT IS CERTAINLY NOT OUTSIDE THE REALM OF POSSIBILITY.
PREV DISCUSSION
/ISSUED 731 PM CHST SAT JAN 24 2026/
MARIANAS SYNOPSIS...
SATELLITE AND RADAR OBSERVATIONS SHOW SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS ACROSS THE REGION. ALTIMETRY DATA SHOWS COMBINED SEAS
BETWEEN 8 AND 10 FEET ACROSS THE MARIANAS.
DISCUSSION...
THE FORECAST FOR THE MARIANAS REMAINS QUITE COMPLEX. A NEAR-
STATIONARY FRONT THAT TRANSITIONS INTO A SHEARLINE INTERACTING WITH A
TROPICAL WAVE AND A REMNANT LOW IS OUTSIDE THE CLIMATOLOGICAL NORM
FOR THE MARIANAS. ADDITIONALLY, THIS PATTERN WILL ALLOW FOR A BRIEF
DECREASE IN WINDS ALOFT OVER GUAM LEADING TO ISLAND EFFECT SHOWERS,
WHICH IS ALSO OUTSIDE THE CLIMATOLOGICAL NORM FOR THIS TIME OF THE
YEAR. THE ISLAND EFFECT SHOWERS, AND THE BOUNDARY TO THE NORTH ARE
THE MAIN WEATHER CONCERNS THROUGH THE PERIOD.
00Z MODEL GUIDANCE SHOWS LIGHT WINDS OUT OF THE SOUTH-SOUTHWEST FROM
THE SURFACE TO ABOUT 600MB. THE COMBINATION OF THE LIGHT WINDS
RUNNING PARALLEL TO GUAM, AND PWAT VALUES EXCEEDING 2.25 INCHES,
THERE IS CONCERN FOR ISLAND EFFECT SHOWERS AND THUNDERSTORMS. THERE
IS SOME CONCERN FOR CLOUD COVER IN THE MORNING, BUT UPPER LEVEL FLOW
IS EXPECTED TO BE EASTERLY, WHICH SHOULD LIMIT CIRRUS FROM MOVING
TOWARDS GUAM FROM CONVECTION TO THE NORTH. THERE IS A CHANCE THAT
SHOWERS MAY ALREADY BE ONGOING SOUTH OF GUAM AS WELL, WHICH WOULD
SHIFT THE FOCUS FROM ISLAND EFFECT TO ISLAND ENHANCED SHOWERS. EITHER
WAY, LOCALLY HEAVY RAINFALL WILL BE POSSIBLE WITH THESE SHOWERS.
SATELLITE OBSERVATIONS SHOW THE CONVECTIVE EDGE OF THE NEAR-
STATIONARY FRONT NORTH OF THE MARIANAS HAS PROPAGATED SOUTHWARD FROM
AGRIHAN TO JUST NORTH OF ANATAHAN TODAY. THIS PROPAGATION IS LIKELY
DUE TO THE COLD POOLS FORMED FROM INTENSE CONVECTION THROUGHOUT
TODAY. THE LINE OF CONVECTION HAS BEGUN TO STRATIFY OUT, LIKELY
INFLUENCED BY DIURNAL MINIMUM. THIS SHOULD SLOW THE SOUTHWARD
PROGRESS OF THE BOUNDARY UNTIL CONVECTION RE-IGNITES TOMORROW.
GUIDANCE STILL DIFFERS ON THE TIMING AND LOCATION OF WHERE THE
BOUNDARY IS EXPECTED TO STALL AND THEN LIFT NORTH. THE GFS HAS BEEN
ON THE SOUTHERN SIDE OF GUIDANCE WHILE THE ECMWF IS ON THE NORTHERN
SIDE. HOW CONVECTIVELY ACTIVE THE BOUNDARY STAYS WILL DETERMINE JUST
HOW FAR SOUTH IT GETS. WHERE THE BOUNDARY STALLS IS WHERE THE RISK
OF VERY HEAVY RAINFALL WILL BE. SEE HYDROLOGY SECTION FOR MORE
DETAILS.
MARINE...
COMBINED SEAS OF 8 TO 10 FEET HAVE LED TO SEAS BEING HAZARDOUS TO
SMALL CRAFT ACROSS THE MARIANAS. SEAS MAY RISE ANOTHER FOOT OR SO
TONIGHT BEFORE A DOWNWARD TREND BEGINS SUNDAY NIGHT. HAZARDOUS SURF
IS ALSO SEEN ALONG NORTH AND WEST FACING REEFS. SURF LOOKS TO REMAIN
HAZARDOUS THROUGH EARLY NEXT, BUT COULD REMAIN ELEVATED FOR NORTH
FACING REEFS TOWARDS THE MIDDLE OF THE WEEK. COMBINED SEAS MAY
REMAIN ELEVATED FOR SAIPAN AND TINIAN WHILE FALLING BELOW HAZARDOUS
TO SMALL CRAFT LEVELS MONDAY NIGHT FOR GUAM AND ROTA. ANOTHER ROUND
OF NORTHERLY SWELL LOOKS TO IMPACT THE REGION NEXT WEEKEND, WHICH
COULD BRING SEAS BACK TO HAZARDOUS TO SMALL CRAFT ACROSS THE
MARIANAS.
HYDROLOGY...
HEAVY TO VERY HEAVY RAINFALL IS EXPECTED ALONG A NARROW BAND OF THE
NEAR-STATIONARY FRONTAL BOUNDARY BEGINNING SUNDAY NIGHT AND ENDING
WEDNESDAY AFTERNOON. WIDESPREAD RAINFALL WILL GENERALLY BE 2 TO 4
INCHES ACROSS THE MARIANAS, HOWEVER, RAINFALL IN THE CONVECTIVE BAND
COULD RANGE FROM 8 TO 12 INCHES. AT THIS TIME THE LOCATION OF THE
BAND AND ITS SIZE REMAIN UNCERTAIN. CONFIDENCE WAS TOO LOW TO ISSUE A
FLOOD WATCH, BUT DUE TO THE POTENTIAL IMPACTS ALONG THE CONVECTIVE
LINE, A FREE TEXT HEADLINE WAS ISSUED. CURRENT GUIDANCE FAVORS THE
CONVECTIVE LINE TO SETTLE OVER SAIPAN AND TINIAN, BUT PROPAGATION
FROM ONGOING THUNDERSTORMS ALONG THE BOUNDARY COULD SHIFT THAT SOUTH
TO ROTA OR GUAM. THOSE IN THE MARIANAS SHOULD CONTINUE TO MONITOR
FORECASTS FOR UPDATES AND ADDITIONAL INFORMATION.
EASTERN MICRONESIA...
SATELLITE THIS AFTERNOON SHOWS EXTENSIVE CLOUD COVER ACROSS KOSRAE
STATE AND THE SOUTHWESTERN MARSHALL ISLANDS, ASSOCIATED IN PART WITH
A PRIOR BAND OF STRONG CONVECTION THAT DEVELOPED THIS MORNING JUST
EAST OF KOSRAE, AND WITH SCATTERED TO NUMEROUS SHOWERS WHICH
CONTINUE ACROSS THE AREA. SHOWERS ARE ASSOCIATED WITH A BROAD TRADE-
WIND TROUGH EXTENDING FROM NORTHWEST TO SOUTHEAST, JUST EAST OF
KOSRAE, AND WITH A BAND OF TRADE CONVERGENCE OVER THE RMI, ALONG THE
BACK SIDE OF THE TROUGH. MODELS DEPICT DECREASING SHOWERS ACROSS THE
REGION LATE TONIGHT THROUGH THE REST OF THE WEEKEND AS THE WEAK
DISTURBANCE AND ASSOCIATED CONVERGENCE SHIFT TOWARD THE SOUTH AND
DIMINISH. THEREAFTER, A MOSTLY DRY TRADE-WIND PATTERN PREVAILS
THROUGH MUCH OF THE FORECAST PERIOD, WITH A SLIGHT INCREASE IN
SHOWERS AROUND MIDWEEK THROUGH THE LATTER HALF OF THE WEEK, WITH THE
PASSAGE OF SEVERAL WEAK TRANSIENT TROUGHS.
POHNPEI BUOY AND ALTIMETRY DATA INDICATE COMBINED SEAS AROUND 3 TO 5
FEET FOR POHNPEI AND KOSRAE AND 4 TO 6 FEET NEAR MAJURO. WINDS WILL
BE LIGHT TO MODERATE THROUGHOUT THE FORECAST PERIOD, BECOMING
INCREASINGLY FRESH TOWARD THE LATTER HALF OF THE COMING WEEK AS THE
REGIONAL PRESSURE GRADIENT STRENGTHENS AND TRADES BEGIN TO SURGE. THE
NORTHEAST TRADE SWELL WILL ALSO INCREASE BY A FOOT OR TWO, WHICH
COULD BEGIN TO GENERATE HAZARDOUS SURF ALONG NORTH FACING REEFS OF
POHNPEI AND MAJURO, AND NORTH AND EAST FACING REEFS OF KOSRAE, AROUND
WEDNESDAY LASTING INTO THE WEEKEND. THE INCREASE IN TRADE WINDS AND
DEVELOPING SWELL WILL BE CLOSELY MONITORED FOR POSSIBLE HAZARD
ISSUANCES NEXT WEEK.
WESTERN MICRONESIA...
SATELLITE IMAGERY SHOWS MOSTLY CLOUDY SKIES FOR PALAU, WITH PARTLY
CLOUDY SKIES OVER YAP AND CHUUK. SPOTTY SHOWERS ARE FOUND ACROSS THE
REGION FROM PALAU EASTWARD, WITH NUMEROUS SHOWERS AND ISOLATED
THUNDERSTORMS SEEN WELL WEST AND NORTH OF PALAU. ALTIMETRY SHOWS
SEAS OF 8 TO 11 FEET JUST WEST OF PALAU AND YAP, WITH 4 TO 6 FEET
FOR CHUUK.
THE DRY PATTERN CONTINUES ACROSS WESTERN MICRONESIA THIS EVENING,
WITH ONLY SPOTTY SHOWERS SEEN NEAR ALL THREE FORECAST POINTS.
MODERATE TO DEEP CONVECTION IS SEEN TO THE WEST AND NORTH OF PALAU,
WEST OF 130E, AND NORTH OF 10N. THE DRY PATTERN LOOKS TO CONTINUE
THROUGH THE WEEK FOR PALAU, WITH YAP SEEING A BIT OF AN INCREASE IN
CONVECTION AROUND TUESDAY NEXT WEEK AS THE SHEAR LINE TO THE NORTH
OF 10N DRIFTS FAR ENOUGH SOUTH. THIS INCREASE IN SHOWERS WILL BE
SHORT-LIVED, WITH DRIER CONDITIONS RETURNING BY THE MIDDLE OF NEXT
WEEK. FOR CHUUK, WENO LOOKS TO REMAIN FAIRLY DRY THROUGH THE MIDDLE
OF NEXT WEEK. AROUND THURSDAY NEXT WEEK, INCREASED SHOWERS COULD
APPROACH CHUUK FROM THE EAST AS A TRADE-WIND TROUGH APPROACHES FROM
EASTERN MICRONESIA.
THE AFOREMENTIONED SHEAR LINE IS THE MAIN PLAYER FOR THE REGION OVER
THE NEXT FEW DAYS. THIS FEATURE IS PRODUCING A LARGE NORTHWEST TO
NORTH SWELL THAT WILL MAINTAIN HAZARDOUS SURF CONDITIONS ALONG WEST
AND NORTH FACING REEFS OF PALAU AND YAP. THE LATEST ALTIMETRY DATA
SHOWS SEAS OF 8 TO 11 FEET WEST OF PALAU AND WEST OF YAP PROPER. A
SOFAR BUOY TO THE NORTHWEST OF PALAU IS SHOWING SEAS BETWEEN 12 AND
14 FEET. BASED ON THE AVAILABLE DATA, THE SMALL CRAFT ADVISORY WAS
EXTENDED BY 12 HOURS FOR BOTH YAP AND PALAU, WHILE THE HIGH SURF
ADVISORY WAS ALSO EXTENDED 12 HOURS FOR BOTH LOCATIONS. THE SHEAR
LINE WILL BE MONITORED CLOSELY, ALONG WITH ALTIMETRY DATA, TO
DETERMINE IF THE ADVISORIES NEED ADDITIONAL EXTENSIONS. WINDS LOOK
TO BE LIGHT TO GENTLE FOR YAP AND PALAU THROUGH THE COMING WEEK. FOR
CHUUK, ALTIMETRY SHOWS SEAS BETWEEN 4 AND 6 FEET. SEAS LOOK TO
REMAIN AT THIS LEVEL THROUGH MONDAY NIGHT, THEN BEGIN TO BUILD
THROUGH MIDWEEK. SEAS ARE NOT EXPECTED TO REACH LEVELS HAZARDOUS
FOR SMALL CRAFT AT THIS TIME. A BRIEF HIGH SURF ADVISORY IS POSSIBLE
AROUND THE MIDDLE OF NEXT WEEK. WINDS WILL BE MOSTLY GENTLE TO
MODERATE THROUGH NEXT WEEK.
GUM WATCHES/WARNINGS/ADVISORIES
GU...HIGH RIP CURRENT RISK THROUGH MONDAY AFTERNOON FOR GUZ001.
HIGH SURF ADVISORY UNTIL 6 PM CHST MONDAY FOR GUZ001.
MP...HIGH RIP CURRENT RISK THROUGH MONDAY AFTERNOON FOR MPZ001>003.
HIGH SURF ADVISORY UNTIL 6 PM CHST MONDAY FOR MPZ001>003.
MARIANAS WATERS...SMALL CRAFT ADVISORY UNTIL 6 PM CHST MONDAY FOR
PMZ151>154.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: STANKO
MARIANAS: WILLIAMS
EAST MICRONESIA: DECOU
WEST MICRONESIA: KLEESCHULTE
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