796
FXPQ50 PGUM 191906
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
506 AM CHST SUN JUL 20 2025
MARIANAS UPDATE
AN AREA OF TRADE-WIND CONVERGENCE REMAINS OVER THE REGION, WITH
DEEPENING CONVECTION TO THE WEST, WHERE A BROAD MONSOON PATTERN
CONVERGES WITH THE TRADE-WIND PATTERN. THE TROPICAL UPPER
TROPOSPHERIC TROUGH (TUTT) CONTINUES TO DRIFT NORTHWEST AWAY FROM THE
REGION, ALTHOUGH WE ARE STILL EXPECTING SHOWERY WEATHER AND ISOLATED
THUNDERSTORMS TO PERSIST TODAY EVEN WITHOUT THE STRONGER UPPER-LEVEL
SUPPORT THAT WE HAVE SEEN OVER THE PAST COUPLE DAYS. THE ONLY CHANGE
WAS TO INCREASE SHOWERS TO NUMEROUS WITH LOCALLY HEAVY SHOWERS
POSSIBLE TODAY, THEN GRADUALLY TAPERING BACK DOWN TO SCATTERED IN THE
EVENING.
COMBINED SEAS OF 3 TO 5 FEET ARE EXPECTED OVER THE NEXT FEW DAYS,
INCREASING TO 4 TO 6 FEET IN THE LATTER HALF OF THE WEEK, BUT COULD
POTENTIALLY BE HIGHER DEPENDING ON THE DEVELOPMENT OF THE WEST-
SOUTHWEST MONSOON SWELL. THIS COULD ALSO POTENTIALLY INCREASE SURF
ENOUGH TO PRODUCE A MODERATE RISK OF RIP CURRENTS ALONG SOUTH AND
WEST FACING REEFS AROUND THE MIDDLE OF THE WEEK.
EASTERN MICRONESIA UPDATE
LITTLE CHANGE HAS BEEN MADE TO THE FORECAST. DELAYED POHNPEI'S
SCATTERED SHOWERS TO THE AFTERNOON, BUT INCREASED POPS SLIGHTLY AS
THAT TROUGH BUILDS FURTHER UPSTREAM. A LARGE SWATH OF DEEP CONVECTION
SPANNING ACROSS MUCH OF THE ITCZ IN EASTERN MICRONESIA, WILL CONTINUE
TO PUMMEL KOSRAE AND MAJURO WITH HEAVY SHOWERS AND SOME
THUNDERSTORMS, WITH COVERAGE EXPECTED TO REMAIN HIGH AT KOSRAE
THROUGH TONIGHT. MEANWHILE, THE MARINE FORECAST REMAINS UNCHANGED.
WESTERN MICRONESIA UPDATE
THE FORECAST REMAINS LARGELY UNCHANGED FOR PALAU AND CHUUK.
MEANWHILE AT YAP, MODEL GUIDANCE CONTINUES TO GO A LITTLE HOT IN
SHOWER AND THUNDER COVERAGE DUE TO LOCAL MOISTURE COLUMNS AND
EXPECTED SHIFT IN WINDS TOWARD THE MONSOON TROUGH TO THE NORTH. AS
THIS SHIFT HAS BEEN A LITTLE SLOW TO PAN OUT, IN ADDITION TO A LULL
IN WINDS AND SHOWERS FORMING AROUND YAP, DIMINISHED POPS TO SCATTERED
THROUGH TONIGHT. OTHER THAN THAT, THE MARINE FORECAST REMAINS
UNCHANGED FOR ALL THREE FORECAST LOCATIONS.
PREV DISCUSSION
/ISSUED 609 PM CHST SAT JUL 19 2025/
MARIANAS SYNOPSIS...
SATELLITE IMAGERY SHOWS OVERCAST SKIES, AND DOPPLER RADAR SHOWS
NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS OVER THE MARIANAS.
ALTIMETRY SHOWS COMBINED SEAS OF 4 TO 5 FEET, AND RITIDIAN AND IPAN
BUOYS CONFIRM THIS. WINDS ARE LIGHT TO MODERATE.
DISCUSSION...
AN UNSETTLED PATTERN WILL PERSIST THROUGH THE NIGHT. AT THE SURFACE-
LEVEL AN AREA OF SPEED CONVERGENCE IS GRADUALLY PUSHING THROUGH THE
MARIANAS. UPPER-LEVEL SUPPORT IS ENHANCING THESE SHOWERS. THIS
FEATURE IS EXPECTED TO MOVE TO THE WEST CAUSING THE SHOWERS TO
GRADUALLY DIMINISH OVER THE WEEKEND AND BEGINNING OF THE NEXT WEEK. A
LULL IN THE SHOWERS MAY ARRIVE AROUND TUESDAY, HOWEVER BY MIDWEEK
SHOWERS MAY RETURN FOR THE REST OF THE FORECAST PERIOD.
MARINE...
COMBINED SEAS ARE EXPECTED TO REMAIN NEAR 4 TO 6 FEET. THE TRADE-WIND
SWELL IS EXPECTED TO GRADUALLY WEAKEN WHILE THE MONSOON SWELL IS
EXPECTED TO STRENGTHEN, OVERALL THE SEA HEIGHTS ARE EXPECTED TO
REMAIN ABOUT THE SAME THROUGH THE FORECAST PERIOD. WITH THE TRADE-
WIND SWELL DIMINISHING, SO TOO WILL THE SURF ALONG EAST FACING
REEFS AND LIKEWISE THE STRENGTHENING MONSOON SWELL WILL INCREASE THE
SURF ALONG SOUTH AND WEST FACING REEFS. THE RISK OF RIP CURRENTS
WILL BECOME MODERATE ONCE THE MONSOON SWELL MOVES IN.
EASTERN MICRONESIA...
THERE IS A SIGNIFICANT CHANGE TO THE FORECAST REASONING FOR EASTERN
MICRONESIA THIS AFTERNOON. THE LATEST SURFACE ANALYSIS AND SATELLITE
DATA SHOW A STRENGTHENING INTER-TROPICAL CONVERGENCE ZONE (ITCZ)
EXTENDING WEST FROM THE DATE LINE ACROSS THE MARSHALLS TO KOSRAE.
SEVERAL TRADE-WIND TROUGHS MOVING THROUGH THE REGION ARE HELPING TO
STRENGTHEN THE ITCZ AND GENERATE ENHANCED CONVECTION ACROSS THE
REGION. MODEL GUIDANCE MAINTAINS THIS PATTERN INTO THE COMING WEEK,
WITH THE ITCZ BEING STRONGEST SUNDAY INTO SUNDAY NIGHT. FOR TONIGHT,
HIGH-END SCATTERED SHOWERS ARE EXPECTED AT KOSRAE THROUGH THE NIGHT.
FOR MAJURO, THERE IS A LULL IN THE CONVECTION FOR NOW THAT LOOKS TO
END LATER THIS EVENING AS ANOTHER TRADE-WIND TROUGH APPROACHES THE
MARSHALLS. FOR POHNPEI, CONVECTION ALSO LOOKS TO INCREASE THERE LATER
TONIGHT, NEAR MIDNIGHT. BY SUNDAY, A STRONG BAND OF CONVERGENCE
ALONG THE ITCZ IS EXPECTED TO STRETCH ACROSS ALL THREE FORECAST
POINTS, WHILE TRADE-WIND TROUGHS ARE SET TO AFFECT ALL THREE AS WELL.
THIS WILL RESULT IN NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS WITH
LOCALLY HEAVY RAINFALL. BY SUNDAY EVENING, CONVECTION LOOKS TO
DECREASE A BIT OVER MAJURO AND POHNPEI AS THE TROUGHS AFFECTING THEM
MOVE OUT OF THE AREA. HOWEVER, THE TROUGH MOVING OUT OF THE MARSHALLS
LOOKS TO MOVE SOUTHWEST INTO KOSRAE, MAINTAINING NUMEROUS SHOWERS
THERE THROUGH SUNDAY NIGHT. THE ITCZ WILL THEN GRADUALLY WEAKEN, WITH
DECREASING CONVECTION THROUGH THE COMING WEEK. KOSRAE AND POHNPEI
CAN EXPECT POPS (PROBABILITY OF PRECIPITATION) TO DROP TO AROUND 20
PERCENT BY THE MIDDLE OF NEXT WEEK. THE ITCZ WILL REMAIN OVER THE
MARSHALLS THE LONGEST, SO MAJURO WILL SEE HIGHER POPS THROUGH THE
MIDDLE OF NEXT WEEK, WITH POPS DROPPING TO THE 20 PERCENT RANGE
AROUND THURSDAY.
CHOPPY SEAS ARE POSSIBLE AT ALL THREE LOCATIONS SUNDAY AND AT KOSRAE
SUNDAY NIGHT DUE TO GUSTY WINDS WITH THE SHOWERS AND THUNDERSTORMS.
OTHERWISE, FAIRLY BENIGN MARINE CONDITIONS ARE EXPECTED FOR THE
COMING WEEK. SEAS LOOK TO BE BETWEEN 5 TO 7 FEET THROUGH THE
REMAINDER OF THE WEEKEND FOR MAJURO AND BETWEEN 4 AND 5 FEET FOR
KOSRAE AND POHNPEI. SEAS WILL GRADUALLY SUBSIDE NEXT WEEK FOR MAJURO,
DROPPING TO BETWEEN 3 AND 5 AROUND THE MIDDLE OF THE WEEK. FOR
POHNPEI AND KOSRAE, SEAS WILL BOUNCE AROUND A BIT, BUT WILL MAINLY BE
BETWEEN 3 AND 5 FEET.
WESTERN MICRONESIA...
AN ACTIVE MONSOON PATTERN CONTINUES TO BRING UNSETTLED WEATHER ACROSS
FAR WESTERN MICRONESIA. SATELLITE THIS AFTERNOON REVEALS WIDESPREAD
CLOUDINESS AND SHOWERS OVER THE REPUBLIC OF PALAU AND WESTERN YAP
STATE, WITH GLD NETWORK DATA SHOWING ISOLATED THUNDERSTORMS EMBEDDED
IN THE SHOWER BANDS TO THE NORTH AND EAST OF YAP PROPER. THESE
SHOWERS ARE MAINLY FOCUSED ALONG AND NORTH OF A NEWLY-FORMING
MONSOON TROUGH AXIS, WHICH EXTENDS ROUGHLY WEST TO EAST ACROSS THE
REGION FROM THE SOUTHERN PHILIPPINES INTO WESTERN YAP STATE, PASSING
JUST NORTH OF PALAU AND OVER YAP PROPER. SCATTEROMETRY DATA FROM
THIS MORNING SHOWED A BROAD AREA OF MODERATE TO FRESH WESTERLY FLOW
EXTENDING EASTWARD ACROSS THE REGION TO JUST SOUTH OF YAP PROPER.
EMBEDDED IN THIS FLOW, A SMALLER AREA OF FRESH TO STRONG WINDS WAS
SEEN OVER PALAU ALONG THE LEADING EDGE OF A MONSOON SURGE, WHICH
NECESSITATED THE ISSUANCE OF A SMALL CRAFT ADVISORY LATE OVERNIGHT
THROUGH THIS MORNING.
GFS DETERMINISTIC MODEL GUIDANCE SUGGESTS SUSTAINED WINDS COULD
BRIEFLY APPROACH SMALL CRAFT LEVELS (25 MPH OR GREATER) ONCE MORE BY
SUNDAY NIGHT, ASSOCIATED WITH A DEVELOPING MONSOON DISTURBANCE NORTH
OF PALAU, BUT OTHER DETERMINISTIC MODELS AND ENSEMBLE GUIDANCE ARE
TRENDING FURTHER NORTH REGARDING THE DISTURBANCE AND STRONGER WINDS.
FOR NOW, ONLY GENTLE TO MODERATE WESTERLIES ARE REFLECTED IN PALAU'S
FORECAST FOR SUNDAY AND SUNDAY NIGHT. OVERALL MODEL GUIDANCE SHOWS
THE MONSOON TROUGH AND DISTURBANCE SHIFTING NORTH OVER THE NEXT FEW
DAYS, GRADUALLY MORPHING INTO A BROADER CYCLONIC GYRE OVER THE
PHILIPPINE SEA EARLY NEXT WEEK. THIS PATTERN LOOKS TO MAINTAIN
NUMEROUS SHOWERS FOR YAP INTO AT LEAST MONDAY, WITH SLIGHTLY LOWER
SHOWER COVERAGE EXPECTED FOR PALAU TOMORROW THROUGH EARLY NEXT WEEK.
LOCALLY HEAVY SHOWERS AND STRONG GUSTS WILL BE POSSIBLE THROUGH THE
REMAINDER OF THE WEEKEND.
CHUUK CAN EXPECT FAIRLY QUIET CONDITIONS FOR THE REST OF THE WEEKEND
BEFORE A TROUGH SHIFTS WEST INTO THE AREA EARLY NEXT WEEK, RIDING
ALONG THE WESTERN EDGE OF THE ITCZ. THIS BROAD CONVERGENCE AND MOIST
SOUTHERLY FLOW WILL BRING SCATTERED SHOWERS THROUGH THE MIDDLE OF
NEXT WEEK. MODELS HINT AT THE POSSIBILITY OF A WEAK DISTURBANCE
FORMING NEAR CHUUK BY TUESDAY, WHICH MAY BEAR MONITORING OVER THE
NEXT FEW DAYS.
COMBINED SEAS OF 4 TO 6 FEET ARE EXPECTED TO CONTINUE FOR PALAU AND
YAP, COMPRISED OF A WEST TO SOUTHWEST MONSOON SWELL AND WEAKER
EASTERLY TRADE SWELL. SEAS WILL GRADUALLY DIMINISH BY A FOOT OR TWO
NEXT WEEK AS THE SURFACE RIDGE BUILDS IN AND THE MONSOON SWELL
DECREASES. COMBINED SEAS OF 2 TO 4 FEET ARE EXPECTED FOR CHUUK
WATERS FOR MUCH OF THE FORECAST PERIOD, DRIVEN BY THE PRIMARY TRADE
SWELL. MOSTLY LIGHT WINDS ARE EXPECTED FOR CHUUK INTO EARLY NEXT
WEEK.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS UPDATE: CRUZ
EAST/WEST MICRONESIA UPDATE: MONTVILA
MARIANAS: BOWSHER
EAST MICRONESIA: KLEESCHULTE
WEST MICRONESIA: DECOU
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