677
FXPQ50 PGUM 160817
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
617 PM CHST THU OCT 16 2025
MARIANAS SYNOPSIS
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ASSOCIATED WITH A WEAK
TROUGH THAT IS TRAILING BEHIND INVEST 96W, ARE STARTING TO DECREASE
ACROSS THE ISLANDS AS THE AFOREMENTIONED TROUGH MOVES OFF TO THE
WEST. DRIER WEATHER IS EXPECTED FRIDAY BEFORE THE NEXT SERIES OF
TROUGHS MOVE INTO THE AREA. WINDS ARE GENTLE TO MODERATE, WITH
ALTIMETRY AND BUOY DATA SHOWING SEAS AROUND 4 TO 6 FEET THIS EVENING.
DISCUSSION
THE BLENDED TPW DATA SHOWS THAT DRIER AIR, WITH PW OF 1.5 TO 2.0
INCHES IS FINALLY STARTING TO MOVE INTO THE EASTERN WATERS OF THE
MARIANAS. THIS ALONG WITH A WEAK SURFACE TROUGH PULLING AWAY WILL
LEAD TO A REDUCTION IN SHOWERS AND THUNDERSTORMS THROUGH FRIDAY.
CURRENT CLOUD COVER WILL LIKELY LINGER THROUGH THE OVERNIGHT HOURS
AS THE LOWER ATMOSPHERIC MOISTURE IS MOSTLY ABOVE 700MB ACCORDING TO
THE ADVECTED LAYER PRECIPITABLE WATER PRODUCT, SO LOW TO MID-LEVEL
CLOUD COVER WILL LIKELY CONTINUE UNTIL THE CURRENT INSTABILITY THAT
WAS ASSOCIATED WITH THE PASSING TROUGH STABILIZES. SHOWER AND
THUNDERSTORM CHANCES WILL INCREASE SLIGHTLY SATURDAY NIGHT AS A
TROUGH PASSES SOUTH OF THE MARIANAS, AND AGAIN SUNDAY NIGHT INTO THE
BEGINNING OF THE WEEK AS MODELS SHOW ANOTHER TROUGH MOVING INTO THE
REGION FROM THE EAST.
MARINE
MODERATE EAST WINDS WILL CONTINUE INTO NEXT WEEK, INCREASING
BRIEFLY TO MODERATE TO FRESH SATURDAY NIGHT AS A TROUGH PASSES
NEAR OR JUST SOUTH OF THE MARIANAS AND INCREASING THE PRESSURE
GRADIENT SLIGHTLY. SEAS HAVE BRIEFLY DROPPED TO 4 TO 6 FEET BASED ON
LATEST BUOY AND ALTIMETRY DATA, BUT WILL REBUILD TO 5 TO 7 FEET AS
THE EAST SWELL BUILDS ABOUT A FOOT. THE NORTH SWELL IS EXPECTED TO
DROP BY 1 TO 2 FEET OVER THE NEXT 2 TO 3 DAYS, BUT WAVE MODEL
GUIDANCE SHOWS A PULSE OF NORTHERLY SWELL ENTERING THE REGION NEXT
WEEK, GENERATED BY DISTANT MID-LATITUDE SYSTEMS. LINGERING SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED TO DECREASE
OVERNIGHT AS DRIER AIR CONTINUES TO MOVE IN. SHOWERS AND THUNDERSTORM
CHANCES WILL INCREASE AGAIN THIS WEEKEND AS A COUPLE OF WEAK SURFACE
TROUGHS PASS NEAR THE MARIANAS.
TROPICAL SYSTEMS
INVEST 96W CONTINUES TO MOVE WESTWARD ACROSS THE OPEN WATERS OF THE
PHILIPPINE SEA, PASSING NORTH OF YAP AND PALAU. THERE IS STILL NO
DISCERNIBLE LOW-LEVEL CIRCULATION CENTER, JUST A AREA OF CONVECTION
DEVELOPING OVER A OPEN TROUGH, CENTERED 14N137E. SOME PERIPHERAL
SHOWERS AND THUNDERSTORMS ARE STILL AFFECTING PALAU AND YAP THE
EVENING AND WILL LIKELY CONTINUE FOR THE NEXT COUPLE OF DAYS AS 96W
MOVES AWAY. THE JOINT TYPHOON WARNING CENTER CONTINUES TO KEEP
INVEST 96W'S POTENTIAL FOR DEVELOPMENT RATED AS LOW, MEANING
DEVELOPMENT INTO A TROPICAL CYCLONE IS UNLIKELY WITHIN 24 HOURS. FOR
UPDATED INFORMATION ON 96W, PLEASE REFER TO THE SIGNIFICANT TROPICAL
WEATHER ADVISORY, ISSUED BY THE JOINT TYPHOON WARNING CENTER, UNDER
WMO HEADER ABPW10 PGTW.
LOOKING JUST EAST OF THE DATE LINE, SCATTEROMETER SHOWS A BROAD
TRADE-WIND DISTURBANCE, WITH AN EMBEDDED CIRCULATION NEAR 10N177W.
SCATTERED TO NUMEROUS SHOWERS EXTENDED ALONG THE TRADE-WIND
DISTUBANCE, WITH SOME GUSTY WINDS AROUND 20 TO 30 KT NOTED ON THE
NORTHWEST EDGE OF THE EMBEDDED CIRCULATION. CURRENT MODEL GUIDANCE
KEEPS THIS TRADE-WIND DISTURBANCE BROAD, AND EVEN OPENING BACK INTO
A TROUGH AS IT MOVES TOWARDS THE MARSHALL ISLANDS OVER THE NEXT FEW
DAYS.
EASTERN MICRONESIA
THE TROPICAL DISTURBANCE THAT HAS BEEN MOVING ACROSS EASTERN
MICRONESIA HAS FINALLY DEGRADED INTO AN BROAD SURFACE TROUGH, AND IS
EXPECTED TO CONTINUE BRINGING ON-AND-OFF SHOWERS AND SOME
THUNDERSTORMS TO POHNPEI, WHILE A NEWLY FORMED RIDGE IN ITS WAKE
BRINGS A QUIETER PATTERN TO KOSRAE AND MAJURO, BOTH THROUGH FRIDAY.
AN ANOMALOUS TRADE-WIND DISTURBANCE, NOW LOCATED EAST OF THE DATE
LINE, WILL SLOWLY MAKE ITS WAY INTO EASTERN MICRONESIA AND BRING
ELEVATED SHOWERS AND THUNDERSTORMS TO MAJURO FRIDAY NIGHT AND
SATURDAY, BEFORE SHIFTING SLIGHTLY NORTHWARD AND DODGING KOSRAE AND
POHNPEI, WITH ONLY LOW-END SCATTERED SHOWERS EXPECTED THERE THROUGH
THE WEEKEND. LAST BUT NOT LEAST, WINDS ARE THEN EXPECTED TO INCREASE
AT ALL THREE FORECAST LOCATIONS IN THE FIRST HALF OF NEXT WEEK, AS
THE PRESSURE GRADIENT BETWEEN THE TROPICS AND THE MID-LATITUDES
INCREASES, SIGNALING A STRENGTHENING SUBTROPICAL HIGH INDUCED BY
SEASONAL COOLING.
COMBINED SEAS OF 5 TO 7 FEET NEAR POHNPEI AND MAJURO, AND 4 TO 6
FEET NEAR KOSRAE, ARE COMPRISED OF A DOMINANT NORTHERLY SWELL
GENERATED BY DISTANT CYCLONES, AND A SECONDARY TRADE SWELL. THIS
NORTHERLY SWELL IS PRODUCING ELEVATED SURF ALONG NORTH FACING REEFS
OF ALL THREE FORECAST POINTS, TO THEN BEGIN TO SLOWLY DIMINISH FOR
THE REST OF THE WEEK THEREAFTER. THIS NORTHERLY SWELL IS EXPECTED TO
TAPER DOWN ENOUGH TO BE OVERTAKEN BY THE EAST SWELL SOMETIME EARLY
NEXT WEEK. AS THESE SWELLS DECREASE, SO WILL THE SEAS, WHICH ARE
EXPECTED TO DROP 2 TO 3 FEET ACROSS THE REGION BY THE WEEKEND.
WESTERN MICRONESIA
AN AREA OF CONVERGENT INFLOW INTO INVEST 96W SITS JUST OVER AND
EXTENDING NORTH OF YAP AND PALAU, PRODUCING SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS ACROSS FAR WESTERN MICRONESIA. SHOWERS FOR
TONIGHT WILL REMAIN MAINLY FOCUSED NEAR YAP, INCREASING FOR PALAU
THROUGH FRIDAY AS 96W AND THE ATTENDENT SURFACE TROUGH SHIFTS
WESTWARD ACROSS THE PHILIPPINE SEA. PALAU WILL THEN SEE DIMINISHING
SHOWERS THROUGH THE WEEKEND, EXPERIENCING A BRIEF SURFACE RIDGE. YAP
WILL CONTINUE TO SEE PERIODS OF SCATTERED SHOWERS THROUGH EARLY NEXT
WEEK AS A SERIES OF WEAK SURFACE TROUGHS CROSS THE AREA. PALAU WILL
STAY SOUTH OF THE HIGHER SHOWER COVERAGE THIS WEEKEND, BUT
APPROACHING TROUGHS WILL EVENTUALLY BRING MORE SHOWERS THERE EARLY
NEXT WEEK.
TO THE EAST, CHUUK SITS WITHIN AN AREA OF CONVERGENCE ALONG A BROAD,
WEST-SOUTHWEST TO EAST-NORTHEAST ORIENTED TRADE-WIND TROUGH, WHICH IS
BRINGING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE
REGION. THIS WILL MAINTAIN A WET PATTERN FOR CHUUK OVERNIGHT, BUT
SHOWER CHANCES WILL FALL OFF FRIDAY THROUGH SATURDAY AS A SURFACE
RIDGE BUILDS IN BEHIND THE TRANSITING TROUGH. SHOWERS THEN REBUILD
LATE IN THE WEEKEND THROUGH EARLY NEXT WEEK AS A SIMILARLY BROAD,
ROBUST SURFACE TROUGH CROSSES THE AREA.
LATEST ALTIMETRY DATA INDICATES COMBINED SEAS AROUND 3 TO 5 FEET
NEAR PALAU AND YAP AND AROUND 4 TO 6 FEET NEAR CHUUK, COMPRISED OF A
PRIMARY NORTHEAST SWELL. SIMILAR CONDITIONS WILL PREVAIL FOR MUCH OF
THE FORECAST PERIOD, WITH SEAS INCREASING A FOOT OR SO THIS WEEKEND
FOR YAP AND CHUUK AS A SLIGHTLY HIGHER PULSE OF NORTHEAST SWELL
ENTERS THE REGION. LIGHT TO MODERATE WINDS ARE EXPECTED ACROSS THE
REGION FOR MUCH OF THE FORECAST PERIOD.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: SCHANK
EAST MICRONESIA: MONTVILA
WEST MICRONESIA: DECOU
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