369
FXPQ50 PGUM 112026
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
626 AM CHST WED AUG 12 2026
MARIANAS UPDATE
AN EMBEDDED DISTURBANCE, INVEST 91W, IS WITHIN THE MONSOON TROUGH TO
OUR NORTH AND CONTINUES TO FOCUS UNSETTLED WEATHER WEST AND NORTHWEST
OF THE FAR NORTHERN MARIANAS. THIS MONSOON DISTURBANCE TO OUR NORTH
AND A WEAK TROPICAL DISTURBANCE WELL TO OUR SOUTHEAST ARE INDUCING
WEAK DIFFLUENT FLOW ACROSS THE MARIANAS. RADAR IMAGERY INDICATES
A LINE OF PATCHY SHOWERS MOVING ACROSS GUAM AND ROTA WATERS, BUT
OVERALL, ISOLATED SHOWERS ARE EXPECTED THROUGH TONIGHT.
A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR TINIAN AND SAIPAN
THROUGH THURSDAY AFTERNOON. THE HIGH SURF ADVISORY AND A HIGH RIP
CURRENT RISK CONTINUES ALONG WEST-FACING REEFS OF THE MARIANAS
THROUGH THURSDAY AFTERNOON AS WELL. SURF HAS DROPPED BELOW HAZARDOUS
LEVELS OF 9 FEET ALONG NORTH-FACING REEFS, BUT WILL REMAIN ELEVATED
OVER THE NEXT FEW DAYS, POTENTIALLY INCREASING BACK UP TO HAZARDOUS
LEVELS, AS THE MONSOON PATTERN AND ASSOCIATED WEST TO NORTHWEST
SWELLS CONTINUE INTO NEXT WEEK.
TROPICAL SYSTEMS UPDATE
INVEST 91W IS AN EMBEDDED CIRCULATION WITHIN THE MONSOON TROUGH,
LOCATED NEAR 22N141E, WELL NORTH-NORTHWEST OF THE MARIANAS (ABOUT
534 MILES NNW OF SAIPAN). 91W WAS UPGRADED TO "MEDIUM" FOR
DEVELOPMENT, MEANING TROPICAL CYCLONE DEVELOPMENT IS LIKELY, BUT
EXPECTED TO OCCUR BEYOND 24 HOURS. MAXIMUM SUSTAINED WINDS ARE
ESTIMATED AT 12-18 KT WITH OVERNIGHT SCATTEROMETRY DATA SHOWING THE
STRONG MONSOONAL FLOW TO THE SOUTHEAST STRENGTHENING TO AROUND 27 KT.
91W IS FORECAST TO TRACK NORTHEASTWARD, MOVING AWAY FROM THE MARIANAS
AND PASSING TO THE SOUTHEAST OF IWO TO LATER THIS AFTERNOON AND
EVENING. FOR MORE INFORMATION ON INVEST 91W, PLEASE SEE BULLETINS
ISSUED BY JTWC UNDER WMO HEADER ABPW10 PGTW.
INVEST 90W CONTINUES TO MOVE ACROSS THE NORTHWESTERN RMI, LOCATED
NEAR 12N165E. IT IS STILL RATED "SUB-LOW", MEANING DEVELOPMENT IS
POSSIBLE, BUT IS NOT EXPECTED OVER THE NEXT DAY OR SO. THIS BROAD
TROPICAL DISTURBANCE CONTINUES TO HAVE FLARING DEEP CONVECTION
ALONG ITS WESTERN FLANK AND CONTINUES TO INFLUENCE THE BROADER
WEATHER PATTERN ACROSS EASTERN MICRONESIA AS IT DRIFTS WESTWARD AND
BECOMES MORE ELONGATED, NORTHWEST TO SOUTHEAST.
EASTERN MICRONESIA UPDATE
AN UNSETTLED, BUT UNORGANIZED PATTERN CONTINUES ACROSS THE REGION.
CLUSTERS OF SHOWERS AND THUNDERSTORMS ARE LOOSELY ORGANIZED AROUND
INVEST 90W, IN THE NORTHWEST RMI, AND ALONG AN AREA OF CONVERGENT
WESTERLY FLOW AND TRADE WINDS TO THE EAST OF THE RMI. CONVECTION IS
ALSO FOCUSED ACROSS SOUTHERN KOSRAE STATE, TIED TO A BROAD
DISTURBANCE AND AN UNSETTLED PATTERN SOUTH OF THE EQUATOR. OVERALL,
NO MAJOR CHANGES TO THE FORECAST. SCATTERED SHOWERS CONTINUE ACROSS
POHNPEI AND KOSRAE TODAY. INCREASED THE SHOWERS TO SCATTERED AT
MAJURO DUE TO THE AREA OF CONVERGENCE TO THE EAST.
STRONG SOUTHEAST TRADES AND A CIRCULATION SOUTH OF THE EQUATOR
CONTINUE TO GENERATE SOUTH TO SOUTHEAST SWELL INTO EASTERN
MICRONESIA. AS THE CIRCULATION MEANDERS TOWARDS THE SOLOMON ISLANDS,
SWELL TURNS MORE SOUTHWEST LATE WEEK AND OVER THE WEEKEND. FOR NOW,
HAZARDOUS SURF UP TO 8 FEET IS EXPECTED ALONG SOUTH FACING REEFS OF
KOSRAE THROUGH EARLY THURSDAY MORNING, POSSIBLY SEEING ANOTHER BOOST
IN SURF HEIGHTS OVER THE WEEKEND. A HIGH SURF ADVISORY REMAINS IN
EFFECT ALONG SOUTH FACING REEFS OF KOSRAE THROUGH AT LEAST EARLY
THURSDAY MORNING.
WESTERN MICRONESIA UPDATE
NO MAJOR CHANGES WERE MADE TO THE FORECAST. CONTINUE TO EXPECT FAIR
WEATHER AT YAP AND PALAU TODAY. MEANWHILE, MOSTLY CLOUDY SKIES AND
SCATTERED SHOWERS CONTINUE ACROSS CHUUK THROUGH THIS AFTERNOON,
RETURNING LATE TONIGHT OR EARLY THURSDAY MORNING AS AN INCREASE
NORTHWESTERLY CONVERGENCE SETS UP ACROSS POHNPEI AND NORTHEASTERN
CHUUK STATE.
PREV DISCUSSION
/ISSUED 606 PM CHST TUE AUG 11 2026/
MARIANAS SYNOPSIS...
SCATTERED, LOCALLY HEAVY SHOWERS ARE VISIBLE OVER THE MARIANAS AND
EXPECTED TO CONTINUE OVERNIGHT WITH ISOLATED THUNDERSTORMS POSSIBLE.
MODERATE TO STRONG WESTERLY WINDS ARE PREVAILING. BUOYS AND MODELS
INDICATE COMBINED SEAS OF 7 TO 10 FEET.
DISCUSSION...
THE MOIST MONSOONAL FLOW CONTINUES TO BRING HEAVIER SHOWERS AND
ISOLATED THUNDERSTORMS ACROSS THE MARIANAS, ESPECIALLY FOR TINIAN AND
SAIPAN TONIGHT. AS NEWLY FORMED INVEST 91W DEVELOPS AND SHIFTS
NORTHEAST, THE MONSOON FLOW WILL DRIFT NORTH WITH IT BY TOMORROW.
DRIER AIR IS THEN EXPECTED TO MOVE INTO THE MARIANAS AND LOWER
PRECIPITATION CHANCES THROUGH SATURDAY, ESPECIALLY FOR GUAM AND ROTA.
BY SUNDAY, MONSOONAL MOISTURE MAY RETURN TO BRING MORE SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS THROUGH EARLY NEXT WEEK.
MARINE...
MODERATE TO STRONG WESTERLIES PREVAIL ACROSS THE MARIANAS,
GRADUALLY DECREASING TO GENTLE TO FRESH IN THE SECOND HALF OF THE
WEEK. SIGNIFICANT WEST SWELL, NORTHERLY SWELLS AND LARGE
LOCALIZED WIND WAVES ARE PRODUCING COMBINED SEAS OF 7 TO 10 FEET,
MAINTAINING HAZARDOUS CONDITIONS TO SMALL CRAFT ACROSS TINIAN AND
SAIPAN WATERS THROUGH AT LEAST THURSDAY AFTERNOON. SEA CONDITIONS
LOOK TO REMAIN JUST BELOW LEVELS HAZARDOUS TO SMALL CRAFT THROUGH
THE END OF THE WEEK FOR GUAM AND ROTA. THERE IS A HIGH RISK OF RIP
CURRENTS ALONG WEST AND NORTH FACING REEFS THROUGH THURSDAY
AFTERNOON, POTENTIALLY DROPPING BELOW HAZARDOUS LEVELS BY TOMORROW
ALONG NORTH-FACING REEFS. A MODERATE RISK OF RIP CURRENTS CONTINUES
SOUTH FACING REEFS OVER THE NEXT FEW DAYS. SCATTERED SHOWERS ARE
EXPECTED TONIGHT WITH ISOLATED THUNDERSTORMS LASTING THROUGH
WEDNESDAY NIGHT. LOCALLY HEAVY SHOWERS ARE POSSIBLE FOR TINIAN AND
SAIPAN TONIGHT.
TROPICAL SYSTEMS...
AT 1:00 PM, TROPICAL STORM PEILOU WAS CENTERED WELL NORTHEAST OF
SAIPAN, AND WELL WEST-NORTHWEST OF WAKE ISLAND, NEAR 25.1N 156.5E,
MOVING NE AT 29 MPH. PEILOU IS NOW NORTH OF THE GUAM AREA OF
RESPONSIBILITY (AOR). PEILOU WEAKENED TO A TD OVERNIGHT, BUT
STRENGTHENED AGAIN TO TS THIS MORNING, WITH MAXIMUM SUSTAINED WINDS
OF 40 MPH. PEILOU IS EXPECTED TO MAINTAIN THIS INTENSITY THROUGH THIS
EVENING, THEN BEGIN TO WEAKEN AS IT MOVES RAPIDLY NORTHEAST.
FOR MORE INFORMATION ON TS PEILOU, PLEASE SEE BULLETINS ISSUED BY
THE JOINT TYPHOON WARNING CENTER (JTWC) UNDER WMO HEADER WTPN32 PGTW
AND BY THE NATIONAL WEATHER SERVICE UNDER WMO HEADER WTPQ32 PGUM.
A BROAD, WEAK CIRCULATION, INVEST 90W, IS FOUND NNW OF KWAJALEIN,
CENTERED NEAR 11.5N 167.1E, MOVING SLOWLY WEST. A RELATIVELY CLOUD
FREE LOW-LEVEL CIRCULATION CENTER (LLCC) IS SEEN ON VISIBLE SATELLITE
IMAGERY. INVEST 90W IS CURRENTLY RATED SUB-LOW, MEANING IT IS NOT
EXPECTED TO BECOME A SIGNIFICANT TROPICAL CYCLONE OVER THE NEXT FEW
DAYS. 90W IS EXPECTED TO CONTINUE MOVING SLOWLY WEST OVER THE NEXT
FEW DAYS WITH LITTLE TO NO CHANGE IN INTENSITY.
ANOTHER WEAK CIRCULATION, INVEST 91W, IS CENTERED NEAR 22.2N 136.6E,
MOVING SLOWLY EASTWARD. INVEST 91W IS CURRENTLY RATED LOW, MEANING
DEVELOPMENT IS UNLIKELY WITHIN THE NEXT 24 HOURS. LATEST SATELLITE
DATA INDICATES AN ELONGATED TROUGH WITH CONVECTION SEEN ALONG THE
SOUTHERN PERIPHERY OF 91W. 91W IS IN A FAVORABLE AREA FOR
DEVELOPMENT, WITH LOW VERTICAL WIND SHEAR, GOOD OUTFLOW ALOFT AND
WARM SEA SURFACE TEMPERATURES. MODEL CONSENSUS ON SHORT TERM
DEVELOPMENT OF A LLCC WITHIN THE NEXT 24 HOURS. INVEST 91W WILL
CONTINUE TO BE MONITORED AS IT MOVES ENE OVER THE NEXT COUPLE OF
DAYS.
FOR MORE INFORMATION ON INVEST 91W, PLEASE SEE BULLETINS ISSUED BY
JTWC UNDER WMO HEADER ABPW10 PGTW.
EASTERN MICRONESIA...
A FAIRLY DRY PATTERN HAS MOVED INTO THE MARSHALL ISLANDS AS INVEST
90W SLOWLY DRIFTS WEST. 90W DOESN'T LOOK LIKE IT WILL DEVELOP INTO
ANYTHING OVER THE NEXT SEVERAL DAYS, SO IT LOOKS LIKE THE MARSHALLS
WILL REMAIN DRY THROUGH THE WEEKEND. THEREFORE, POPS (PROBABILITY OF
PRECIPITATION) WERE REDUCED TO AROUND 20 PERCENT FOR MAJURO THROUGH
NEXT SUNDAY.
FOR POHNPEI AND KOSRAE, THE MAIN CHANGE IN THE FORECAST WAS TO
REDUCE POPS A BIT. NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS ARE
STILL EXPECTED TO CONTINUE THROUGH TONIGHT, WITH POPS DECREASING TO
THE 30 TO 50 PERCENT RANGE, OR SCATTERED, FOR THE REMAINDER OF THE
WEEK AND THE WEEKEND. THE MAIN WEATHER PRODUCERS FOR TONIGHT ARE A
SERIES OF WEAK TROUGHS INTERACTING WITH SOME UPPER-LEVEL DIVERGENCE.
AS THE TROUGHS MOVE EAST AND THE DIVERGENCE MOVES WEST, CONVECTION
WILL DECREASE. HOWEVER, INFLUENCE FROM WEAK INVEST 90W WILL HELP
MAINTAIN POPS IN THE 30 TO 50 PERCENT RANGE THROUGH THE WEEKEND.
STRONG SOUTHEAST TO SOUTH WINDS IN THE SOUTHERN HEMISPHERE WILL
MAINTAIN A SOUTH SWELL OF AROUND 6 FEET INTO KOSRAE. THIS LOOKS TO
CONTINUE FOR A BIT LONGER THAN PREVIOUSLY EXPECTED, SO DECIDED TO
EXTEND THE HIGH SURF ADVISORY THROUGH 3 AM THURSDAY MORNING. BENIGN
CONDITIONS LOOK TO CONTINUE FOR MAJURO AND POHNPEI.
WESTERN MICRONESIA...
FAIRLY QUIET CONDITIONS PREVAIL ACROSS FAR WESTERN MICRONESIA, WITH
VISIBLE SATELLITE IMAGERY SHOWING HIGH-ALTITUDE CIRRUS CLOUDS
STREAMING OVER YAP AND PALAU FROM DISTANT THUNDERSTORMS FAR
NORTHEAST OF THE REGION. OTHERWISE, CONDITIONS ARE MOSTLY CLEAR
ACROSS THE AREA. TO THE SOUTH, SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS ARE SEEN OVER FAR SOUTHERN YAP STATE, MAINLY SOUTH OF
THE OUTERMOST ISLANDS, ASSOCIATED WITH A BAND OF CONVERGENCE WITHIN
THE CROSS-EQUATORIAL SOUTHERLIES. LOOKING EASTWARD, WIDESPREAD
CLOUDINESS BLANKETS CHUUK STATE THIS AFTERNOON, FROM NEARBY SCATTERED
SHOWERS AND PRIOR DEEP CONVECTION ASSOCIATED WITH AN UNSETTLED
PATTERN OVER POHNPEI STATE. CHUUK WILL CONTINUE TO SEE PERIPHERAL
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS FROM THE UNSETTLED
WEATHER PATTERN OVER EASTERN MICRONESIA, FOR AT LEAST THE NEXT FEW
DAYS. THEN, MODEL GUIDANCE SHOWS A WEAK DISTURBANCE BUILDING WESTWARD
INTO CHUUK STATE AROUND FRIDAY, SLOWLY MEANDERING ACROSS THE AREA
THROUGH THE WEEKEND. DEPENDING ON THE DEVELOPMENT AND MOVEMENT OF
THIS PATTERN, SHOWERS COULD BECOME NUMEROUS AT TIMES STARTING AROUND
FRIDAY NIGHT, WITH LOCALLY HEAVY RAINFALL POSSIBLE. FOR NOW, SHOWER
CHANCES ASSOCIATED WITH THIS PATTERN WERE KEPT AT 50 PERCENT IN THE
FORECAST FOR CHUUK, BUT WILL LIKELY SEE CHANGES IN THE COMING DAYS
AS UNCERTAINTY DECREASES.
ALTIMETRY AND YAP BUOY DATA SHOW COMBINED SEAS BETWEEN 5 AND 7 FEET
ACROSS THE REGION, COMPRISED MAINLY OF A PRIMARY WEST TO NORTHWEST
SWELL. BENIGN SEA CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THE
FORECAST PERIOD.
GUM WATCHES/WARNINGS/ADVISORIES
GU...HIGH RIP CURRENT RISK THROUGH THURSDAY AFTERNOON FOR GUZ001.
HIGH SURF ADVISORY UNTIL 4 PM CHST THURSDAY FOR GUZ001.
MP...HIGH RIP CURRENT RISK THROUGH THURSDAY AFTERNOON FOR MPZ001>003.
HIGH SURF ADVISORY UNTIL 4 PM CHST THURSDAY FOR MPZ001>003.
MARIANAS WATERS...SMALL CRAFT ADVISORY UNTIL 5 PM CHST THURSDAY FOR PMZ153-154.
MARIANAS/EAST AND WEST MICRONESIA/TROPICAL UPDATE: CRUZ
MARIANAS: OGLE
EAST MICRONESIA/TROPICAL: KLEESCHULTE
WEST MICRONESIA: DECOU
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