581
FXPQ50 PGUM 252116
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
716 AM CHST WED AUG 26 2026
MARIANAS UPDATE
INCREASED CONVERGENCE ALONGSIDE A BROAD MONSOON DISTURBANCE WELL TO
OUR EAST, INVEST 90W, BROUGHT A QUICK INCREASE IN SHOWERS AND
THUNDERSTORMS STARTING EARLY THIS MORNING. HEAVIEST SHOWERS AND
THUNDERSTORMS ARE SKEWED CLOSER TO GUAM AND FARTHER SOUTH AND EAST.
RADAR IMAGERY HAS SHOWN BANDS OF HEAVIER SHOWERS FORMING ALONG THE
STRENGTHENING NORTHWESTERLY CONVERGENCE, CAUSING URBAN AND SMALL
STREAM FLOODING ACROSS GUAM THIS MORNING. THE MAIN CHANGE WAS TO
INCREASE SHOWER CHANCES OVERALL, WITH NUMEROUS LOCALLY SHOWERS FOR
GUAM. OCCASIONAL GUSTS TO 20 MPH WILL ALSO BE POSSIBLE NEAR HEAVIER
SHOWERS AND THUNDERSTORMS.
TROPICAL SYSTEMS UPDATE
INVEST 99W WAS UPGRADED TO MEDIUM, MEANING TROPICAL CYCLONE
DEVELOPMENT IS LIKELY, BUT EXPECTED TO OCCUR BEYOND 24 HOURS. THE
CENTER OF 99W HAS SHIFTED NORTHWEST TO AROUND 16N162E. PERSISTENT,
DEEP CONVECTION IS FOLLOWING BROAD, WEAK CURVATURE AROUND 99W, WHILE
OBSCURING THE LOW-LEVEL CIRCULATION CENTER, AS SHOWN ON INFRARED
SATELLITE IMAGERY. FOR MORE INFORMATION ON 99W, PLEASE REFER TO
BULLETINS FROM JTWC UNDER WMO HEADER ABPW10 PGTW.
JTWC OPENED INVEST 90W OVERNIGHT WITH A CENTER APPROXIMATED AROUND
13N152E. THE INVEST IS RATED SUB-LOW BY JTWC, MEANING SIGNIFICANT
DEVELOPMENT IS NOT EXPECTED OVER THE NEXT FEW DAYS. ITS ELONGATED
CENTER AND ATTENDANT TROUGH IS ORIENTED WNW TO ESE. POCKETS OF
FLARING, DEEP CONVECTION HAS CONTINUES DEVELOP ALONG ITS
SOUTHWESTERN FLANK. MODEL GUIDANCE SHOWS A LACK OF ORGANIZED
DEVELOPMENT OVER THE NEXT 24 HOURS, SHOWING THE ELONGATED CENTER
BECOMING MORE STRETCHED OUT, WITH ONE VORTICITY LOBE DRIFTING WEST-
NORTHWESTWARD ACROSS THE CNMI, WHILE THE OTHER VORTICITY CENTER
LINGERS NEAR OR EAST OF 150E.
EASTERN MICRONESIA UPDATE
LIGHT TO MODERATE SOUTHWEST WINDS, MOSTLY CLOUDY SKIES, AND
SCATTERED SHOWERS PREVAIL ACROSS THE REGION THIS MORNING. RECENT
ALTIMETRY DATA SHOWS COMBINED SEAS OF 4 TO 6 FEET. NO MAJOR CHANGES
WERE MADE TO THE FORECAST. MADE A FEW CHANGES TO THE SURF HEADLINES
FOR KOSRAE AND MAJURO. SOUTH TO SOUTHEAST SWELL CONTINUES TO MAKE
SURF ELEVATED AT TIMES ALONG SOUTH-FACING REEFS OF KOSRAE OVER THE
NEXT FEW DAYS, BUT SAW LESS SUPPORT FOR THIS FOR MAJURO.
WESTERN MICRONESIA UPDATE
AN ACTIVE MONSOON PATTERN CONTINUES TO PRODUCE NUMEROUS TO
WIDESPREAD SHOWERS AND ISOLATED TO SCATTERED THUNDERSTORMS ACROSS
YAP STATE, AND SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS
CHUUK STATE. ISOLATED SHOWERS CONTINUE AT PALAU, WITH CIRRUS CLOUDS
DRIFTING ALOFT FROM DEEPER CONVECTION NEAR YAP. ALTIMETRY SHOW
COMBINED SEAS BETWEEN 5 TO 7 FEET ACROSS YAP AND CHUUK, AND 4 TO 6
FEET ACROSS PALAU. NO CHANGES WERE MADE TO THE FORECAST.
PREV DISCUSSION
/ISSUED 558 PM CHST TUE AUG 25 2026/
MARIANAS SYNOPSIS...
ISOLATED TO SCATTERED SHOWERS ARE VISIBLE OVER THE MARIANAS THIS
EVENING AS A COL CONTINUES TO REMAIN OVER THE REGION. THIS IS KEEPING
WEST WINDS FAIRLY LIGHT, ESPECIALLY OVER TINIAN AND SAIPAN WHICH SAW
MINOR ISLAND EFFECT SHOWERS JUST OFF THE COASTLINE TODAY. MODELS
INDICATE COMBINED SEAS ARE 6 TO 7 FEET.
DISCUSSION...
ISOLATED SHOWERS AND THUNDERSTORMS TONIGHT ARE EXPECTED TO BECOME
MORE SCATTERED FOR GUAM AND ROTA TONIGHT, THOUGH MORE SO OVER THE
COASTAL WATERS THAN ON LAND. THIS PATTERN SHOULD REMAIN THROUGH
TOMORROW MORNING BEFORE DAYTIME HEATING AND LIGHT WINDS ALLOW FOR
SCATTERED ISLAND EFFECT SHOWERS AND ISOLATED THUNDERSTORMS TO
DEVELOP OVER TINIAN AND SAIPAN. THESE ISLAND EFFECT STORMS WILL ALSO
BE POSSIBLE THURSDAY FOR TINIAN AND SAIPAN. WINDS APPEAR LIKELY TO
REMAIN JUST HIGH ENOUGH FOR ANY ISLAND EFFECT OVER GUAM TO STAY
OFFSHORE. HOWEVER, SCATTERED MONSOONAL SHOWERS AND ISOLATED
THUNDERSTORMS WILL REMAIN POSSIBLE. THIS MONSOON FLOW IS EXPECTED TO
SLOWLY DRIFT NORTH THROUGHOUT THE WEEK, BRINGING SLIGHTLY HIGHER
WINDS AND MOISTURE TO THE MARIANAS AS SOON AS THURSDAY NIGHT. LOCALLY
HEAVY SHOWERS WILL BE POSSIBLE AS WELL BUT THE FLOOD RISK REMAINS
LOW. THIS MONSOON PATTERN MAY THEN CONTINUE FOR THE REST OF THE
FORECAST PERIOD.
MARINE...
COMBINED SEAS OF 6 TO 7 FEET TONIGHT WILL DECREASE TO ABOUT 4 TO 5
FEET BY WEDNESDAY NIGHT AS THE WEST-SOUTHWESTERLY MONSOON SWELL
DECREASES. THIS MAY START TO BUILD BACK IN BY FRIDAY OR THE WEEKEND.
THERE IS A MODERATE RISK OF RIP CURRENTS ALONG NORTH, SOUTH, AND WEST
FACING REEFS FOR THE NEXT FEW DAYS. THE LONG PERIOD EAST SWELL IS
SMALL ENOUGH FOR EAST FACING REEFS TO BE AT LOW RISK. THERE IS ALSO A
MODERATE RISK OF LIGHTNING FOR THE NEXT SEVERAL DAYS ALONG THE
COASTLINES. LIGHT TO GENTLE WEST WINDS WILL REMAIN FOR THE NEXT FEW
DAYS. AN UNSETTLED, BUT DISORGANIZED MONSOON PATTERN CONTINUES TO
BRING PERIODS OF SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS
THE MARIANAS THIS WEEK WITH LOCALLY HEAVY SHOWERS POSSIBLE BEGINNING
FRIDAY.
TROPICAL SYSTEMS...
TROPICAL DEPRESSION ATSANI CONTINUES TO PUSH TO THE NORTH THIS
AFTERNOON WITH LITTLE CONVECTION NOTED IN SATELLITE IMAGERY. AS OF
06Z, ATSANI IS LOCATED AROUND 21N137E WITH MAXIMUM SUSTAINED WINDS
AT 30 MPH. THE CURRENT FORECAST FROM THE JOINT TYPHOON WARNING
CENTER (JTWC) NOW DISSIPATES ATSANI AS A SIGNIFICANT TROPICAL
CYCLONE, AND THE FINAL WARNING HAS BEEN ISSUED. FOR MORE INFORMATION
ON TROPICAL DEPRESSION ATSANI PLEASE REFER TO BULLETINS FROM JTWC
UNDER WMO HEADER WTPN33 PGTW AND FROM THE NATIONAL WEATHER SERVICE
UNDER WMO HEADER WTPQ33 PGUM.
JTWC OPENED INVEST 99W THIS MORNING WITH A CENTER APPROXIMATED
AROUND 13N163E. THE INVEST IS RATED SUB-LOW BY JTWC, MEANING NO
DEVELOPMENT IS EXPECTED OVER THE NEXT FEW DAYS. ENSEMBLE GUIDANCES
SUGGESTS THIS DISTURBANCE WILL DRIFT TO THE WEST OVER THE NEXT DAY OR
SO BEFORE LIFTING TO THE NORTH.
EASTERN MICRONESIA...
HIGH-END SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED
TONIGHT AT BOTH KOSRAE AND POHNPEI WITH SHOWER CHANCES RETURNING TO
ISOLATED OR LOW-END SCATTERED ON WEDNESDAY, CONTINUING THROUGH AT
LEAST THURSDAY. MOSTLY DRY CONDITIONS ARE EXPECTED TO PREVAIL AT
MAJURO THROUGH FRIDAY WITH SHOWER CHANCES TOPPING OUT AROUND 30
PERCENT. GENTLE TO MODERATE WEST TO SOUTHWEST WINDS ARE EXPECTED TO
PERSIST OVER THE NEXT COUPLE OF DAYS AT POHNPEI AND KOSRAE BEFORE
EASING SLIGHTLY ON FRIDAY. WINDS WILL BE HIGHEST AT POHNPEI WITH LOW-
END FRESH WINDS STILL POSSIBLE THROUGH WEDNESDAY. WINDS WILL BE
MOSTLY LIGHT AT MAJURO THROUGH THE REST OF THE WEEK. COMBINED SEAS OF
MOSTLY 4 TO 6 FEET ARE EXPECTED AT ALL THREE SITES FOR THE NEXT
SEVERAL DAYS. SEAS CONSIST OF A SOUTHEAST SWELL AND A NORTHEAST
SWELL. OTHERWISE, ELEVATED SURF WILL CONTINUE THROUGH THE WEEK ALONG
SOUTH-FACING REEFS AT BOTH KOSRAE AND MAJURO.
WESTERN MICRONESIA...
SATELLITE IMAGERY SHOWS NUMEROUS TO WIDESPREAD SHOWERS AND SCATTERED
THUNDERSTORMS ACROSS YAP STATE AND SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS ACROSS CHUUK STATE. ISOLATED SHOWERS ARE SEEN ACROSS
PALAU. ALTIMETRY SHOW COMBINED SEAS BETWEEN 6 TO 8 FEET ACROSS YAP
AND 4 TO 7 FEET ACROSS PALAU AND CHUUK.
THE MAIN CONCERN IS THE ACTIVE MONSOON PATTERN MOVING ACROSS YAP AND
CHUUK STATES THIS EVENING. SCATTERED THUNDERSTORMS HAVE BEEN PRESENT
ACROSS WESTERN YAP STATE TODAY WITH ISOLATED THUNDERSTORMS SEEN
ACROSS EASTERN YAP STATE AND INTO CHUUK STATE. OVER THE COMING DAYS,
THIS MONSOON PATTERN LOOKS TO SLOWLY LIFT NORTHWARD IMPACTING CHUUK
THROUGH WEDNESDAY NIGHT AND YAP THROUGH THURSDAY. A LULL IN SHOWER
ACTIVITY IS EXPECTED AFTER THE ACTIVE PORTION OF THE MONSOON LIFTS
NORTHWARD. A NEW ROUND OF MONSOONAL SHOWERS AND THUNDERSTORMS WILL
BE POSSIBLE ACROSS CHUUK THIS WEEKEND AS THE MONSOON TROUGH
REORIENTS ITSELF ACROSS THE REGION. A SPECIAL WEATHER STATEMENT IS
CURRENTLY IN EFFECT ACROSS YAP STATE FOR ADDITIONAL HEAVY RAIN THIS
WEEK THAT COULD LEAD TO FLASH FLOODING AND MUDSLIDES.
PALAU LOOKS TO REMAIN DRY FOR THE FORESEEABLE FUTURE AND DROUGHT
CONCERNS COULD GROW OVER THE COMING WEEKS IF THE ACTIVE MONSOON
PATTERN REMAINS NORTH OF THEM.
CHOPPY SEAS OF 6 TO 8 FEET ARE OCCURRING ACROSS YAP THIS EVENING IN
COMBINATION WITH THUNDERSTORMS PRODUCING FREQUENT LIGHTNING. CHOPPY
SEAS LOOK TO CONTINUE THROUGH THURSDAY. TOWARDS THE END OF THE WEEK,
A SIGNIFICANT WESTERLY SWELL MAY DEVELOP AND BRING SEAS NEAR
HAZARDOUS CONDITIONS FOR SMALL CRAFTS AND HAZARDOUS SURF TO WEST AND
NORTH FACING REEFS OF YAP. FOR PALAU AND CHUUK, BENIGN SEAS ARE
EXPECTED THROUGH THE FORECAST PERIOD.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA/TROPICAL UPDATE: CRUZ
MARIANAS: OGLE
EAST MICRONESIA: WHISNANT
WEST MICRONESIA: WILLIAMS
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