797
FXPQ50 PGUM 220741
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
541 PM CHST THU OCT 22 2026
MARIANAS SYNOPSIS
HIMAWARI VISIBLE SATELLITE AND DOPPLER RADAR IMAGERY THIS AFTERNOON
SHOW PARTLY CLOUDY SKIES AND ISOLATED TO SCATTERED SHOWERS ACROSS THE
AREA. BUOY AND ALTIMETRY DATA DEPICT COMBINED SEAS AROUND 6 TO 8
FEET.
DISCUSSION
THE MARIANAS ARE SITUATED ON THE NORTHWEST PERIPHERY OF A BROAD, WEAK
CIRCULATION, INVEST 98W, CENTERED BETWEEN SATAWAL AND CHUUK LAGOON
NEAR 8N150E. A TRADE-WIND TROUGH EXTENDS NORTHWARD FROM INVEST 98W,
WITH NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS SEEN ALONG THE AXIS,
APPROACHING THE ISLANDS FROM THE EAST. SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS ARE EXPECTED TONIGHT AS THE TRADE-WIND TROUGH
SHIFTS WESTWARD INTO THE AREA, SUPPORTED IN PART BY DIVERGENCE ALOFT
ASSOCIATED WITH AN UPPER-LEVEL LOW AND TROUGH. OVER THE NEXT FEW
DAYS, MODEL GUIDANCE SHOWS MOST OF THE SHOWERS AND THUNDERSTORMS
DEVELOPING NEAR TINIAN AND SAIPAN WHERE THE STRONGEST CONVERGENCE
LOOKS TO SET UP, AS INVEST 98W SLOWLY MEANDERS WESTWARD SOUTH OF THE
ISLANDS, AND AN ATTENDANT TROUGH TO ITS NORTHEAST MOVES THROUGH THE
AREA. LATE THIS WEEKEND INTO EARLY NEXT WEEK, A QUIETER RIDGING
PATTERN LOOKS TO MOVE IN BEHIND 98W.
MARINE/SURF
GENTLE TO MODERATE NORTHEAST TO EAST WINDS WILL PREVAIL ACROSS
GUAM AND ROTA WATERS THOUGH AT LEAST FRIDAY NIGHT, AND START TO
DIMINISH SATURDAY AS WIND DIRECTION BRIEFLY SHIFTS SOUTHEAST. FOR
SAIPAN AND TINIAN, WINDS WILL BE MODERATE TO FRESH OUT OF THE EAST
OVER THE NEXT FEW DAYS WITH OCCASIONAL STRONG GUSTS FRIDAY AS
TRADE WINDS BRIEFLY SURGE ACROSS THE FAR NORTHERN CNMI. COMBINED
SEAS OF 6 TO 8 FEET COULD BRIEFLY INCREASE A FOOT TONIGHT AS THE
HIGHEST PULSE OF THE NORTHEASTERLY SWELL ARRIVES THEN, FOR TINIAN
AND SAIPAN WATERS. SEAS LOOK TO DIMINISH THEREAFTER AS THIS SWELL
BEGINS TO WEAKEN. MEANWHILE, THERE WILL BE A MODERATE RISK OF RIP
CURRENTS THROUGH THE WEEKEND, MAINLY ALONG NORTH AND EAST FACING
REEFS. THERE WILL ALSO BE MODERATE RISK OF LIGHTNING THROUGH AT LEAST
FRIDAY NIGHT, MAINLY FOR TINIAN AND SAIPAN.
TROPICAL SYSTEMS
TWO INVEST AREAS WERE OPENED BY THE JOINT TYPHOON WARNING CENTER
(JTWC) TODAY. A WEAK TROPICAL DISTURBANCE IS LOCATED OVER THE
NORTHERN MARSHALL ISLANDS NEAR 11N167E, DESIGNATED INVEST 97W BY JTWC
AS OF 1000 AM CHST. INVEST 97W IS CURRENTLY RATED "LOW" FOR
DEVELOPMENT, MEANING DEVELOPMENT IS UNLIKELY WITHIN THE NEXT 24
HOURS. LATEST HIMAWARI VISIBLE SATELLITE SHOWS BROAD, PATCHY CLOUD
COVER ACROSS THE REGION WITH CONVECTION FOCUSING NEAR THE CENTER OF
97W. THE ANIMATED SATELLITE IMAGERY LOOP, AND LATEST SCATTEROMETRY
DATA THIS MORNING, DEPICT A WEAK, BUT CLEARLY VISIBLE SURFACE
CIRCULATION IN THE VICINITY OF RONGELAP AND BIKINI ATOLLS. ALTHOUGH
THERE ARE SEVERAL WEAK CIRCULATIONS ACROSS EASTERN AND CENTRAL
MICRONESIA, MODELS FAVOR 97W MOST FOR DEVELOPMENT, WITH LATEST
GUIDANCE SHOWING GRADUAL ORGANIZATION OVER THE NEXT FEW DAYS AS IT
REMAINS QUASI-STATIONARY, STRENGTHENING MORE THIS COMING WEEKEND AS
IT BEGINS TO MOVE NORTH. IT IS TOO EARLY TO SAY MUCH ABOUT THE
EVENTUAL STRENGTH OR TRACK AS 97W IS A NEWLY-FORMED SYSYEM, BUT IT
WILL CONTINUE TO BE MONITORED IN THE COMING DAYS.
TO THE WEST, A BROAD, ELONGATED SURFACE CIRCULATION IS CENTERED
BETWEEN SATAWAL AND CHUUK LAGOON NEAR 8N150E, NOW DUBBED INVEST 98W
BY JTWC. SCATTERED TO NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS
ARE SEEN ACROSS THE AREA, MAINLY WITHIN THE CONVERGENT SOUTH TO
SOUTHWEST FLOW INTO THE DISTURBANCE. INVEST 98W LOOKS TO REMAIN
BROAD AND DISORGANIZED AS IT SHIFTS WEST THROUGH THE NEXT FEW DAYS,
MAINTAINING A GENERALLY WETTER PATTERN FOR CHUUK AND THE MARIANAS
INTO THE END OF THE WEEK. INVEST 98W IS ALSO RATED "SUB-LOW" BY
JTWC, AS IT IS NOT EXPECTED TO DEVELOP IN THE NEXT FEW DAYS.
IF INVEST 97W OR 98W ORGANIZE AND BECOME RATED "LOW" OR HIGHER,
ADDITIONAL INFORMATION ON THESE DISTURBANCES WILL BE FOUND IN
BULLETINS ISSUED BY JTWC UNDER WMO HEADER ABPW10 PGTW.
EASTERN MICRONESIA
SCATTERED SHOWERS FROM THE MONSOON TROUGH WILL CONTINUE THROUGH
TONIGHT FOR MAJURO AND POSSIBLY POHNPEI, BUT ARE EXPECTED TO REMAIN
FAIRLY LIGHT WITH NO THUNDERSTORMS. KOSRAE IS SEEING DRYER CONDITIONS
AND THIS IS EXPECTED TO CONTINUE FOR THE ENTIRE FORECAST PERIOD AS
THE MONSOON TROUGH STAYS WEAK AND GENERALLY TO THE NORTH. WINDS ARE
BECOMING LIGHT BY TOMORROW OVER POHNPEI WHICH MAY ALLOW FOR SOME
SCATTERED ISLAND EFFECT SHOWERS IN THE AFTERNOON. LIGHT TO GENTLE
WINDS OVER KOSRAE WILL BE STEADY UNTIL POTENTIALLY INCREASING
SLIGHTLY TO GENTLE TO FRESH SATURDAY. MAJURO HAS THE HIGHEST WINDS,
WITH GENTLE TO MODERATE WINDS EXPECTED MOST OF THE FORECAST PERIOD,
POTENTIALLY BECOMING FRESH FRIDAY NIGHT AS THE MONSOON SURGE PEAKS
NEARBY TO THE NORTHWEST AND FEEDS INTO THE DEVELOPING INVEST 97W.
HOWEVER, WITH THIS SYSTEM STAYING NORTH, BOTH POHNPEI AND MAJURO WILL
ALSO STAY GENERALLY DRY WITH ISOLATED SHOWERS WITH THE EXCEPTION OF
LOW-END SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS FRIDAY NIGHT
FOR MAJURO AND SUNDAY FOR POHNPEI.
FOR THE MARINE FORECAST, COMBINED SEAS OF 5 TO 6 FEET WILL REMAIN
STEADY FOR POHNPEI AND KOSRAE THROUGH THE WHOLE FORECAST PERIOD.
MAJURO MAY SEE 6 TO 7 FOOT SEAS THIS WEEKEND DUE TO INCREASED CHOPPY
SEAS FROM THE MONSOON SURGE. OTHERWISE, SEAS WILL LIKELY DROP BACK
DOWN TO 4 TO 5 FOOT BY MIDWEEK FOR MAJURO.
WESTERN MICRONESIA
THE MAIN FOCUS CONTINUES TO BE ON THE "NEWLY-MINTED" INVEST 98W,
CURRENTLY LOCATED NEAR CHUUK AT 7.9N 150.0E. THIS FEATURE LOOKS TO
MOVE OFF TO THE NORTH-NORTHWEST WITH LITTLE DEVELOPMENT EXPECTED, AS
EVIDENT BY MODEL DATA AND JTWC'S (THE JOINT TYPHOON WARNING CENTER)
"SUB-LOW" RATING. STILL, IT LOOKS TO KEEP A PROLONGED PERIOD OF
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS GOING AS RAINFALL
ASSOCIATED WITH THE CIRCULATION AND IT'S "INFLOW" PERSISTS. FARTHER
WEST, PALAU AND YAP CAN EXPECT JUST ISOLATED SHOWERS THIS FORECAST
PERIOD.
WINDS AND WAVES WILL BE HIGHEST WITH 98W, AS WAVES FROM DISTANT STY
CHAMPI CONTINUE TO DECREASE. OVERALL, SEAS OF 4 TO 6 FEET ARE
EXPECTED AT YAP AND PALAU UNDER LIGHT TO GENTLE WINDS. FOR CHUUK,
MODERATE TO FRESH WINDS WILL BECOME LIGHT TO GENTLE BY THE WEEKEND
WITH SEAS OF 5 TO 7 FEET DECREASING A FOOT BY EARLY NEXT WEEK.
AS A SIDE NOTE, PALAU LOOKS TO SEE A CONTINUATION OF LIGHT HAZE DUE
TO WILDFIRE SMOKE FROM INDONESIA, AS EVIDENT IN SATELLITE IMAGERY.
THIS LOOKS TO IMPROVE SLIGHTLY OVER THE NEXT FEW DAYS AS CHAMPI MOVES
FARTHER AWAY AND WEAK EASTERLIES MOVE CLEANER AIR INTO THE REGION.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/TROPICAL SYSTEMS: DECOU
EAST MICRONESIA: OGLE
WEST MICRONESIA: DOLL
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