174
FXPQ50 PGUM 300859
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
659 PM CHST SUN AUG 30 2026
MARIANAS SYNOPSIS
SCATTERED SHOWERS HAVE DEVELOPED ACROSS THE MARIANAS WATERS, WITH
ISOLATED THUNDERSTORMS OVER SOUTHEAST GUAM COASTAL WATERS. LIGHT TO
MODERATE WINDS PREVAIL ACROSS THE REGION. LATEST ALTIMETRY DATA SHOWS
SEAS OF 4 TO 6 FEET WEST OF THE MARIANAS.
DISCUSSION
SHOWER COVERAGE FINALLY BEGAN TO INCREASE ACROSS THE MARIANAS THIS
AFTERNOON, WITH NUMEROUS HEAVY SHOWERS SEEN ACROSS GUAM AND SCATTERED
SHOWERS ELSEWHERE EARLIER THIS AFTERNOON. POPS (PROBABILITY OF
PRECIPITATION) AROUND ON THE LOW-END, AROUND 30 PERCENT, FOR THE CNMI
AND AROUND 50 PERCENT FOR GUAM, WHICH LOOKS TO BE THE RULE THROUGH
THE REST OF THE NIGHT. LATEST GUIDANCE TRIES TO BRING IN NUMEROUS
SHOWERS FOR THE NEXT COUPLE OF DAYS FOR GUAM, WITH VERY DRY
CONDITIONS ACROSS THE CNMI. HOWEVER, DECIDED TO MAINTAIN POPS AT 30
TO 50 PERCENT FOR GUAM DUE TO THIS INCREASE IN CONVECTION BEING
LINKED TO THE DEVELOPMENT OF A WEAK MONSOON DISTURBANCE BOTH
SOUTHEAST AND SOUTHWEST OF GUAM OVER THE NEXT FEW DAYS. IT APPEARS
THAT DEVELOPMENT, IF IT OCCURS, WILL BE A BIT FARTHER AWAY FROM GUAM,
HEADING ALMOST DUE NORTH, KEEPING THE HEAVIER SHOWERS AND HIGHER
POPS AWAY FROM THE MARIANAS. THEREFORE, GUAM LOOKS TO MAINTAIN
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS FOR THE NEXT FEW DAYS,
WITH THE CNMI SEEING ONLY ISOLATED SHOWERS BY MONDAY MORNING.
MARINE
FOR MARINE CONDITIONS, THE WINDS LOOKS TO REMAIN FAIRLY BENIGN FOR
THE MARIANAS THROUGH AT LEAST WEDNESDAY. THEN, SEAS COULD INCREASE A
BIT AROUND MIDWEEK. LATEST WAVEWATCH GUIDANCE IS SPREAD ACROSS A WIDE
RANGE OF SEA HEIGHTS. THE ECMWF WAVE MODEL SHOWS SEAS REMAINING AT OR
BELOW 6 FEET UNTIL THURSDAY, THEN ONLY BUILDING TO AROUND 7 FEET. THE
GFS WAVE, GLOBAL WAVE AND NWPS SHOW SEAS REACHING 10 TO 12 FEET
THURSDAY DUE TO THE GFS PREDICTING THE DEVELOPMENT OF A TROPICAL
DISTURBANCE ON THE EAST-NORTHEAST AND SOUTHWEST SIDE OF GUAM. SINCE
THE DEVELOPMENT IS POSSIBLE, YET NOT EXPECTED AT THIS TIME, DECIDED
TO USE A 75 PERCENT ECMWF AND 25 PERCENT GFS WAVE MODEL BLEND,
BRINGING SEAS UP TO 9 FEET. THIS WILL LIKELY CHANGE OVER THE NEXT
COUPLE OF DAYS AS IT BECOMES MORE EVIDENT WHETHER THESE SYSTEMS WILL
OR WILL NOT DEVELOP. FOR WINDS, MOSTLY LIGHT TO GENTLE THROUGH
MIDWEEK, WITH WINDS BECOMING OCCASIONALLY FRESH AFTER MIDWEEK DUE TO
EITHER THE DEVELOPMENT OF AFOREMENTIONED DISTURBANCES OR AN
INCREASING MONSOON SURGE.
TROPICAL SYSTEMS
A MONSOON DEPRESSION, INVEST 94W, IS CENTERED W OF THE FAR NORTHERN
CNMI NEAR 20N 134E, MOVING SLOWLY WEST. 94W IS NOW A SUBJECT OF A
TROPICAL CYCLONE FORMATION ALERT (TCFA), MEANING DEVELOPMENT INTO A
SIGNIFICANT TROPICAL CYCLONE IS LIKELY WITHIN THE NEXT 24 HOURS.
ENHANCED INFRARED SATELLITE DATA CURRENTLY SHOWS A WEAK, DISORGANIZED
LOW-LEVEL CIRCULATION CENTER (LLCC) WITH PERSISTENT, PULSING
CONVECTION OBSCURING THE CENTER. THE LATEST 925MB ANALYSIS SHOWS AN
ELONGATED LLCC WITH WEAK SURROUNDING WINDS. LOW VERTICAL WIND SHEAR
AND FAVORABLE EQUATORWARD OUTFLOW COMBINED WITH THE FAVORABLE SEA
SURFACE TEMPERATURES INDICATE CONDITIONS CONDUCIVE FOR DEVELOPMENT.
EASTERN MICRONESIA
SATELLITE IMAGERY INDICATES NUMEROUS SHOWERS AT POHNPEI, HIGH-END
SCATTERED SHOWERS AT KOSRAE, AND SCATTERED SHOWERS AT MAJURO, WITH
ISOLATED THUNDERSTORMS NEAR ALL THREE FORECAST POINTS. SCATTEROMETRY
INDICATES MODERATE TO FRESH SOUTHWESTERLIES ACROSS MUCH OF POHNPEI
AND KOSRAE, AND GENTLE TO MODERATE SOUTHWESTERLIES AT MAJURO.
ALTIMETRY AND BUOY DATA INDICATES COMBINED SEAS OF 5 TO 7 FT NEAR
POHNPEI AND KOSRAE, AND 4 TO 6 FT AT MAJURO.
A MONSOON SURGE AIDED BY A BROAD CIRCULATION WELL TO THE NORTHWEST IS
PRODUCING WIDESPREAD CONVECTION WITH NUMEROUS SHOWERS AND LOCALLY
HEAVY RAINFALL OVER POHNPEI. MODEL GUIDANCE INDICATES THIS PATTERN
CONTINUING THROUGH MONDAY NIGHT, SO A HEADLINE WITH ADDITIONAL
WORDING WAS INCLUDED IN THE FORECAST WITHOUT THE NEED FOR A SPECIAL
WEATHER STATEMENT AS FLOODING AND MUDSLIDES ARE NOT A CONCERN AS OF
NOW. SHOULD CONDITIONS LAST LONGER OR INTENSIFY MORE THAN PREVIOUSLY
ANTICIPATED, AN SPS MAY NEED TO BE ISSUED. THIS SITUATION WILL
CONTINUE TO BE MONITORED.
AS FOR KOSRAE, THE HEAVIEST CONVECTION AND STRONGEST WINDS SHOULD
REMAIN TO THE NORTH, BUT NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS
ARE STILL EXPECTED AT LEAST THROUGH MONDAY AFTERNOON. FINALLY, MAJURO
WILL REMAIN WITHIN DIFFUSIVE FLOW AND NEAR A COL TO THE NORTHEAST,
SO LIGHT WINDS, SCATTERED SHOWERS, AND ISOLATED THUNDERSTORMS ARE
POSSIBLE THROUGH MONDAY NIGHT. AFTERWARDS, THE ACTIVE WEATHER
PATTERN MAY SETTLE DOWN THROUGH THE REST OF THE WEEK FOR THE ENTIRE
REGION.
A BRIEF PULSE IN THE WESTERLY SWELL IS EXPECTED AT POHNPEI,
TEMPORARILY INCREASING COMBINED SEAS IN THEIR COASTAL WATERS AS WELL
AS SURF HEIGHTS ALONG WEST-FACING REEFS. AS OF NOW, THERE IS LITTLE
CONCERN FOR HAZARDOUS SEAS TO SMALL CRAFT NOR HAZARDOUS SURF BECAUSE
THE SWELL PULSE IS NOT EXPECTED TO LAST BEYOND MONDAY NIGHT.
HOWEVER, A HEADLINE WAS INCLUDED FOR THE ELEVATED SURF ALONG WEST-
FACING REEFS, SO BEACHGOERS SHOULD REMAIN VIGILANT IN OR NEAR THE
WATERS AS THE RISK OF RIP CURRENTS WILL BE MODERATE. AS FOR KOSRAE
AND MAJURO, BENIGN SEAS WILL CONTINUE WITH VARIOUS SWELL DIRECTIONS
FROM THE WEST, SOUTH, AND EAST.
WESTERN MICRONESIA
A MONSOON SURGE ENHANCED BY NEARBY TROPICAL DISTURBANCE IS BRINGING
VERY FRESH TO STRONG SOUTHWESTERLIES, ALONG WITH HEAVY, INTENSE
RAINFALL TO CHUUK TONIGHT, WHICH WILL BEGIN TO SLOWLY TAPER DOWN
THEREAFTER AS CONVECTION DIMINISHES AND A DRY SPELL RETURNS IN THE
SECOND HALF OF THE WEEK. BACKBUILDING OF CONVECTION BY THE
AFOREMENTIONED MONSOON SURGE IS EXPECTED TO SIGNIFICANTLY INCREASE
SHOWERS AT YAP BEGINNING LATE TONIGHT, WITH SCATTERED SHOWERS
DEVELOPING INTO NUMEROUS AND HEAVY WITH SOME THUNDERSTORMS AND
OCCASIONALLY STRONG GUSTS MONDAY, AS THE WET PATTERN PERSISTS UNTIL
MIDWEEK. A MINOR TROPICAL RIDGE ANCHORED AGAINST THE EQUATOR ACROSS
THE INDONESIAN ISLANDS OF AJU AND BRAS IS BRINGING DIFFUSIVE FLOW
ACROSS PALAU, WITH MOSTLY CLEAR SKIES EXPECTED OVERNIGHT, FOLLOWED BY
A RETURN TO PATCHY SHOWERS BEGINNING MONDAY NIGHT.
COMBINED SEAS OF 3 TO 4 FEET NEAR PALAU AND 4 TO 6 FEET NEAR YAP, ARE
EXPECTED TO CONTINUE AS SUCH FOR THE NEXT SEVERAL DAYS, COMPRISED OF
A DOMINANT WESTERLY SWELL. SEAS ARE EXPECTED TO TAPER DOWN A FEW FEET
NEAR YAP BY THE NEXT WEEKEND AS SWELLS AND WIND WAVES DIMINISH.
COMBINED SEAS OF 7 TO 9 FEET WILL QUICKLY DROP SEVERAL FEET OVER THE
NEXT FEW DAYS AS LOCALIZED WIND WAVES DROP SIGNIFICANTLY, TO THEN
REMAIN IN THE 3 TO 5 FOOT RANGE THROUGH THE END OF THE WEEK.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/TROPICAL: KLEESCHULTE
EAST MICRONESIA: MESA
WEST MICRONESIA/TROPICAL: MONTVILA
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