510
FXPQ50 PGUM 280742
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
542 PM CHST MON SEP 28 2026
MARIANAS SYNOPSIS
LIGHT TO GENTLE EASTERLIES PREVAIL ACROSS THE MARIANAS. SATELLITE
IMAGERY AND DOPPLER RADAR INDICATE A LINE OF SHOWERS JUST OFF THE
NORTHERN SHORES OF GUAM. RECENT ALTIMETRY PASSES INDICATE SEAS ARE
AROUND 3 TO 4 FEET.
DISCUSSION
AN UNSETTLED WEATHER PATTERN PRODUCED BY AN EXTENSIVE MONSOON TROUGH
DOMINATED PRIMARILY BY A DEVELOPING DISTURBANCE KNOWN AS INVEST 93W
WELL TO THE EAST, IS EXPECTED TO CONTINUE AS SUCH THE NEXT FEW DAYS.
MOSTLY DRY CONDITIONS ARE EXPECTED OVERNIGHT, FOLLOWED BY SOME
ISLAND SHOWERS DEVELOPING TUESDAY AFTERNOON. AFTER, CONDITIONS WILL
DETERIORATE ONCE AGAIN AS INVEST 93W CONTINUES TO CONSOLIDATE AND
PASS TO THE NORTHEAST OF THE MARIANAS SOMETIME THURSDAY THROUGH
FRIDAY, INDUCING A SIGNIFICANT MONSOON SURGE THAT WILL BRING A PEAK
IN SHOWER AND THUNDER POTENTIAL BY THE WEEKEND. CONDITIONS ARE THEN
EXPECTED TO REMAIN WET COMING INTO NEXT WEEK AS A SOUTHERWESTERLY
MONSOON REGIME CONTINUES.
MARINE
SEAS AROUND 3 FEET WILL REMAIN OVERNIGHT, TO THEN INCREASE THEREAFTER
AS INVEST 93W CONTINUES TO CONSOLIDATE TO THE EAST OF THE MARIANAS
AND ALLOWING A SOUTHWESTERLY MONSOON TO RETURN ACROSS THE REGION
TOWARD THE NEXT WEEKEND. AS 93W PASSES TO THE NORTHEAST AND A MONSOON
SURGE DEVELOPS, SEAS ARE EXPECTED TO SURPASS 10 FEET BEGINNING
THURSDAY, LIKELY BECOMING HAZARDOUS TO SMALL CRAFT. A LOW RISK OF RIP
CURRENTS IS EXPECTED ALONG ALL REEFS OF THE MARIANAS THROUGH AT
LEAST WEDNESDAY, WHEN A MODERATE RIP CURRENT RISK MAY DEVELOP ALONG
WEST FACING REEFS. THERE IS SOME LIKELIHOOD FOR HAZARDOUS SURF TO
DEVELOP ALONG SOUTH, WEST AND NORTH FACING REEFS OF THE MARIANAS IN
THE SECOND HALF OF THE WEEK, HIGHLY DEPENDENT ON THE DEVELOPMENT OF
93W AND ASSOCIATED SOUTHWESTERLY MONSOON SURGE.
TROPICAL SYSTEMS
A DEVELOPING DISTURBANCE, INVEST 93W, IS FOUND ALONG THE MONSOON
TROUGH, CENTERED WELL EAST OF THE MARIANAS, NORTH-NORTHEAST OF WENO,
CHUUK, NEAR 15N157E. THIS SYSTEM IS RATED AS A SUB-LOW. 93W HAS
MOVED SLOWLY WEST-NORTHWEST AND IS EXPECTED TO SLOWLY STRENGTHEN AS
IT CONTINUES TO MOVE WEST-NORTHWEST TO NORTHWEST OVER THE NEXT FEW
DAYS, POSSIBLY PASSING NORTH OF SAIPAN, MOVING THROUGH THE NORTHERN
CNMI. RESIDENTS OF THE MARIANAS, ESPECIALLY TINIAN, SAIPAN AND THE
NORTHERN CNMI, SHOULD MONITOR FORECASTS FOR ANY CHANGES TO EXPECTED
DEVELOPMENT AND MOVEMENT OVER THE NEXT FEW DAYS.
EASTERN MICRONESIA
A VERY DRY PATTERN IS NOW IN PLACE OVER POHNPEI AND KOSRAE AND IS
EXPECTED TO CONTINUE THROUGH THE REMAINDER OF THE WEEK. FOR MAJURO,
DRY CONDITIONS WILL CONTINUE THROUGH TUESDAY NIGHT. THEN, THE EASTERN
END OF THE MONSOON TROUGH LOOKS TO BECOME A BIT MORE ACTIVE AS INVEST
93W MOVES OUT TO THE WEST-NORTHWEST AND DRAGS THE TROUGH OVER THE
MARSHALL ISLANDS. THE TROUGH LOOKS TO MAKE A VERY SLOW PROGRESSION
TOWARD KOSRAE AND POHNPEI AND COULD POSSIBLY BEGIN TO AFFECT BOTH
LOCATIONS OVER THE WEEKEND.
FAIRLY BENIGN MARINE CONDITIONS LOOK TO CONTINUE ACROSS THE REGION
THROUGH THE WEEK, WITH SEAS OF 3 TO 5 FEET AND LIGHT TO GENTLE WINDS
AT ALL THREE LOCATIONS THROUGH AT LEAST FRIDAY.
WESTERN MICRONESIA
THE MONSOON TROUGH REMAINS THE DOMINANT FEATURE IN THE REGION. THE
TROUGH AXIS IS LOCATED NEAR 10N130E AND EXTENDS EASTWARD ACROSS MUCH
OF MICRONESIA AND ENDING NEAR 10N155E. THIS FEATURE IS PRODUCING
SCATTERED TO NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS, WITH THE
STRONGEST SHOWERS NEAR 10N. AS INVEST 93W CONSOLIDATES AND MOVES
WEST- NORTHWEST, THE AXIS IS EXPECTED TO TURN INTO A MORE NE-SW
DIRECTION.
PALAU IS SOUTH OF THE TROUGH, FAR ENOUGH THAT SHOWERS WILL VARY
BETWEEN ISOLATED AND SCATTERED THROUGH ABOUT THURSDAY. DURING THIS
TIME, 93W IS EXPECTED TO CONTINUE CONSOLIDATING AND MOVING WEST-
NORTHWEST DIRECTION, THIS WILL CAUSE A SHIFT IN THE TROUGH'S AXIS,
ALLOWING FOR MORE FAVORABLE CONDITIONS FOR SHOWERS TO BE PRODUCED
OVER PALAU FOR THE WEEKEND.
YAP IS THE CLOSEST ISLAND TO THIS TROUGH AND EXPECTED TO SEE
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS THROUGH THE WEEK. MODEL
GUIDANCE SUGGESTS UP TO 1 INCH OF RAIN EACH DAY THROUGH THE
REMAINDER OF THE WEEK. OVERALL, A WET WEEK IS TO BE EXPECTED.
CHUUK IS ON THE SOUTHERN EDGE OF THE CONVECTIVE ACTIVITY PRODUCED BY
THE MONSOON TROUGH. HERE IS WHERE BLOW-OFF CLOUD COVER IS THE
GREATEST. THIS CLOUD COVER IS EXPECTED TO PRODUCE ISOLATED SHOWERS
WHILE THE TROUGH REMAINS IN A E-W ORIENTATION. ONCE 93W STARTS
PULLING THE TROUGH AWAY, DRIER CONDITIONS ARE EXPECTED TO RETURN
FOR THE WEEKEND AND INTO NEXT WEEK.
ALTIMETRY SHOWS COMBINED SEAS BETWEEN 3 AND 5 FEET ACROSS THE
REGION. WINDS WILL BE LIGHT TO MODERATE THROUGH THURSDAY, THEN WINDS
ARE EXPECTED TO BUILD TO GENTLE TO FRESH NEAR THE WEEKEND. SEA
CONDITIONS ARE EXPECTED TO REMAIN BENIGN THROUGH THURSDAY, AFTERWARDS
SEAS ARE ANTICIPATED TO BUILD TO AROUND 9 FEET ALONG THE NORTHERN
PORTIONS OF THE REGION. A SMALL CRAFT ADVISORY MAY BECOME NECESSARY
FOR THE WEEKEND.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: MONTVILA
EAST MICRONESIA/TROPICAL SYSTEMS: KLEESCHULTE
WEST MICRONESIA: BOWSHER
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