263
FXPQ50 PGUM 180800
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
600 PM CHST FRI SEP 18 2026
MARIANAS SYNOPSIS
AFTERNOON SATELLITE AND RADAR IMAGERY SHOW MOSTLY CLOUDY SKIES WITH
SCATTERED SHOWERS ACROSS GUAM AND ROTA, WITH PATCHIER SHOWERS ARE
ACROSS TINIAN AND SAIPAN. GENTLE TO MODERATE WEST TO SOUTHWEST WINDS
PERSIST ACROSS THE REGION AND ALTIMETRY DATA SHOWS COMBINED SEAS OF 5
TO 7 FEET.
DISCUSSION
DISTANT TROPICAL STORM DUJUAN HAS MOVED NORTH OF 25N AND HAS EXITED
THE REGION. DUJUAN CONTINUES TO STEER RELATIVELY DRIER AIR SOUTH OF
20N, LEADING TO SPOTTY SHOWERS ACROSS TINIAN AND SAIPAN, THEN SHOWERS
BECOME INCREASINGLY SCATTERED ACROSS GUAM AND ROTA, CLOSER IN
PROXIMITY TO THE TRAILING BAND OF MONSOONAL MOISTURE AND CONVERGENCE.
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS PREVAIL ACROSS THE
REGION, MORESO ACROSS GUAM AND ROTA THROUGH SATURDAY, THEN SHOWERS
SPREAD NORTHWARD ACROSS TINIAN AND SAIPAN EARLY NEXT WEEK. A BRIEF
PERIOD OF NUMEROUS SHOWERS ARE EXPECTED TO BUILD ACROSS SOUTHERN GUAM
WATERS OVERNIGHT, WITH LOCALLY HEAVY SHOWERS AND OCCASIONAL GUSTS TO
25 MPH POSSIBLE ACROSS GUAM. THE MAIN BAND OF MONSOONAL MOISTURE
CONTINUES TO LINGER NEAR AND SOUTH OF GUAM, WITH MODEL GUIDANCE
SHOWING SOME POTENTIAL OF A NEARBY WEAK DISTURBANCE FORMING IN THE
MONSOON TROUGH EARLY NEXT WEEK. DEPENDING ON THIS SCENARIO OR IF
THERE IS A NORTHWARD SHIFT IN THE MONSOON TROUGH, THIS COULD
POTENTIALLY RESULT IN PERIODS OF SCATTERED TO NUMEROUS SHOWERS WITH
MODERATE TO STRONG GUSTS EARLY NEXT WEEK.
MARINE
GENTLE TO MODERATE WEST TO SOUTHWEST WINDS DECREASE TO LIGHT TO
GENTLE OVER THE WEEKEND, THEN SHIFT TO THE SOUTH TO SOUTHEAST
NEXT WEEK. COMBINED SEAS OF 5 TO 7 FEET ARE COMPRISED OF SOUTHWEST
MONSOON SWELL, NORTHERLY SWELL FROM DISTANT TROPICAL STORM
DUJUAN, AND LIGHT NORTHEAST SWELL. SEAS ARE EXPECTED TO SUBSIDE TO
4 TO 6 FEET OVER THE WEEKEND AND EARLY NEXT WEEK DUE TO A SLIGHT
DECREASE IN WIND WAVES AND SWELLS.
EASTERN MICRONESIA
A RATHER SLOW-MOVING STAGNANT PATTERN REMAINS IN PLACE, WITH A RIDGE
AXIS CENTERED OVER POHNPEI, A SLIGHTLY ELEVATED LOW JUST NORTH-
NORTHWEST OF MAJURO. AN INCREASED PRESSURE GRADIENT BETWEEN THE TWO
FROM NEAR POHNPEI SOUTHEAST TO KOSRAE. HERE, GENTLE TO MODERATE WINDS
PERSIST, AND THIS LOOKS TO CONTINUE THROUGH SUNDAY NIGHT. THEN, THE
RIDGE AXIS WEAKENS SOME AS IT DRIFTS WEST, ALLOWING THE GRADIENT TO
SLACKEN.
HOWEVER, THIS AMPLIFIED (FOR THE TROPICS) PATTERN IS ALLOWING FOR A
WEDGE OF MOISTURE TO STRETCH FROM NEAR POHNPEI TO KOSRAE, ROUNDING
THE BASE OF A TROUGH WEST OF MAKIN, THEN SHOOTING NORTH AS IT GRAZES
MAJURO TO THE EAST. GIVEN THE SLOW PROGRESSION OF THE SYNOPTIC
PATTERN OBSERVED OVER THE LAST FEW DAYS, AND WITH MODEL TRENDS
SHOWING MORE OF THE SAME, WE OPTED TO GO WITH A LONG PERIOD OF
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS AT POHNPEI AND KOSRAE,
WHILE EVENTUALLY DROPPING THEM BACK TO ISOLATED SHOWERS AT MAJURO
EARLY NEXT WEEK. ALTHOUGH, THIS MAY NEED TO BE INCREASED IN LATER
FORECASTS IF THE MONSOON TROUGH SINKS SOUTH FAR ENOUGH TO HAVE AN
INFLUENCE, AS THE PATTERN REORIENTATES ITSELF OVER THE NEXT SEVERAL
DAYS.
AS FOR MARINE CONDITIONS, AS MENTIONED ABOVE, GENTLE TO MODERATE
WINDS WILL PERSIST THROUGH SUNDAY NIGHT FOR POHNPEI AND KOSRAE,
BECOMING LIGHT TO GENTLE THEREAFTER. LIGHT TO GENTLE WINDS WILL
PREVAIL AT MAJURO THROUGHOUT THE FORECAST PERIOD. SEAS WILL HOLD IN
THE 4 TO 6 FOOT RANGE.
WESTERN MICRONESIA
SATELLITE IMAGERY SHOWS SCATTERED SHOWERS OVER YAP AND ISOLATED
SHOWERS OVER PALAU AND CHUUK. ALTIMETRY SHOWS COMBINED SEAS ARE
BETWEEN 5 AND 8 FEET ACROSS THE REGION.
QUIET CONDITIONS ARE CURRENTLY IN PLACE ACROSS WESTERN MICRONESIA.
WIDELY SCATTERED SHOWERS ARE SEEN ACROSS YAP, WHILE ISOLATED SHOWERS
ARE SEEN ELSEWHERE. THE MONSOON TAIL THAT FEATURES HEAVIER SHOWERS
HAS MOSTLY CUT-OFF FROM TROPICAL STORM DUJUAN. THIS MONSOON TAIL MAY
CONTINUE TO SHIFT NORTH OVER THE NEXT DAY BEFORE SHIFTING SOUTH BY
SUNDAY OR MONDAY. THIS WILL PLACE THE FOCUS OF HEAVIER SHOWERS OVER
YAP LATE THIS WEEKEND AND INTO NEXT WEEK. THE EASTERN EDGE OF THE
MONSOON PATTERN WILL INTERACT WITH A SURFACE RIDGE NEAR CHUUK. THIS
WILL ALLOW FOR AN INCREASE IN SHOWERS ACROSS CHUUK STATE SATURDAY
NIGHT AND PERSISTING INTO NEXT WEEK. QUIET CONDITIONS ARE EXPECTED
EARLY IN THE FORECAST CYCLE FOR PALAU, THEN LATE THIS WEEKEND,
CONVERGING INFLOW WINDS INTO A TROPICAL DISTURBANCE WEST OF THE
MARIANAS WILL HELP BRING SHOWERS AND THUNDERSTORMS.
THE SMALL CRAFT ADVISORY FOR YAP WAS EXPIRED AT 5 PM CHST TODAY.
CHOPPY SEAS WILL REMAIN POSSIBLE THROUGH SUNDAY DUE TO AN ELEVATED
WEST SWELL. ELSEWHERE SEAS LOOK TO REMAIN BENIGN THROUGH THE PERIOD,
BUT SOME CHOPPY SEAS WILL BE POSSIBLE NEAR HEAVIER SHOWERS.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: CRUZ
EAST MICRONESIA: DOLL
WEST MICRONESIA: WILLIAMS
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