917
FXPQ50 PGUM 050647
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
447 PM CHST FRI SEP 5 2025
MARIANAS SYNOPSIS
THE SCATTERED TO NUMEROUS SHOWERS THAT PASSED THROUGH THE MARIANAS
THIS MORNING ARE NOW STRATIFYING OUT WEST OF GUAM, AND SCATTERED
SHOWERS PERSIST OVER WESTERN GUAM WATERS THIS AFTERNOON. SHOWERS ARE
ISOLATED ACROSS THE REST OF THE MARIANAS, WITH MOSTLY CLOUDY SKIES.
DISCUSSION
SCATTERED SHOWERS WITH ISOLATED THUNDERSTORMS LOOK TO CONTINUE
THROUGH MUCH OF THE WEEKEND AS A ROBUST TROUGH, EVIDENT ON SATELLITE
TO THE EAST OF COASTAL WATERS, CROSSES THE AREA. A MORE SUBTLE AREA
OF TROUGHING EXISTS CLOSE NEARBY, WHICH WILL SUPPORT ANOTHER ROUND
OF SCATTERED SHOWERS OVERNIGHT AS THE ATMOSPHERE DESTABILIZES ONCE
MORE. CIMSS MIMIC PRECIPITABLE WATER (PWAT) AMOUNTS RANGE 2.2 TO 2.5
INCHES UPSTREAM OF THE MARIANAS FOCUSED MAINLY JUST EAST OF GUAM,
WHICH MAY SEE MOST OF THE SHOWER COVERAGE OVER THE NEXT DAY OR SO.
THE MORE NOTABLE TROUGH AXIS LOOKS TO SHIFT WEST OF THE MARIANAS ON
SUNDAY, WITH PERIODS OF LIGHT AND VARIABLE WINDS EXPECTED ALONG AND
BEHIND IT, PARTICULARLY OVER GUAM AND ROTA. THIS MAY SUPPORT A
FAVORABLE ENVIRONMENT FOR ISLAND CONVECTION IN THE AFTERNOON,
ESPECIALLY IF SKIES CLEAR AND A LIGHT SOUTHERLY FLOW IS ABLE TO SET
UP BEHIND THE TROUGH. FOR NOW, LINGERING CLOUD COVER LOOKS TO BE THE
MOST LIKELY LIMITING FACTOR FOR ISLAND EFFECT SHOWERS ON SUNDAY.
THE MARIANAS MAY SEE INCREASED LIGHTNING POTENTIAL AS A TROPICAL
UPPER TROPOSPHERIC TROUGH (TUTT) LOW PASSES WEST OVER THE NORTHERN
CNMI EARLY NEXT WEEK. THIS LOOKS TO INCREASE UPPER-LEVEL DIVERGENCE
OVER THE ISLANDS, WHICH MAY ENHANCE SHOWER AND THUNDERSTORM CHANCES
WITH A PASSING TRADE-WIND TROUGH, MAINLY MONDAY NIGHT AND TUESDAY
BEFORE THE UPPER LOW BEGINS TO MOVE AWAY.
MARINE
BUOY AND ALTIMETRY DATA SHOW COMBINED SEAS OF AROUND 2 TO 4 FEET OVER
MARIANAS WATERS, COMPRISED OF THE EASTERLY TRADE SWELL AND INCOMING
NORTH SWELL. EXPECT LIGHT TO GENTLE WINDS THROUGH THE WEEKEND,
BECOMING GENTLE TO MODERATE EARLY NEXT WEEK. SEAS OF 2 TO 4 FEET
COULD DIMINISH SLIGHTLY TO BETWEEN 2 AND 3 FEET OVER THE WEEKEND.
PASSING TRADE-WIND TROUGHS WILL BRING PERIODS OF SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS TONIGHT THROUGH THE WEEKEND.
EASTERN MICRONESIA
AS TRADE-WIND TROUGHS MOVE OUT OF EASTERN MICRONESIA AND THE INTER-
TROPICAL CONVERGENCE ZONE (ITCZ) CONTINUES TO DISSIPATE, A DRY
TRADE-WIND PATTERN HAS MOVED IN ACROSS THE REGION. THIS DRY PATTERN
LOOKS TO CONTINUE FOR THE NEXT COUPLE OF DAYS. LATEST MODEL GUIDANCE
SHOWS FAIRLY DRY CONDITIONS CONTINUING THROUGH MOST OF THE WEEKEND.
POPS (PROBABILITY OF PRECIPITATION) ARE EXPECTED TO REMAIN AROUND 20%
THROUGH SUNDAY. BY SUNDAY NIGHT, ANOTHER ROUND OF INCREASED
CONVECTION IS EXPECTED AS THE ITCZ REDEVELOPS ACROSS THE REGION.
MODELS VARY ON THE STRENGTH OF THE DEVELOPING ITCZ, HOWEVER, THEY ALL
PRETTY MUCH AGREE THAT IT WILL DEVELOP. SHOWERS LOOK TO BEGIN TO
INCREASE SUNDAY NIGHT, WITH THE HIGHEST PROBABILITY OF SHOWERS AND
THUNDERSTORMS BEING EARLY TO MIDWEEK NEXT WEEK. MAINTAINED HIGHEST
POPS AT AROUND 50% BASED ON THE UNCERTAINTY OF HOW ACTIVE THE ITCZ
WILL BE. REGARDLESS, A MORE ACTIVE PATTERN LOOKS TO RETURN LATE IN
THE WEEKEND INTO THE MIDDLE OF NEXT WEEK.
BENIGN MARINE CONDITIONS WILL CONTINUE FOR AT LEAST THE NEXT SEVERAL
DAYS. LATEST BUOY DATA FROM KOSRAE AND POHNPEI BUOYS SHOW SEAS
BETWEEN 3 AND 5 FEET WHILE ALTIMETRY SHOWS 3 TO 6 FEET. SEAS LOOK TO
SLOWLY SUBSIDE OVER THE NEXT COUPLE OF DAYS, DROPPING TO BETWEEN 3
AND 4 FEET OVER THE WEEKEND. WINDS WILL MOSTLY BE LIGHT TO GENTLE,
KOSRAE AND MAJURO WILL SEE OCCASIONAL MODERATE WINDS OVER THE
WEEKEND.
WESTERN MICRONESIA
A LEADING EDGE OF THE ITCZ IS BRINGING HEAVIER SHOWERS,
THUNDERSTORMS, AND POTENTIALLY GALE-FORCE GUSTS TO CHUUK IN THE
EARLY EVENING HOURS, BASED ON SATELLITE IMAGERY ANALYSIS OF THE
INCOMING LINES OF CONVECTION ENTERING CHUUK WATERS. AFTER THIS LINE
PASSES AND MOVES INTO EASTERN YAP STATE, SHOWERS ARE EXPECTED TO
DIMINISH AT CHUUK THROUGH SUNDAY, FOLLOWED BY ANOTHER PULSE IN THE
TRADES THAT WILL BRING PATCHY SHOWERS AND SOME THUNDERSTORMS FOR THE
REST OF THE FORECAST PERIOD. A GENERALLY UNSETTLED PATTERN INDUCED BY
THE AFOREMENTIONED ITCZ FRAGMENT AND MULTIPLE TRADE-WIND TROUGHS, IS
EXPECTED TO CONTINUE TO BRING ON-AND-OFF SHOWERS AND SOME
THUNDERSTORMS THE NEXT FEW DAYS AT YAP, AND OVERNIGHT AT PALAU,
FOLLOWED BY A RETURN OF A DRIER CYCLE FOR MUCH OF NEXT WEEK.
COMBINED SEAS OF 3 TO 4 FEET ARE EXPECTED ACROSS MUCH OF WESTERN
MICRONESIA THROUGH THE WEEKEND AND THE FIRST HALF OF NEXT WEEK,
CONSISTING PRIMARILY OF A BACKGROUND TRADE SWELL.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: CRUZ
EAST MICRONESIA: KLEESCHULTE
WEST MICRONESIA: MONTVILA
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