345
FXPQ50 PGUM 260819
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
ISSUED BY NATIONAL WEATHER SERVICE HONOLULU HI
619 PM CHST THU JUN 26 2025
MARIANAS SYNOPSIS
SATELLITE AND RADAR ARE SHOWING CLOUDY SKIES AND NUMEROUS SHOWERS
OVER THE MARIANAS. RAINFALL REPORTS OF 3 TO 5+ INCHES WERE
COMMONPLACE TODAY. NEARBY BUOYS ARE INDICATING SEAS OF 4 TO 6 FEET.
DISCUSSION
MOIST, CONVERGENT FLOW ALONG THE EASTERN EDGE OF THE MONSOON TROUGH
AND DEVELOPING TROPICAL DISTURBANCE (INVEST 97W) WILL PERSIST OVER
THE MARIANAS. LATEST DETERMINISTIC AND ENSEMBLE MODEL GUIDANCE HAVE
TRENDED TOWARDS 97W DEVELOPING SLOWER AND TRACKING FURTHER WEST OF
THE MARIANAS. WHILE THIS CASTS DOUBT ON THE POTENTIAL FOR WIND
HAZARDS, THE CONTINUING EXPECTATION IS FOR A VERY WET PERIOD TO
CONTINUE THROUGH THE WEEKEND. HIGH-END SCATTERED TO NUMEROUS SHOWERS
AND ISOLATED THUNDERSTORMS ARE EXPECTED, WITH LOCALLY HEAVY DOWNPOURS
POSSIBLE. A FLOOD WATCH REMAINS IN EFFECT THROUGH SUNDAY NIGHT. INTO
NEXT WEEK, MODELS DIFFER QUITE A BIT, BUT THE GENERAL TREND IS FOR A
MONSOON FLOW TO DEVELOP OVER THE MARIANAS, WITH A INCREASED CHANCE
OF SHOWERS AND THUNDERSTORMS CONTINUING.
MARINE
GENTLE TO MODERATE WINDS FOR GUAM AND ROTA TONIGHT, AND MODERATE TO
FRESH FOR TINIAN AND SAIPAN, WILL DIMINISH AND BECOME MORE SOUTHERLY
FRIDAY. THROUGH THE WEEKEND, A TROPICAL DISTURBANCE, INVEST 97W, IS
EXPECTED TO DEVELOP WEST OF THE MARIANAS, BRINGING HEAVIER SHOWERS
THE NEXT FEW DAYS. COMBINED SEAS OF 3 TO 6 FEET FOR GUAM AND ROTA AND
4 TO 7 FEET FOR TINIAN AND SAIPAN, LOOK TO BUILD LATE WEEKEND INTO
EARLY NEXT WEEK AS THE MONSOON SWELL BUILDS INTO THE REGION AS 97W
DEPARTS. WINDS ALSO LOOK TO BECOME SOUTHWEST MODERATE TO FRESH.
THERE WILL BE A MODERATE RISK OF RIP CURRENTS ALONG EAST AND SOUTH
FACING REEFS OF THE MARIANAS FOR THE NEXT FEW DAYS. SURF COULD RISE
ALONG SOUTH AND WEST FACING REEFS LATE WEEKEND INTO EARLY NEXT WEEK
WITH THE POTENTIAL FOR AN ELEVATED SOUTHWEST MONSOON SWELL.
HYDROLOGY
THE MONSOON TROUGH AND DEVELOPING TROPICAL DISTURBANCE, INVEST 97W,
ARE EXPECTED TO BRING WIDESPREAD SHOWERS THROUGH THE WEEKEND.
RAINFALL AMOUNTS TODAY HAVE TOTALED 3 TO 5+ INCHES ALREADY. TOTAL
RAINFALL AMOUNTS OF 5 TO 10 INCHES ARE EXPECTED THROUGH THE WEEKEND,
WITH LOCALLY HEAVY AMOUNTS POSSIBLE, MAINLY ACROSS GUAM AND ROTA.
THIS RAINFALL IS EXPECTED TO PRODUCE MINOR FLOODING ACROSS THE
ISLANDS, WITH FLASH FLOODING POSSIBLE IN THE AREAS OF HEAVIER
RAINFALL.
RESIDENTS IN THE MARIANAS, ESPECIALLY THOSE IN FLOOD-PRONE AREAS,
SHOULD MONITOR THIS DEVELOPING WEATHER PATTERN CLOSELY AS ADVISORIES
AND WARNINGS COULD BE ISSUED LATE THIS WEEK.
TROPICAL SYSTEMS
INVEST 97W IS WEST OF THE MARIANAS, CENTERED NEAR 16N142E. 97W IS
CURRENTLY RATED LOW BY THE JOINT TYPHOON WARNING CENTER (JTWC),
MEANING THAT DEVELOPMENT INTO A SIGNIFICANT TROPICAL CYCLONE (TC) IS
UNLIKELY WITHIN THE NEXT 24 HOURS. MODERATE TO DEEP CONVECTION IS
OCCURRING NEAR THE CENTER AND TO THE NORTH AND EAST WHERE CONVERGENT
SOUTHERLY AND EASTERLY FLOW MEET, INCLUDING OVER THE MARIANAS. MUCH
UNCERTAINTY IN THE TRACK AND DEVELOPMENT OF INVEST 97W STILL
PERSISTS, BUT LATEST DETERMINISTIC AND ENSEMBLE MODEL GUIDANCE HAVE
TRENDED TOWARDS 97W DEVELOPING SLOWER AND TRACKING FURTHER WEST OF
THE MARIANAS.
EASTERN MICRONESIA
THE INTER-TROPICAL CONVERGENCE ZONE (ITCZ) HAS DRIFTED NORTH OVER
POHNPEI AND KOSRAE TO JUST SOUTH OF MAJURO. HAVE INCREASED SHOWERS
COVERAGE TO NUMEROUS AND LOCALLY HEAVY FOR POHNPEI AND KOSRAE
TONIGHT. SHOWERS EXPECTED TO INCREASE IN COVERAGE FOR MAJURO TONIGHT
AS THE ITCZ LIFTS NORTH, BUT KEEP COVERAGE SCATTERED. SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED THROUGH FRIDAY NIGHT
WITH PROBABILITY OF PRECIPITATION (POP) OF 40 TO 50 PERCENT. GUSTY
WINDS WILL BE POSSIBLE AT TIMES NEAR HEAVIER SHOWERS. THE ITCZ IS
EXPECTED TO DISSIPATE, AND MAINLY ISOLATED TO LOW-END SCATTERED
SHOWERS ARE EXPECTED OVER THE WEEKEND. SHOWERS AND THUNDERSTORM
CHANCES INCREASE EARLY NEXT WEEK AS THE ITCZ LOOKS TO RE-ESTABLISH
ITSELF OVER EASTERN MICRONESIA.
REGIONAL SEAS WILL REMAIN A MIX OF TRADE AND SE SWELL. SEAS WILL
RANGE BETWEEN 4 AND 6 FEET FOR POHNPEI AND KOSRAE. SLIGHTLY HIGHER
TRADE SWELL IS LIKELY FOR WELL-EXPOSED WATERS AROUND MAJURO, WITH
SEAS UP TO 7 FEET THROUGH FRIDAY. ASIDE FROM SOME FRESH WINDS TONIGHT
AT MAJURO, WINDS WILL GENERALLY BE GENTLE TO MODERATE THE NEXT FEW
DAYS. WINDS LOOK TO INCREASE AND BECOME MODERATE TO FRESH BEGINNING
SUNDAY AT MAJURO AND EARLY NEXT WEEK FOR KOSRAE AND POHNPEI AS THE
TRADE FLOW STRENGTHENS. RESIDENTS SHOULD BE AWARE OF THE LARGE TIDES
THE NEXT SEVERAL DAYS DUE TO THE NEW MOON PHASE DESPITE THE FACT NO
NOTABLE SWELLS ARE CURRENTLY FORECAST.
WESTERN MICRONESIA
CHUUK REMAINS UNDER A SURFACE TROUGH SERVING AS THE BOUNDARY BETWEEN
EASTERLY TRADES TO THE EAST, AND WEST TO NORTHWEST FLOW TO THE WEST.
THIS FEATURE WILL LIKELY TRIGGER BURSTS OF SHOWERS AND THUNDERSTORMS
AT TIMES THROUGH FRIDAY NIGHT. CHUUK CONDITIONS WILL BE QUITE
CHANGEABLE OVER THE WEEKEND INTO EARLY NEXT WEEK AS THE BROADER
SYNOPTIC PATTERN EVOLVES IN RESPONSE TO 97W AS IT LIFTS NORTHWESTWARD
THE NEXT FEW DAYS, BUT GENERALLY LOWER COVERAGE OF SHOWERS AND
THUNDERSTORMS EXPECTED. WINDS WILL BE LIGHT TO GENTLE. SEAS 3 TO 5
FEET LOOK TO DECREASE SLIGHTLY BY THE WEEKEND AS THE TRADE SWELL
SUBSIDES.
FURTHER WEST, MODEST MONSOON FLOW WILL RESULT IN SCATTERED SHOWERS
(POPS 30-40 PERCENT) AND ISOLATED THUNDERSTORMS FOR YAP AND PALAU
THROUGH FRIDAY. OVER THE WEEKEND INTO EARLY NEXT WEEK, THE WEST TO
SOUTHWEST MONSOON FLOW IS EXPECTED TO INCREASE AS THE A POTENTIAL
TROPICAL DISTURBANCE (INVEST 97W) LOOKS TO DEVELOP WEST OF THE
MARIANAS, BUT LIKELY STAYING WELL NORTH OF YAP AND PALAU, WITH
SHOWERS AND THUNDERSTORM POTENTIAL TRENDING HIGHER. SEAS OF 2 TO 3
FEET AND LIGHT TO GENTLE WINDS LOOK TO CONTINUE THROUGH THE END OF
THE WORK WEEK. WINDS AND SEAS WILL TREND UP THROUGH THE WEEKEND INTO
EARLY NEXT WEEK AS THE MONSOON FLOW INCREASES. MODERATE TO FRESH
WINDS AND SEAS OF 4 TO 6 FEET ARE EXPECTED BY THE WEEKEND. SURF ALSO
LOOKS TO RISE ALONG SOUTH AND WEST FACING REEFS. RESIDENTS SHOULD BE
AWARE OF THE LARGE TIDES THE NEXT SEVERAL DAYS DUE TO THE NEW MOON
PHASE.
GUM WATCHES/WARNINGS/ADVISORIES
GU...FLOOD WATCH THROUGH LATE SUNDAY NIGHT FOR GUZ001.
MP...FLOOD WATCH THROUGH LATE SUNDAY NIGHT FOR MPZ001>003.
MARIANAS WATERS...NONE.
MARIANAS: SLAGLE
MARINE: SLAGLE
TROPICAL: SLAGLE
HYDROLOGY: SLAGLE
EAST MICRONESIA: SLAGLE
WEST MICRONESIA: SLAGLE
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