894
FXPQ50 PGUM 250820
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
ISSUED BY NATIONAL WEATHER SERVICE HONOLULU HI
620 PM CHST WED JUN 25 2025
MARIANAS SYNOPSIS
SATELLITE AND LOCAL SURFACE OBSERVATIONS ARE SHOWING MOSTLY CLOUDY
SKIES AND SCATTERED SHOWERS, WITH FRESH TO STRONG GUSTS MEASURED WITH
THE PASSING SHOWERS. NEARBY BUOYS ARE INDICATING SEAS OF 4 TO 6 FEET.
DISCUSSION
MOIST, CONVERGENT SOUTHEAST FLOW ALONG THE EASTERN EDGE OF THE
MONSOON TROUGH WILL PERSIST OVER THE MARIANAS. SCATTEROMETRY
CONTINUES TO SHOW STRONGER EAST TO SOUTHEAST FLOW PUSHING INTO THE
MARIANAS AND GUSTS TO 30+ MPH HAVE BEEN MEASURED THIS AFTERNOON
ACROSS THE MARIANAS WITH THE PASSING SHOWERS, ESPECIALLY AT TINIAN
AND SAIPAN. THE LATEST GFS AND MULTIPLE ENSEMBLE MEMBERS CONTINUE TO
DEVELOP A TC NEAR TO WEST OF THE MARIANAS AND MEANDER IT THROUGH THE
ISLANDS OVER WEEKEND, WHILE THE REST OF MODEL GUIDANCE IS MUCH LESS
ENTHUSIASTIC. WHILE THIS CASTS DOUBT ON THE POTENTIAL FOR WIND
HAZARDS, THE CONTINUING EXPECTATION IS FOR A VERY WET PERIOD
BEGINNING THURSDAY AND CONTINUING THROUGH THE WEEKEND, WITH NUMEROUS,
LOCALLY HEAVY SHOWERS AND ISOLATED THUNDERSTORMS. A FLOOD WATCH HAS
BEEN ISSUED FOR THIS TIME FRAME.
MARINE/SURF
GENTLE TO MODERATE EAST TO SOUTHEAST WINDS FOR GUAM AND ROTA, AND
MODERATE TO FRESH WINDS FOR SAIPAN AND TINIAN WINDS WILL CONTINUE
THROUGH THURSDAY BEFORE DIMINISHING AND SHIFTING TO SOUTH OR
SOUTHWEST BY FRIDAY. PASSING SHOWERS WILL BRING WIND GUSTS OF 25 TO
30 KT TO SAIPAN AND TINIAN TONIGHT AND A SMALL CRAFT ADVISORY HAS
BEEN ISSUED. A WET PATTERN WILL PERSIST THE NEXT SEVERAL DAYS WITH
HEAVIER SHOWERS REDEVELOPING ACROSS THE REGION AROUND THURSDAY.
COMBINED SEAS OF 4 TO 6 FEET WILL BUILD A FOOT FOR GUAM AND ROTA
WATERS BY FRIDAY. ACROSS SAIPAN AND TINIAN, SEAS WILL BE HIGHER,
BUILDING TO BETWEEN 6 AND 8 FT THURSDAY, THEN FALLING ABOUT A FOOT BY
SUNDAY.
A MODERATE RISK OF RIP CURRENTS IS EXPECTED ALONG EAST FACING REEFS
OF THE MARIANAS FOR THE NEXT FEW DAYS. A MODERATE RISK IS ALSO
EXPECTED ALONG SOUTH FACING REEFS OF TINIAN AND SAIPAN.
HYDROLOGY
A TROPICAL DISTURBANCE ANTICIPATED TO DEVELOP LATER THIS WEEK
IS EXPECTED TO BRING WIDESPREAD SHOWERS BEGINNING THURSDAY AND
CONTINUING THROUGH THE WEEKEND. RAINFALL AMOUNTS OF 5 TO 10 INCHES
ARE POSSIBLE, WITH LOCALLY HEAVY AMOUNTS POSSIBLE, ESPECIALLY 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 WATCHES,
ADVISORIES AND WARNINGS COULD BE ISSUED LATE THIS WEEK.
TROPICAL SYSTEMS
THE MOST RECENT RUNS OF THE GFS AND MULTIPLE MEMBERS OF THE GEFS
CONTINUE TO SHOW A TROPICAL CYCLONE DEVELOPING NEAR TO WEST OF THE
MARIANAS BY THE END OF THE WEEK AND MEANDER OVER OR NEAR THE ISLANDS
THROUGH THE WEEKEND. HOWEVER, THE REST OF MODEL GUIDANCE IS MUCH LESS
ENTHUSIASTIC, WITH GENERALLY A SLOWER DEVELOPING TROPICAL CYCLONE
WITH A MORE PROGRESSIVE TRACK TO THE WEST OF THE MARIANAS. WHILE THIS
CASTS DOUBT ON THE POTENTIAL FOR WIND HAZARDS, THE CONTINUING
EXPECTATION IS FOR A VERY WET PERIOD IN THE COMING DAYS, WITH GUSTY
WINDS NEAR SHOWERS AND THUNDERSTORMS. THE JOINT TYPHOON WARNING
CENTER (JTWC) AS UPGRADED THE POTENTIAL FORMATION AREA TO 60 PERCENT
FOR THE AREA OVER TO WEST OF GUAM AND THE MARIANAS.
EASTERN MICRONESIA
THE INTER-TROPICAL CONVERGENCE ZONE (ITCZ) IS CURRENTLY SOUTH OF THE
FORECAST POINTS AND IS EXPECTED TO DRIFT NORTH AND WEST AND GRADUALLY
WEAKEN. EXPECT SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS THROUGH
THE END OF THE WORK WEEK, WITH PROBABILITY OF PRECIPITATION (POP) OF
30 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.
COMBINED SEAS OF 4 TO 5 FEET LOOK TO CONTINUE FOR POHNPEI AND KOSRAE
THROUGH THE FORECAST PERIOD, AS EASTERLY SWELL SLOWLY DIMINISHES AND
A SOUTHEASTERLY SWELL STRENGTHENS. SLIGHTLY HIGHER TRADE SWELL IS
LIKELY FOR WELL-EXPOSED WATERS AROUND MAJURO, WITH SEAS UP TO 7 FEET.
WINDS WILL GENERALLY BE GENTLE TO MODERATE FOR THE PERIOD. WINDS LOOK
TO BECOME FRESH AT TIMES THROUGH THURSDAY FOR MAJURO. 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 SITS BETWEEN THE PRIMARY SYNOPTIC PLAYERS WITH THE MONSOON TO
THE WEST AND THE TRADES AND ITCZ TO THE EAST. SUBTLE FEATURES
EMBEDDED IN THE LOW-LEVEL FLOW ARE LIKELY TO TRIGGER BURSTS OF
SHOWERS AND THUNDERSTORMS AT TIMES THROUGH EARLY WEEKEND, THEN MAINLY
ISOLATED TRADE SHOWERS FOR LATE WEEKEND INTO EARLY NEXT WEEK. WINDS
WILL BE LIGHT TO GENTLE. SEAS FOR 3 TO 5 FEET LOOK TO DECREASE
SLIGHTLY BY THE WEEKEND AS THE TRADE SWELL SUBSIDES.
FURTHER WEST, MODEST MONSOON FLOW WILL RESULT IN LOW-END SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS FOR YAP AND PALAU THROUGH FRIDAY.
OVER THE WEEKEND, THE WEST TO SOUTHWEST MONSOON FLOW IS EXPECTED TO
INCREASE AS THE A POTENTIAL TROPICAL DISTURBANCE LOOKS TO DEVELOP
NEAR TO WEST OF THE MARIANAS, BUT LIKELY STAYING WELL NORTH OF YAP
AND PALAU, WITH SHOWERS AND THUNDERSTORM POTENTIAL TRENDING HIGHER.
SEAS WILL BE BENIGN FOR PALAU AND YAP DUE TO THE LACK OF ELEVATED
WINDS LOCALLY OR IN A DISTANT SENSE. 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 SUNDAY. 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.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...SMALL CRAFT ADVISORY UNTIL 6 AM CHST THURSDAY
FOR PMZ153-154.
MARIANAS: SLAGLE
EAST/WEST MICRONESIA: SLAGLE
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