617
FXPQ50 PGUM 270643
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
ISSUED BY NATIONAL WEATHER SERVICE HONOLULU HI
443 PM CHST FRI JUN 27 2025
MARIANAS SYNOPSIS
SATELLITE AND RADAR IMAGERY ARE SHOWING PARTLY CLOUDY SKIES WITH
ISOLATED SHOWERS ACROSS TINIAN AND SAIPAN, WITH MOSTLY CLOUDY SKIES
AND SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS GUAM AND
ROTA. LOCAL BUOYS AND RECENT ALTIMETRY PASSES ARE INDICATING SEAS OF
3 TO 5 FEET.
DISCUSSION
INVEST 97W CONTINUES TO PUSH NORTHWEST AWAY FROM THE MARIANAS. A
MONSOON TROUGH LOOKS TO LINGER NEAR GUAM AND ROTA THROUGH THE
WEEKEND, WITH SCATTERED TO AT TIMES NUMEROUS SHOWERS AND ISOLATED
THUNDERSTORMS THROUGH WEEKEND. DRIER, STABLE AIR NORTH OF THE TROUGH
HAS FILTERED INTO FOR TINIAN AND SAIPAN TODAY, HOWEVER, SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS WILL BE POSSIBLE AT TIMES THROUGH
THE WEEKEND. THE FLOOD WATCH REMAINS IN EFFECT FOR GUAM AND ROTA
THROUGH SUNDAY NIGHT BUT HAS BEEN CANCELLED FOR TINIAN AND SAIPAN.
INTO NEXT WEEK, MODELS DIFFER QUITE A BIT, BUT THE GENERAL TREND IS
FOR MONSOON FLOW TO DEVELOP OVER THE MARIANAS, WITH AN INCREASED
CHANCE OF SHOWERS AND THUNDERSTORMS.
MARINE
LIGHT TO GENTLE SOUTHERLY FLOW WILL PREVAIL THROUGH THE WEEKEND AS
INVEST 97W, CENTERED WELL WEST-NORTHWEST OF THE MARIANAS, SHIFTS
FURTHER AWAY. COMBINED SEAS OF 4 TO 5 FEET LOOK TO INCREASE NEXT WEEK
AS A SOUTHWEST MONSOON SWELL BUILDS INTO THE REGION. WINDS LOOK TO
BECOME MODERATE TO FRESH FROM THE SOUTHWEST AS WELL.
A MODERATE RISK FOR RIP CURRENTS WILL CONTINUE ALONG EAST FACING
REEFS, WITH A LOW RISK ALONG ALL OTHER REEFS. A MODERATE RISK FOR
LIGHTNING WILL CONTINUE THROUGH THE WEEKEND. SURF LOOKS TO RISE ALONG
SOUTH AND WEST FACING REEFS BEGINNING EARLY NEXT WEEK WITH THE
POTENTIAL ARRIVAL OF AN ELEVATED SOUTHWEST SWELL.
HYDROLOGY
THE OVERALL RAINFALL FORECAST THROUGH THE WEEKEND HAS TRENDED
DOWNWARD ACROSS THE MARIANAS, AS IMPACTS FROM DEPARTING TROPICAL
DISTURBANCE INVEST 97W APPEAR MINIMAL. A MONSOON TROUGH LOOKS TO SET
UP NEAR GUAM AND ROTA, AND SCATTERED TO AT TIMES NUMEROUS SHOWERS ARE
EXPECTED THROUGH THE WEEKEND. SCATTERED SHOWERS WILL STILL BE
POSSIBLE ACROSS TINIAN AND SAIPAN, BUT THE POTENTIAL FOR SIGNIFICANT
HEAVY RAINFALL AND FLASH FLOODING HAS DIMINISHED. AS A RESULT, THE
FLOOD WATCH HAS BEEN CANCELLED FOR TINIAN AND SAIPAN, BUT STILL
CONTINUES FOR GUAM AND ROTA THROUGH THE WEEKEND.
TROPICAL SYSTEMS
INVEST 97W, CENTERED NEAR 17N138E, CURRENTLY HAS A LOW RATING BY THE
JOINT TYPHOON WARNING CENTER (JTWC), MEANING THAT DEVELOPMENT INTO A
SIGNIFICANT TROPICAL CYCLONE IS UNLIKELY WITHIN THE NEXT 24 HOURS.
UNCERTAINTY IN THE TRACK AND DEVELOPMENT OF INVEST 97W STILL
PERSISTS, BUT THE GENERAL FORECAST TREND IS FOR 97W DEVELOPING SLOWER
AND FURTHER TO THE NORTHWEST, WITH MINIMAL, IF ANY, IMPACTS FOR THE
MARIANAS AND WESTERN MICRONESIA.
EASTERN MICRONESIA
A BREAKDOWN IN THE TRADES HAS ALLOWED VARIOUS DISTURBANCES TO DEVELOP
ACROSS MUCH OF EASTERN MICRONESIA, BRINGING ELEVATED SHOWERS AND SOME
THUNDERSTORMS TO POHNPEI, KOSRAE AND MAJURO TONIGHT. BEGINNING
SATURDAY, CONDITIONS WILL IMPROVE CONSIDERABLY AT KOSRAE AND MAJURO
AS WINDS PICK UP, BUT UNSETTLED WEATHER WILL PERSIST AT POHNPEI FOR
MUCH OF THE FORECAST PERIOD DUE TO THE INFLUENCE OF A DEVELOPING
MONSOON GYRE ACROSS THE REST OF MICRONESIA TO THE WEST.
COMBINED SEAS OF 4 TO 6 FEET AT POHNPEI AND KOSRAE ARE EXPECTED TO
INCREASE A FOOT OR TWO AROUND THE MIDDLE OF NEXT WEEK AS TRADE SWELL
AND SOUTHEASTERLY SWELLS STRENGTHEN. MEANWHILE AT MAJURO, COMBINED
SEAS OF 5 TO 7 FEET ARE EXPECTED FOR MUCH OF THE FORECAST PERIOD.
WESTERN MICRONESIA
SATELLITE OBSERVATIONS SHOW PARTLY CLOUDY SKIES ACROSS PALAU AND YAP
AND MOSTLY CLOUDY SKIES ACROSS CHUUK. COMBINED SEAS ARE GENERALLY
BETWEEN 2 TO 3 FEET ACROSS PALAU AND YAP, AND 3 TO 4 FEET ACROSS
CHUUK.
GENERALLY QUIET CONDITIONS ARE SEEN ACROSS WESTERN MICRONESIA, WITH
SCATTERED SHOWERS SEEN ACROSS CHUUK DURING THE AFTERNOON. A MONSOON-
LIKE PATTERN LOOKS TO DEVELOP OVER THE NEXT DAY OR SO ACROSS PALAU
AND YAP AND LOOKS TO PERSIST THROUGH THE EARLY WEEK PERIOD. THE BULK
OF THE MONSOON IMPACTS LOOK TO REMAIN NORTH OF PALAU AND YAP,
HOWEVER, HIGH END (50%) SCATTERED SHOWERS ARE EXPECTED, AND WINDS
COULD APPROACH 20 KT SATURDAY NIGHT AND SUNDAY FOR PALAU. A RELATIVE
LULL IS FORECASTED FOR CHUUK ON SATURDAY, WITH LOW-END SCATTERED
(30%) SHOWERS FORECASTED. CHUUK LOOKS TO BE IN-BETWEEN CONVERGENT
AND DIVERGENT SURFACE FLOW AS THE MONSOON TROUGH LIES TO THE NORTH.
AN UPTICK IN SHOWERS IS EXPECTED SATURDAY NIGHT THROUGH SUNDAY NIGHT,
WITH A BRIEF DECREASE TO ISOLATED SHOWERS ON MONDAY. THE FORECAST
TOWARDS THE LATTER HALF OF THE WEEK WILL BE DEPENDENT ON THE
DEVELOPMENT OF THE MONSOON TROUGH TO THE NORTH.
SOME CHANGES WERE MADE TO THE MARINE FORECAST. THE MAIN ONE WAS TO
BLEND THE GFS AND ECMWF FOR THE SWELL DIRECTION. ALTHOUGH A MONSOON-
LIKE PATTERN IS EXPECTED OVER PALAU AND YAP, SWELL LOOKS TO REMAIN
SOUTHEASTERLY THROUGH THE NEXT SEVERAL DAYS. THE GFS DOES BUILD IN A
WESTERLY SWELL FOR PALAU AND YAP, BUT IT IS ALSO THE MOST AGGRESSIVE
WITH THE MONSOON PATTERN TO THE NORTH. THERE IS SOME UNCERTAINTY IN
THIS GFS SOLUTION AS THE GFS PERFORMANCE HAS BEEN QUESTIONABLE THE
LAST FEW DAYS, SO THE FORECAST LEANS CLOSER TO THE ECMWF. MARINE
CONDITIONS ARE NOT EXPECTED TO BECOME HAZARDOUS TO SMALL CRAFT.
GUM WATCHES/WARNINGS/ADVISORIES
GU...FLOOD WATCH THROUGH LATE SUNDAY NIGHT FOR GUZ001.
MP...FLOOD WATCH THROUGH LATE SUNDAY NIGHT FOR MPZ001.
MARIANAS WATERS...NONE.
MARIANAS: SLAGLE
EAST MICRONESIA: MONTVILA
WEST MICRONESIA: WILLIAMS
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