946
FXPQ50 PGUM 050652
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
452 PM CHST THU JUN 5 2025
MARIANAS SYNOPSIS
SATELLITE AND RADAR OBSERVATIONS SHOW ISOLATED SHOWERS ACROSS THE
MARIANAS, WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS JUST OFF
TO THE EAST.
DISCUSSION
THERE WERE A FEW ADJUSTMENTS MADE TO THE PRECIPITATION
FORECAST FOR THE MARIANAS. THE MAIN CHANGE WAS ADJUSTING THE TIMING
FOR THE NUMEROUS SHOWERS FOR GUAM AND ROTA. BOTH THE GFS AND ECMWF
SHIFTED THE TIMING TOWARDS DAY TIME AND AFTERNOON FRIDAY AS OPPOSED
TO OVERNIGHT FRIDAY. THE BEST CHANCE FOR PRECIPITATION COULD BORDER
THE LATE AFTERNOON AND EVENING TIME PERIODS, SO POPS MAY NEED TO BE
ADJUSTED FOR THE FIRST HALF OF FRIDAY NIGHT WITH THE NEXT PACKAGE.
ANOTHER LULL LOOKS TO OCCUR FRIDAY NIGHT INTO EARLY SATURDAY BEFORE
ADDITIONAL ROUNDS OF SCATTERED SHOWERS WILL BE POSSIBLE SATURDAY AND
SUNDAY. MODEL GUIDANCE HAS EXTENDED THE PERIOD OF UPPER DIVERGENCE
ACROSS THE MARIANAS THROUGH SUNDAY. THIS ALLOWS FOR INCREASED SHOWER
ACTIVITY AS THE TUTT CELL NORTH OF THE MARIANAS CONTINUES TO INTERACT
WITH SURFACE TROUGHS. THIS WILL ALSO KEEP THUNDERSTORMS IN THE
FORECAST. THINGS LOOK TO START DRYING OUT AS WE HEAD INTO NEXT WEEK.
MARINE
NO CHANGES WERE MADE TO THE MARINE FORECAST. BENIGN SEAS OF
3 TO 5 FEET ARE EXPECTED TO CONTINUE THROUGH FRIDAY NIGHT BEFORE
DROPPING A FOOT OR SO THIS WEEKEND. A WESTERLY SWELL REMAINS
POSSIBLE TOWARDS THE MIDDLE OF NEXT WEEK, BUT WILL BE DEPENDENT ON
THE EVOLUTION OF JTWC'S INVEST 92W AND THE POSITIONING OF THE
MONSOON TROUGH. FOR NOW, USED A COMBINATION OF THE GFS AND ECMWF,
WHICH KEEPS THE WESTERLY SWELL ALONG THE WESTERN COASTAL WATERS OF
THE MARIANAS.
TROPICAL SYSTEMS
A LOOSELY-ORGANIZED TROPICAL DISTURBANCE, KNOWN AS JTWC'S INVEST 92W,
IS CENTERED NEAR 12N136E NORTHWEST OF YAP PROPER, NOW UPGRADED FROM A
"SUB-LOW" TO A "LOW". MODERATE TO OCCASIONALLY DEEP CONVECTION IS
ASSOCIATED WITH THIS FEATURE, PRODUCING NUMEROUS HEAVY SHOWERS AND
SOME THUNDERSTORMS ACROSS A WIDE SWATH OF WESTERN MICRONESIA,
COVERING MOST OF WESTERN YAP STATE. THIS FEATURE IS EXPECTED TO
CONTINUE TO MOVE NORTHWEST AS IT CONSOLIDATES, BUT ENTERING A LESS
FAVORABLE ENVIRONMENT MAY STALL ITS DEVELOPMENT. EVEN SO, THE
ASSOCIATED MONSOON TROUGH WILL CONTINUE TO BRING WEATHER ACROSS PALAU
AND YAP OVER THE NEXT FEW DAYS. THIS SYSTEM IS NOT LIKELY TO BECOME
A SIGNIFICANT TROPICAL CYCLONE IN NWS GUAM'S AOR AT THIS TIME.
EASTERN MICRONESIA
THE INTER-TROPICAL CONVERGENCE ZONE (ITCZ) STRETCHES EAST-NORTHEAST
FROM SOUTH OF POHNPEI NEAR THE EQUATOR, THROUGH A CIRCULATION SOUTH
OF KOSRAE AND UP TO THE SOUTHWEST OF MAJURO, WHERE IT THEN BECOMES
MORE FRAGMENTED AND TRANSITIONS TO MORE OF A SURFACE TROUGH. THE ITCZ
FLARED UP LAST NIGHT, BUT CONVECTION HAS BEEN ON A DOWNWARD TREND
TODAY AS IT SLOWLY SHIFTS NORTH AND WEST. SHOWER AND THUNDERSTORM
POTENTIALS LOOK TO INCREASE TONIGHT AT KOSRAE, THEN ON FRIDAY AT
POHNPEI. SHOWERS LOOK TO BECOME ISOLATED FOR MAJURO BY FRIDAY AS THE
ITCZ/SURFACE TROUGH SHIFT WEST. BOTH POHNPEI AND KOSRAE WILL SEE
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS THROUGH THE WEEKEND AS
THE ITCZ FLUCTUATES AND THE WEAK CIRCULATION STAYS JUST SOUTH AS IT
DRIFTS SLOWLY WEST, WITH POPS BOUNCING MOSTLY BETWEEN 30 AND 50
PERCENT. EARLY NEXT WEEK, ALL THREE FORECAST POINTS COULD SEE A
CHANCE OF SHOWERS (PROBABILITY OF PRECIPITATION 30 PERCENT) AND A
SLIGHT CHANCE OF THUNDERSTORMS AS THE ITCZ OR TRADE CONVERGENT ZONE
BUILDS INTO EASTERN MICRONESIA.
LIGHT TO GENTLE WINDS SHOULD PREVAIL THROUGH THE WEEKEND. WINDS COULD
BECOME MODERATE WITH FRESH GUSTS NEAR HEAVIER SHOWERS TONIGHT FOR
KOSRAE AS THE WEAK CIRCULATION PASSES TO THE SOUTH. COMBINED SEAS OF
3 TO 5 FEET WILL BECOME 2 TO 4 FEET BY FRIDAY AS WIND WAVES AND TRADE
SWELL CONTINUE TO SUBSIDE. WINDS AND SEAS LOOK TO RISE EARLY NEXT
WEEK AS THE TRADE FLOW STRENGTHENS AND A BACKGROUND SOUTHERLY SWELL
INCREASES.
WESTERN MICRONESIA
AN UNSETTLED WEATHER PATTERN REMAINS IN STORE FOR PALAU AND YAP FOR
THE REST OF THE WEEK. A TROPICAL DISTURBANCE, KNOWN AS JTWC'S INVEST
92W IS CENTERED JUST NORTHWEST YAP PROPER, AND IS EXPECTED TO FURTHER
CONSOLIDATE WELL NORTHWEST OF YAP AND PALAU OVER THE NEXT FEW DAYS. A
SERIES OF SOUTHWESTERLY MONSOON SURGES WILL CONTINUE TO PUMMEL BOTH
PALAU AND YAP AS WELL.
MODEL GUIDANCE HAS INDICATED SIGNIFICANT STALLING IN DEVELOPMENT
ASSOCIATED WITH INVEST 92W, WITH LITTLE LIKELIHOOD OF DEVELOPING INTO
A SIGNIFICANT TROPICAL CYCLONE OVER THE NEXT 24 HOURS AS IT CONTINUES
TO MOVE AWAY FROM THE MAIN ISLANDS OF PALAU AND YAP. EVEN SO, THE
SOUTHWESTERLY MONSOON TROUGH AND ASSOCIATED SURGES WILL CONTINUE TO
BRING SIGNIFICANT RAINFALL AND THUNDER TO PALAU AND YAP OVER THE NEXT
FEW DAYS. DUE TO THE LACKLUSTER NATURE OF THE CURRENT STAGE OF THE
MONSOON AND THE AFOREMENTIONED POTENTIAL DISTURBANCE, VARIABILITY IN
AREAS OF CONVECTIVE DEVELOPMENT MAY PRODUCE PERIODS OF LITTLE TO NO
WEATHER FOLLOWED BY SPORADIC HEAVY SHOWERS AND THUNDERSTORMS. IN
ADDITION, HIGH UNCERTAINTY REMAINS REGARDING RAINFALL AMOUNTS, BUT
THE TREND CONTINUES TO INDICATE AN ADDITIONAL 3 TO 5 INCHES AT
PALAU, AND ANOTHER 4 TO 6 INCHES AT YAP OVER THE NEXT 48 HOURS. AT
THIS TIME, LANDSLIDES CONTINUE TO BE UNLIKELY; HOWEVER, IF SOILS
BECOME SATURATED, ANY ADDITIONAL RAINFALL MAY QUICKLY BECOME RUNOFF
AND INCREASE MUDSLIDE RISKS, ESPECIALLY AT PALAU. CONDITIONS ARE
EXPECTED TO IMPROVE BEGINNING EARLY NEXT WEEK.
WHILE TRADE SWELLS HAVE WEAKENED, LOCALIZED WIND WAVES AND A
DEVELOPING SOUTHWEST SWELL WILL PRODUCE CHOPPY SEAS IN PALAU AND YAP
COASTAL WATERS OVER MUCH OF THE WEEK. SURF WILL CONTINUE TO INCREASE
ALONG SOUTH AND WEST FACING REEFS OF PALAU AND YAP, BUT ARE NOT
LIKELY TO BECOME HAZARDOUS AT THIS TIME. FOR NOW, EXPECT 3 TO 5 FOOT
SEAS FOR THE NEXT FEW DAYS, OCCASIONALLY BEING A FOOT OR TWO HIGHER
THROUGHOUT THE WEEK. MEANWHILE AT CHUUK, 4 TO 5 FOOT SEAS MAY DROP A
FOOT BY THE WEEKEND.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: WILLIAMS
EASTERN MICRONESIA: SLAGLE
WESTERN MICRONESIA/TROPICAL: MONTVILA
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