261
FXPQ50 PGUM 301817
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
417 AM CHST FRI MAY 1 2026
MARIANAS UPDATE
THE FORECAST REMAINS IN GOOD SHAPE WITH NO SIGNIFICANT CHANGES
NEEDED. IN GENERAL, LOOK FOR A FEW HIT-AND-MISS SHOWERS TODAY
(THEY'LL BE LIGHT AND BRIEF), WINDS MAY BECOME A LITTLE GUSTY DURING
THE AFTERNOON. FOR MARINERS, SEAS OF 5 TO 7 FEET MAY BUILD A FOOT
SATURDAY.
EASTERN MICRONESIA UPDATE
THE MAIN CHANGE HERE WAS TO INCREASE SHOWER COVERAGE TO NUMEROUS AT
POHNPEI, INCREASING RAINFALL POTENTIAL TO 70 PERCENT, AND WE ADDED
LOCALLY HEAVY RAINFALL WORDING. THIS IS DUE TO A FAIRLY STOUT TROUGH
JUST TO YOUR EAST. INFRARED SATELLITE IMAGERY HAS SHOWN PERSISTENT
DEEP CONVECTION WITH CLOUD TOP TEMPERATURES IN THE -75 TO -85 DEG. C
RANGE, INDICATIVE OF THE HEAVY RAINFALL. A FAIR AMOUNT OF LIGHTNING
HAS ALSO BEEN CONSISTENTLY OBSERVED THROUGH THE NIGHT. AS A RESULT OF
THE INCREASED CLOUD DENSITY AND RAIN-COOLED AIR, WE DROPPED
AFTERNOON HIGHS BACK INTO THE MID 80S. OTHERWISE, NO ADDITIONAL
CHANGES WERE NEEDED.
FOR KOSRAE AND MAJURO, THE FORECAST REMAINS IN GOOD SHAPE WITH NO
SIGNIFICANT CHANGES NEEDED.
WESTERN MICRONESIA UPDATE
THE FORECAST REMAINS ON TRACK FOR ALL OF WESTERN MICRONESIA. WE
THOUGHT ABOUT DROPPING SHOWER COVERAGE TO ISOLATED AT PALAU, BUT WE
ENDED UP MAINTAINING LOW-END SCATTERED SHOWERS (30 PERCENT
PROBABILITIES) AS SATELLITE IMAGER SHOWS A CLUSTER OF VERY SMALL BUT
RESPECTABLE CLOUD SIGNATURES, BUT, CLOUDS AREN'T VERY TALL AS
TEMPERATURES REMAIN BELOW -50 DEG. C. THUS, LIGHT TO MODERATE SHOWERS
WILL CONTINUE THROUGH THE MORNING, PERHAPS INCREASING THIS AFTERNOON
AS A WEAK TROUGH MOVES OVERHEAD AND INTERACTS WITH LIGHT WINDS AND
OROGRAPHICS.
FOR YAP, ISOLATED SHOWERS ARE THE MOST WE CAN HOPE FOR TODAY AND
TONIGHT. AT CHUUK, A WEAK CIRCULATION TO YOUR SOUTHWEST AND A SURFACE
TROUGH OVERHEAD SHOULD BE SUFFICIENT FOR SCATTERED SHOWERS TO PERSIST
TODAY, WITH NO CHANGES NEEDED THIS FORECAST CYCLE.
PREV DISCUSSION
/ISSUED 609 PM CHST THU APR 30 2026/
MARIANAS SYNOPSIS...
A FAIRLY DRY TRADE-WIND PATTERN EXTENDS ACROSS THE MARIANAS. VISIBLE
SATELLITE IMAGERY SHOWS A COUPLE OF TRANSIENT TRADE-WIND TROUGHS,
WITH ONE PRODUCING SPOTTY SHOWERS ACROSS THE ISLANDS NORTH OF SAIPAN
AND THE OTHER WELL TO THE EAST OF THE ISLANDS NEAR 150E. WIND ACROSS
ARE MAINLY MODERATE AND BUOY AND ALTIMETRY DATA ARE REPORTING SEAS
AROUND 5 TO 7 FEET.
DISCUSSION...
BESIDES FOR A COUPLE OF TRANSIENT TRADE-WIND TROUGHS MOVING THROUGH
THE BACKGROUND FLOW, A DRY TRADE-WIND PATTERN EXTENDS ACROSS THE
MARIANAS WITH MODERATE WINDS AROUND 10 TO 15 MPH EXPECTED THROUGH
FRIDAY NIGHT, THEN INCREASING TO 15 TO 20 MPH THIS WEEKEND AND INTO
NEXT WEEK. AROUND MONDAY, MODEL GUIDANCE SUPPORTS A WEAK TRADE-WIND
TROUGH MOVING ACROSS THE ISLANDS, BRINGING A BRIEF PERIOD OF
SCATTERED SHOWERS. BEYOND MONDAY, MODELS SHOW THE POTENTIAL FOR A
UNSETTLE WEATHER PATTERN TO DEVELOP WITHIN CENTRAL TO EASTERN
MICRONESIA, BUT THERE REMAINS A WIDE ARRAY OF SOLUTIONS, WITH SOME
SHOWING THE UNSETTLED WEATHER PASSING SOUTH OF THE MARIANAS, SOME
LIFTING IT NORTH OF THE MARIANAS, WHILE OTHERS HAVE THE PATTERN
EVENTUALLY WEAKENING WITHOUT MUCH IMPACT TO THE REGION. FOR NOW, WE
ARE NOT EXPECTING ANY SIGNIFICANT CHANGES IN THE OVERALL WEATHER
PATTERN ACROSS THE MARIANAS AT THIS TIME, BUT WILL CONTINUE TO
MONITOR THE PATTERN IN CENTRAL/EASTERN MICRONESIA FOR ANY CHANGES IN
THE FORECAST FOR THE LONG-TERM.
MARINE...
THE EAST SWELL HAS SUBSIDE SLIGHTLY, ALLOWING THE RISK OF RIP
CURRENTS TO DECREASE TO MODERATE ALONG EAST FACING REEFS THIS
AFTERNOON, AND SUPPORTING COMBINED SEAS AROUND 5 TO 7 FEET. WINDS
ARE EXPECTED INCREASE SLIGHTLY THIS WEEKEND, BUILDING SEAS TO AROUND
6 TO 8 FEET AS THE EAST SWELL STARTS TO BUILD EARLY NEXT WEEK. THIS
COULD INCREASE THE RISK OF RIP CURRENTS ALONG EAST FACING REEFS TO
HIGH ONCE AGAIN. A FAIRLY DRY PATTERN IS EXPECTED FOR MOST OF THE
FORECAST PERIOD, THOUGH A WEAK TROUGH EAST OF THE MARIANAS IS
EXPECTED TO BRING A SLIGHT INCREASE IN SHOWERS MONDAY AS IT PASSES
THROUGH THE REGION.
TROPICAL SYSTEMS...
INVEST 91W REMAINS A VERY WEAK TROPICAL DISTURBANCE SOUTH-SOUTHWEST
OF CHUUK, NEAR 5N151E, WITH THE BROAD CIRCULATION SEEN IN VISIBLE
SATELLITE IMAGERY THIS MORNING BECOMING MORE ELONGATED. THIS
CIRCULATION COULD EVENTUALLY OPEN INTO THE BROAD SURFACE TROUGH NEAR
CHUUK OVER THE NEXT 24 HOURS, SUPPORTING A WETTER PATTERN OVERALL,
WITH LOCALLY HEAVY SHOWERS POSSIBLE, BUT DECREASING THE RISK OF A
TROPICAL CYCLONE DEVELOPMENT IN THE AREA IN THE SHORT-TERM. IF THE
CIRCULATION CONTINUES TO ELONGATE INTO A TROUGH AS FORECASTED, JOINT
TYPHOON WARNING CENTER MAY CLOSE INVEST 91W. WHILE LONG-RANGE MODEL
GUIDANCE SUGGEST THE OVERALL WEATHER PATTERN COULD BECOME SUPPORTIVE
OF TROPICAL CYCLONE DEVELOPMENT OVER THE NEXT 7 TO 10 DAYS WITHIN
EASTERN AND CENTRAL MICRONESIA, THE CURRENT PATTERN NOT SUPPORTIVE AT
THIS TIME, AND GIVEN THE LARGE RANGE OF SOLUTIONS WITHIN THE MODEL
ENSEMBLES, WITH LITTLE CONSENSUS BETWEEN THE DIFFERENT MODELS (GFS,
ECMWF, CANADIAN, AND OTHERS) CONFIDENCE THAT SOMETHING WILL DEVELOP
OVER THE NEXT 7 TO 10 DAYS IS LOW. FOR NOW CONTINUE TO MONITOR THE
FORECAST FOR ANY UPDATES BUT NO OTHER ACTIONS ARE NEEDED AT THIS
TIME.
EASTERN MICRONESIA...
INTERACTIONS BETWEEN PASSING TRADE-WIND TROUGHS AND FRAGMENTS OF THE
ITCZ CONTINUE DRIVE SCATTERED TO NUMEROUS SHOWERS AND ISOLATED
THUNDERSTORMS ACROSS PORTIONS OF EASTERN MICRONESIA. ONE TROUGH IS
LOCATED NORTH OF POHNPEI, THE NEXT IS LOCATED NORTH OF KOSRAE, AND
THE LAST IS LOCATED ACROSS THE MARSHALL ISLANDS JUST WEST OF MAJURO.
THESE AND ADDITIONAL UPSTREAM TROUGHS WILL CONTINUE TO PROMOTE
PERIODS OF SCATTERED TO NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS
ACROSS ALL FORECAST POINTS AS THEY PROPAGATE WESTWARD THROUGH THE
WEEKEND. THE ITCZ WILL REMAIN FRAGMENTED AND QUASI-STATIONARY
THROUGH AT LEAST FRIDAY WITH POTENTIAL ORGANIZATION AND STRENGTHENING
THIS WEEKEND. INVEST 91W HAS SLOWLY EXITED EASTERN MICRONESIA AND IS
NOW WEST-SOUTHWEST OF CHUUK, PLEASE SEE THE TROPICAL SYSTEMS
DISCUSSION FOR ADDITIONAL DETAILS ON INVEST 91W.
MODERATE TO FRESH EAST TO NORTHEAST WINDS WILL CONTINUE AT MAJURO
THROUGH EARLY FRIDAY WITH A GRADUAL EASING TO MOSTLY MODERATE EAST-
NORTHEAST WINDS THROUGHOUT THE DAY ON FRIDAY. VARIABLE WINDS ARE
EXPECTED AT POHNPEI AND KOSRAE THROUGH FRIDAY WITH WIND SPEEDS
REMAINING BELOW 10 KNOTS. A NORTHEAST SWELL WILL CONTINUE TO MOVE
THROUGH THE WATERS THROUGH THE REST OF THE WEEK WHILE A SMALL, NORTH
SWELL CONTINUES TO DECAY. SEAS UP TO 9 FEET AT MAJURO WILL BE
POSSIBLE THROUGH TONIGHT AND WILL THEN DIMINISH THROUGH THE REST OF
THE WEEK. ELEVATED SURF ALONG EAST-FACING REEFS WILL BE POSSIBLE AT
KOSRAE THROUGH SATURDAY AS THE NORTHEAST SWELL MOVES THROUGH THE
WATERS AND SLOWLY DIMINISHES THIS WEEKEND. COMBINED SEAS OF 4 TO 6
FEET ARE EXPECTED AT KOSRAE AND POHNPEI THROUGH THE REST OF THE WEEK.
SEAS ARE FORECAST TO BUILD LATE THIS WEEKEND INTO EARLY NEXT WEEK AS
ANOTHER NORTHEAST SWELL BUILDS INTO THE REGION. OTHERWISE, NUISANCE
COASTAL INUNDATION WILL BE POSSIBLE AT MAJURO THROUGH SATURDAY AT
TIMES OF HIGH TIDE DUE TO THE FULL MOON CYCLE.
WESTERN MICRONESIA...
THERE ARE FOUR MAIN FEATURES IN THE REGION: A CONVERGENCE ZONE
BETWEEN YAP AND PALAU, INVEST 91W, AN ITCZ FRAGMENT, DRY PATTERN
REGIME NEAR YAP PROPER NORTH OF THE CONVERGENCE ZONE.
THIS CONVERGENCE ZONE IS PRODUCING A BUILD UP OF CONVECTION AROUND
PALAU AND TO THE EAST. THESE SHOWERS ARE EXPECTED TO MOVE WESTWARDS
OVER THE NEXT DAY OR SO. SATELLITE IMAGERY SHOWS THAT THESE SHOWERS
ARE SHALLOW, THIS WILL KEEP RAINFALL TOTALS ON LOW SIDE. PROBABILITY
OF PRECIPITATION (POPS) HAS BEEN REDUCED TO REFLECT THE HIT OR MISS
NATURE OF THESE SHOWERS.
INVEST 91W IS LOCATED SOUTH OF CHUUK LAGOON NEAR 5N151E. THIS
FEATURE CONTINUES TO WEAKEN AS IT MOVES THROUGH UNFAVORABLE
CONDITIONS. THIS FEATURE WILL LIKELY BECOME A BROAD SURFACE TROUGH
OVER THE NEXT DAY. THIS FEATURE WILL ALSO GRADUALLY MOVE WESTWARD
OVER THE COMING DAYS AND MAY PROVIDE SOME RAIN TO PALAU OVER THE
WEEKEND. TO REFLECT THIS PALAU'S POPS REMAIN AT 30 PERCENT FOR
SATURDAY AND SATURDAY NIGHT.
THE ITCZ FRAGMENT WITH EMBEDDED TROUGHS IS EXPECTED TO CONTINUE TO
MOVE WESTWARD OVER THE NEXT SEVERAL DAYS. SHOWERS PRODUCED BY THIS
FEATURE ARE EXPECTED TO ARRIVE AT CHUUK LAGOON TONIGHT, AND REMAIN
THROUGH THE MIDDLE OF NEXT WEEK. DAILY RAINFALL TOTALS ARE ESTIMATED
TO BE AROUND HALF AN INCH. SHOWERS MAY INTENSIFY AROUND THE MIDDLE OF
NEXT WEEK.
A DRY PATTERN REGIME HAS SET UP FOR YAP PROPER. THESE DRIER
CONDITIONS ARE EXPECTED TO REMAIN THROUGH THE MIDDLE OF NEXT WEEK.
THEN, SHOWERS MAY ARRIVE AS THE ITCZ FRAGMENT MAKES ITS WAY NEAR
YAP.
ALTIMETRY SHOWS COMBINED SEAS OF 3 TO 5 FEET FOR THE REGION. WINDS
ARE EXPECTED TO BE LIGHT TO MODERATE THROUGH THE FORECAST PERIOD.
SEAS AND WINDS MAYBE ELEVATED NEAR HEAVIER SHOWERS.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA/TROPICAL UPDATE: DOLL
THERE ARE FOUR MAIN FEATURES IN THE REGION: A CONVERGENCE ZONE
MARIANAS/TROPICAL: SCHANK
EAST MICRONESIA: WHISNANT
WEST MICRONESIA: BOWSHER
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