065
FXPQ50 PGUM 230848
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
648 PM CHST SAT MAY 23 2026
MARIANAS SYNOPSIS
RADAR AND SATELLITE IMAGERY SHOW SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS OVER THE COASTAL WATERS OF THE MARIANAS AS A TRADE WIND
TROUGH, ASSOCIATED WITH INVEST 99W TO THE SOUTH, MOVES THROUGH. THE
CHANCE OF SHOWERS DECREASES SUNDAY IN BETWEEN TROUGHS AND THEN
INCREASES SUNDAY NIGHT AS A NEW TROUGH MOVES IN. A WET PATTERN WILL
THEN CONTINUE THROUGH MID TO LATE NEXT WEEK AS 99W REMAINS NEARBY.
ADDITIONAL MOISTURE FROM INVEST 90W POTENTIALLY MOVING INTO THE
MARIANAS REMAINS UNCERTAIN BUT COULD BRING HEAVIER SHOWERS AND
ISOLATED THUNDERSTORMS TO THE ISLANDS AS SOON AS WEDNESDAY. COMBINED
SEAS OF 4 TO 6 FEET TONIGHT ARE EXPECTED TO GRADUALLY LESSEN THROUGH
MONDAY BEFORE INCREASING AGAIN.
DISCUSSION
MOISTURE ASSOCIATED WITH THE NORTHERN EDGE OF INVEST 99W CONTINUES
TO BRING INCREASED SHOWERS AND ISOLATED THUNDERSTORMS OVER THE
COASTAL WATERS TO ALL OF THE MARIANAS. SHOWERS ARE EXPECTED TO
CONTINUE ALL WEEK WITH THE HIGHEST RAINFALL ACCUMULATIONS LIKELY TO
BE OVER GUAM AND DECREASE TO THE NORTH WITH INCREASED DISTANCE FROM
99W. WHILE THE SYSTEM IS STILL DISORGANIZED, MODELS HAVE HIGHER
AGREEMENT FOR 99W TO TRACK OVER YAP AND INTO THE PHILLIPINE SEA, SO
THE TRADE WIND THREAT HAS DECREASED SLIGHTLY LATE THIS WEEKEND.
HOWEVER, THE INTERACTION OF 99W AND 90W MID WEEK COULD BRING HEAVY
RAINFALL AND ISOLATED THUNDERSTORMS TO THE MARIANAS. THIS SITUATION
REMAINS HIGHLY UNCERTAIN AND WILL BE MONITORED CLOSELY. CONFIDENCE IN
A POTENTIAL TROPICAL DISTURBANCE TO IMPACT THE REGION NEXT WEEK
REMAINS LOW.
MARINE
BUOY AND ALTIMETRY DATA SHOW A STEADY TRADE WIND SWELL WITH COMBINED
SEAS OF 4 TO 6 FEET, NOW EXPECTED TO DECREASE SLOWLY THROUGH MONDAY
BEFORE THE ARRIVAL MONDAY NIGHT OR TUESDAY OF A SMALL NORTH SWELL
FROM A LOW PRESSURE SYSTEM OFF OF JAPAN. THERE IS A MODERATE RISK OF
RIP CURRENTS ALONG NORTH, EAST, AND SOUTH EXPOSED REEFS TONIGHT THAT
WILL DROP TO ONLY EAST EXPOSED REEFS TOMORROW. THE POTENTIAL
DEVELOPMENT OF A SOUTHEAST SWELL LATER IN THE WEEK IS HIGHLY
UNCERTAIN BUT MAY CAUSE HAZARDOUS SURF AND SEAS MID TO LATE WEEK
DEPENDING ON THE STRENGTH OF 99W. THIS SITUATION WILL BE MONITORED
CLOSELY.
TROPICAL SYSTEMS
INVEST 99W IS CURRENTLY LOCATED NEAR 8N144E AND CONTINUES TO BE
DISORGANIZED OVER EASTERN YAP STATE. THE JTWC CONTINUES TO RATE
INVEST 99W A SUB-LOW, WHICH MEANS SIGNIFICANT DEVELOPMENT INTO A
TROPICAL CYCLONE IS NOT EXPECTED THROUGH THE NEXT FEW DAYS. LITTLE TO
NO IMPROVEMENT WAS MADE IN THE ORGANIZATION OF 99W THROUGH MUCH OF
THE DAY. HOWEVER, CONVECTION HAS INCREASED ON THE SOUTHERN SIDE OF
THE BROAD CIRCULATION OVER THE LAST COUPLE OF HOURS. GUIDANCE IS IN
A BETTER AGREEMENT THAT A NORTHWARD TURN WILL HAPPEN, BUT STILL
DISAGREE ON WHEN. A TURN TO THE NORTH IS GENERALLY EXPECTED TO BE
WEST OF THE MARIANAS, BUT HOW FAR WEST REMAINS IN QUESTION. DUE TO
THE BROAD NATURE OF 99W, THE IMPACTS FROM HEAVY RAINFALL AND GUSTY
WINDS WILL BE FELL WELL AWAY FROM THE CENTER. AS INVEST 99W LIFTS
NORTHWARD, A MONSOON SURGE IS EXPECTED TO OCCUR ON THE SOUTH SIDE.
THIS WILL KEEP PARTS OF PALAU AND YAP WITHIN HEAVY RAINFALL AND GUSTY
WINDS FOR A PROLONGED PERIOD OF TIME.
INVEST 90W IS SEEN SOUTH OF KOSRAE NEAR 2N163E AND REMAINS
DISORGANIZED. 90W IS ALSO RATED A SUB-LOW BY THE JTWC AND IS NOT
EXPECTED TO BECOME A TROPICAL CYCLONE WITHIN THE NEXT FEW DAYS.
ROBUST CONVECTION IS SEEN WELL NORTH OF 90W AND KOSRAE, BUT
CONVECTION HAS INCREASED CLOSER TO THE CENTER OVER THE LAST COUPLE OF
HOURS. INVEST 90W IS EXPECTED TO LIFT NORTHWESTWARD OVER THE COMING
DAYS. UNCERTAINTY REMAINS HIGH IN HOW 90W WILL INTERACT WITH 99W AND
WHETHER OR NOT 90W BECOMES ITS OWN TRACTABLE STORM OR IF MERGES WITH
99W OVER THE COMING DAYS. FOR NOW, 90W WILL CONTINUE TO BRING HEAVY
SHOWERS AND THUNDERSTORMS TO KOSRAE AND POHNPEI OVER THE NEXT COUPLE
OF DAYS.
EASTERN MICRONESIA
INVEST 90W SOUTH OF KOSRAE CONTINUES TO SLOWLY ORGANIZE, WITH
CONVECTION MOST PREVALENT TO THE NORTH OF THE CIRCULATION CENTER,
WHICH HAS BEEN IMPACTING KOSRAE ALL DAY. THIS WILL CONTINUE THROUGH
THE NIGHT WITH NEAR 100 PERCENT POPS (PROBABILITY OF PRECIPITATION)
AND LOCALLY HEAVY RAINFALL WORDING ALREADY IN THE FORECAST. THIS WILL
CONTINUE INTO SUNDAY GRADUALLY TAPERING DOWN SUNDAY NIGHT INTO
MONDAY, AS THE INVEST CONTINUES MOVING AWAY (BY THEN) AS IT HEADS
WEST-NORTHWEST. AS OF RIGHT NOW, THE MOST CONCENTRATED AREA OF
CONVECTION MAY JUST PASS BY POHNPEI TO THE SOUTH MONDAY INTO TUESDAY,
BUT IT'LL BE CLOSE. FOR NOW, WE LEFT OUT LOCALLY HEAVY RAINFALL
WORDING BUT DO HAVE HIGH-END NUMEROUS SHOWER WORDING WITH 70 PERCENT
PROBABILITIES. THE HEAVY RAINFALL WORDING AND INCREASE IN SHOWER
COVERAGE/PROBABILITIES REMAIN POSSIBLE DEPENDING HOW QUICKLY 90W
ORGANIZES AND HOW MUCH OF A NORTHERLY COMPONENT IT HAS AS IT PASSES
BY POHNPEI.
FURTHER EAST, MAJURO REMAINS TO BE THE "TIP OF THE ITCZ (INTER-
TROPICAL CONVERGENCE ZONE) SPEAR", AS THE MOST CONCENTRATED AND
HEAVIEST CONVECTION HAS BEEN TO YOUR EAST. THE QUESTION REMAINS AS TO
IF THIS WILL CONTINUE TO REMAIN THE CASE THE NEXT 24 TO 6 HOURS. FOR
NOW, WE HAVE HIGH-END SCATTERED SHOWER COVERAGE (50 PERCENT
PROBABILITIES) BUT THIS TOO MAY NEED TO BE INCREASES DEPENDING HOW
MOTHER NATURE BEHAVES THE NEXT FEW DAYS.
FOR THE MARINERS, MAINLY LIGHT TO GENTLE WINDS WILL CONTINUE TO
AFFECT THE REGION, WITH SEAS HOLDING IN THE 5 TO 7 FOOT RANGE. WITH
THAT SAID, HIGHER WIND GUSTS AND SEAS, LOCALLY HEAVY RAINFALL, AND
REDUCED VISIBILITIES COULD OCCUR AT ANY TIME, ESPECIALLY NEAR INVEST
90W.
WESTERN MICRONESIA
SATELLITE IMAGERY SHOWS SCATTERED SHOWERS ACROSS THE REGION WITH
NUMEROUS SHOWERS OVER WENO. ALTIMETRY SHOWS COMBINED SEAS BETWEEN 4
AND 6 FEET.
LOW-END SCATTERED SHOWERS ARE OBSERVED ACROSS PALAU AND YAP. A
RELATIVE LULL IS IN PLACE ACROSS PALAU AND YAP PROPER. SHOWER
ACTIVITY LOOKS TO REMAIN ISOLATED TO SCATTERED THIS WEEKEND BEFORE
INVEST 99W BEGINS TO APPROACH FROM THE EAST. UNCERTAINTY REMAINS
HIGH ON HOW FAR WEST INVEST 99W GOES BEFORE TURNING TO THE NORTH.
HOWEVER, THE DIRECT TRACK OF 99W WILL HAVE LITTLE INFLUENCE ON
IMPACTS DUE TO IMPACTS BEING FELT WELL AWAY FROM THE CIRCULATION.
GUIDANCE CONTINUES TO SHOW A MONSOON TAIL FORMING ON THE SOUTHSIDE
OF 99W AS IT MOVES NORTHWARD AND BEGINS TO ORGANIZE NEXT WEEK.
WESTERLY MONSOONAL OR MONSOON-LIKE WINDS WOULD BRING FRESH TO STRONG
WINDS AND HEAVY RAINFALL NEAR PALAU AND YAP PROPER TOWARDS THE
LATTER HALF OF THE WEEK.
WENO REMAINS IN THE CONVERGENT ZONE ON THE EAST SIDE OF INVEST 99W.
NUMEROUS SHOWERS ARE ONGOING AND ARE EXPECTED TO CONTINUE THROUGH
THE WEEKEND. LOCALLY HEAVY RAINFALL WILL BE POSSIBLE SUNDAY AND
SUNDAY NIGHT. AS 99W BEGINS TO SHIFT TO THE WEST-NORTH WEST, THERE
WILL BE A TEMPORARY DECREASE IN SHOWER ACTIVITY EARLY NEXT WEEK.
THEN, THE INFLUENCES OF INVEST 90W WILL BEGIN TO IMPACTS PORTIONS OF
EASTERN CHUUK STATE NEXT WEEK.
COMBINED SEAS ARE BETWEEN 4 AND 6 FEET AND LOOK TO REMAIN WITHIN
THAT RANGE THROUGH TUESDAY NIGHT. LOCALIZED CHOPPY SEAS WILL BE
POSSIBLE NEAR HEAVIER SHOWERS FROM INVEST 99W. AS 99W ORGANIZES AND
PULLS TO THE NORTH, WESTERLY FLOW ON THE SOUTH SIDE WILL STRENGTHEN.
THIS WILL ALLOW SEAS TO APPROACH 10 FEET LATE THIS WEEK WHERE WINDS
ARE THE STRONGEST. TIMING AND LOCATION FOR THIS MONSOON SURGE REMAIN
UNCERTAIN WITH MOST GUIDANCE KEEPING THE STRONGEST WINDS AND SEAS
OUTSIDE OF THE COASTAL WATER OF PALAU. MARINERS SHOULD CONTINUE TO
MONITOR THE FORECAST OVER THE COMING DAYS AS WE WATCH THE
PROGRESSION OF 99W.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: WILLIAMS/DOLL/OGLE
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