923
FXPQ50 PGUM 260900
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
700 PM CHST TUE MAY 26 2026
MARIANAS SYNOPSIS
VISIBLE SATELLITE AND RADAR IMAGERY SHOW SCATTERED SHOWERS MOVING
ACROSS GUAM THIS AFTERNOON, WITH THIN UPPER-LEVEL CLOUDS SPREADING
FARTHER NORTH, ACROSS ROTA, TINIAN, AND SAIPAN FROM DEEPER CONVECTION
TO THE SOUTH. ALTIMETRY AND BUOY DATA REVEAL COMBINED SEAS HAVE
SLIGHTLY INCREASED TO 4 TO 6 FEET COMPRISED OF EASTERLY TRADE SWELL
AND LONGER-PERIOD NORTHERLY SWELL.
DISCUSSION
SOUTHWEST OF THE REGION, A TROPICAL DISTURBANCE, INVEST 99W, IS
WITHIN A DEVELOPING MONSOON PATTERN IN YAP STATE. THE MARIANAS
REMAIN IN THE NORTHEASTERN PERIPHERY OF THIS UNSETTLED PATTERN
WITH ONLY SCATTERED SHOWERS MOVING ACROSS THE REGION. DEPENDING
ON DEVELOPMENT AND THE NORTHWESTWARD TRACK OF 99W, SHOWERS ARE
EXPECTED TO BUILD ACROSS THE CONVERGING MONSOON AND TRADE-WIND
PATTERNS, BRINGING SCATTERED LOCALLY HEAVY SHOWERS AND ISOLATED
THUNDERSTORMS TO THE REGION WEDNESDAY AND WEDNESDAY NIGHT, MAINLY
ACROSS GUAM AND ROTA. LATEST MODEL GUIDANCE SHOWS THE BULK OF THE
UNSETTLED PATTERN FARTHER OFFSET TO THE WEST, SO THERE IS LESS
CONFIDENCE IN LOCALLY HEAVY SHOWERS WEDNESDAY THROUGH THURSDAY,
ESPECIALLY FOR TINIAN AND SAIPAN. SUSTAINED WINDS ALSO DECREASED TO
10 TO 15 MPH, HOWEVER, CONVECTIVELY-DRIVEN GUSTS OF 25 MPH ARE STILL
LIKELY.
MARINE/SURF
COMBINED SEAS OF 4 TO 6 FEET ARE EXPECTED TO INCREASE TO 5 TO 7 FEET
AS SOUTHWEST SWELL BUILDS INTO THE REGION OVER THE NEXT FEW DAYS,
POTENTIALLY PUSHING SEAS UP TO 8 FEET. MODERATE EASTERLY TRADE WINDS
BECOME SOUTHEASTERLY WEDNESDAY, THEN DIMINISH BACK DOWN TO LIGHT TO
MODERATE STARTING WEDNESDAY NIGHT. THERE WILL BE A MODERATE RISK OF
RIP CURRENTS ALONG NORTH AND EAST FACING REEFS OF THE MARIANAS
THROUGH THE WEEKEND. A LOW RIP RISK ALONG SOUTH AND WEST FACING REEFS
MAY BECOME MODERATE THURSDAY OR FRIDAY, AS A SOUTHWEST SWELL BUILDS
INTO THE REGION. THERE IS SOME UNCERTAINTY ON THE MAGNITUDE OF THE
SOUTHWEST SWELL. THE GFSWAVE SHOWS IT BUILDING UP TO 6 FEET, BUT THIS
IS DEPENDENT ON THE DEVELOPMENT OF 99W AND THE MONSOON PATTERN IN
WESTERN MICRONESIA.
TROPICAL SYSTEMS
INVEST 99W HAS SHIFTED WESTWARD TO AROUND 7N139E, SOUTH-SOUTHEAST
OF YAP PROPER, AND HAS BEEN UPGRADED TO MEDIUM BY THE JOINT
TYPHOON WARNING CENTER (JTWC). THIS MEANS THAT DEVELOPMENT INTO A
SIGNIFICANT TROPICAL CYCLONE IS LIKELY, BUT EXPECTED TO OCCUR
BEYOND 24 HOURS. 99W IS STILL LARGELY DISORGANIZED, BUT REMAINS
ENTRENCHED IN A DEVELOPING MONSOON PATTERN. DENSE CLOUD COVER AND
FLARING, DEEP CONVECTION ARE DISPLACED TO ITS SOUTH AND EAST,
ALONG THE EASTWARD EXTENT OF THE MONSOON SURGE. SCATTERED SHOWERS
SPAN ACROSS THE WESTERN AND NORTHERN SIDES OF THE SYSTEM, DUE TO
RELATIVELY DRIER AND WEAKER TRADE-WIND CONVERGENCE. 99W LOOKS TO
GRADUALLY BECOME MORE ORGANIZED OVER THE NEXT FEW DAYS, MERGING
WITH A MONSOON DISTURBANCE NEAR PALAU AS IT DRIFTS WEST-
NORTHWEST, PASSING NEAR OR OVER YAP PROPER LATE TONIGHT AND
WEDNESDAY. THEN INVEST 99W WILL BEGIN TO LIFT NORTHWARD, POTENTIALLY
BECOMING A TROPICAL DEPRESSION WITH A DEVELOPING MONSOON TAIL
FORMING ON THE SOUTH SIDE.
FOR MORE INFORMATION ON INVEST 99W, SEE BULLETINS ISSUED BY JTWC
UNDER WMO HEADER ABPW10 PGTW.
EASTERN MICRONESIA
VISIBLE SATELLITE IMAGERY DEPICTS THE INTERACTION BETWEEN AN ITCZ
FRAGMENT AND TRAILING MONSOON CONVERGENCE JUST NORTH OF POHNPEI AND
KOSRAE. THIS INTERACTION HAS PRODUCED A NORTHWEST-TO-SOUTHEAST
ORIENTED BAND OF NUMEROUS TO WIDESPREAD SHOWERS AND ISOLATED
THUNDERSTORMS THAT ARE NOW BACK FILLING ACROSS POHNPEI AND KOSRAE
DUE TO CONVERGENCE WITH SOUTHERLY CROSS-EQUATORIAL FLOW. THIS PRIMARY
WEATHER MAKER IS EXPECTED TO WEAKEN AND LIFT NORTHWARD, DECREASING
POPS FOR POHNPEI AND KOSRAE FOR THE NEXT DAY. THE BAND ENDS WELL
SOUTHWEST OF MAJURO, LEAVING MOST OF THE MARSHALLS IN A DRIER,
NORTHEASTERLY TRADE-WIND REGIME. CONDITIONS MAY BEGIN TO CHANGE
STARTING AROUND THURSDAY AS A DEVELOPING ITCZ IN THE CENTRAL PACIFIC
POSSIBLY ENTERS THE MARSHALLS, INCREASING THE POTENTIAL FOR SHOWERS
AND THUNDERSTORMS ACROSS EASTERN MICRONESIA, ESPECIALLY OVER MAJURO.
POPS ARE FORECASTED TO PEAK FROM THURSDAY TO FRIDAY FOR POHNPEI AND
KOSRAE WHEREAS MAJURO MAY SEE INCREASED POPS THROUGH THE WEEKEND, BUT
TIMING IS ALL DEPENDENT ON THE INTENSITY AND MOVEMENT OF THE ITCZ
WITHIN THE COMING DAYS.
OVERALL SEA STATE REMAINS STEADY WITH COMBINED SEAS OF 4 TO 6 FEET
ACROSS POHNPEI AND KOSRAE AND UP TO 7 FEET NEAR MAJURO. LIGHT TO
GENTLE EASTERLY WINDS PREVAIL ACROSS THE ENTIRE REGION. GUSTS WILL BE
STRONGER NEAR THUNDERSTORMS WITHIN COASTAL WATERS. A MINOR NORTH
SWELL IS EXPECTED TO SPREAD ACROSS THE REGION ON WEDNESDAY,
POTENTIALLY INCREASING SURF ALONG NORTH-FACING REEFS. IN ADDITION,
DISTANT WEATHER FEATURES IN THE SOUTHERN HEMISPHERE HAVE INDUCED A
MINOR SOUTHERLY SWELL, BUT WAS OMITTED FROM THE FORECAST AS EFFECTS
WILL REMAIN MINIMAL, ESPECIALLY ONCE THE NORTHERLY SWELL ENTERS THE
REGION. OVER THE WEEKEND, SEAS MAY GRADUALLY SUBSIDE AS THE EASTERLY
AND NORTHERLY SWELLS DECREASE.
WESTERN MICRONESIA
A SMALL CRAFT AND HIGH SURF ADVISORIES HAVE BEEN ISSUED FOR PALAU AND
YAP.
FOR PALAU AND YAP, CONDITIONS ARE EXPECTED TO DETERIORATE AS INVEST
99W IS EXPECTED TO CONTINUE DEVELOPING OVER THE NEXT FEW DAYS. PALAU
IS EXPECTED TO SEE THESE CONDITIONS FIRST, THEN BY TOMORROW YAP WILL
ALSO SEE THESE CONDITIONS. WIDESPREAD SHOWERS AND ISOLATED TO
SCATTERED THUNDERSTORMS ARE EXPECTED AT BOTH LOCATIONS THROUGH AT
LEAST FRIDAY AS 99W MOVES WEST-NORTHWEST OVER THE COMING DAYS. WINDS
AT PALAU ARE EXPECTED TO BE FROM THE WEST AT 10 TO 15 KT WITH
FREQUENT GUSTS TO 25 KT BUILDING TO AROUND 30 KT WITH GUSTS TO 40
KT FOR PALAU, AND 35KT WITH GUSTS UP TO 55 KT AROUND WEDNESDAY NIGHT
INTO THURSDAY. LOOKING INTO THE LATTER HALF OF THE WEEK, THE MONSOON
TROUGH IS EXPECTED TO KEEP BOTH LOCATIONS WET AND BREEZY. THIS MAY
CAUSE THE ADVISORIES TO BE EXTENDED INTO THE WEEKEND.
FOR CHUUK, A SHORT LULL IN SHOWERS IS EXPECTED FOR THE NEXT DAY OR
TWO. SHOWERS ARE EXPECTED TO RETURN FOR THE LATTER HALF OF THE WEEK
AS THE MONSOON TROUGH CONTINUES TO EXPAND ACROSS FSM AND IN TO
EASTERN MICRONESIA. THIS FEATURE IS EXPECTED TO PRODUCE SCATTERED
SHOWER AND ISOLATED THUNDERSTORMS, HOWEVER AT THIS TIME, THERE ARE
LITTLE TO NO CONCERNS FOR HAZARDOUS CONDITIONS NEAR WENO.
COMBINED SEAS OVER THE REGION ARE GENERALLY 4 TO 6 FEET EXCEPT NEAR
INVEST 99W. WINDS ARE ALSO EXPECTED TO BE GENERALLY AROUND LIGHT TO
GENTLE EXPECT NEAR 99W AND THE WESTERLY INFLOW. WINDS AND SEAS NEAR
99W ARE EXPECTED TO DETERIORATE AS THE EVENING PROGRESSES, WITH WINDS
BUILDING TO 30 TO 35 KT WITH GUSTS TO 55 KT BY WEDNESDAY NIGHT. FOR
THESE REASONS A SMALL CRAFT ADVISORY AND A HIGH SURF ADVISORY HAS
BEEN ISSUED FOR BOTH PALAU AND YAP. PALAU WILL BE THE FIRST TO SEE
THE SEA CONDITIONS DETERIORATE LATER TONIGHT, THEN AROUND THE
AFTERNOON, YAP WILL SEE THE SAME THING HAPPEN.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: CRUZ
EAST MICRONESIA: MESA
WEST MICRONESIA: BOWSHER
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