883
FXPQ50 PGUM 302011
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
611 AM CHST TUE MAR 31 2026
MARIANAS UPDATE
SCATTERED SHOWERS PERSISTED NEAR SAIPAN AND TINIAN OVERNIGHT ALONG
THE EDGE OF A FRAGMENTED SHEAR LINE, WHICH HAVE PRODUCED OCCASIONAL
FRESH TO STRONG GUSTS. OVERNIGHT SCATTEROMETRY SHOWS A BROAD AREA OF
FRESH WINDS EXTENDING TO THE EAST AND WEST OF THE NORTHERN CNMI, JUST
NORTH OF THE SHEAR LINE BOUNDARY, AND GENTLE TO MODERATE WINDS TO THE
SOUTH. SATELLITE AND RADAR IMAGERY EARLY THIS MORNING SHOW AN AREA
OF SHOWERS DRIFTING WEST OF ROTA AND TINIAN WATERS ALONG THE EDGE OF
THE SHEAR LINE FRAGMENT, AND ISOLATED TO SCATTERED SHALLOW SHOWERS
APPEAR JUST EAST TO NORTHEAST OF SAIPAN. FOR GUAM AND ROTA, MOSTLY
CLEAR CONDITIONS ARE SEEN UPSTREAM TO THE EAST. SCATTERED SHOWERS
WERE MAINTAINED IN THE FORECAST FOR TINIAN AND SAIPAN TODAY,
INCLUDING OCCASIONAL GUSTS UP TO 30 MPH NEAR PASSING SHOWERS.
THERE WAS LITTLE CHANGE IN THE MARINE AND SURF FORECASTS. TANAPAG
BUOY DATA AND ALTIMETRY SHOW COMBINED SEAS AROUND 5 TO 8 FEET,
COMPRISED PRIMARILY OF NORTH TO NORTHEAST SWELL WITH SECONDARY EAST-
NORTHEAST TRADE SWELL. THE HIGHEST SEAS ARE SEEN OVER NORTHERN SAIPAN
AND TINIAN WATERS IN THE VICINITY OF THE FRAGMENTED SHEAR LINE,
WHERE WINDS AND WIND WAVES ARE STRONGEST. WINDS ARE EXPECTED TO BE
MAINLY GENTLE TO MODERATE OUT OF THE NORTHEAST TO EAST FOR MOST OF
THE WEEK, WITH OCCASIONAL FRESH TO STRONG GUSTS EXPECTED AT TINIAN
AND SAIPAN THROUGH TONIGHT. SEAS MAY INCREASE BY A FOOT OR SO THIS
COMING WEEKEND AS THE EAST-NORTHEAST TRADE WINDS AND SWELL
STRENGTHEN.
TROPICAL SYSTEMS UPDATE
THE WEAK CIRCULATION THAT WAS THE SUBJECT OF JOINT TYPHOON WARNING
CENTER (JTWC)'S INVEST 99W HAS MOSTLY DISSIPATED. OVERNIGHT
SCATTEROMETRY DEPICTS A BROAD AREA OF LIGHT TO GENTLE WINDS IN THE
AREA JUST WEST TO NORTHWEST OF POHNPEI AND EAST OF CHUUK, WITH SPARSE
CONVECTION SEEN WITHIN THE REMNANT SURFACE TROUGHING, AND INVEST 99W
HAS BEEN CLOSED. THE BROAD CIRCULATION JUST EAST OF THE SOUTHERN
MARSHALL ISLANDS, CENTERED NEAR 4N177E, REMAINS OF INTEREST, BUT NO
NEW INVEST AREA HAS BEEN OPENED AT THIS TIME. A BROAD ROBUST SURFACE
TROUGH EXTENDS WEST-NORTHWEST FROM THE CIRCULATION CENTER ACROSS THE
RMI, WITH THE AXIS JUST SOUTH OF MAJURO ATOLL, WITH NUMEROUS TO
WIDESPREAD HEAVY SHOWERS AND SCATTERED THUNDERSTORMS FOCUSED ALONG
IT. IN THE SHORT TERM, MODELS DEPICT VERY LITTLE DEVELOPMENT WITH
THIS SYSTEM AS IT MEANDERS SLOWLY WEST ACROSS EASTERN MICRONESIA THIS
WEEK.
EASTERN MICRONESIA UPDATE
THE CIRCULATION THAT WAS INVEST 99W HAS LARGELY DISSIPATED TO THE
NORTHWEST OF POHNPEI. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
EXTEND ACROSS THE AREA WITHIN THE REMNANT SURFACE TROUGHING, MAINLY
NORTHWEST OF POHNPEI, AND ROUGHLY HALFWAY BETWEEN POHNPEI AND KOSRAE.
THE MAIN FEATURE WITHIN THE REGION IS THE BROAD, ROBUST SURFACE
TROUGH, DISCUSSED ABOVE, EXTENDING ACROSS THE RMI JUST SOUTH OF
MAJURO INTO A SURFACE CIRCULATION NEAR 4N177E. NUMEROUS TO WIDESPREAD
HEAVY SHOWERS AND SCATTERED THUNDERSTORMS ARE SEEN ACROSS THE REGION.
PROBABILITY OF PRECIPITATION (POP) FOR MAJURO WAS INCREASED FROM 20
PERCENT TO 50 PERCENT TODAY WITH LOCALLY HEAVY SHOWERS POSSIBLE, WITH
THE STRONGEST CONVECTION STILL EXPECTED TO REMAIN SOUTH OF THE ATOLL.
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS CONTINUE, BUT DECREASE
OVERNIGHT AS THE BROAD TROUGH EXTENDING FROM THE CIRCULATION SHIFTS
SOUTHWARD. POPS MAY NEED TO BE UPDATED OR ADJUSTED UPWARD IN THE
NEXT FORECAST PACKAGE DEPENDING ON THE DEVELOPMENT OF THESE FEATURES.
WESTERN MICRONESIA UPDATE
THERE WAS LITTLE CHANGE IN THE OVERNIGHT UPDATE. NUMEROUS SHOWERS
ARE SEEN JUST EAST TO NORTHEAST OF THE MAJOR ISLANDS OF PALAU, WITHIN
THE BROAD CONVERGENCE ZONE ALONG THE NORTHERN PERIPHERY OF THE VERY
BROAD WEAK CIRCULATION CENTERED NEAR 4N138E. SHOWERS WERE INCREASED
FROM SCATTERED TO NUMEROUS TODAY WITH LOCALLY HEAVY SHOWERS POSSIBLE.
MODEL GUIDANCE SHOWS THIS AREA OF CONVERGENCE WEAKENING SIGNIFICANTLY
AS IT SHIFTS FURTHER WEST ACROSS PALAU, LARGELY DIMINISHING TONIGHT.
SCATTERED SHOWERS WERE MAINTAINED FOR YAP TODAY AS THE CONVERGENCE
BOUNDARY AND SHOWERS SHIFT NEARBY JUST TO THE SOUTH. CHUUK IS
EXPECTED TO REMAIN MOSTLY DRY TODAY, BUT LOOKS TO SEE A SLIGHT
INCREASE IN SHOWERS BY TONIGHT AS THE REMNANTS OF INVEST 99W MOVE
NEARBY.
PREV DISCUSSION
/ISSUED 531 PM CHST MON MAR 30 2026/
MARIANAS SYNOPSIS...
A WEAK FRAGMENTING SHEAR LINE EXTENDS THROUGH THE MARIANAS JUST NORTH
OF SAIPAN AND IS GENERATING MOSTLY CLOUDY SKIES AND SCATTERED SHOWERS
NEAR TINIAN AND SAIPAN AND OVER THE ISLANDS TO THE NORTH. FURTHER
SOUTH PARTLY CLOUDY SKIES AND ISOLATED SHOWERS EXTEND OVER ROTA AND
GUAM, WITH SOME LINGERING ISLAND-ENHANCED CONVECTION FOUND IN THE
WATERS WEST OF GUAM. SEAS ARE AROUND 5 TO 7 FEET ACCORDING TO
ALTIMETRY AND TANAPAG BUOY WITH GENTLE TO MODERATE NORTHEAST WINDS
ACROSS THE COASTAL WATERS.
DISCUSSION...
THE MAIN FEATURE CURRENTLY NEAR THE MARIANAS IS THE FRAGMENTING SHEAR
LINE THAT EXTENDS FROM A WEAK COLD FRONT WELL NORTHEAST OF THE
ISLANDS. HI-RES MODELS SHOW A SLIGHT NORTHWARD SHIFT IN THE BROKEN
BAND OF CLOUD COVER AND SCATTERED SHOWERS ASSOCIATED WITH THE SHEAR
LINE LATE THIS EVENING, SO EXPECT SHOWERS TO BECOME ISOLATED AT
TINIAN AND SAIPAN BY MIDNIGHT. HI-RES MODELS THEN SHOW SHOWERS
SHIFTING BACK IN TUESDAY MORNING AS THE SHEAR LINE CONTINUES TO
FRAGMENT AND ONE OF THESE FRAGMENTS SHIFT OVER SAIPAN AND TINIAN.
GUAM AND ROTA ARE EXPECTED TO REMAIN FAIRLY DRY AND WELL SOUTH OF ANY
OF THESE FRAGMENTS. AS THE TRADE-WINDS SLOWLY STRENGTHEN, THIS
SHOULD PUSH WHAT REMAINS OF THE SHEAR LINE WEST OF THE MARIANAS, WITH
A RELATIVELY DRY PATTERN EXPECTED FOR MOST OF THE WEEK, THOUGH
GLOBAL MODELS SHOW A COUPLE OF WEAK TROUGHS PASSING NEAR THE MARIANAS
AROUND FRIDAY AND THEN MONDAY WHICH MAY LEAD TO A COUPLE PERIODS OF
INCREASED CLOUD COVER AND LOW-END SCATTERED SHOWERS. LONG-RANGE
GUIDANCE SHOWS A POTENTIAL SURGE IN THE TRADE WINDS LATE IN THE
WEEKEND THAT COULD CAUSE BREEZY CONDITIONS AROUND 25 MPH TO DEVELOP
ACROSS THE MARIANAS.
MARINE...
ALTIMETRY AND BUOY DATA NEAR SAIPAN SHOW SEAS ARE AROUND 5 TO 7 FEET
THIS EVENING, DRIVEN BY NORTH TO NORTHEAST SWELL AND WEAK EASTERLY
TRADE SWELL. WINDS ARE EXPECTED TO BE GENTLE TO MODERATE OUT OF THE
NORTHEAST TO EAST FOR MOST OF THE WEEK. SEAS MAY INCREASE BY A FOOT
OR SO IN THE LATTER HALF OF THE WEEK AS THE TRADE WINDS AND SWELL
STRENGTHEN SLIGHTLY. THIS PATTERN WILL SUPPORT A MODERATE RISK OF RIP
CURRENTS ALONG NORTH AND EAST FACING REEFS THROUGH THE REST OF THE
WEEK.
TROPICAL SYSTEMS...
INVEST 99W LOOKS LIKE IT'S FINALLY STARTING TO WEAKEN AS MOST OF THE
CONVECTION HAS DISSIPATED SINCE THIS MORNING, AS IT'S LOCATED
NORTHWEST OF POHNPEI NEAR 11N157E, AND IS DRIFTING WEST. CIMSS
ANALYSIS SHOWS A TITLING VORTICITY FIELD FROM THE SURFACE TO 700MB,
THEN SOUTHWARD AT 500MB. THE MODELS DISSOLVE THIS FEATURE IN THE NEXT
18 TO 36 HOURS.
THEN, ANOTHER CIRCULATION 3.5N180. IT'S CENTER REMAINS BROAD, WITH
NO SIGNIFICANT CONVECTION NEAR IT'S CENTER. THE LATEST OPERATIONAL
AND ENSEMBLE MEMBERS DRIFT THIS FEATURE WEST-SOUTHWEST THE NEXT FEW
DAYS WITH PERHAPS A SLIGHT IMPROVEMENT IN ORGANIZATION BY THE
WEEKEND. LONG-RANGE MODEL GUIDANCE AND ENSEMBLE MEMBERS ALSO HAVE IT
BECOMING BETTER ORGANIZED, BUT NOT UNTIL THE FIRST PART OR THE
MIDDLE OF NEXT WEEK, AT WHICH TIME THE CENTER MAY BE NEAR KOSRAE.
THUS, IF THE DELAY TRENDS CONTINUE, MAJURO AND POINTS SOUTH STILL MAY
GET SOME HEAVY RAINFALL, BUT THAT LOOKS TO BE ABOUT IT.
EASTERN MICRONESIA...
AS 99W CONTINUES TO WEAKEN AND MOVE AWAY FROM THE REGION, CONVECTION
MAY DECREASE THE NEXT FEW DAYS, WITH A PERIOD OF ISOLATED SHOWER
COVERAGE NOT TOTALLY OUT OF THE QUESTION FOR POHNPEI, AND MAYBE
KOSRAE. WITH THAT SAID, A TROUGH STRETCHING NEAR BOTH PLACES WILL
PROBABLY KEEP SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS GOING FOR
MOST OF THE FORECAST AT BOTH LOCATIONS, WHILE CONTINUING AT MAJURO AS
WELL. LIGHT TO GENTLE WINDS WILL BE GENTLE TO MODERATE AT TIMES. SEAS
OF 4 TO 6 FEET WILL INCREASE A FOOT BY THE WEEKEND.
WESTERN MICRONESIA...
AFTERNOON SATELLITE IMAGERY SHOWS A MONSOON-LIKE NET BLANKETED
ACROSS WESTERN MICRONESIA WITH AN EMBEDDED CIRCULATION SOUTH-
SOUTHEAST OF PALAU. MOSTLY CLOUDY SKIES AND ISOLATED TO SCATTERED
SHOWERS ACCOMPANY THE NET AND EMBEDDED CIRCULATION AND THESE
CONDITIONS CAN BE EXPECTED AT BOTH YAP AND PALAU THROUGH TUESDAY.
ISOLATED THUNDERSTORMS WILL BE POSSIBLE AT PALAU TONIGHT, MAINLY
AFTER MIDNIGHT. GENERALLY DRIER CONDITIONS ARE EXPECTED FOR PALAU
AND YAP FROM WEDNESDAY THROUGH FRIDAY. INVEST 99W WILL CONTINUE TO
WEAKEN AS IT MOVES WESTWARD AND IS EXPECTED TO BRING SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS STARTING TUESDAY NIGHT FOR CHUUK
AS THE WEAKENING DISTURBANCE APPROACHES. DRIER CONDITIONS ARE THEN
EXPECTED AT CHUUK FOR THE BACK HALF OF THE WORK WEEK.
WINDS WILL REMAIN GENTLE TO MODERATE AT YAP THROUGH MUCH OF THE
WEEK, WITH GENTLE TO MODERATE WINDS WEAKENING TO MOSTLY GENTLE AT
PALAU STARTING WEDNESDAY. WINDS WILL INCREASE FROM LIGHT TO GENTLE TO
GENTLE TO MODERATE STARTING TUESDAY NIGHT AT CHUUK AS THE WEAKENING
DISTURBANCES APPROACHES. COMBINED SEAS OF 3 TO 6 FEET WILL PREVAIL
AT ALL FORECAST SITES THROUGH MUCH OF THE WEEK, WITH SEAS INCREASING
TO AROUND 7 FEET AT CHUUK BY THE WEEKEND AND POTENTIALLY UP TO 10
FEET BY THE END OF THE WEEKEND.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA/TROPICAL UPDATE: DECOU
MARIANAS: SCHANK
EAST MICRONESIA/TROPICAL: DOLL
WEST MICRONESIA: WHISNANT
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