992
FXPQ50 PGUM 171857
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
457 AM CHST MON MAY 18 2026
MARIANAS UPDATE
NO SIGNIFICANT CHANGES WERE NEEDED AS THE FORECAST REMAINS IN GOO
SHAPE. OVERALL, THE MAIN CONCERN CONTINUES TO BE THE HIGH RIP RISK
FOR EAST FACING REEFS THAT'LL CONTINUE THROUGH TUESDAY AFTERNOON. THE
SURF MAY BRIEFLY DROP BELOW RISK THRESHOLDS FOR TODAY, BUT WILL
REBOUND TO 9 FEET (HIGH RIP RISK) TONIGHT. FOR THE SIMPLICITY OF
MESSAGING, THE HEADLINE WAS LEFT IN TACT.
EASTERN MICRONESIA UPDATE
THE MAIN CHANGE WAS TO TO INCREASE SHOWER COVERAGE TO NUMEROUS (70
PERCENT PROBABILITIES) AT POHNPEI TODAY, AS A SURFACE TROUGH AND
EXCELLENT SURFACE CONVERGENCE IS LEADING TO ROBUST SHOWER AND
THUNDERSTORM DEVELOPMENT THIS MORNING. CLOUD TOPS HAVE SURPASSED -85
DEG. C AT TIMES, INDICATIVE OF LOCALLY HEAVY RAINFALL. THIS WORDING
WAS IN THAT ZONE FOR TONIGHT, BUT WE ADDED IT FOR TODAY AS WELL.
AT KOSRAE, WE LOWERED RAINFALL POTENTIAL TO LOW-END SCATTERED SHOWERS
(30 PERCENT PROBABILITIES) FOR TONIGHT, DUE TO UNIMPRESSIVE UPSTREAM
DEVELOPMENT CURRENTLY. AT MAJURO, HERE TOO RAINFALL POTENTIAL WAS
LOWERED SLIGHTLY TO 30 PERCENT FOR SIMILAR REASONS (NOT MUCH
CONVECTION DEVELOPING OVER OR EAST OF THE AREA, ASIDE FROM A COUPLE
SHOWERS THAT HAVE JUST RECENTLY STARTED TO DEVELOP.
WESTERN MICRONESIA UPDATE
THE MAIN CHANGE WAS TO DECREASE SHOWER COVERAGE TO ISOLATED (20
PERCENT POTENTIAL) FOR TODAY GIVEN A DEARTH OF CONVECTION IN THE
REGION. AT YAP, DELAYED SCATTERED SHOWER COVERAGE UNTIL THIS
AFTERNOON. OTHERWISE, THE FORECAST LOOKED GOOD THERE. AT CHUUK,
YOU'REW INBETWEEN SURFACE TROUGHS WITH NOT MUCH CONVECTION CURRENTLY
DEVELOPING. WITH THAT SAID, WEAK CONVERGENCE MAY BE SUFFICIENT FOR
SCATTERED SHOWER DEVELOPMENT TODAY AND TONIGHT. AS SUCH, WE LOWERED
RAINFALL POTENTIAL SLIGHTLY TO 40 PERCENT AND WILL SEE HOW THINGS
DEVELOP LATER THIS MORNING AND INTO THE AFTERNOON.
PREV DISCUSSION
/ISSUED 441 PM CHST SUN MAY 17 2026/
MARIANAS SYNOPSIS...
SATELLITE AND RADAR IMAGERY SHOW PARTLY CLOUDY SKIES AND ISOLATED
SHOWERS ACROSS THE REGION. ALTIMETRY AND BUOY DATA SHOW COMBINED
SEAS BETWEEN 6 AND 8 FEET.
DISCUSSION...
A FEW CHANGES WERE MADE TO THE SHORT TERM FORECAST. THE MAIN ONE WAS
TO SIGNIFICANTLY REDUCE POPS OVER THE NEXT FEW DAYS. GUIDANCE HAS
BACKED OFF ON SCATTERED SHOWERS, SHIFTING THE BULK OF SHOWERS AND
THUNDERSTORMS SOUTH OF THE MARIANAS. LOW END (30%) SCATTERED SHOWERS
REMAIN IN THE FORECAST FOR MONDAY NIGHT, BUT TRENDS WILL NEED TO BE
MONITORED AS THE FORECAST COULD CONTINUE TO DECREASE IN CONFIDENCE. A
MOISTURE SURGE IS LOOKING TO PUSH INTO THE MARIANAS LATE THIS WEEK.
THIS SURGE IN MOISTURE LOOKS TO BE ASSOCIATED WITH A SHARP SURFACE
TROUGH THAT LOOKS TO APPROACH THE REGION ON SATURDAY.
MARINE...
COMBINED SEAS ARE BETWEEN 6 AND 8 FEET AND ARE EXPECTED TO PERSIST
THROUGH THE MIDDLE OF THE WEEK. A HIGH RISK FOR RIP CURRENTS IS IN
EFFECT FOR EAST FACING REEFS UNTIL TUESDAY AFTERNOON. A BRIEF LULL IN
RIP CURRENTS OF 9 FEET IS FORECASTED ON MONDAY BEFORE RISING TO 9
FEET MONDAY NIGHT AND INTO TUESDAY. SEAS LOOK TO FALL TOWARDS THE
END OF THE WEEK WITH COMBINED SEAS 4 TO 6 FEET EXPECTED ON FRIDAY.
EASTERN MICRONESIA...
AN UNSETTLED, DISORGANIZED PATTERN PREVAILS ACROSS EASTERN
MICRONESIA. HIMAWARI VISIBLE SATELLITE IMAGERY THIS AFTERNOON SHOWS
MODERATE TO DEEP CONVECTION DEVELOPING NEAR AND EAST OF POHNPEI, AND
TO THE NORTH OF KOSRAE, ASSOCIATED WITH CONVERGENCE ALONG A BROAD
TRADE-WIND TROUGH EXTENDING SOUTH THROUGH THE REGION. TO THE EAST,
CLOUD COVER IS PATCHY AND WIDESPREAD, MAINLY FROM THE CENTRAL RMI
NORTHWARD, AND ALONG A TRADE-WIND TROUGH APPROACHING FROM THE EAST,
LOCATED NEAR THE DATE LINE. ISOLATED TO SCATTERED SHOWERS PREVAIL
ACROSS MUCH OF THE REGION, WITH NUMEROUS SHOWERS SEEN ALONG AND EAST
OF THE DATE LINE.
MODEL GUIDANCE DEPICTS AN UNSETTLED PATTERN CONTINUING THROUGH MUCH
OF THE WEEK AS TRADE-WIND TROUGHS PROPAGATE WESTWARD ACROSS THE
AREA, ALONG A DEVELOPING INTERTROPICAL CONVERGENCE ZONE (ITCZ). THE
ITCZ BECOMES BETTER-ORGANIZED MONDAY NIGHT AND TUESDAY AS IT EXTENDS
WEST OF KOSRAE AND POHNPEI, WHERE A MORE ROBUST DISTURBANCE BEGINS TO
FORM. MEANWHILE,AN UPPER-LEVEL LOW, CURRENTLY CENTERED NORTH OF THE
MARSHALLS, WILL MEANDER WESTWARD JUST NORTH OF THE REGION,
INTERACTING WITH THESE FEATURES AT THE SURFACE TO DEVELOP SHOWERS AND
THUNDERSTORMS ACROSS THE AREA. SHOWERS ARE EXPECTED TO BECOME
NUMEROUS FOR POHNPEI MONDAY NIGHT, WITH LOCALLY HEAVY RAINFALL
POSSIBLE, WITH AT LEAST SCATTERED SHOWERS EXPECTED THROUGH THE REST
OF THE FORECAST PERIOD. SHOWERS WILL REMAIN SCATTERED FOR MUCH OF
THIS WEEK FOR KOSRAE AND MAJURO AS WELL, AS TRADE-WIND TROUGHS AND
A FRAGMENTED ITCZ MAINTAIN A WETTER PATTERN, POTENTIALLY WITH SUPPORT
FROM UPPER-LEVEL TROUGHING.
BENIGN MARINE CONDITIONS ARE EXPECTED THROUGH THE WEEK. LATEST
ALTIMETRY DATA INDICATES COMBINED SEAS BETWEEN 5 AND 7 FEET ACROSS
THE REGION, PEAKING NEAR 8 FEET NORTHEAST OF THE RMI. MODELS DEPICT A
GRADUAL RELAXATION OF THE EAST TO NORTHEAST TRADE SWELL THROUGHOUT
THE WEEK, ALLOWING SEAS TO GRADUALLY DECREASE BY A FOOT OR TWO OVER
THE NEXT SEVERAL DAYS.
WESTERN MICRONESIA...
THE MAIN WEATHER MAKERS FOR THE REGIONS IS RATHER LARGE BAND OF
CONVERGENCE SPANNING ACROSS MOST OF THE REGIONS. MOST OF THE SHOWERS
ARE FROM NORTH OF CHUUK TO SOUTH OF PALAU. WITHIN THIS BAND SCATTERED
TO NUMEROUS SHOWERS ARE EXPECTED AND SOME MAY BE LOCALLY HEAVY AT
TIMES. FOR NOW THIS IS MAINLY EFFECTING THE OUTER ISLANDS OF YAP
STATE, HOWEVER AS TIME MARCHES ON THIS FEATURE WILL MOVE WESTWARD
BRINGING SHOWERS TO BOTH YAP AND PALAU AS EARLY AS MONDAY. CURRENT
MODEL ESTIMATIONS SUGGEST THIS FEATURE WILL BRING SHOWERS TO BOTH YAP
AND PALAU THROUGH THE END OF THE WEEK.
MEANWHILE IN CHUUK AS OF THIS WRITING, SHOWERS APPEAR TO BE FAIRLY
MINIMAL. HOWEVER, THAT IS EXPECTED TO CHANGE AS SHOWER ARE EXPECTED
TO FILL IN TONIGHT. THEN OVER THE WEEK, THE SHOWERS AND TROUGHS THAT
ARE EFFECTING POHNPEI NOW ARE EXPECTED TO MOVE INTO WENO MAKING FOR
A FAIRLY WET WEEK.
BENIGN MARINE CONDITIONS CONTINUE THROUGH MUCH OF THE UPCOMING WEEK.
ALTIMETRY SHOWS 2 TO 4 FOOT SEAS AT PALAU AND YAP, INCREASING TO 4
TO 6 FOOT AT CHUUK. TRADE-WIND SWELL CONTINUES TO BUILD INTO THE
REGION, AND IS EXPECTED TO INCREASE SEAS TO 4 TO 6 FEET AT YAP AND
SLIGHTLY INCREASE SEAS AT PALAU TO 3 TO 4 FEET MONDAY AND MONDAY
NIGHT. AFTERWARDS, TRADE WINDS AND SWELL SUBSIDE, ALLOWING SEAS TO
DECREASE BACK DOWN TO 3 TO 5 FEET TOWARDS THE SECOND HALF OF THE
WEEK.
GUM WATCHES/WARNINGS/ADVISORIES
GU...HIGH RIP CURRENT RISK THROUGH TUESDAY AFTERNOON FOR GUZ001.
MP...HIGH RIP CURRENT RISK THROUGH TUESDAY AFTERNOON FOR MPZ001>003.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: DOLL
MARIANAS: WILLIAMS
EAST MICRONESIA: DECOU
WEST MICRONESIA: BOWSHER
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