964
FXPQ50 PGUM 181901
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
501 AM CHST TUE MAY 19 2026
MARIANAS UPDATE
THE MARIANAS FORECAST REMAINS IN GOOD SHAPE WITH NO UPDATES NEEDED,
A FEW SHOWERS WILL CONTINUE TO CROSS THE AREA THIS MORNING,
DIMINISHING BY SUNRISE. A HIGH RISK OF RIP CURRENTS FOR THE EAST
FACING REEFS THROUGH THIS AFTERNOON.
EASTERN MICRONESIA UPDATE
THE MAIN FORECAST CHANGES WERE TO DECREASE RAINFALL POTENTIAL
DOWNWARD TO 40 PERCENT FOR TODAY AND TONIGHT, AS THE BETTER SURFACE
CONVERGENCE SLIDES WEST WITH NOT MUCH ACTIVITY NOTED UPSTREAM ON
SATELLITE ANALYSIS. AT MAJURO, WE ALSO DROPPED SHOWER COVERAGE TO
ISOLATED (20 PERCENT) PROBABILITIES FOR TODAY ONLY, AS THE BETTER
SURFACE CONVERGENCE AND SHOWER COVERAGE WILL BE DELAYED UNTIL THIS
EVENING OR LATER TONIGHT FOR THE ONSET. OTHERWISE, NO ADDITIONAL
UPDATES WERE NEEDED.
WESTERN MICRONESIA UPDATE
THE MAIN CHANGES WERE TO LOWER RAINFALL POTENTIAL AT PALAU TO 30
PERCENT BASED ON A LACK OF UPSTREAM ACTIVITY. AT YAP, WE RAMPED POPS
(PROBABILITY OF PRECIPITATION) TO NEAR 100 PERCENT FOR TODAY AS
CONVECTION WILL BE PREVALENT THIS MORNING, BECOMING NUMEROUS SHOWERS
AND ISOLATED THUNDERSTORMS BY THE AFTERNOON. GIVEN CLOUD TOPS
SURPASSING -80 C, LOCALLY HEAVY RAINFALL WORDING WAS ADDED AS WELL.
WE THEN WENT WITH 50 PERCENT PROBABILITIES FOR TONIGHT.THE CHUUK
FORECAST REMAINS IN GOOD SHAPE WITH NO UPDATES NEEDED.
PREV DISCUSSION
/ISSUED 615 PM CHST MON MAY 18 2026/
MARIANAS SYNOPSIS...
MOSTLY CLOUDY SKIES AND SCATTERED SHOWERS ARE FORECASTED FOR THE
MARIANAS TONIGHT. A RETURN TO ISOLATED SHOWERS AND PARTLY CLOUDY
SKIES MAY CONTINUE UNTIL THE WEEKEND. COMBINED SEAS ARE BETWEEN 6 TO
8 FEET, AND A HIGH RISK OF RIP CURRENTS REMAINS ALONG EAST-FACING
REEFS AT LEAST THROUGH TUESDAY AFTERNOON.
DISCUSSION...
SATELLITE AND MODEL TRENDS SHOW LOW-END SCATTERED SHOWERS AS THE
TRADE-WIND SURGE AND SURFACE TROUGHS CONTINUE TO PRODUCE SHOWERS
MOVING DOWNSTREAM TOWARDS THE MARIANAS, SO PROBABILITY OF
PRECIPITATION (POPS) VALUES WILL REMAIN AT 30 PERCENT FOR THE ENTIRE
REGION TONIGHT. ISOLATED SHOWERS ARE EXPECTED TO REMAIN THROUGH THE
REST OF THE WEEK, BUT MOISTURE TRENDS WILL CONTINUE TO BE MONITORED
AS THE TROUGHS SOUTH OF WAKE ISLAND PROGRESS DOWNSTREAM OVER THE NEXT
SEVERAL DAYS. SCATTEROMETRY SHOWS SOME POCKETS OF ELEVATED TRADE
WINDS OVER OPEN WATERS TO THE FAR EAST, BUT MODELS (VALIDATED BY
TODAY'S OBSERVATIONS) INDICATE WINDS REMAINING 15 TO 20 MILES PER
HOUR WITH GUSTS UP TO 25 MILES PER HOUR FOR THE REGION UNTIL THE
LATTER HALF OF THE WEEK WHEN THE TRADES POTENTIALLY DOWNTREND THROUGH
THE WEEKEND. A SLIGHT CHANCE OF THUNDERSTORMS IS INTRODUCED IN THE
LAST FEW PERIODS OF THE FORECAST, BUT CONFIDENCE IS LOW AS MODELS
STRUGGLE TO AGREE ON THE SOURCE, WHETHER IT BE A WEAK TROUGH OR A
POTENTIAL DISTURBANCE PASSING SOUTH OF GUAM. REGARDLESS, THIS WILL
CONTINUE TO BE MONITORED AND COMMUNICATED AS THE WEEK PROGRESSES.
MARINE...
BUOY AND ALTIMETRY DATA INDICATED COMBINED SEAS OF 6 TO 8 FEET ACROSS
THE REGION AND IS EXPECTED TO CONTINUE UNTIL MIDWEEK WHEN SEA HEIGHTS
MAY DROP A FOOT OR TWO THROUGH THE REST OF THE WEEK. THE EASTERLY
TRADE WINDS ARE EXPECTED TO REMAIN MODERATE TO FRESH THROUGH THE REST
OF THE WEEK BEFORE POTENTIALLY DROPPING TO JUST MODERATE OVER THE
WEEKEND. SURF WILL REMAIN AT 9 FEET TONIGHT ALONG EAST-FACING REEFS,
SO A HIGH RISK OF RIP CURRENTS REMAINS AT LEAST THROUGH TUESDAY
AFTERNOON. SURF CONDITIONS WILL CONTINUE TO BE MONITORED AS THE RIP
CURRENT RISK WILL NEED TO BE RE-EVALUATED TOMORROW AFTERNOON.
TROPICAL SYSTEMS...
A WEAK SUBTROPICAL DISTURBANCE ON THE NORTHWESTERN EDGE OF GUAM'S
AREA OF RESPONSIBILITY (AOR), CENTERED NEAR 22N131E, HAS BEEN
DUBBED INVEST 98W BY THE JOINT TYPHOON WARNING CENTER. 98W EXISTS
ON THE SOUTHWESTERN EDGE OF A DECAYING STATIONARY FRONTAL BOUNDARY TO
THE EAST OF TAIWAN, WHICH EXTENDS EAST-NORTHEAST TO A LOW-PRESSURE
SYSTEM WELL BEYOND 25N137E. NUMEROUS SHOWERS AND SCATTERED
THUNDERSTORMS ARE SEEN WITHIN THE MOIST CONVERGENT FLOW WRAPPING INTO
98W ALONG ITS EASTERN FLANK, JUST SOUTH OF THE NEARLY-DISSIPATED
BAROCLINIC ZONE EXTENDING FROM IT. INVEST 98W LOOKS TO REMAIN WITHIN
THE REGION ONLY BRIEFLY, WITH MODEL GUIDANCE DEPICTING A NORTH TO
NORTH-NORTHWEST MOVEMENT ALONG 130E, EXITING NORTH AND WEST OF THE
AOR BY LATE TUESDAY MORNING. 98W THEN LOOKS TO MERGE WITH AN
EASTWARD-PROPAGATING MID-LATITUDE SYSTEM AROUND MIDWEEK.
EASTERN MICRONESIA...
A DISORGANIZED, UNSETTLED PATTERN CONTINUES ACROSS THE REGION.
POHNPEI SAW NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS THROUGHOUT
THE MORNING HOURS, DUE TO STRONG CONVERGENCE ALONG A NEARBY TRADE-
WIND TROUGH. THIS WAS SUPPORTED BY AN AREA OF DIVERGENCE ALOFT,
ASSOCIATED WITH A BROAD UPPER-LEVEL LOW CENTERED WELL NORTHEAST OF
POHNPEI, TO THE SOUTH OF WAKE ISLAND. HIMAWARI VISIBLE SATELLITE THIS
AFTERNOON SHOWS LINGERING WIDESPREAD CLOUD COVER ACROSS POHNPEI STATE,
WITH PATCHY STRATIFORM SHOWERS NEARBY. MUCH DRIER CONDITIONS PREVAIL
OVER KOSRAE AND MAJURO, WITH MOST OF THE SHOWERS FOCUSED WELL TO THE
NORTH OF KOSRAE, AND OVER THE NORTHEASTERN MARSHALL ISLANDS. NUMEROUS
SHOWERS ARE ALSO SEEN TO THE SOUTHWEST OF KOSRAE, NEAR AND SOUTH OF
THE EQUATOR, ASSOCIATED WITH AN INTERTROPICAL CONVERGENCE ZONE (ITCZ)
FRAGMENT OVER FAR SOUTHERN POHNPEI STATE.
THE UPPER-LEVEL LOW TO THE SOUTH OF WAKE ISLAND LOOKS TO SHIFT
SLIGHTLY WESTWARD OVER THE NEXT DAY OR SO AS IT EXTENDS TOWARD THE
WEST-SOUTHWEST. THE CHANGE IN ORIENTATION OF THE LOW, IN ADDITION TO
THE DEVELOPMENT OF AN UPPER-LEVEL HIGH TO ITS WEST NEAR THE
MARIANAS, LOOKS TO FOCUS STRONG UPPER-LEVEL DIVERGENCE OVER CHUUK AND
POHNPEI STATES OVER THE NEXT FEW DAYS. THIS LOOKS TO INTERACT WITH A
TROUGH AND CONVERGENCE BOUNDARY AT THE SURFACE, TO SUPPORT NUMEROUS
SHOWERS AND ISOLATED THUNDERSTORMS FOR POHNPEI AROUND TUESDAY AND
TUESDAY NIGHT. THE UPPER-LEVEL LOW LOOKS TO GRADUALLY OPEN INTO A
TROUGH, WHICH WILL LINGER AND WEAKEN THROUGHOUT THE REST OF THE WEEK.
MODEL GUIDANCE INDICATES AN UNSETTLED PATTERN WILL CONTINUE THROUGH
THE WEEK, WITH NUMEROUS TO WIDESPREAD SHOWERS FOCUSING FARTHER TO THE
WEST, MAINLY OVER CENTRAL MICRONESIA. MEANWHILE, AN ITCZ LOOKS TO
DEVELOP NEAR THE MARSHALLS BY THE END OF THE WEEK, WITH A SERIES OF
WEAK TROUGHS PROPAGATING WESTWARD ALONG IT. THESE FEATURES WILL
MAINTAIN A WET PATTERN ACROSS THE REGION, WITH AT LEAST SCATTERED
SHOWERS EXPECTED INTO THE END OF THE WEEK FOR ALL THREE FORECAST
POINTS.
BENIGN MARINE CONDITIONS ARE EXPECTED THROUGH THE WEEK. LATEST
ALTIMETRY DATA INDICATES COMBINED SEAS BETWEEN 5 AND 7 FEET ACROSS
MUCH OF THE REGION. MODELS DEPICT A GRADUAL RELAXATION OF THE EAST
TO NORTHEAST TRADE SWELL THROUGHOUT THE WEEK, ALLOWING SEAS TO
DIMINISH BY A FOOT OR TWO OVER THE NEXT SEVERAL DAYS.
WESTERN MICRONESIA...
THE MAIN WEATHER MAKERS FOR THE REGION ARE A BAND OF CONVERGENCE
BETWEEN CHUUK AND POHNPEI, A SECOND BAND OF CONVERGENCE NEAR YAP
PROPER, AND A TROUGH OVER SOUTHERN PALAU.
OVER SOUTHERN PALAU, AN EAST-TO-WEST ORIENTED TROUGH HAS SET UP AND
IS PRODUCING SCATTERED SHOWERS. MODEL GUIDANCE SUGGESTS THIS TROUGH
WILL MOVE THROUGH THE REGION OVER THE NEXT DAY OR SO. LOOKING FURTHER
OUT, A TRADE-WIND REGIME IS EXPECTED TO RETURN THROUGH NEXT WEEK.
NEAR YAP, THE CONVERGENCE BAND IS INTERACTING WITH A SUBTLE TROUGH
AND IS PRODUCING SCATTERED SHOWERS THAT IS EXPECTED TO BUILD INTO
WIDESPREAD SHOWERS WITH ISOLATED THUNDERSTORMS OVER THE EVENING AND
EARLY MORNING HOURS. THIS INTERACTION IS ANTICIPATED TO REMAIN IN THE
YAP PROPER AREA FOR A DAY OR TWO. THEN, A SERIES OF TROUGHS IS
EXPECTED TO PASS THROUGH THE BEGINNING OF NEXT WEEK, ANTICIPATED TO
BRING SCATTERED SHOWERS TO YAP.
MEANWHILE IN CHUUK, SATELLITE IMAGERY SHOWS TRADE-WIND CONVERGENCE
SHOWERS TO THE SOUTH OF WENO. SHOWERS ARE EXPECTED TO BUILD INTO
CHUUK'S COASTAL WATERS OVERNIGHT. THEN OVER THE WEEK, THE SHOWERS
AND TROUGHS THAT ARE AFFECTING POHNPEI NOW ARE EXPECTED TO MOVE INTO
WENO MAKING FOR A FAIRLY WET WEEK.
BENIGN MARINE CONDITIONS ARE EXPECTED TO CONTINUE THROUGH MUCH OF
THE UPCOMING WEEK. ALTIMETRY SHOWS 2 TO 4 FOOT SEAS AT PALAU AND YAP,
AND 4 TO 6 FEET AT CHUUK.
GUM WATCHES/WARNINGS/ADVISORIES
GU...HIGH RIP CURRENT RISK UNTIL 4 PM CHST THIS AFTERNOON FOR GUZ001.
MP...HIGH RIP CURRENT RISK UNTIL 4 PM CHST THIS AFTERNOON FOR MPZ001>003.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA/TROPICAL UPDATE: DOLL
MARIANAS: MESA
EAST MICRONESIA: DECOU
WEST MICRONESIA: BOWSHER
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