036
FXPQ50 PGUM 191924
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
524 AM CHST THU NOV 20 2025
MARIANAS UPDATE
FORECAST REMAINS UNCHANGED. A TRADE-WIND SURGE CAUSED BY INCREASING
PRESSURE GRADIENT BETWEEN THE TROPICS AND THE MID-LATITUDES IS STILL
EXPECTED TO BRING BREEZY TO POTENTIALLY WINDY CONDITIONS TO THE
MARIANAS BEGINNING FRIDAY, WHICH MAY PRODUCE SEAS HAZARDOUS TO SMALL
CRAFT. A SIGNIFICANT EASTERLY SWELL PRODUCED BY A TRADE-WIND SURGE
UPSTREAM IS GENERATING HIGHER SURF ACROSS THE MARIANAS SOONER THAN
PREVIOUSLY EXPECTED, WHICH IN TURN IS PRODUCING A HIGH RIP CURRENT
RISK ALONG EAST FACING REEFS. AS SUCH, A HIGH RIP CURRENT RISK
STATEMENT HAS BEEN ISSUED.
EASTERN MICRONESIA UPDATE
A CONVECTIVELY ACTIVE INTERTROPICAL CONVERGENCE ZONE (ITCZ)
CONTINUES TO BE THE PRIMARY WEATHER MAKER ACROSS EASTERN MICRONESIA.
INCREASED SHOWERS AND GUSTS IN TODAY'S FORECAST FOR POHNPEI AND
KOSRAE DUE TO FURTHER DETERIORATION IN WEATHER CONDITIONS EXPECTED,
AS INDICATED BY RECENT SATELLITE IMAGERY, SCATTEROMETER PASSES AND
MODEL GUIDANCE TREND. WHILE SEAS ARE EXPECTED TO REMAIN JUST BELOW
LEVELS HAZARDOUS TO SMALL CRAFT NEAR POHNPEI AND MAJURO, SEAS WILL
CONTINUE TO BE CHOPPY THE NEXT SEVERAL DAYS AS TRADE SWELL REMAINS
ELEVATED, AND A BACKGROUND NORTHERLY SWELL MIXES IN.
WESTERN MICRONESIA UPDATE
FORECAST REMAINS UNCHANGED. A LEADING EDGE OF THE AFOREMENTIONED ITCZ
WILL CONTINUE TO MOVE WEST UNTIL IT CLASHES WITH THE NET SITUATED
ACROSS WESTERN MICRONESIA, WHICH WILL BRING INCREASING SHOWERS AND
THUNDERSTORMS TO CHUUK BEGINNING TODAY, AND TO YAP AND PALAU AS EARLY
AS FRIDAY. THE POTENTIAL DISTURBANCE MENTIONED IN THE PREVIOUS
DISCUSSION CONTINUES TO BE A CONCERN COMING INTO THE WEEKEND AS IT
ATTEMPTS TO FORM WITHIN A NORTHWARD-MOVING NET, BUT TIMING OF SHOWERS
AND THUNDERSTORMS DURING PASSAGE CONTINUES TO BE HIGHLY UNCERTAIN.
PREV DISCUSSION
/ISSUED 607 PM CHST WED NOV 19 2025/
MARIANAS SYNOPSIS...
SATELLITE IMAGERY SHOWS PARTLY CLOUDY SKIES OVER THE MARIANAS AND A
FEW ISOLATED SHOWERS MOVING INTO THE WATERS OF GUAM AND SAIPAN.
ALTIMETRY SHOWS COMBINED SEAS OF 6 TO 7 FEET, WHILE BUOY DATA ALSO
SHOWS 6 TO 7 FOOT SEA HEIGHTS. A HIGH RISK OF RIP CURRENTS WAS
ISSUED FOR EAST FACING REEFS OF THE MARIANAS, STARTING THURSDAY
NIGHT.
DISCUSSION...
OVERALL NOT MANY CHANGES WERE NEEDED TO THE FORECAST. PLEASANT BUT
WINDIER WEATHER IS EXPECTED FOR TONIGHT AND TOMORROW. THEN A SURFACE
TROUGH THAT IS BETWEEN THE MARIANAS AND WAKE ISLAND WILL BEGIN TO
PUSH INTO THE REGION AND IS PRODUCING ONLY A SMALL AMOUNT OF
CONVECTION. OVER THE NEXT 24 HOURS OR SO, THIS TROUGH IS EXPECTED TO
GAIN SOME UPPER-LEVEL SUPPORT AS THE TWO UPPER-LEVEL LOWS NEAR
POHNPEI ARE EXPECTED TO MERGE AND EXPAND. SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS ARE EXPECTED ONCE THESE TWO FEATURES START
INTERACTING, WITH THE HIGHEST POPS (PROBABILITY OF PRECIPITATION)
OVER GUAM. THE DOMAIN WAS LEFT SPLIT DUE TO THE DIFFERENCE IN POPS
AND WINDS OVER THE ISLANDS. ONCE THESE FEATURES PASS, PLEASANT BUT
WINDIER CONDITIONS ARE ANTICIPATED TO RETURN.
MARINE/SURF...
MODERATE TO FRESH TRADE WINDS ARE EXPECTED THROUGHOUT THE WEEK.
COMBINED SEAS OF 6 TO 8 FEET ARE EXPECTED TO INCREASE TO BETWEEN
7 AND NEAR 10 FEET BY FRIDAY. WITH WINDS NEAR 22 KNOTS AND SEAS
APPROACHING 10 FEET, THIS INCOMING TRADE SWELL WILL PUSH SEA
CONDITIONS CLOSE TO THE THRESHOLD OF A SMALL CRAFT ADVISORY.
REGARDLESS, SEAS ARE EXPECTED TO BE VERY CHOPPY. THERE WILL BE A
MODERATE RISK OF RIP CURRENTS ALONG NORTH AND EAST FACING REEFS OF
THE MARIANAS THROUGH THURSDAY. TRADE-WIND SWELL AND SURF WILL THEN
BUILD THURSDAY NIGHT AND FRIDAY CAUSING THE RISK OF RIP CURRENTS TO
BECOME HIGH ALONG EAST FACING REEFS. THIS RISK IS EXPECTED TO LINGER
THROUGH AT LEAST THE MIDDLE OF NEXT WEEK.
EASTERN MICRONESIA...
THERE'S TWO MAIN ITEMS OF INTEREST TO KEEP AN EYE ON FOR THE NEXT
SEVERAL DAYS. THE FIRST WILL BE A BUILDING NORTHEASTERLY SWELL,
COURTESY OF AN AREA OF ENHANCED TRADES (NEAR 20 KNOTS SUSTAINED)
CENTERED TO THE NORTH BETWEEN 12N AND 17N FROM 165E TO THE DATE LINE.
THE MODELS SHOW THESE HIGHER WAVE HEIGHTS (MAINLY VIA INCREASED WIND
WAVES) SHOULD ARRIVE IN THE REGION STARTING FRIDAY, LASTING FOR ABOUT
36 HOURS, IF MODEL TRENDS HOLD. THIS COULD POTENTIALLY CREATE SOME
SURF CONCERNS, ESPECIALLY AT KOSRAE, WHERE WE THOUGHT ABOUT HOISTING
A HEADLINE. HOWEVER, WE OPTED TO GIVE IT ANOTHER 12 TO 24 HOURS TO
SEE IF HOW THE WIND FIELDS EVOLVE TO THE NORTH VIA SCATTEROMETER
DATA, AND THE ASSOCIATED WAVE HEIGHTS FORECAST TRENDS.
THE OTHER CONCERN IS THE ITCZ (INTER-TROPICAL CONVERGENCE ZONE) IS
FORECAST TO STRENGTHEN THROUGH THE WEEKEND, BEFORE THE EASTERN EXTENT
OF IT WEAKENS SOME EARLY NEXT WEEK. GIVEN A RECENT UPTICK IN
CONVECTION AREA-WIDE, BUMPED UP POPS AT POHNPEI AND KOSRAE FOR THE
NEXT 36 HOURS. AFTER THAT, SCATTERED SHOWERS/CHANCE PROBABILITIES
WILL BE HIGHEST AT POHNPEI, LOWEST AT MAJURO EARLY NEXT WEEK AS THE
MODELS SHOW THE TAIL END OF THE ITCZ WEAKENING.
MAINLY GENTLE TO MODERATE WINDS ARE ANTICIPATED THE NEXT SEVERAL
DAYS, BUT THEY MAY BECOME STRONG FROM TIME TO TIME. SEAS WILL
INCREASE A FOOT OR SO FRIDAY THROUGH SATURDAY, BEFORE DECREASING A
FOOT EARLY NEXT WEEK.
WESTERN MICRONESIA...
SATELLITE EARLY THIS EVENING DEPICTS A MOSTLY DRY TRADE-WIND REGIME
ACROSS THE REGION, WITH MOST OF THE SHOWERS ALONG THE NEAR-
EQUATORIAL TROUGH (NET) NOW FOCUSED FURTHER SOUTH OF KOROR COASTAL
WATERS, EXTENDING EAST-SOUTHEAST ACROSS THE SOUTHERN REPUBLIC OF
PALAU AND SOUTHERN YAP STATE. LOW-END SCATTERED SHOWERS ARE SEEN NEAR
AND EAST OF CHUUK. SHOWERS ARE EXPECTED TO SEE AN INCREASING TREND
FOR CHUUK LATE OVERNIGHT THROUGH THE END OF THE WEEK, AS A BROAD
TROUGH, A REMNANT FRAGMENT OF THE ITCZ, GRADUALLY BUILDS INTO THE
AREA FROM OVER POHNPEI AND KOSRAE. LATEST MODEL RUNS HAVE BEEN
SLOWER TO INCREASE SHOWERS NEAR CHUUK, AND GIVEN CURRENT SATELLITE
TRENDS, SHOWERS WERE DECREASED SLIGHTLY FOR TONIGHT. SHOWERS ARE
STILL EXPECTED TO BECOME NUMEROUS WITH LOCALLY HEAVY RAINFALL
POSSIBLE, AND THIS HAS BEEN PUSHED BACK TO THURSDAY NIGHT AND FRIDAY
IN THE FORECAST TO BETTER ALIGN WITH CURRENT MODEL TRENDS. SHOWERS
WILL THEN DIMINISH THROUGH THE WEEKEND AS THE DISTURBANCE SHIFTS
WESTWARD TOWARD YAP PROPER.
ALTHOUGH FAIRLY DRY WEATHER WILL CONTINUE FOR THE NEXT DAY OR SO, YAP
WILL SEE AN INCREASINGLY WET PATTERN FROM FRIDAY THROUGH EARLY NEXT
WEEK AS THE BROAD TROUGH MOVES WEST INTO THE REGION FROM OVER CHUUK,
INTERACTING WITH THE NET TO THE SOUTH. DETERMINISTIC AND ENSEMBLE
MODEL GUIDANCE DEPICT THIS INTERACTION FORMING A WEAK, ELONGATED
CIRCULATION WITHIN THE NET, WITH THE GFS TAKING THE MOST AGGRESSIVE
APPROACH, DEVELOPING A TROPICAL DEPRESSION OR EVEN WEAK TROPICAL
STORM LATE IN THE WEEKEND AFTER THE DISTURBANCE HAS MOVED WEST OF THE
REGION. THIS SOLUTION REMAINS AN OUTLIER FOR NOW, BUT THE OVERALL
PATTERN LOOKS TO BRING THE DEVELOPING DISTURBANCE WEST TO
NORTHWESTWARD NEAR YAP AND PALAU LATE IN THE WEEK THROUGH THE
WEEKEND, BRINGING WET CONDITIONS AND GUSTY WINDS, THEN MOVING INTO
THE PHILIPPINES EARLY NEXT WEEK. FOR NOW, YAP LOOKS TO RECEIVE MOST
OF THE SHOWERS AND THUNDERSTORMS, WITH NUMEROUS SHOWERS IN THE
FORECAST SATURDAY THROUGH SUNDAY, AND LOCALLY HEAVY SHOWERS WILL BE
POSSIBLE AT TIMES. THE TIMING AND POPS WILL LIKELY SEE A LOT OF
REFINEMENT OVER THE NEXT FEW DAYS AS UNCERTAINTY DECREASES WITH THE
DEVELOPING PATTERN.
LATEST ALTIMETRY DATA INDICATES COMBINED SEAS OF GENERALLY 4 TO 6
FEET ACROSS THE REGION, INCREASING TO AROUND 7 FEET JUST NORTHEAST OF
CHUUK. SATELLITE SCATTEROMETRY INDICATES MODERATE TO FRESH WINDS
ACROSS MUCH OF THE REGION, WITH MORE MODERATE WINDS NEAR PALAU.
ELEVATED TRADE WINDS AND TRADE SWELL WILL MAINTAIN FAIRLY CHOPPY SEAS
FOR YAP AND CHUUK THROUGH THE WEEKEND. CHUUK WILL SEE AN INCREASE IN
SEAS AROUND FRIDAY AS A PULSE OF ELEVATED LONG-PERIOD NORTH TO
NORTHEAST SWELL, EMANATING FROM DISTANT STRONG MID-LATITUDE SYSTEMS
FAR TO THE NORTHEAST AND REINFORCED BY ELEVATED TRADE SWELL, ENTERS
THE AREA BEFORE DIMINISHING EARLY NEXT WEEK. THE INCOMING SWELL WILL
BE MONITORED FOR ANY POSSIBILITY OF GENERATING HAZARDOUS SURF ALONG
NORTH FACING REEFS OF CHUUK THIS WEEKEND.
GUM WATCHES/WARNINGS/ADVISORIES
GU...HIGH RIP CURRENT RISK FROM THURSDAY EVENING THROUGH WEDNESDAY
AFTERNOON FOR GUZ001.
MP...HIGH RIP CURRENT RISK FROM THURSDAY EVENING THROUGH WEDNESDAY
AFTERNOON FOR MPZ001>003.
MARIANAS WATERS...NONE.
MARIANAS/EAST/WEST MICRONESIA UPDATE: MONTVILA
MARIANAS: BOWSHER
EAST MICRONESIA: DOLL
WEST MICRONESIA: DECOU
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