173
FXPQ50 PGUM 191853
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
453 AM CHST MON JUL 20 2026
MARIANAS UPDATE
THE PROXIMITY OF SMALL POCKETS OF SHOWERS DEVELOPING ALONG THE
NORTHERN PERIPHERIES OF THE MONSOON TROUGH GIVES HIGHER PROBABILITY
FOR SHOWERS TO ARRIVE SOONER, SO BROUGHT IN SCATTERED SHOWERS TO
BEFORE NOON FOR GUAM AND AFTERNOON ELSEWHERE TODAY. OTHERWISE, THE
WEATHER FORECAST AND MARINE FORECAST REMAIN UNCHANGED.
EASTERN MICRONESIA UPDATE
SHOWERS HAVE BEEN STRUGGLING TO BUILD ACROSS THE REGION OVERNIGHT,
BUT CONFIDENCE REMAINS IN INCREASING SHOWER COVERAGE DURING THE PEAK
DAYTIME HEATING. AS SUCH, DECREASED SHOWER COVERAGE SLIGHTLY FOR
POHNPEI AND DOWN TO JUST ISOLATED SHOWERS NEAR KOSRAE, AS THUNDER IS
NO LONGER LIKELY IN THE VICINITY. MAJURO'S FORECAST REMAINS
UNCHANGED, AS THE NEARBY DISTURBANCE BRINGS ON-AND-OFF SHOWERS FOR
MUCH OF TODAY. OTHER THAN THAT, THE MARINE FORECAST REMAINS UNCHANGED
ACROSS ALL THREE COASTAL WATERS.
WESTERN MICRONESIA UPDATE
THE FORECAST REMAINS UNCHANGED AT ALL THREE LOCATIONS. A MONSOONAL
SURGE WILL CONTINUE TO BUILD ACROSS THE REGION, BRINGING HEAVY AND
INTENSE SHOWERS WITH STRONG TO NEAR GALE GUSTS TO PALAU AND YAP FOR
MUCH OF TODAY, WITH A CHANCE FOR HEAVIER SHOWERS DEVELOPING AT CHUUK.
THE MARINE FORECAST REMAINS UNCHANGED OVERNIGHT AS WELL.
PREV DISCUSSION
/ISSUED 754 PM CHST SUN JUL 19 2026/
MARIANAS SYNOPSIS...
SATELLITE SHOWS PARTLY CLOUDY SKIES AND ISOLATED SHOWERS OVER MUCH OF
THE MARIANAS COASTAL WATERS THIS EVENING, WITH MOSTLY CLOUDY SKIES
LINGERING OVER GUAM FROM PRIOR ISLAND-EFFECT SHOWERS. ALTIMETRY AND
TANAPAG BUOY DATA SHOW COMBINED SEAS BETWEEN 2 AND 4 FEET, COMPRISED
OF A PRIMARY SOUTHWEST SWELL AND SECONDARY NORTHEAST TRADE SWELL.
DISCUSSION...
THE WEATHER PATTERN ACROSS THE MARIANAS IS INFLUENCED BY A VERY
BROAD TROUGH AND EMBEDDED WEAK LOW TO THE WEST, THE REMNANTS OF
INVEST 90W TO THE EAST-SOUTHEAST, AND A DEVELOPING MONSOON PATTERN
ACROSS WESTERN MICRONESIA. SCATTEROMETRY FROM THIS MORNING SHOWS AN
AREA OF LIGHT TO GENTLE SOUTH-SOUTHWEST TO SOUTH WINDS ACROSS THE
COASTAL WATERS. WINDS REMAIN LIGHT TO GENTLE TONIGHT AS THEY
GRADUALLY SHIFT SOUTHEASTERLY, INCREASING SLIGHTLY TOMORROW, WHICH
WILL PUSH MORE OF THE ISLAND-EFFECT SHOWERS OFF-SHORE IN THE
AFTERNOON. MODELS THEN DEPICT A COMPLEX PATTERN UNFOLDING OVER THE
NEXT FEW DAYS AS THE MONSOON PATTERN STRENGTHENS SOUTH OF THE
ISLANDS, AND A TROUGH LOOKS TO APPROACH FROM THE NORTHEAST. THESE
FEATURES WILL INTERACT TO GENERATE SCATTERED SHOWERS AROUND TUESDAY
NIGHT AND WEDNESDAY, AS THE OVERALL MONSOON PATTERN BEGINS TO LIFT
NORTHWEST. WITHIN THE EASTERN PERIPHERY OF THIS MONSOON PATTERN,
MODEL GUIDANCE DEPICTS THE FORMATION OF A BROAD DISTURBANCE SOUTH TO
SOUTHWEST OF THE MARIANAS IN THE LATTER HALF OF THE WEEK. AS THIS
FEATURE MOVES NORTHWEST AND PASSES NEAR OR SOUTHWEST OF THE AREA, AT
LEAST SCATTERED SHOWERS ARE EXPECTED, CONTINUING INTO THE WEEKEND.
THERE IS A LARGE DEGREE OF UNCERTAINTY IN HOW THE PATTERN WILL EVOLVE
IN THE COMING DAYS. IF THIS FEATURE DEVELOPS OR PASSES CLOSER TO THE
ISLANDS, SHOWERS MAY BECOME NUMEROUS TO WIDESPREAD AT TIMES, AND
WINDS COULD BECOME BREEZY AND GUSTY. FOR NOW, MODELS DEPICT THE
DISTURBANCE DEVELOPING FARTHER WEST OF THE MARIANAS, KEEPING THE
ISLANDS ALONG ITS EASTERN PERIPHERY.
MARINE/SURF...
LIGHT TO GENTLE SOUTH TO SOUTHEAST WINDS WILL PREVAIL ACROSS THE
MARIANAS THROUGH THIS WEEK, BECOMING LIGHT TO MODERATE THURSDAY.
COMBINED SEAS OF 3 TO 4 FEET WILL PERSIST FOR MUCH OF THE UPCOMING
WEEK, INCREASING BY A FOOT OR SO IN THE LATTER HALF OF THE WEEK
WITH AN INCREASE IN SOUTHWEST MONSOON SWELL. THE DEVELOPING MONSOON
PATTERN TO THE SOUTH WILL BRING INCREASING CHANCES FOR SHOWERS AND
THUNDERSTORMS TOWARD THE END OF THE WEEK. MEANWHILE, A LOW RISK OF
RIP CURRENTS IS EXPECTED TO CONTINUE ALONG ALL REEFS FOR THE NEXT FEW
DAYS. BY THE END OF THE WEEK, THE RIP RISK MAY INCREASE ONCE AGAIN
TO MODERATE DUE TO THE INCREASE IN SOUTHWEST SWELL.
TROPICAL SYSTEMS...
A TROPICAL DISTURBANCE, INVEST 90W, LOCATED NORTH-NORTHEAST OF CHUUK
NEAR 12N153E, CONTINUED TO WEAKEN OVER THE COURSE OF THE DAY AND
JOINT TYPHOON WARNING CENTER (JTWC) CLOSED THE INVEST EARLIER THIS
AFTERNOON. REMNANTS OF 90W WILL CONTINUE TO BLEND IN WITH THE
OVERARCHING MONSOON PATTERN ACROSS WESTERN MICRONESIA.
EASTERN MICRONESIA...
A BUFFER CIRCULATION SOUTH OF THE EQUATOR HAS ABSORBED ALL OF THE
ENERGY FROM WHAT USE TO BE INVEST 90W, WITH THAT CIRCULATION HAVING
LOST ALL OF ITS DEEPER (STRONGER) CONVECTION. AS A RESULT, THE MID
SHIFT'S TREND OF REDUCED RAINFALL POTENTIAL LOOKS GOOD, AND THIS WAS
CONTINUED THROUGH THE FORECAST, WITH NO MENTION OF HEAVY RAINFALL.
SHOWERS WILL STILL BECOME SCATTERED IN COVERAGE FROM TIME TO TIME,
BUT THE SYNOPTIC PATTERN IS CHANGING, WITH WHAT LOOKS LIKE A MONSOON
GYRE SETUP DEVELOPING NORTHWEST OF THE REGION. THIS COULD STILL SEND
SOME SCATTERED SHOWERS TOWARDS POHNPEI, BUT FOR NOW JUST SHOWERS IN
THE SOUTHWEST TO WESTERLY FLOW LOOKS TO BE THE MAIN MECHANISM FOR
CONVECTIVE DEVELOPMENT THE NEXT FEW DAYS, POSSIBLY LONGER.
SEAS LOOK TO REMAIN IN THE 4 TO 6 FOOT RANGE, SLIGHTLY LOWER EAST OF
THE ATOLLS AS THEY DISRUPT WAVE FETCH LENGTH. MAINLY LIGHT TO GENTLE
WINDS WILL PERSIST WELL INTO NEXT WEEK.
WESTERN MICRONESIA...
INVEST 90W HAS SHIFTED NORTH OF CHUUK STATE AND HAS WEAKENED. FOR
THIS REASON, JTWC HAS CLOSED THIS INVEST. PERIODS OF LOCALLY HEAVY
SHOWERS WILL CONTINUE TO BE ASSOCIATED WITH A MONSOON PATTERN ACROSS
WESTERN MICRONESIA OVER THE NEXT FEW DAYS. AN AREA OF DIFFLUENCE
BETWEEN THE REMNANTS OF 90W AND A BROAD CIRCULATION SOUTH OF THE
EQUATOR IS FRAGMENTING THE LEADING EDGE OF THE MONSOON PATTERN OVER
CHUUK STATE THIS EVENING. STILL, LIGHT TO MODERATE WESTERLY WINDS AND
SCATTERED TO NUMEROUS SHOWERS CONTINUE THROUGH MIDWEEK DUE TO THE
PROXIMITY OF THE MONSOON TROUGH. THE LAST SPECIAL WEATHER STATEMENT
WAS ISSUED THIS EVENING TO CONCLUDE RELATED IMPACTS WITH 90W.
FOR YAP AND PALAU, A SPECIAL WEATHER STATEMENT WAS ISSUED FOR THE
DEVELOPING MONSOON PATTERN IN THE REGION. THIS PATTERN IS PRODUCING
FRESH WEST-SOUTHWESTERLIES AND A SURGE OF NUMEROUS TO WIDESPREAD
LOCALLY HEAVY SHOWERS AND THUNDERSTORMS, ACCOMPANIED BY STRONG TO
NEAR-GALE GUSTS. THERE IS SOME INDICATION THAT A BROAD MONSOON
DISTURBANCE WILL GRADUALLY FORM TO THE NORTH-NORTHEAST, WHICH COULD
LEAD TO AN INTENSIFIED MONSOON SURGE ACROSS PALAU AND YAP. MODEL
TRENDS INDICATE 3 TO 5 INCHES OF RAINFALL THROUGH MIDWEEK. THERE IS
AN ESTIMATED 2 TO 4 INCHES OF ADDITIONAL RAINFALL IN THE LATTER HALF
OF THE WEEK, WITH HIGHER AMOUNTS POSSIBLE DEPENDING ON WHEN THE
MONSOON TROUGH BEGINS TO SHIFT NORTHWARD. PROLONGED PERIODS OF HEAVY
DOWNPOURS MAY PRODUCE MINOR FLOODING AT TIMES.
ALTIMETRY AND YAP BUOY DATA REVEAL COMBINED SEAS REMAIN AROUND 4 TO
6 FEET, LARGELY COMPRISED OF WESTERLY SWELL ACROSS THE REGION, ALONG
WITH LIGHT SOUTH-SOUTHEAST SWELL PUSHING INTO CHUUK STATE. DEPENDING
ON 90W'S DEVELOPMENT, THE MONSOONAL FLOW MAY STRENGTHEN SLIGHTLY,
BUILDING SEAS TO 5 TO 7 FEET NEXT WEEK. FOR YAP AND PALAU, CHOPPY
SEAS FROM LOCALIZED WIND WAVES AND A DEVELOPING WESTERLY SWELL ARE
ALREADY CREATING CHALLENGING CONDITIONS FOR SMALL CRAFT. WITH THE
MONSOON PATTERN GRADUALLY STRENGTHENING OVER THE NEXT FEW DAYS,
SUSTAINED WINDS LOOK TO EXCEED HAZARDOUS LEVELS OF 22 KT AROUND
TUESDAY NIGHT. THIS AND PERSISTENT WESTERLY SWELL AIM TO BUILD
COMBINED SEAS TO 5 TO 7 FEET BY MIDWEEK AND MAINTAIN MODERATE TO
ELEVATED SURF ALONG WEST-FACING REEFS OVER THIS WEEK.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: MONTVILA
MARIANAS: DECOU
EAST MICRONESIA: DOLL
WEST MICRONESIA: CRUZ
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