257
FXPQ50 PGUM 200809
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
609 PM CHST MON JUL 20 2026
MARIANAS SYNOPSIS
SATELLITE SHOWS PARTLY CLOUDY SKIES AND ISOLATED TO SCATTERED SHOWERS
OVER THE MARIANAS THIS EVENING. WINDS WERE HIGH ENOUGH TO PREVENT ANY
SIGNIFICANT ISLAND EFFECT SHOWERS TODAY. ALTIMETRY, BUOY, AND MODEL
DATA SUGGESTS COMBINED SEAS OF 2 TO 4 FEET ARE SLOWLY INCREASING AS
THE PRIMARY SOUTHWEST MONSOON SWELL BUILDS BACK IN.
DISCUSSION
A DEVELOPING MONSOON TROUGH TO THE SOUTHWEST OF THE MARIANAS IS
PUSHING OCCASIONALLY SCATTERED SHOWERS INTO THE REGION ALONG WITH
SOUTHEASTERLY WINDS. THIS DISTURBANCE IS EXPECTED TO KEEP ITS
DISTANCE AND KEEP THE MARIANAS DRY OVERALL FOR THE NEXT FEW DAYS.
GUAM MAY RECEIVE SLIGHTLY MORE RAINFALL DUE TO ITS CLOSER PROXIMITY
TO THE MONSOON FEATURE. LIGHT TO GENTLE WINDS MAY ALSO ALLOW FOR
ISLAND EFFECT SHOWERS FOR GUAM TOMORROW, THOUGH LIKELY REMAINING
ISOLATED TO OVER OR JUST OFFSHORE OF AGAT AND APRA HARBOR. ISOLATED
THUNDERSTORMS WILL BE POSSIBLE AS SOON AS TUESDAY NIGHT,
PARTICULARLY IF THE MONSOON TROUGH STRENGTHENS MORE THAN EXPECTED.
MODELS INDICATE THE TROUGH PUSHING AWAY TO THE WEST AND BEING
REPLACED BY A NEW WEAK TROUGH SOMETIME THURSDAY WHICH MAY BRING IN
MORE SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS TO THE MARIANAS.
MINOR ISLAND EFFECT REMAINS POSSIBLE FOR CENTRAL AND NORTHEAST GUAM
WEDNESDAY, POTENTIALLY BECOMING MORE SIGNIFICANT THURSDAY AND
SPREADING TO ALL ISLANDS AS MODELS INDICATE A FURTHER DECREASE IN
WINDS.
MARINE
LIGHT SOUTHEASTERLIES WILL BECOME EASTERLY LATE TONIGHT, ONLY
INCREASING TO LIGHT TO GENTLE DURING THE DAY TOMORROW. COMBINED SEAS
OF 3 TO 4 FEET MAY INCREASE SLIGHTLY STARTING TUESDAY NIGHT WITH AN
INCREASE IN SOUTHWEST MONSOON SWELL, POSSIBLY PEAKING WEDNESDAY. A
LOW RISK OF RIP CURRENTS WILL CONTINUE ALONG ALL REEFS BEFORE WEST
AND/OR SOUTH FACING REEFS POTENTIALLY BECOME MODERATE TUESDAY NIGHT.
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE POSSIBLE BY TUESDAY
NIGHT, WITH AT LEAST ISOLATED THUNDERSTORMS CONTINUING THROUGH THE
WEEKEND. THEREFORE, A MODERATE RISK OF LIGHTNING IS POSSIBLE TUESDAY
NIGHT AND CONTINUING THROUGH THE WEEKEND FOR ALL BEACHES.
EASTERN MICRONESIA
POHNPEI AND KOSRAE SIT ALONG THE FAR NORTHERN OUTSKIRTS OF A BROAD
BUFFER CIRCULATION CENTERED SOUTH OF THE EQUATOR. SATELLITE THIS
AFTERNOON SHOWS PATCHES OF SCATTERED SHOWERS RACING EASTWARD TO
SOUTHEASTWARD ACROSS POHNPEI AND KOSRAE COASTAL WATERS, ASSOCIATED
WITH CONVERGENT NORTHWESTERLY INFLOW INTO THE DISTANT BUFFER
CIRCULATION. TO THE EAST, PATCHY SCATTERED SHOWERS ARE SEEN ACROSS
EASTERN PORTIONS OF THE RMI WITHIN A WEAK SURFACE CIRCULATION LOCATED
JUST SOUTHEAST OF MAJURO. THIS CIRCULATION CONNECTS TO ANOTHER WEAK
DISTURBANCE TO THE NORTHEAST ACROSS THE DATE LINE, AND TO THE BROAD
MONSOON TROUGH THAT EXTENDS ACROSS MUCH OF MICRONESIA. THESE FEATURES
WILL MAINTAIN SCATTERED SHOWERS IN THE FORECAST FOR POHNPEI, KOSRAE,
AND MAJURO THROUGH TUESDAY, BEFORE A QUIET DOLDRUM-LIKE PATTERN SETS
UP AROUND TUESDAY NIGHT THROUGH THURSDAY. WETTER CONDITIONS RESUME
TOWARD THE END OF THE WEEK, MAINLY FOR POHNPEI AND KOSRAE, AS
CONVERGENCE INCREASES ACROSS THE AREA ALONG THE FAR NORTHERN EDGE OF
THE NORTHWARD-LIFTING BUFFER CIRCULATION. ALTIMETRY DATA SHOWS
COMBINED SEAS BETWEEN 3 AND 6 FEET ACROSS MUCH OF THE REGION,
COMPRISED MAINLY OF A SOUTHEAST SWELL EMANATING FROM DISTANT
FEATURES IN THE SOUTHERN HEMISPHERE, WITH A LIGHT, SECONDARY WEST TO
SOUTH-SOUTHWEST SWELL. SEAS MAY SEE A GRADUAL, SLIGHT DIMINISHING BY
THE END OF THE WEEK AS THESE SWELLS SUBSIDE.
WESTERN MICRONESIA
FOR PALAU AND YAP, A SPECIAL WEATHER STATEMENT REMAINS IN EFFECT
FOR THE DEVELOPING MONSOON PATTERN. THIS PATTERN IS PRODUCING UP TO
FRESH TO STRONG WINDS OVER THE NEXT SEVERAL DAYS. NUMEROUS TO
WIDESPREAD LOCALLY HEAVY SHOWERS ARE TO BE EXPECTED THIS WEEK. MODEL
GUIDANCE SUGGESTS 3 TO 5 INCHES THROUGH THE MIDDLE OF THE WEEK, AND
AN ADDITIONAL 2 TO 4 INCHES THROUGH THE LATTER HALF OF THE WEEK,
TOTALING 5 TO 9 INCHES BY THE WEEKEND. AT THIS TIME LANDSLIDES
POTENTIAL IS LOW BUT NOT ZERO. THIS MONSOON PATTERN WILL KEEP CHOPPY
SEAS FOR THE SEAS NEAR PALAU AND YAP. SEA CONDITIONS ARE EXPECTED TO
BE NEAR SMALL CRAFT ADVISORY CRITERIA OF 22 KNOTS, HOWEVER THE ACTUAL
SEA HEIGHT IS EXPECTED TO BUILD TO 6 TO 8 FEET. THE PEAK SEA
CONDITIONS MAY ARRIVE AROUND THURSDAY. THE MONSOON PATTERN MAY BEGIN
TO RELAX AS EARLY AS SATURDAY.
FOR CHUUK, THE REMAINS OF WHAT WAS INVEST 90W ARE EXPECTED TO BRING
IN ONE MORE INFLUX OF MOISTURE TO THE LAGOON. TO REFLECT THIS
NUMEROUS SHOWERS ARE EXPECTED FOR TUESDAY. THIS IS EXPECTED TO BE THE
LAST HURRAH. LESS THAN AN INCH OF RAIN IS ANTICIPATED. THEN, A DRIER
WEATHER PATTERN IS EXPECTED TO SET UP. SEAS NEAR CHUUK ARE EXPECTED
TO REMAIN BENIGN AT 3 TO 4 FEET THROUGH THE WEEK.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: OGLE/AYDLETT
EAST MICRONESIA: DAVID
WEST MICRONESIA: BOWSHER
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