824
FXPQ50 PGUM 271938
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
538 AM CHST MON SEP 28 2026
MARIANAS UPDATE
SATELLITE IMAGERY AND RADAR SHOW PARTLY CLOUDY SKIES WITH SCATTERED
SHOWERS ACROSS THE MARIANAS. ALTIMETRY SHOWS COMBINED SEAS AROUND 3
FEET.
THE MAIN CHANGE WITH THIS FORECAST PACKAGE WAS TO INCREASE SHOWER
COVERAGE TO SCATTERED ACROSS THE MARIANAS. SCATTERED SHOWERS ARE SEEN
THIS MORNING ON THE EAST SIDE OF A WEAK SURFACE CIRCULATION. ISOLATED
THUNDERSTORMS ARE EXPECTED LATER THIS MORNING AS SHOWERS INTENSIFY.
THESE SHOWERS AND THUNDERSTORMS COULD PRODUCE LOCALLY HEAVY RAINFALL.
SHOWER COVERAGE IS EXPECTED TO FALL TO ISOLATED TONIGHT. NO CHANGES
WERE MADE TO THE REST OF THE FORECAST PACKAGE.
NO CHANGES WERE MADE WITH THE MARINE FORECAST. COMBINED SEAS WILL BE
SLOW TO RISE DURING THE FIRST HALF OF THE WEEK, GENERALLY REMAINING
AROUND 3 FEET. BY WEDNESDAY, SEAS LOOK TO QUICKLY RISE AND BECOME
HAZARDOUS TO SMALL CRAFT BY THURSDAY.
TROPICAL UPDATE
THE JOINT TYPHOON WARNING CENTER HAS DESIGNATED A TROPICAL
DISTURBANCE TO THE EAST OF THE MARIANAS AS INVEST 93W. INVEST 93W IS
CURRENTLY RATED SUB-LOW WHICH MEANS TC DEVELOPMENT IS NOT EXPECTED
OVER THE NEXT FEW DAYS. 93W REMAINS DISORGANIZED AS THE SURFACE
CIRCULATION REMAINS ELONGATED. INVEST 93W DOES HAVE A SONG MID-
LEVEL CIRCULATION LEADING TO ENHANCED CONVECTION. RESIDENTS ACROSS
THE MARIANAS SHOULD CONTINUE TO MONITOR THIS DEVELOPING WAVE OVER THE
COMING DAYS.
EASTERN MICRONESIA UPDATE
SATELLITE IMAGERY SHOWS PARTLY TO MOSTLY CLOUDY SKIES ACROSS EASTERN
MICRONESIA. COMBINED SEAS ARE BETWEEN 5 AND 8 FEET ACROSS THE REGION.
NO CHANGES WERE MADE WITH THIS FORECAST PACKAGE. THE MONSOON TROUGH
HAS SHIFTED NORTH OF THE REGION, KEEPING THE HEAVIEST SHOWERS REFINED
TO THE FAR NORTHERN MARSHALL ISLANDS. A FEW SCATTERED SHOWERS WILL BE
POSSIBLE TODAY FOR POHNPEI AND KOSRAE.
NO CHANGES WERE MADE TO THE MARINE FORECAST. COMBINED SEAS BETWEEN 5
AND 8 FEET ARE EXPECTED TO CONTINUE THROUGH THE PERIOD.
WESTERN MICRONESIA UPDATE
SATELLITE IMAGERY SHOWS SCATTERED SHOWERS ACROSS PALAU AND YAP, AND
ISOLATED SHOWERS ACROSS CHUUK. COMBINED SEAS ARE BETWEEN 3 AND 6
FEET.
NO CHANGES WERE MADE WITH THE WESTERN MICRONESIA FORECAST THIS
MORNING. SATELLITE SHOWS A LINE OF SHOWERS AND THUNDERSTORMS
ENTERING THE NORTHERN COASTAL WATERS OF YAP AND PALAU. THESE LINES OF
SHOWERS ARE EXPECTED TO STRENGTHEN THIS MORNING, POTENTIALLY BRINGING
LOCALLY HEAVY SHOWERS TO PORTIONS OF YAP AND PALAU. ISOLATED SHOWERS
ARE EXPECTED TODAY AT CHUUK.
COMBINED SEAS ARE BETWEEN 3 AND 6 FEET. LITTLE TO NO CHANGE IS
EXPECTED THROUGH THE FORECAST ACROSS WESTERN MICRONESIA.
PREV DISCUSSION
/ISSUED 607 PM CHST SUN SEP 27 2026/
MARIANAS SYNOPSIS...
ISOLATED SHOWERS ARE VISIBLE FROM RADAR AND SATELLITE ACROSS THE
MARIANAS THIS EVENING WITH SOME SCATTERED SHOWERS JUST OUTSIDE THE
COASTAL WATERS MOVING INTO TINIAN AND SAIPAN. WINDS ARE LIGHT AND
VARIABLE FOR GUAM AND ROTA AND LIGHT TO GENTLE FROM THE EAST FOR
TINIAN AND SAIPAN. MODELS AND OBSERVATIONS INDICATE COMBINED SEAS OF
AROUND 3 FEET.
DISCUSSION...
ISOLATED SHOWERS AND THUNDERSTORMS ARE EXPECTED TONIGHT AND TOMORROW
MORNING FOR GUAM AND ROTA WITH SHOWER COVERAGE BECOMING SCATTERED
OVER TINIAN AND SAIPAN. SHOWER COVERAGE WILL BECOME SCATTERED FOR ALL
ISLANDS BY TOMORROW AFTERNOON AS LIGHT AND VARIABLE WINDS ALLOW
ISLAND EFFECT SHOWERS TO DEVELOP OVER AT LEAST GUAM AND ROTA. MONDAY
NIGHT THROUGH WEDNESDAY, DRY WEATHER WILL PERSIST WITH VERY GRADUALLY
INCREASING WESTERLIES PUSHING ANY ISLAND EFFECT SHOWERS OFFSHORE. BY
WEDNESDAY NIGHT, A DEVELOPING TROPICAL DISTURBANCE TO THE NORTHEAST
WILL BRING INCREASED MOISTURE INTO THE MARIANAS WITH BREEZY
CONDITIONS DEVELOPING THURSDAY NIGHT OR FRIDAY. THIS DISTURBANCE WILL
BE MONITORED CLOSELY FOR POTENTIAL IMPACTS TO THE MARIANAS. MODELS
CURRENTLY INDICATE IT DRIFTING NORTH OF THE MARIANAS WITH A MONSOON
TAIL BRINGING POTENTIALLY HEAVY PRECIPITATION, PARTICULARLY TO
TINIAN AND SAIPAN. HOWEVER, HIGH UNCERTAINTY REMAINS WHETHER THE
STRONGEST PART OF THE MONSOON TAIL SITS OVER THE MARIANAS OR OVER THE
FAR NORTHERN CNMI. A HYDROLOGIC OUTLOOK MAY BE NECESSARY IN THE
COMING DAYS DEPENDING ON THE TRACK AND INTENSITY OF THIS DISTURBANCE.
MARINE...
LIGHT AND VARIABLE WINDS WILL PREVAIL THROUGH MONDAY. SEAS AROUND
3 FEET WILL REMAIN UNTIL WEDNESDAY EVENING BEFORE STARTING TO
INCREASE DUE TO AN EXPECTED TROPICAL DISTURBANCE DEVELOPING TO THE
NORTHEAST AND ITS ASSOCIATED MONSOON INFLOW SHIFTING NORTH INTO
THE MARIANAS. THE RISK OF RIP CURRENTS IS CURRENTLY LOW ALONG ALL
REEFS AS ONLY A VERY SMALL SOUTHWEST SWELL AND EAST-NORTHEAST SWELL
REMAIN. SEAS MAY BECOME HAZARDOUS TO SMALL CRAFT BY THURSDAY, WITH
THE SURF POTENTIALLY BECOMING HAZARDOUS AS WELL. ISOLATED
THUNDERSTORMS WILL BE POSSIBLE THROUGH MONDAY AND THEN AGAIN BY
WEDNESDAY NIGHT THROUGH THE END OF THE FORECAST PERIOD.
EASTERN MICRONESIA...
SIMILAR TO YESTERDAY, RAINFALL WAS THE BIGGEST FORECAST CHALLENGE AS
THE REGION REMAINS ON THE SOUTHERN EDGE OF THE DEEPER MOISTURE.
MAJURO HAS SEEN THE "BEST" COVERAGE OF SHOWERS AS THEY'RE CLOSEST TO
THE TROUGH (WHICH STRETCHES FROM UTIRIK TO 9N180). SOME OF THE
SHOWERS HAVE BEEN AT LEAST MODERATELY HEAVY AS AFTER ONE SUCH SHOWER
EARLIER MAJURO DROPPED FROM 87 DEGREES TO 82 DEGREES, AND THEY REMAIN
COOLER AT 83 DEGREES CURRENTLY. AS FOR RAINFALL POTENTIAL, MAJURO
IS ON THE EDGE OF THE CONVECTION, WITH MODELS SHOWING DECREASED
POTENTIAL FOR MONDAY INTO TUESDAY, BEFORE POTENTIAL INCREASES ONCE
AGAIN. AS SUCH, THE FORECAST WAS TRENDED IN THAT DIRECTION.
FARTHER SOUTH AND WEST, BOTH POHNPEI AND KOSRAE HAS SEEN LITTLE IN
THE WAY OF SHOWER ACTIVITY, WITH ABUNDANT MID TO HIGH LEVEL CLOUD
COVER OFFERING SOME RELIEF, AS TEMPERATURES THIS AFTERNOON WERE IN
THE MID 80S. GIVEN THIS BEING A SECOND DAY OF MORE CONVECTIVE DEBRIS
THAN ACTUAL SHOWER COVERAGE, RAINFALL PROBABILITIES WERE DROPPED TO
30 PERCENT FOR TONIGHT AND MONDAY. FOR MONDAY NIGHT ONWARD, LOOK FOR
JUST ISOLATED SHOWER COVERAGE WITH PROBABILITIES IN THE 10 TO 20
PERCENT RANGE.
AS FOR MARINE CONDITIONS, LOOK FOR LIGHT TO GENTLE WINDS TO PREVAIL
WITH SEAS HOLDING IN THE 3 TO 5 FOOT RANGE.
WESTERN MICRONESIA...
THE MONSOON TROUGH REMAINS THE DOMINANT FEATURE IN THE REGION. THE
TROUGH IS LOCATED 10N130E AND EXTENDS EASTWARD THROUGH THE REGION
AND ENTERS EASTERN MICRONESIA NEAR 10N155E. THIS FEATURE IS PRODUCING
SCATTERED TO NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS, WITH THE
STRONGEST SHOWERS NEAR 10N. THESE SHOWERS ARE MOST PREVALENT NEAR
YAP, AND SOME SHOWERS OVER THE NORTHERN PORTIONS OF PALAU AND CHUUK
WATERS. THE MONSOON TROUGH IS EXPECTED TO REMAIN QUASI-STATIONARY.
THIS FEATURE IS EXPECTED TO REMAIN THROUGH MOST OF NEXT WEEK.
ALTIMETRY SHOWS COMBINED SEAS BETWEEN 3 AND 5 FEET. WINDS ARE
EXPECTED TO BE LIGHT TO MODERATE. SEA CONDITIONS ARE EXPECTED TO
REMAIN BENIGN.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA UPDATE: WILLIAMS
MARIANAS: OGLE
EAST MICRONESIA: DOLL
WEST MICRONESIA: BOWSHER
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