251
FXPQ50 PGUM 301039
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
839 PM CHST WED SEP 30 2026
MARIANAS SYNOPSIS
SATELLITE AND RADAR IMAGERY INDICATES MOSTLY CLOUDY SKIES AND
SCATTERED SHOWERS ACROSS THE MARIANAS, WITH HEAVIER CONVECTION EAST
OF THE REGION. ALTIMETRY INDICATES COMBINED SEAS OF 4 TO 6 FT.
DISCUSSION
THE MONSOON TROUGH EXTENDING INTO TROPICAL DEPRESSION (TD) 26W WILL
LIFT NORTHWARD AS 26W APPROACHES THE FAR NORTHERN CNMI THROUGH
THURSDAY. THIS WILL LEAD TO INCREASING SHOWERS, CONVECTION, AND WINDS
FOR THE REGION. THE ZONES WERE SPLIT AS SAIPAN AND TINIAN ARE
FORECASTED FOR NUMEROUS SHOWERS AND STRONG SOUTHWESTERLIES WITH GALE-
FORCE GUSTS POSSIBLE BEGINNING THURSDAY NIGHT. GUAM AND ROTA CAN
EXPECT HIGH-END (50%) SCATTERED SHOWERS INCREASING TO NUMEROUS
SHOWERS ON FRIDAY AND FRESH TO STRONG SOUTHWESTERLIES WITH NEAR GALE-
FORCE GUSTS POSSIBLE. AS OF EARLY THIS EVENING, A FLOOD WATCH WAS
NOT ISSUED AS ENSEMBLE GUIDANCE SIGNIFICANTLY DIFFERS, SHOWING THE
HIGHER RANGES OF RAINFALL TOTALS OVER THE FAR NORTHERN CNMI. HOWEVER,
FLOODING POTENTIALS WILL BE RE-EVALUATED WITH THE NEXT FORECAST
PERIOD, SO ANY HYDROLOGY PRODUCT SHOULD NOT BE RULED OUT. IN
ADDITION, THERE IS POTENTIAL FOR A WIND ADVISORY THIS WEEKEND FOR ALL
THE MARIANAS AS SUSTAINED WINDS OF 30 TO 39 MPH ARE POSSIBLE. AS
TIME CONTINUES, THIS PRODUCT MAY ALSO BE ISSUED WITHIN THE NEXT FEW
FORECAST PERIODS. WITH THE CURRENT FORECAST TRACK, SAIPAN AND TINIAN
WILL MOST LIKELY BE INCLUDED IN A TS WATCH WITH THE NEXT FORECAST
UPDATE. AS FOR NEXT WEEK, A DRY SPELL MAY OCCUR BEFORE SHOWERS
INCREASE AGAIN LATE NEXT WEEK.
MARINE
COMBINED SEAS OF 4 TO 6 FT WILL INCREASE AS THE BUILDING MONSOONAL
FLOW ELEVATES THE SOUTHWESTERLY SWELL AND INDUCES A LONG-PERIOD
NORTHERLY SWELL FROM TD 26W. A SMALL CRAFT ADVISORY IS ISSUED BUT
WILL BE IN EFFECT STARTING THURSDAY EVENING AS SEAS REACH 10 TO 12
FT AND WILL CONTINUE AT LEAST THROUGH SUNDAY EVENING. SEAS ARE
FORECAST TO REACH 12 TO 14 FT OVER THE WEEKEND, AND MAY POTENTIALLY
EXCEED 15 FT WHICH COULD WARRANT A HAZARDOUS SEAS WARNING ISSUANCE
WITHIN THE NEXT FEW FORECAST PERIODS. SURF WILL INCREASE ALONG ALL
REEFS, WITH WEST-FACING REEFS MOST LIKELY REACHING HAZARDOUS
CRITERIA ON THURSDAY NIGHT. A HIGH SURF ADVISORY AND A HIGH RIP
CURRENT RISK STATEMENT MAY ALSO BE ISSUED WITH THE NEXT FORECAST
UPDATE AT LEAST FOR WEST-FACING REEFS.
TROPICAL SYSTEMS
TROPICAL DEPRESSION 26W CONTINUES TO SLOWLY ORGANIZE EAST OF
ANATAHAN. IT'S CURRENTLY LOCATED NEAR 15.9N 150.4E, AND IS MOVING
WEST AT 9 MPH. 26W IS EXPECTED TO CONTINUE TO STRENGTHEN, LIKELY
BECOMING A TROPICAL STORM EITHER LATE TONIGHT OR EARLY THURSDAY
MORNING. THE DISTURBANCE WILL THEN CONTINUE STRENGTHENING, POSSIBLY
CROSSING THE CNMI AS A STRONG TROPICAL STORM SOMEWHERE NEAR ALAMAGAN
OR PAGAN OVER THE WEEKEND. THE MODELS INDICATE THE SYSTEM MAY STALL
EITHER AS IT CROSSES THE CNMI OR JUST TO THE WEST, WHICH COULD GIVE
ALAMAGAN, PAGAN, AND AGRIHAN PROLONGED TROPICAL STORM FORCE
CONDITIONS. THOSE THREE LOCATIONS ARE CURRENTLY UNDER A TROPICAL
STORM WATCH, AS THE ONSET OF DAMAGING WINDS OF 39 MPH OR MORE ARE
POSSIBLE WITHIN THE NEXT 48 HOURS. ADDITIONALLY, TINIAN AND SAIPAN
ARE NOW UNDER A TROPICAL STORM WATCH, AS THE SOUTHERN EDGE OF THE TS
WIND FIELD IS FORECAST TO INCLUDE THESE ISLANDS.
ONE THING THAT IS MORE CERTAIN IS BREEZY AND WET CONDITIONS WILL
DEVELOP BY SATURDAY FROM SAIPAN DOWN TO GUAM. EVEN AT GUAM SUSTAINED
WINDS OF 20 TO 30 MPH REMAIN POSSIBLE WITH GUSTS IN STRONGER SHOWERS
POTENTIALLY REACHING 45 OR 50 MPH. AGAIN, DEPENDENT ON HOW 26W
EVOLVES. THE FURTHER NORTH YOU GO FROM GUAM, THE SLIGHTLY HIGHER THE
WINDS WILL BE, AS YOU'LL BE CLOSER TO THE LOW-LEVEL CIRCULATION
CENTER OF THE TROPICAL DEPRESSION/POTENTIAL TROPICAL STORM. LOCALLY
HEAVY RAINFALL WILL LIKELY DEVELOP ACROSS THIS REGION AS WELL AS THE
SOUTHWEST MONSOON STRENGTHENS.
FOR THE TIME BEING, RESIDENTS FROM SAIPAN SOUTH TO GUAM SHOULD
CONTINUE TO MONITOR THE FORECAST UPDATES. MAKE SURE POOR DRAINAGE
AREAS ARE CLEARED OF DEBRIS, AND LISTEN FOR ANY FURTHER INSTRUCTIONS
SHOULD THEY BE NEEDED.
FOR MORE INFORMATION PLEASE REFER TO BULLETINS FROM THE JOINT
TYPHOON WARNING CENTER UNDER WMO HEADER WTPN32 PGTW AND FROM THE
NATIONAL WEATHER SERVICE UNDER WMO HEADER WTPQ32 PGUM.
EASTERN MICRONESIA
THE MAIN FORECAST CHALLENGE WAS RAINFALL POTENTIAL AT MAJURO, AS
POHNPEI AND KOSRAE WILL REMAIN REMOVED FROM THE BEST MOISTURE AND
LIFT THIS FORECAST PERIOD. AT MAJURO THOUGH, THE MONSOON TROUGH WILL
REMAIN IN YOUR AREA WITH THE MODELS SHOWING SECONDARY CYCLOGENESIS
(PRIMARY IS TD 26W EAST OF THE CNMI) NORTH OF KWAJALEIN (OR
NORTHWEST). AS THIS OCCURS, SOUTHEAST INFLOW INTO THIS DEVELOPING
SECONDARY SYSTEM LOOKS TO TAKE PLACE OVER THE WEEKEND, WITH MODELS
SHOWING INCREASED SURFACE CONVERGENCE AND CONVECTION INCREASING IN
COVERAGE. THUS, ALTHOUGH THERE'S NOT MUCH CONVECTION CURRENTLY
ONGOING NEAR MAJURO, WE STAYED WITH THE MODEL GUIDANCE WHICH WAS IN
LINE WITH PREVIOUS FORECASTS. THUS, ONLY MINIMAL RAINFALL POTENTIAL
AND TEMPERATURE REFINEMENTS WERE NEEDED.
AS FOR WINDS, MAINLY LIGHT TO GENTLE WINDS ARE EXPECTED, BUT THEY MAY
BECOME MODERATE FROM TIME TO TIME AT POHNPEI THROUGH THIS WEEKEND.
SEAS LOOK TO HOLD IN THE 4 TO 6 FOOT RANGE.
WESTERN MICRONESIA
SATELLITE IMAGERY THIS EVENING SHOWS PATCHY SHOWER BANDS EXTENDING
ACROSS MUCH OF WESTERN MICRONESIA, WITHIN THE BROAD MONSOON PATTERN
SOUTH TO SOUTHWEST OF TD 26W. SCATTEROMETRY FROM THIS MORNING SHOWS A
BROAD AREA OF MODERATE TO FRESH WEST TO SOUTHWEST WINDS ACROSS THE
REGION, WITH THE HIGHEST WINDS OVER NORTHERN CHUUK STATE, NORTH OF
CHUUK LAGOON. THE MONSOON TAIL TRAILING SOUTH OF 26W WILL MAINTAIN
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS IN THE FORECAST FOR
PALAU AND YAP THROUGH MUCH OF THE FORECAST PERIOD, WITH MODEL
GUIDANCE DEPICTING A PERSISTENT, BUT NARROW BAND OF HIGHER
PRECIPITATION MEANDERING OVER AND JUST NORTH OF PALAU AND YAP, AND
REMAINING FAR NORTH OF CHUUK, WHICH CAN EXPECT MOSTLY DRY CONDITIONS
THROUGH EARLY NEXT WEEK. HOWEVER, WINDS, SEAS, AND SURF WILL INCREASE
OVER THE NEXT SEVERAL DAYS AS THE BROAD MONSOON PATTERN SURGES TO THE
SOUTH OF 26W, AS IT CONTINUES TO STRENGTHEN NEAR THE MARIANAS, THEN
PASS THROUGH THE NORTHERN CNMI ON FRIDAY. CURRENT GUIDANCE SUGGESTS
THE HIGHEST WINDS AND SEAS WILL BE FELT ACROSS THE OUTER ISLANDS
BETWEEN YAP AND CHUUK LAGOON, LEADING TO HAZARDOUS INTERISLAND
TRAVEL. SEAS MAY BECOME HAZARDOUS TO SMALL CRAFT LATE THIS WEEKEND
FOR PALAU AND YAP AS THE MONSOON SURGE STRENGTHENS AND WINDS INCREASE
TO SUSTAIN AT AROUND 22 KNOTS, ESPECIALLY FOR YAP. AT THE SAME TIME,
BUILDING NORTH AND WEST SWELL FROM 26W MAY LEAD TO HAZARDOUS SURF FOR
YAP AND CHUUK. IN THE MEAN TIME, MARINE AND SURF CONDITIONS REMAIN
BENIGN. PALAU AND YAP BUOY DATA, AND ALTIMETRY DATA, DEPICT COMBINED
SEAS OF ROUGHLY 3 TO 5 FEET.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...SMALL CRAFT ADVISORY FROM 5 PM THURSDAY TO 5 PM
CHST SUNDAY FOR PMZ151>154.
MARIANAS: MESA
EAST MICRONESIA/TROPICAL SYSTEMS: DOLL
WEST MICRONESIA: DECOU
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