900
FXPQ50 PGUM 040823
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
623 PM CHST SUN OCT 4 2026
MARIANAS SYNOPSIS
SATELLITE IMAGERY SHOWS PARTLY TO MOSTLY CLOUDY SKIES ACROSS THE
MARIANAS WITH ISOLATED TO SCATTERED SHOWERS. ALTIMETRY SHOWS COMBINED
SEAS BETWEEN 11 AND 14 FEET.
DISCUSSION
TYPHOON CHOI-WAN HAS STEADILY MOVED NORTHEAST TODAY, MOVING AWAY
FROM THE FAR NORTHERN MARIANA ISLANDS. ALL TROPICAL STORM AND TYPHOON
WATCHES AND WARNINGS HAVE ENDED AND TYPHOON CHOI-WAN WILL CONTINUE
TO MOVE AWAY FROM THE REGION. IN ITS PLACE THE MONSOON SURGE WILL
REMAIN DRAPED OVER THE MARIANAS. A RELATIVE LULL IN SHOWER ACTIVITY
IS EXPECTED TONIGHT THROUGH TUESDAY WITH ISOLATED TO LOW-END (30%)
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS. THE WET PHASE OF THE
MONSOON IS EXPECTED TO RETURN TUESDAY NIGHT AS THE MONSOON
REORGANIZES. THERE IS POTENTIAL FOR ANOTHER ROUND OF HEAVY RAINFALL
DURING THE SECOND HALF OF THIS WEEK AND A HYDROLOGICAL PRODUCTS MAY
BE NECESSARY. ANOTHER LULL LOOKS TO DEVELOP LATE THIS WEEKEND.
MARINE
HAZARDOUS MARINE CONDITIONS REMAIN ACROSS THE MARIANAS. COMBINED SEAS
RANGE BETWEEN 11 AND 14 FEET. A GALE WARNING REMAINS IN EFFECT UNTIL
10 PM FOR FREQUENT GUSTS TO 40 KT ACROSS SAIPAN AND TINIAN. BY 10 PM
GUSTS ARE EXPECTED TO DECREASE AND BECOME OCCASIONAL. THE GALE
WARNING WILL BE REPLACED WITH A SMALL CRAFT ADVISORY. GUAM AND ROTA
ARE UNDER A SMALL CRAFT ADVISORY UNTIL TUESDAY AFTERNOON. SURF
REMAINS HAZARDOUS ALONG NORTH, WEST, AND SOUTH FACING REEFS. SURF
WILL REMAIN HAZARDOUS THROUGH AT LEAST MONDAY AFTERNOON, BUT WILL
LIKELY NEED TO BE EXTENDED IN TIME. SEAS LOOK TO QUICKLY SUBSIDE THIS
WEEK, POTENTIALLY BECOMING BENIGN ON THURSDAY NIGHT.
TROPICAL SYSTEMS
TYPHOON CHOI-WAN (26W) IS CURRENTLY LOCATED WELL NORTH OF THE MAUG
ISLANDS, NEAR 23N147E. CHOI-WAN HAS BEEN CONSUMING HIGH-OCTANE OCEAN
FUEL TODAY, RAPIDLY INTENSIFYING FROM A 90 KNOT MID-GRADE CATEGORY 2
STORM EARLY THIS MORNING TO A POWERFUL 125 KNOT CATEGORY 4 TYPHOON,
NEARLY APPROACHING SUPER TYPHOON STATUS. CHOI-WAN WILL CONTINUE TO
MOVE AWAY FROM THE REGION AND IS FORECAST TO EXIT OUR AREA OF
RESPONSIBILITY LATE TONIGHT OR MONDAY MORNING. CHOI-WAN WILL CONTINUE
TO HAVE AN INFLUENCE OVER THE MARIANAS OVER THE COMING DAYS AS THE
MONSOON SURGE REMAINS LOCKED OVER THE REGION. CHOI-WAN WILL ALSO
PRODUCE A DISTANT NORTH SWELL THAT WILL HELP KEEP SURF HIGH THE NEXT
FEW DAYS.
FOR MORE INFORMATION ON TY CHOI-WAN, SEE BULLETINS ISSUED BY THE
JOINT TYPHOON WARNING CENTER (JTWC) UNDER WMO HEADER WTPN32 PGTW AND
BY THE NATIONAL WEATHER SERVICE UNDER WMO HEADERS WTPQ32 PGUM AND
WTPQ82 PGUM.
A DEVELOPING DISTURBANCE KNOWN AS INVEST 94W BY THE JOINT TYPHOON
WARNING CENTER (JTWC) IS LOCATED ABOUT 54 MILES SOUTHWEST OF
KWAJALEIN. DEVELOPMENT IS RATED MEDIUM, MEANING TROPICAL CYCLONE
DEVELOPMENT IS LIKELY BEYOND 24 HOURS. SCATTEROMETRY DATA INDICATES
15 TO 20 KT WINDS NEAR KWAJALEIN, EBADON, UJAE, BIKINI, AND RONGELAP,
WITH WINDS UP TO 25 KT NEAR HEAVIER SHOWERS. INVEST 94W WILL BE
GENERALLY SLOW TO MOVE, REMAINING OVER THE NORTHERN MARSHALL ISLANDS
THROUGH TUESDAY NIGHT. SCATTERED TO NUMEROUS SHOWERS AND ISOLATED
THUNDERSTORMS MAY LEAD TO LOCALLY HEAVY RAINFALL AND FLOODING.
THROUGH FRIDAY, 4 TO 6 INCHES OF RAIN WITH LOCALLY HIGHER AMOUNTS IS
POSSIBLE.
GUSTY WINDS AND ELEVATED, CHOPPY SEAS WILL MAKE MARINE CONDITIONS
DIFFICULT. RESIDENTS MAY NEED TO RECONSIDER PLANS FOR INTER-ISLAND
BOATING AS THE WEEK CONTINUES.
94W WILL CONTINUE TO DEVELOP NEAR KWAJALEIN OVER THE NEXT DAY OR
TWO, SO RESIDENTS IN THE NORTHERN REPUBLIC OF MARSHALL ISLANDS (RMI)
SHOULD MONITOR THE FORECAST FOR THE NEXT SEVERAL DAYS.
FOR MORE INFORMATION ON INVEST 94W PLEASE SEE THE JTWC HEADER
ABPW10. ALSO KEEP UP TO DATE WITH THE LATEST INFORMATION
FROM YOUR LOCAL EMERGENCY MANAGEMENT AGENCY.
EASTERN MICRONESIA
INVEST 94W, WHICH ORGANIZED FAIRLY QUICKLY THE LAST 24 HOURS,
CONTINUES TO SPIN JUST NORTH OF KWAJALEIN. CONVECTION CONTINUES TO
TRY TO WRAP AROUND THE CENTER, WITH THE CYCLONIC FLOW STRENGTHENING
ACROSS THE REGION. THIS HAS LEAD TO INCREASED SURFACE CONVERGENCE AND
SHOWERS DEVELOPING NEAR KOSRAE. WE EXPECT THIS TREND TO CONTINUE WITH
CONVECTIVE COVERAGE ALSO DEVELOPING NEAR MAJURO OVERNIGHT, AND NEAR
POHNPEI MONDAY NIGHT. AS SUCH, RAINFALL COVERAGE/PROBABILITIES WERE
INCREASED AT KOSRAE AND POHNPEI. AT MAJURO, THE FORECAST HAS
MAINTAINED SCATTERED SHOWERS FOR A FEW DAYS NOW AND THIS LOOKS GOOD.
IT'S NOT OUT OF THE QUESTION THAT SHOWER COVERAGE MAY NEED TO BE
INCREASED TO NUMEROUS THERE WITH LATER FORECASTS, DEPENDING HOW
QUICKLY 94W EVOLVES TOWARDS A TROPICAL DEPRESSION. THE CURRENT
THINKING IS THIS MAY HOLD OFF UNTIL LATE MONDAY NIGHT OR TUESDAY WHEN
THE SYSTEM STARTS TO PULL AWAY FROM THE AREA TO THE NORTH-NORTHWEST,
WHICH WOULD DECREASE RAINFALL POTENTIAL.
AS FOR MARINE CONDITIONS, THE MAJORITY OF THE NUMERICAL GUIDANCE
INCREASES THE SOUTHWEST WINDS WRAPPING INTO 94W, WITH GUIDANCE
SUGGESTING SUSTAINED WINDS JUST SHY OF 22 KNOTS, BUT WITH FREQUENT
GUSTS ABOVE THAT STARTING LATER TONIGHT AND CONTINUING THROUGH EARLY
TUESDAY MORNING AT MAJURO. AS SUCH, WE HOISTED A SMALL CRAFT
ADVISORY FOR FREQUENT GUSTS TO 25 KNOTS TO ACCOUNT FOR THIS,
ESPECIALLY CONSIDERING THE INCREASING CONVECTION EXPECTATION, WHICH
COULD MIX DOWN SOME GUSTS IN THE 25 TO 30 KNOT RANGE (PERHAPS A TAD
HIGHER ON AN ISOLATED BASIS). HERE, MODERATE TO FRESH WINDS WILL
PERSIST THROUGH TUESDAY, BECOMING LIGHT TO GENTLE FOR THE LATTER HALF
OF THE WEEK. FOR POHNPEI AND KOSRAE, MAINLY LIGHT TO GENTLE WINDS
ARE EXPECTED.
SEAS LOOK TO HOLD IN THE 4 TO 6 FOOT RANGE AREA-WIDE, BUT THEY MAY
TOUCH 7 FEET AT POHNPEI AND MAJURO TUESDAY, BEFORE 94W MOVES FAR
ENOUGH AWAY TO HAVE LESSENING EFFECTS.
WESTERN MICRONESIA
THERE IS NOW A SMALL CRAFT ADVISORY IN EFFECT FOR PALAU AND YAP
THROUGH THURSDAY MORNING.
THE MONSOON SURGE REMAINS THE DOMINANT FEATURE IN THE REGION. THIS
FEATURE IS CURRENTLY LOCATED OVER PALAU AND YAP, AND PRODUCING
SCATTERED TO NUMEROUS WITH ISOLATED THUNDERSTORMS, AND 20 TO 30 MPH
(15 TO 20 KT) WITH GUSTS UP TO 35 MPH (30 KT). QPF MODEL GUIDANCE
SUGGESTS ABOUT UP TO AN INCH OF RAIN PER DAY IS POSSIBLE FOR BOTH
ISLANDS. WIND CONDITIONS ARE ANTICIPATED TO IMPROVE AROUND TUESDAY
NIGHT, WHILE SHOWERS ARE EXPECTED TO CONTINUE THROUGH THE WEEK.
OVERALL, A WET WEEK IS TO BE EXPECTED.
FURTHER TO THE EAST, CHUUK CAN EXPECT A QUITE BENIGN WEATHER PATTERN
THROUGH THE WEEK AS A RIDGE OF HIGH PRESSURE HAS SET UP OVER THE
REGION.
ALTIMETRY SHOWS COMBINED SEAS OF 6 TO 8 FEET ACROSS THE REGION, WITH
THE HIGHEST TO THE EAST OF YAP. WINDS ARE EXPECTED TO BE FRESH TO
STRONG WITH GUSTS TO NEAR GALE FOR PALAU AND YAP, WHILE WINDS NEAR
CHUUK IS EXPECTED TO BE LIGHT TO GENTLE. OVERALL, NEAR THE MONSOON
SURGE SEAS ARE EXPECTED TO REMAIN ELEVATED AND CHOPPY WITH WINDS
HAZARDOUS TO SMALL CRAFT OPERATION, THEN BECOMING MORE BENIGN TO THE
EAST.
GUM WATCHES/WARNINGS/ADVISORIES
GU...FLOOD WATCH THROUGH LATE TONIGHT FOR GUZ001.
HIGH RIP CURRENT RISK THROUGH MONDAY AFTERNOON FOR GUZ001.
HIGH SURF ADVISORY UNTIL 4 PM CHST MONDAY FOR GUZ001.
MP...FLOOD WATCH THROUGH LATE TONIGHT FOR MPZ001>003.
HIGH RIP CURRENT RISK THROUGH MONDAY AFTERNOON FOR MPZ001>003.
HIGH SURF ADVISORY UNTIL 4 PM CHST MONDAY FOR MPZ001>003.
WIND ADVISORY UNTIL 10 PM CHST THIS EVENING FOR MPZ002-003.
MARIANAS WATERS...SMALL CRAFT ADVISORY UNTIL 5 PM CHST TUESDAY FOR PMZ151-152.
GALE WARNING UNTIL 4 PM CHST THIS AFTERNOON FOR PMZ153-154.
MARIANAS: WILLIAMS
EAST MICRONESIA: DOLL
WEST MICRONESIA: BOWSHER
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