511
FXPQ50 PGUM 291802
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
402 AM CHST WED APR 30 2025
MARIANAS UPDATE
OVERALL, ONLY MINOR CHANGES WERE MADE WITH THIS FORECAST PACKAGE.
CURRENT SATELLITE AND RADAR OBSERVATIONS SHOW ISOLATED SHOWERS ACROSS
THE REGION. AN ISOLATED WETTING RAIN OF 0.20 INCHES OR HIGHER CAN'T
BE RULED OUT THE NEXT COUPLE OF DAYS BEFORE DRIER CONDITIONS MOVE
INTO THE REGION.
THERE WERE NO CHANGES WITH THE MARINE FORECAST. COMBINED SEAS OF 4
TO 5 FEET MAY INCREASE BY A FOOT ON THURSDAY AND PERSISTING INTO THE
WEEKEND.
FIRE WEATHER
0.17 INCHES OF RAIN FELL AT THE GUAM INTERNATIONAL AIRPORT
YESTERDAY, BUT THERE HAS BEEN NO WETTING RAINFALL OF 0.20 INCHES OR
GREATER SINCE THE 17TH (ALMOST 2 WEEKS). THIS HAS ALLOWED THE KBDI TO
CONTINUE INCREASING WITH TODAY'S READING AT 701, WHICH IS IN THE
HIGH CATEGORY. GENTLE TO MODERATE TRADE WINDS WILL CONTINUE WITH
OCCASIONAL FRESH GUSTS IN THE AFTERNOON, AND ARE EXPECTED TO REMAIN
BELOW CRITICAL RED FLAG CRITERIA. HOWEVER, FIRE DANGER REMAINS
ELEVATED, ESPECIALLY AT HIGHER TERRAIN WHERE STRONGER WINDS ARE
EXPECTED. AFTERNOON RELATIVE HUMIDITY VALUES WILL REMAIN ABOVE 60
PERCENT. A WETTING RAIN IS UNLIKELY, BUT ISOLATED REGIONS COULD PICK
UP A WETTING RAIN THE NEXT COUPLE OF DAYS BEFORE A BROADER DRYING
TREND DEVELOPS.
EASTERN MICRONESIA UPDATE
THE MAIN CHANGE TO THE FORECAST WAS TO DECREASE POPS (PROBABILITY OF
PRECIPITATION) FOR THURSDAY, MAINLY FOR POHNPEI AND KOSRAE. TONIGHT'S
MODEL RUNS ARE LESS ROBUST IN THEIR PRECIP FIELDS, WITH CURRENT
SATELLITE IMAGERY SHOWING NOTHING THAT'S NOTEWORTHY RIGHT NOW, ASIDE
FROM ABUNDANT CLOUD COVER.
SEAS WILL REMAIN IN THE 4 TO 6 FOOT RANGE. AT MAJURO, WINDS WILL BE
GENTLE TO MODERATE THE NEXT SEVERAL DAYS, WHILE BECOMING LIGHT TO
GENTLE FROM TIME TO TIME AT POHNPEI AND KOSRAE.
WESTERN MICRONESIA UPDATE
THE BIGGEST CHANGE TONIGHT WAS JTWC (THE JOINT TYPHOON WARNING
CENTER) OPENING UP INVEST 90W, RATED AS "SUB-LOW", WITH THE
CIRCULATION AT 4N 145.7E. THIS IS AN AREA THAT THE MODELS GRADUALLY
DEVELOP INTO A "MORE ORGANIZED" SYSTEM OVER THE NEXT 3 TO 4 DAYS,
WITH SOME MODELS TRYING TO DEVELOP IT INTO A WEAK DEPRESSION AS IT
APPROACHES/PASSES BY YAP. THERE'S STILL PLENTY OF TIME TO WATCH THE
SATELLITE IMAGERY THOUGH, AND THE CURRENT SPECIAL WEATHER STATEMENT
(SPS) HAS THINGS WELL-COVERED.
THEN WE HAVE INVEST 99W, LOCATED WEST OF PALAU NEAR 6N132E. THIS
SYSTEM CONTINUES TO STRUGGLE TO ORGANIZE, WITH SOME MODELS NOT
SHOWING MUCH IMPROVEMENT UNTIL IT MOVES FURTHER NORTHWEST, AWAY FROM
PALAU. STILL, MODEL UNCERTAINTY IS FAIRLY DECENT WITH THIS SYSTEM AS
WELL, GIVEN THE TREND THE PAST FEW DAYS WAS TO SHOW TWO DISTINCT
SYSTEMS AT SOME POINT IN THE NEXT 3 TO 5 DAYS (POSSIBLE SOONER).
THUS, THE SPS FOR PALAU HAS THINGS WELL-COVERED AS WELL. HEADLINES
ARE ALSO INCLUDED IN THE ZONE AND COASTAL FORECASTS FOR BOTH PALAU
AND YAP.
THE MIDNIGHT ASCAT PASS DIDN'T PASS OVER 99W AS WELL, WHICH IS
UNFORTUNATE AS WE DEBATED KEEPING GUST WORDING IN THE ZONE FORECAST.
WHILE A STRONGER GUST NEAR 30 OR PERHAPS 35 MPH CAN'T BE RULED OUT
WITH ANY STRONG SHOWER OR THUNDERSTORM THAT DEVELOPS, THE LACK OF ANY
APPRECIABLE CONVECTION NEAR THE CIRCULATION, AND THE CONCERN THAT
"WHAT'S LEFT" OF 9(W COULD GET PULLED INTO 90W, GUSTS WERE REMOVED
FROM THE ZONE FORECAST AS AREAL AND TEMPORAL COVERAGE OF SUCH LOOKED
TO BE ISOLATED AT BEST.
PREV DISCUSSION
/ISSUED 602 PM CHST TUE APR 29 2025/
MARIANAS SYNOPSIS...
GENTLE TO MODERATE, MOSTLY DRIER TRADES PREVAIL ACROSS THE REGION.
SATELLITE IMAGERY AND DOPPLER RADAR INDICATE JUST ISOLATED CELLS
POPPING UP IN GUAM'S COASTAL WATERS. THE BUOYS INDICATE SEAS ARE 4 TO
5 FEET.
DISCUSSION...
JUST ISOLATED SHOWERS EXPECTED FOR MUCH OF THE WEEK, AS MOST OF THE
CONVECTION WILL REMAIN WELL SOUTH AND WEST OF THE REGION. OCCASIONAL
UPTICKS IN SHOWERS MAY OCCUR NEAR GUAM BY EARLY NEXT WEEK, AS
POTENTIAL DISTURBANCES MOVE NORTHWARD FROM WESTERN MICRONESIA.
MARINE...
COMBINED SEAS OF 4 TO 5 FEET MAY BRIEFLY INCREASE A FOOT THURSDAY OR
THURSDAY NIGHT. A MODERATE RISK OF RIP CURRENTS IS EXPECTED ALONG
NORTH AND EAST FACING REEFS FOR AT LEAST THE REST OF THE WEEK. SURF
MAY INCREASE A FOOT ALONG NORTH AND EAST FACING REEFS AS TRADE SWELL
STRENGTHENS BRIEFLY THURSDAY AND THURSDAY NIGHT.
FIRE WEATHER...
SO FAR TODAY, 0.16 INCHES OF RAIN HAS FALLEN SINCE MIDNIGHT. WETTING
RAINS ARE NOT LIKELY FOR AT LEAST THE NEXT SEVERAL DAYS, SO THE KBDI
MAY CONTINUE TO CREEP UPWARDS, WHICH IS AT 696 (HIGH CATEGORY). IN
ADDITION, WINDS ARE EXPECTED TO REMAIN GENTLE TO MODERATE, SO
CONDITIONS CRITICAL TO FIRE WEATHER ARE NOT EXPECTED FOR AT LEAST THE
NEXT FEW DAYS.
TROPICAL SYSTEMS...
A LARGE AREA OF DISTURBED WEATHER EXTENDS ACROSS WESTERN MICRONESIA,
ASSOCIATED WITH THE NEAR-EQUATORIAL TROUGH (NET) AND EMBEDDED
DISTURBANCES. THE PRIMARY DISTURBANCE AT THIS TIME IS INVEST 99W, A
BROAD AREA OF ROTATION WEST-SOUTHWEST OF KOROR, PALAU, LOCATED NEAR
5N132E. TODAY'S SATELLITE SCATTEROMETER DATA DOES NOT SHOW A DEFINED
CIRCULATION WITH 99W BUT THIS DISTURBANCE IS ASSOCIATED WITH GUSTY,
LOCALLY HEAVY SHOWERS AND THUNDERSTORMS. THE JOINT TYPHOON WARNING
CENTER RATES 99W AS A "SUB-LOW" FOR DEVELOPMENT, WHICH MEANS
SIGNIFICANT DEVELOPMENT INTO A TROPICAL CYCLONE IS UNLIKELY OVER THE
NEXT 24 HOURS. FARTHER EAST, A BROAD AREA OF MID-LEVEL VORTICITY IS
SEEN NEAR 5N148E, WELL WEST-SOUTHWEST OF CHUUK, AND SIMILAR TO 99W,
SCATTEROMETER DATA DOES NOT SHOW A DEFINED SURFACE CIRCULATION AND
CONVECTION IS DISORGANIZED AROUND THIS FEATURE. THIS MID-LEVEL
VORTICITY CAN HOWEVER BECOME A FOCAL POINT FOR FUTURE CONVECTION AND
EVEN SUPPORT THE DEVELOPMENT OF A SURFACE CIRCULATION, A TREND
SHARED BY SOME, BUT NOT ALL, MODELS OVER THE NEXT SEVERAL DAYS. THERE
CONTINUES TO BE A LARGE AMOUNT OF UNCERTAINTY AND VARIABILITY ACROSS
THE THE DIFFERENT MODELS. HOWEVER THE GENERAL CONSISTENCE FAVORS
ONE, POSSIBLY TWO CIRCULATIONS LIFTING NORTHWEST, WITH SIGNIFICANT
DEVELOPMENT FAVORED NORTHWEST OF PALAU AND YAP.
EASTERN MICRONESIA...
A SERIES OF TROUGHS WITHIN A BROAD AREA OF TRADE-WIND CONVERGENCE
CONTINUES TO BRING UNSETTLED WEATHER ACROSS THE REGION. UPPER-LEVEL
DIFFLUENCE IS ALSO PROVIDING FAVORABLE SUPPORT TO CONVECTION AND
QUICKLY SPREADING CLOUD DEBRIS FROM WEST TO EAST. EARLIER THIS
MORNING, SHOWERS THAT BUILT INTO POHNPEI BROUGHT LOCALLY HEAVY
RAINFALL AND PRODUCED 4.42 INCHES AT A WEATHER STATION ON THE NORTH
SIDE OF THE ISLAND, BUT AN ESTIMATE OF 4 TO 6 INCHES OF RAIN HAS
FALLEN ACROSS THE ISLAND WITH THIS EVENT. SCATTEROMETRY DATA ALSO
REVEALED FRESH TO STRONG WIND GUSTS WITH THESE SHOWERS AND MODEL
TRENDS ARE POINTING TO LOCALLY HEAVY SHOWERS POSSIBLE THROUGH LATE
EVENING, ALONG WITH OCCASIONAL GUSTS TO 30 MPH. AROUND MIDNIGHT,
THE BULK OF CONVECTION IS EXPECT TO MOVE WEST OF POHNPEI, ALLOWING
FOR SHOWERS TO LESSEN IN COVERAGE TO NUMEROUS, THEN DOWN TO SCATTERED
WEDNESDAY. FARTHER EAST, SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS CONTINUE ACROSS KOSRAE AND MAJURO TONIGHT, THEN TRADE-
WIND CONVERGENCE BEGINS TO FRAGMENT AND SHIFT SOUTHWARD, ALLOWING
CONDITIONS TO IMPROVE NEAR MAJURO STARTING WEDNESDAY, ALTHOUGH
MODERATE TRADE-WIND CONVERGENCE CONTINUES NEAR POHNPEI AND KOSRAE,
KEEPING SCATTERED SHOWERS IN THE FORECAST THROUGH AT LEAST SUNDAY.
COMBINED SEAS ARE EXPECTED TO BE BETWEEN 5 AND 7 FEET OVER THE NEXT
SEVERAL DAYS. ASCAT ANALYSIS SHOWS MODERATE TO FRESH TRADES ACROSS
THE REGION, AND CONVECTIVELY-DRIVEN GUSTS TO 25 KT. OCCASIONAL GUSTS
TO 30 KT WILL BE POSSIBLE WITH SHOWERS FOR POHNPEI TONIGHT, WITH
GUST POTENTIALS DECREASING TO 25 KT WEDNESDAY. THEN, WINDS ACROSS THE
REGION SUBSIDE TO LIGHT TO MODERATE LATE WEEK AND OVER THE WEEKEND.
WESTERN MICRONESIA...
THE FORECAST FOR THE REGION, ESPECIALLY FOR PALAU AND YAP, CONTINUES
TO BE CHALLENGING DUE TO THE BROAD BUT DISORGANIZED PATTERN CREATED
BY THE NET AND EMBEDDED DISTURBANCES. THE ECMWF CONTINUES TO DIFFER
FROM THE GFS AND CANADIAN, WITH THE ECMWF FAVORING ONE DISTINCT
CIRCULATION WHILE THE OTHER MODELS SUPPORT TWO DISTINCT CIRCULATIONS
DEVELOPING WITHIN THE NET. THESE DIFFERENCES CREATE A LOT OF
VARIABILITY IN THE LOCATION AND INTENSITY OF SHOWERS AND
THUNDERSTORMS, WHICH ALSO INFLUENCES THE POTENTIAL WIND DIRECTION,
LOCATION OF LOCALLY STRONGER GUSTS AND CHOPPY SEAS. MODELS ARE
CONSISTENT THAT PALAU AND YAP WILL EXPERIENCE A WET PATTERN AS THE
OVERALL FEATURE MOVE TOWARDS PALAU AND YAP, WITH SIGNIFICANT
DEVELOPED FAVORED ONCE THE CIRCULATION(S) ARE NORTHWEST OF PALAU AND
YAP. IF DEVELOPMENT OCCURS NORTHWEST OF PALAU AND YAP, THEN A
MONSOON-LIKE PATTERN WILL LIKELY DEVELOP FOR PALAU AND WESTERN YAP
STATE. MORE DETAILS CAN BE FOUND IN THE SPECIAL WEATHER STATEMENT
ISSUED FOR PALAU AND YAP UNDER WMO HEADER WWPQ82 PGUM.
FOR CHUUK, AN ACTIVE TRADE-WIND PATTERN DRIVEN BY TRADE-WIND
CONVERGENCE AND IS GENERATING SCATTERED TO AT TIMES NUMEROUS SHOWERS
AND ISOLATED THUNDERSTORMS ACROSS THE STATE. SOME OF THESE SHOWERS
AND THUNDERSTORMS ARE EXPECTED TO CREATE OUTFLOW BOUNDARIES THAT
WILL GENERATE PERIODS OF GUSTY WINDS AS THEY PASS THROUGH THE COASTAL
WATERS AND ISLANDS. THIS PATTERN IS EXPECTED TO CONTINUE OVER THE
NEXT FEW DAYS, BUT LATE THIS WEEKEND MODELS SHOW THE BAND OF
CONVERGENCE FRAGMENTING WHICH WILL DECREASE THE POTENTIAL FOR SHOWERS
AND THUNDERSTORMS ACROSS CHUUK STATE.
BUOY AND ALTIMETRY DATA SHOW THAT SEAS ARE MAINLY 3 TO 5 FEET ACROSS
MOST OF THE REGION. ASCAT DATA ALSO SHOWS GENTLE TO MODERATE WINDS
ACROSS THE REGION, BUT THERE ARE POCKETS OF GUSTY WINDS, ASSOCIATED
WITH SHOWERS AND THUNDERSTORMS WHICH ARE LIKELY CREATING CHOPPY SEA
CONDITIONS AT TIMES. GIVEN THE LARGE UNCERTAINTY AND VARIABILITY IN
THE MODELS, THE OVERALL MODEL TRENDS ONLY HAS SEAS INCREASE SLIGHTLY
TO 4 TO 6 FEET LATER THIS WEEK, BUT THIS DOES NOT TAKE INTO ACCOUNT
CHOPPY SEA CONDITIONS CAUSED BY GUSTS NEAR HEAVIER SHOWERS AND
THUNDERSTORMS. MARINERS SHOULD CONTINUE TO MONITOR THE LATEST
FORECAST FOR ANY CHANGES TO MARINE CONDITIONS AS THE PATTERN CHANGES
THROUGH THE WEEK.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS UPDATE: WILLIAMS
EAST/WEST MICRONESIA: DOLL
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