741
FXPQ50 PGUM 040929
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
729 PM CHST WED MAR 4 2026
MARIANAS SYNOPSIS
SATELLITE IMAGERY SHOWS MOSTLY CLOUDY SKIES AND RADAR IMAGERY SHOWS
ISOLATED SHOWERS OVER THE MARIANAS. ALTIMETRY SHOWS SEAS OF 6 TO 7
FEET ABOUT 150 NAUTICAL MILES TO THE WEST OF THE ISLANDS. IPAN BUOY
SHOWS EASTERLY SWELL NEAR 4 FEET AT 9 SECONDS.
THERE IS A HIGH SURF ADVISORY AND A HIGH RISK OF RIP CURRENTS
STATEMENT IN EFFECT FOR NORTH FACING REEFS.
DISCUSSION
THE ISLANDS ARE EXPERIENCING A FEW ISLAND EFFECT SHOWERS ALONG THE
WESTERN SIDE OF THE ISLANDS. SHOWERS FOR THE NEXT DAY OR SO ARE
EXPECTED TO BE MINIMAL. TWO FEATURES ARE EXPECTED TO PLAY A ROLE IN
THE UPCOMING WEATHER PATTERN. INVEST 95W IS EXPECTED TO CONTINUE TO
BUILD AND PROVIDE SHOWERS AND THUNDERSTORMS TO THE REGION. THE OTHER
FEATURE IS A SHEAR LINE IS EXPECTED TO PASS TO THE NORTH OF THE
ISLANDS. SHOWERS ARE ANTICIPATED TO BUILD IN AS EARLY AS FRIDAY
NIGHT. BETWEEN THESE TWO FEATURES, SHOWERS ARE ANTICIPATED FROM THIS
WEEKEND THROUGH THE MIDDLE OF NEXT WEEK.
MARINE/SURF
THE MARINE AND SURF ARE EXPECTED TO BE DIFFICULT FORECASTS FOR THE
COMING DAYS. THE MAIN CAUSE FOR THE DIFFICULTY WILL BE WHEN INVEST
95W'S EFFECTS AND THE SHEAR LINE WILL MOVE THROUGH THE REGION. AS 95W
BUILDS, IT IS EXPECTED TO PRODUCE A SOUTH SWELL THAT WILL INCREASE
SEAS AND SURF ALONG SOUTH AND WEST FACING REEFS. MODEL GUIDANCE HAS
BEEN SHOWING FOR THE PAST SEVERAL DAYS THAT 95W WILL MOVE WESTWARD
THEN EVENTUALLY TURN NORTHWARD. THIS WILL GRADUALLY CHANGE THE
DIRECTION OF THE THE INCOMING SWELL FROM SOUTH TO WEST OVER THE NEXT
SEVERAL DAYS. THE THE SHEAR LINE IS ALSO GOING TO KEEP NORTH FACING
REEF ELEVATED. BOTH FEATURE'S EFFECTS ARE ANTICIPATED TO ARRIVE
AROUND THE WEEKEND. IF THESE MODEL TRENDS CONTINUE, ADDITIONAL MARINE
AND COASTAL PRODUCTS MAY BE ISSUED OVER THE COMING DAYS.
HYDROLOGY
CONFIDENCE CONTINUES TO GROW REGARDING HEAVY RAINFALL POTENTIAL
SOMETIME THIS WEEKEND AND CONTINUING INTO THE FIRST PART OF NEXT
WEEK. CURRENTLY, A BROAD AND WEAK CIRCULATION IS IN THE INITIAL
STAGES OF FORMATION SOUTH-SOUTHEAST OF CHUUK/SOUTH-SOUTHWEST OF
KOSRAE, NORTH OF KAPINGAMARANGI. THIS DISTURBANCE WILL SLOWLY HEAD
WEST-NORTHWEST TOWARDS THE MARIANAS THE NEXT SEVERAL DAYS. AS IT
DOES SO, LOCALLY HEAVY RAINFALL MAY DEVELOP, WITH GUSTY WINDS ALSO
POSSIBLE WITH THE HEAVIER SHOWERS OR THUNDERSTORMS THAT DEVELOP.
AT THIS TIME, MODEL GUIDANCE INDICATES AT LEAST MEDIUM CONFIDENCE
FOR 5 TO 10 INCHES OF RAINFALL, WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. DUE TO ANTECEDENT RAINFALL OF OVER 4 INCHES IN SOME
LOCATIONS, THE POTENTIAL FOR FLASH FLOODING AND MUDSLIDES IS HIGHER
THAN NORMAL. AS WE APPROACH THIS EVENT, IF FORECAST CONFIDENCE
CONTINUES TO INCREASE, A FLASH FLOOD WATCH MAY NEED TO BE ISSUED WITH
LATER FORECASTS.
TROPICAL SYSTEMS
FOR SEVERAL DAYS THE MODELS HAVE BEEN SHOWING A WEAK CIRCULATION
DEVELOPING SOMEWHERE ALONG THE NET (NEAR-EQUATORIAL TROUGH) SOMEWHERE
BETWEEN 142E AND 151E, WITH SEVERAL MEMBERS OF THE EUROPEAN AND GFS
ENSEMBLE HAVING LATCHED ON TO A CENTER SOMEWHERE NEAR 5N149E OVER THE
LAST FEW DAYS. VISIBLE SATELLITE IMAGERY SHOWS A WEAK CIRCULATION
SOUTHEAST OF KOROR NEAR 5N138E, ANOTHER CIRCULATION NEAR 5N149E, AND
A THIRD CIRCULATION NEAR 3N153E. INCIDENTALLY THE LATEST ASCAT PASS
PRETTY CLEARLY SHOWED A CIRCULATION AT THE LATTER POSITION. HOWEVER,
RECENTLY, VISIBLE IMAGERY SHOWS THE 5N149E. THESE TWO CENTERS ARE
TRYING TO MERGE. WE HAD A GREAT COORDINATION CALLS EARLIER WITH JTWC
(THE JOINT TYPHOON WARNING CENTER). GIVEN THAT ASCAT PASS AND THE TWO
CIRCULATIONS WILL LIKELY MERGE, JTWC HAS PLACED INVEST 95W (SUB-LOW)
AT 4.9N 152.5E.
THE GENERAL THEME IS FOR THIS WEAKLY-ORGANIZED CIRCULATION(S) TO
MERGE AS IT HEADS TOWARDS YAP. IT THEN EITHER STALLS OR SLOWS DOWN
SIGNIFICANTLY AS IT TURNS NORTHEAST TOWARDS THE MARIANAS. IT'S WAY,
WAY TOO EARLY TO TALK ABOUT WHAT STRENGTH IT AND THE SUSTAINED WINDS
WILL BE. HOWEVER, WE HAVE MEDIUM CONFIDENCE ON THE TIMING AND HIGH
CONFIDENCE ON LOCALLY HEAVY RAINFALL ASSOCIATED WITH 95W DEVELOPING,
WHICH WAS TALKED ABOUT IN THE HYDROLOGY SECTION ABOVE.
EASTERN MICRONESIA
A POTENTIALLY WET PERIOD (AT TIMES) IS IN STORE FOR THE REGION, AS
INVEST 95W, CURRENTLY SOUTHWEST OF POHNPEI NEAR 4.9N 152.5E SLOWLY
ORGANIZES AND HEADS TOWARDS YAP AND THE MARIANAS. MEANWHILE, A WEAK
ITCZ (INTER-TROPICAL CONVERGENCE ZONE HAS FORMED EAST OF MAJURO AND
EXTENDS PAST THE DATE LINE. AS 95W SLOWLY EDGES WEST-NORTHWEST, THE
MODELS SHOW THE ITCZ RAPIDLY EXPANDING WEST IN THE 36 TO 72 HOUR TIME
FRAME, CONTINUING INTO THE WEEKEND (POSSIBLY LONGER). THIS IS DUE TO
THE SURFACE CONVERGENCE STRENGTHENING AS THE SYNOPTIC PATTERN
MODIFIES. THIS WILL LEAD TO A MAJORITY OF THE TIME LOCATIONS SEEING
AT LEAST SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS. WE THOUGHT
ABOUT INCREASING RAINFALL COVERAGE TO NUMEROUS FOR ALL THREE
LOCATIONS, BUT OPTED TO GIVE IT ANOTHER MODEL RUN OR TWO, AS TODAY IS
THE FIRST DAY THE ITCZ SHOWED A MUCH BETTER SIGNATURE IN THE MODEL
PRECIPITATION FIELDS AND THE GFS GDI (GAVVEZ-DAVISON INDEX)
FORECASTS.
AS FOR MARINE CONDITIONS, LIGHT TO GENTLE WINDS WILL BECOME GENTLE
TO MODERATE AT TIMES. SEAS WILL HOLD IN THE 5 TO 7 FOOT RANGE.
WESTERN MICRONESIA
THE MAIN WEATHER FEATURES AFFECTING WESTERN MICRONESIA THIS EVENING
ARE A TRADE-WIND TROUGH JUST EAST OF CHUUK, WHICH CONNECTS TO A WEAK
CIRCULATION NEAR THE EASTERN END OF THE NEAR-EQUATORIAL TROUGH (NET),
AND THE NET ITSELF WHICH RUNS A LITTLE SOUTH OF KOROR, PALAU.
CHUUK WILL HAVE SCATTERED SHOWERS TONIGHT, NUMEROUS THURSDAY, AND
WIDESPREAD LOCALLY HEAVY SHOWERS THURSDAY NIGHT, BACKING OFF TO
NUMEROUS FRIDAY, THEN SCATTERED FRIDAY NIGHT THROUGH MONDAY. WINDS
WILL BE 10 TO 15 KNOTS THROUGH FRIDAY NIGHT, THEN 5 TO 10 KNOTS
THROUGH MONDAY. SEAS WILL BE 5 TO 7 FEET THROUGH FRIDAY NIGHT, THEN 4
TO 6 FEET SATURDAY, 6 TO 8 FEET SUNDAY, AND 5 TO 7 FEET MONDAY. TAKEN
ALL TOGETHER, MAINLY BENIGN MARINE CONDITIONS WILL HOLD FOR CHUUK
THROUGH NEXT MONDAY.
YAP WILL SEE ISOLATED SHOWERS THROUGH FRIDAY, THEN SCATTERED SHOWERS
THROUGH MONDAY AS THE NEAR-EQUATORIAL TROUGH COMES NEAR. WINDS WILL
BE 10 TO 15 KNOTS THROUGH SATURDAY, THEN BECOME WEST TO NORTHWEST AT
5 KNOTS SUNDAY AND MONDAY. SEAS WILL BE 6 TO 8 FEET THROUGH FRIDAY,
THEN 7 TO 9 FEET THROUGH SUNDAY, AND BACK TO BETWEEN 6 AND 8 FEET
MONDAY. A HIGH SURF ADVISORY IS LIKELY OVER THE WEEKEND, AND MARINE
CONDITIONS WILL BE CHALLENGING, PERHAPS EVEN HAZARDOUS.
KOROR, PALAU WILL EXPERIENCE ISOLATED SHOWERS THROUGH FRIDAY NIGHT AS
THE NEAR-EQUATORIAL TROUGH CONTINUES TO LINGER TO THE SOUTH. THEN FOR
SATURDAY, SUNDAY AND MONDAY, THE TROUGH WILL LIFT UP OVER KOROR,
GIVING THEM SCATTERED SHOWERS OVER THAT TIME. WINDS WILL BE 10 TO 15
KNOTS THURSDAY AND FRIDAY, WITH 5 TO 10 KNOTS THE REST OF THE TIME
FROM TONIGHT THROUGH MONDAY. SEAS WILL BE 5 TO 7 FEET THROUGH THE
FORECAST PERIOD OTHER THAN POSSIBLY SUNDAY WHEN THEY COULD CREEP UP
TO BETWEEN 6 AND 8 FEET. OVERALL THIS WILL LEAD TO BENIGN MARINE
CONDITIONS THROUGH THE FORECAST PERIOD.
GUM WATCHES/WARNINGS/ADVISORIES
GU...HIGH RIP CURRENT RISK THROUGH THURSDAY AFTERNOON FOR GUZ001.
HIGH SURF ADVISORY UNTIL 4 PM CHST THURSDAY FOR GUZ001.
MP...HIGH RIP CURRENT RISK THROUGH THURSDAY AFTERNOON FOR MPZ001>003.
HIGH SURF ADVISORY UNTIL 4 PM CHST THURSDAY FOR MPZ001>003.
MARIANAS WATERS...NONE.
MARIANAS/HYDROLOGY: BOWSHER
EAST MICRONESIA/TROPICAL: DOLL
WEST MICRONESIA: STANKO
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