178
FXPQ50 PGUM 311915
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
515 AM CHST SUN FEB 1 2026
MARIANAS UPDATE
SATELLITE IMAGERY SHOWS SCATTERED SHOWERS ACROSS THE MARIANAS WITH
HEAVIER SHOWERS SEEN BETWEEN ROTA AND TINIAN. ALTIMETRY SHOWS
COMBINED SEAS BETWEEN 8 TO 10 FEET.
NO CHANGE WAS MADE WITH THIS FORECAST PACKAGE. SCATTERED SHOWERS
ALONG THE LEANING EDGE OF THE SHEAR LINE CONTINUE TO IMPACT THE CNMI.
SHOWER COVERAGE HAS BEEN LOWER OVER GUAM, BUT IS EXPECTED TO INCREASE
TODAY AS THE EDGE OF THE SHEAR LINE APPROACHES. WE ARE STILL
MONITORING THE DISTURBANCE THAT IS CURRENTLY DEVELOPING IN CHUUK
STATE, WHICH IS EXPECTED TO BRING A SURGE OF MOISTURE NORTHWARD
TOWARDS THE MARIANAS. THE TIMING OF THIS MOISTURE SURGE AND THE PRE-
EXISTING SHEAR LINE COULD LEAD TO VERY HEAVY RAINFALL WITH A SHARP
CUTOFF ON THE NORTHEAST SIDE. MOST GUIDANCE GENERALLY KEEPS THIS
HEAVIER RAINFALL JUST WEST OF GUAM, BUT THE GEFS HAS BEEN SHOWING THE
PRECIPITATION AXIS A LITTLE FURTHER EAST. THE LATEST EPS HAVE ALSO
SHIFTED NORTHEAST A TOUCH AS WELL. NO CHANGE WAS MADE TO THE EXTENDED
FORECAST, BUT THOSE IN THE MARIANAS SHOULD CONTINUE TO MONITOR
FORECASTS FOR UPDATES WITH THE DEVELOPING DISTURBANCE TO OUR SOUTH.
NO CHANGES WERE MADE TO THE MARINE FORECAST. THE SMALL CRAFT ADVISORY
CONTINUES FOR SAIPAN AND TINIAN AND WILL GO IN EFFECT FOR GUAM AND
ROTA AT 6 AM CHST. SEAS LOOK TO REMAIN HAZARDOUS TO SMALL CRAFT UNTIL
TUESDAY MORNING WHEN SEAS BEGIN TO SUBSIDE. HAZARDOUS SURF WILL
CONTINUE FOR NORTH FACING REEFS UNTIL TUESDAY MORNING AS WELL.
EASTERN MICRONESIA UPDATE
NO CHANGES WERE MADE TO THE EASTERN MICRONESIA FORECAST. SATELLITE
IMAGERY SHOWS SCATTERED SHOWERS ACROSS POHNPEI AND MAJURO, AND
ISOLATED SHOWERS ACROSS KOSRAE. GUIDANCE SHOWS A BRIEF LULL IN
ACTIVITY TONIGHT AND INTO MONDAY BEFORE THE NEAR EQUATORIAL TROUGH
REDEVELOPS, BRINGING INCREASED SHOWERS AND THUNDERSTORMS TO POHNPEI
AND KOSRAE LATER THIS WEEK.
NO CHANGES WERE MADE TO THE MARINE FORECAST. COMBINED SEAS ARE
BETWEEN 7 AND 9 FEET ACROSS POHNPEI AND MAJURO AND 6 TO 8 FEET ACROSS
KOSRAE. SEAS WERE NEAR HAZARDOUS CONDITIONS FOR SMALL CRAFT AT
MAJURO, BUT THE HIGHER SEAS LOOK TO REMAIN JUST EAST OF THE COASTAL
WATERS, WITH GUIDANCE SHOWING A DECREASE IN SEAS TODAY.
WESTERN MICRONESIA UPDATE
THE WESTERN MICRONESIA FORECAST REMAINS STATUS QUO. ALL EYES ARE ON
THE TROPICAL DISTURBANCE LOCATED ACROSS WESTERN CHUUK STATE AND
EASTERN YAP STATE. GUIDANCE CONTINUES TO SHOW ORGANIZATION OF THIS
SYSTEM AS IT MOVES TOWARDS PALAU AND YAP OVER THE COMING DAYS. VERY
HEAVY RAINFALL WILL BE POSSIBLE WITH THIS SYSTEM AS WELL AS GUSTY
WINDS. THOSE IN PALAU AND YAP SHOULD CONTINUE TO MONITOR FORECAST FOR
UPDATES OVER THE COMING DAYS.
NO CHANGES WERE MADE TO THE MARINE FORECAST. BENIGN SEAS ARE EXPECTED
TO CONTINUE THROUGH THE PERIOD, BUT CHOPPY SEAS WILL BE POSSIBLE NEAR
THE TROPICAL DISTURBANCE AND SURROUNDING SHOWERS.
PREV DISCUSSION
/ISSUED 605 PM CHST SAT JAN 31 2026/
MARIANAS SYNOPSIS...
SATELLITE IMAGERY SHOWS MOSTLY CLOUDY SKIES AND SCATTERED SHOWERS
ACROSS SAIPAN AND TINIAN AND INCREASE TOWARDS ROTA AND GUAM AS THE
SHEAR LINE CONTINUES TO PUSH SOUTHWARD. THIS IS ALSO PRODUCING
HAZARDOUS MARINE CONDITIONS ACROSS THE WATERS OF TINIAN AND SAIPAN
THAT WILL EXPAND TO ROTA AND GUAM SUNDAY. THERE IS A HIGH RISK OF RIP
CURRENTS ALONG ALONG NORTH AND EAST FACING REEFS WITH HAZARDOUS SURF
ALONG NORTH FACING REEFS. UNSETTLED AND BREEZY CONDITIONS WILL
CONTINUE THROUGH AT LEAST MONDAY NIGHT.
DISCUSSION...
THE SHEAR LINE IS SLOWLY SHIFTING SOUTHWARD TOWARDS ROTA AND GUAM
AS A RIDGE OF HIGH PRESSURE BUILDS NORTH OF THE SHEAR LINE AND LOW
PRESSURE STRENGTHENS SOUTH OF THE MARIANAS. MOST OF THE SCATTERED
SHOWERS ACROSS THE MARIANAS HAVE LIGHT TO MODERATE RAINFALL RATES AS
NUCAPS SOUNDINGS STILL SHOW A TYPICAL SHEAR LINE MOISTURE PATTERN OF
HIGHER MOISTURE NEAR THE SURFACE AND DRIER AIR ALOFT, BUT THERE HAS
BEEN SOME LOCALIZED HEAVIER SHOWERS WHERE CONDITIONS ARE JUST RIGHT
TO SUPPORT HIGHER RAIN RATES. THE RISK OF THE THUNDERSTORMS REMAINS
LOW DUE TO THE DRIER AIR ALOFT AND THE RISK OF FLOODING REMAINS
LIMITED BUT NOT ZERO. BREEZY WINDS AROUND 25 MPH EXTEND ACROSS TINIAN
AND SAIPAN AND WILL EXTEND INTO ROTA AND GUAM BY SUNDAY. OCCASIONALLY
STRONGER GUSTS UP TO 35 MPH WILL LIKELY OCCUR ACROSS THE ISLANDS
THROUGH MONDAY, ESPECIALLY WITH THE PASSAGE OF SHOWERS.
CONTINUING TO WATCH THE POTENTIAL DISTURBANCE DEVELOPING IN CENTRAL
MICRONESIA AND THEN DRIFTING WESTWARD ACROSS WESTERN MICRONESIA.
OVERALL MODEL GUIDANCE STILL SUPPORTS THE SYSTEM PASSING CLOSER TO
YAP AND PALAU, BUT MOISTURE ON THE NORTHERN SIDE OF THE SYSTEM SHOULD
INCREASE THE POTENTIAL FOR THUNDERSTORMS ACROSS THE MARIANAS MONDAY
OR MONDAY NIGHT WHILE ALSO HELPING TO PROLONG BREEZY CONDITIONS. FOR
NOW, EXPECT THE BREEZY CONDITIONS TO DROP TUESDAY AS THE SHEAR LINE
WEAKENS, BUT THE POTENTIAL FOR SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS WILL LINGER DUE TO THE INFLUX OF MOISTURE.
MARINE...
SURF IS OR WILL SHORTLY BUILD TO AROUND HAZARDOUS LEVELS OF 9 FEET
FOR NORTH FACING REEFS WITH DANGEROUS RIP CURRENTS ALONG NORTH AND
EAST FACING REEFS AS SURF BUILDS DUE TO INCOMING NORTHERLY SWELL AND
BUILDING NORTHEAST SWELL DUE TO THE SHEAR LINE. SURF IS EXPECTED TO
PEAK AROUND 11 FEET SUNDAY BEFORE SLOWLY DECREASING THROUGH MONDAY
NIGHT AS THE SHEAR LINE WEAKENS AND THE NORTHERLY SWELL DIMINISHES.
COMBINED SEAS ARE ALSO BUILDING IN RESPONSE TO THE INCREASED WINDS
ALONG AND NORTH OF THE SHEAR LINE AND DUE TO THE BUILDING NORTH TO
NORTHEAST SWELL. HAZARDOUS MARINE CONDITIONS OF SEAS AROUND 10 FEET
AND WINDS AROUND 25 KT ARE OCCURRING AT TINIAN AND SAIPAN AND WILL
EXPAND TO ROTA AND GUAM WATERS SUNDAY. WINDS AND SEAS ARE EXPECTED
TO DECREASE MONDAY NIGHT INTO TUESDAY AS THE SHEAR LINE WEAKENS,
ALLOWING SEAS TO DROP JUST BELOW 10 FEET AND WINDS BELOW 22 KT
TUESDAY, WITH SURF NOW EXPECTED TO DROP BELOW 9 FEET AROUND THE SAME
TIME, BUT THIS COULD CHANGE DUE TO THE THE COMPLEX MIXTURE OF SWELLS.
TROPICAL SYSTEMS...
WITHIN THE NEAR EQUATORIAL TROUGH, SCATTEROMETER AND VISIBLE
SATELLITE EARLIER TODAY SUGGEST TWO BROAD CIRCULATIONS EXIST SOUTH
OF CHUUK AND POHNPEI, JUST NORTH OF THE EQUATOR. BOTH DETERMINISTIC
AND ENSEMBLE MODELS CONTINUE TO POINT TO A MORE ORGANIZED CIRCULATION
CONSOLIDATING WITHIN WESTERN MICRONESIA SW OF CHUUK EARLY NEXT WEEK
AND SLOWLY HEADING WEST. WHILE INDIVIDUAL MODELS CONTINUE TO VARY ON
TIMING AND EVOLUTION, THE POTENTIAL FOR A DEVELOPING CIRCULATION
EARLY NEXT WEEK BEARS WATCHING. ADDITIONALLY, WITH A SHEAR LINE
ANTICIPATED TO DROP SOUTH OVER THE PHILIPPINE SEA NEXT WEEK, THE TWO
FEATURES COULD COMBINE FOR A WET AND VERY UNSETTLED PATTERN IN FAR
WESTERN MICRONESIA WEST OF 140E AND SOUTH OF 15N.
EASTERN MICRONESIA...
THE MAIN FORECAST CHALLENGES ARE RAINFALL POTENTIAL AND BUILDING SEAS
NEXT WEEK. CURRENTLY, ONE CIRCULATION IS LOCATED WELL SOUTH OF CHUUK
WITH ANOTHER WELL SOUTH OF POHNPEI/SOUTHWEST OF KOSRAE. BOTH
CIRCULATIONS ARE LOCATED ALONG THE NET (NEAR-EQUATORIAL TROUGH),
WITH FAIRLY WIDESPREAD CONVECTION (SOME OF WHICH IS LOCALLY INTENSE)
AFFECTING POHNPEI AND KOSRAE. GIVEN A SLOW PROGRESSION OF THESE
SYSTEMS, POHNPEI LOOKS TO SEE SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS FOR MUCH OF THE PERIOD. AT KOSRAE, YOU'RE LOCATED ON
THE VERY BACK EDGE OF THE INCREASED SURFACE CONVERGENCE AND DEEPER
MOISTURE, WITH THE LATEST MIMIC WATER VAPOR IMAGERY SUGGESTING
DECREASING PRECIPITABLE WATER VALUES (PWATS) CURRENTLY MOVING INTO
THE REGION. WITH THIS IN MIND WE WENT WITH JUST LOW-END SCATTERED
SHOWERS TONIGHT AT KOSRAE GIVEN THIS TREND, BUT WE'LL CONTINUE TO
MONITOR SATELLITE TRENDS.
AT MAJURO, AN AREA OF ENHANCED SURFACE CONVERGENCE IS MOVING INTO THE
REGION, WITH MIMIC IMAGERY SHOWING INCREASING MOISTURE VALUES NORTH
AND EAST OF THIS CONVERGENCE EDGE. HOWEVER, SATELLITE IMAGERY IS LESS
THAN IMPRESSIVE. AS SUCH, WENT WITH LOW-END SCATTERED SHOWER COVERAGE
(30% PROBABILITIES) FOR TONIGHT INTO SUNDAY TO ACCOUNT FOR NOCTURNAL
INFLUENCES, DROPPING BACK TO ISOLATED COVERAGE FOR SUNDAY NIGHT AND
CONTINUING THROUGH THE MIDDLE OF THE WEEK. HOWEVER, IF AN UPSTREAM
TROUGH EAST OF THE DATE LINE BECOMES MORE CONVECTIVELY ACTIVE,
RAINFALL PROBABILITIES MAY NEED TO BE INCREASED BY MIDWEEK.
AS FOR MARINE CONDITIONS, MAINLY GENTLE TO FRESH WINDS WILL PREVAIL,
BUT THEY COULD BRIEFLY BECOME MODERATE TO STRONG AT MAJURO EARLY
NEXT WEEK. MAJURO WILL ALSO SEE CHOPPY SEAS GIVEN A TIGHTENING
PRESSURE GRADIENT AND GOOD FETCH LENGTH, WITH SOMEWHAT MORE TAME SEAS
EXPECTED AT POHNPEI AND KOSRAE.
WESTERN MICRONESIA...
DRY CONDITIONS PREVAIL ACROSS YAP AND PALAU THIS AFTERNOON WITH
MOSTLY CLEAR SKIES AND NO SHOWERS IN THE VICINITY OF EITHER
LOCATION. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE FOUND
ACROSS CHUUK STATE. A SHEAR LINE SITS NORTH OF YAP AND PALAU, ALONG
13N, WHILE A NEAR-EQUATORIAL TROUGH (NET) REMAINS SITUATED TO THE
SOUTH ALONG 3N.
A SHOWERY PATTERN WILL PERSIST ACROSS CHUUK STATE AS A MOIST TRADE
WIND PATTERN KEEPS SHOWERS IN PLACE THROUGH EARLY TO MIDWEEK.
FARTHER WEST, THE DRIER PATTERN WILL CONTINUE THROUGH TONIGHT ACROSS
YAP STATE, AND ANOTHER COUPLE OF DAYS FOR PALAU. BEYOND SUNDAY,
WEATHER CONDITIONS WILL HINGE CLOSELY ON THE EVOLUTION OF A TROPICAL
DISTURBANCE WITHIN THE NET. ASCAT ANALYSIS DEPICTS A BROAD AND WEAK
CIRCULATION WITHIN THE NET, CURRENTLY SOUTH OF CHUUK STATE.
NUMERICAL MODELS MAINTAIN A WESTWARD OR A WEST-NORTHWESTARD TRACK
FOR THIS DISTURBANCE THROUGH MIDWEEK, POTENTIALLY WITH SOME
DEVELOPMENT.
AT THIS EARLY STAGE, A WETTER PATTERN FOR YAP AND PALAU IS EXPECTED,
BEGINNING MONDAY AND CONTINUING THROUGH MIDWEEK. WIND FORECASTS,
SUBJECT TO CHANGE IN THE COMING DAYS, WILL DEPEND ON THE EVOLUTION
OF THE TROPICAL DISTURBANCE: EXACT TRACK, AND WHETHER THERE WILL BE
DEVELOPMENT. RESIDENTS ACROSS THE OUTER ISLANDS AND ATOLLS OF
EASTERN YAP AND WESTERN CHUUK STATES ARE LIKELY EXPERIENCING PERIODS
OF SHOWERS, ISOLATED THUNDERSTORMS AND LOCALLY HEAVY RAINFALL NOW,
OR VERY SOON.
ALTIMETRY INDICATED SEAS OF 5 TO 7 FEET ACROSS MUCH OF YAP AND CHUUK
STATES, WITH SEAS AROUND 4 TO 6 FEET NEAR PALAU. SEAS WILL BUILD
AROUND 1 TO 2 FEET AT ALL LOCATIONS BY MONDAY AS A LARGER NORTH
SWELL PUSHES SOUTHWARD FROM ALONG THE SHEAR LINE.
GUM WATCHES/WARNINGS/ADVISORIES
GU...HIGH RIP CURRENT RISK THROUGH LATE MONDAY NIGHT FOR GUZ001.
HIGH SURF ADVISORY UNTIL 6 AM CHST TUESDAY FOR GUZ001.
MP...HIGH RIP CURRENT RISK THROUGH LATE MONDAY NIGHT FOR MPZ001>003.
HIGH SURF ADVISORY UNTIL 6 AM CHST TUESDAY FOR MPZ001>003.
MARIANAS WATERS...SMALL CRAFT ADVISORY UNTIL 6 AM CHST TUESDAY FOR PMZ151-152.
SMALL CRAFT ADVISORY UNTIL 6 AM CHST TUESDAY FOR PMZ153-154.
MARIANAS: WILLIAMS
EASTERN/WESTERN MICRONESIA: WILLIAMS
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