845
FXPQ50 PGUM 151918
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
518 AM CHST THU JUL 16 2026
MARIANAS UPDATE
LITTLE CHANGE IN THE WEATHER FORECAST. INCREASED SHOWER COVERAGE
SLIGHTLY DUE TO A MINOR SURGE IN SOUTHWESTERLIES, BUT THUNDER SHOULD
BE LIMITED TO THE COASTAL WATERS AS THESE BOUNDARIES ARE NOT LIKELY
TO SURVIVE AS THEY PASS OVER THE ISLANDS. IN ADDITION, WINDS ARE
EXPECTED TO INCREASE, SO INTRODUCED BREEZINESS FOR TODAY.
MARINE FORECAST REMAINS UNCHANGED. COMBINED SEAS OF 5 TO 7 FEET WILL
TAPER DOWN A FOOT BY TONIGHT, TO THEN PERSIST UNTIL THE WEEKEND,
ONCE THE WESTERLY AND SOUTHWESTERLY SWELLS WEAKEN FURTHER.
TROPICAL SYSTEMS UPDATE
THE JOINT TYPHOON WARNING CENTER (JTWC) HAS BEEN EYEING A NEW AREA,
NOW KNOWN AS INVEST AREA 90W CENTERED NEAR 4.6N 160.3E IN POHNPEI
STATE. THIS FEATURE REMAINS LARGELY DISORGANIZED WITH LITTLE TO NO
DISCERNIBLE LOW-LEVEL CIRCULATION CENTER, AND IS NOT LIKELY TO
CHANGE MUCH THE REST OF TODAY. HOWEVER, POTENTIALLY BETTER ODDS AT
CONSOLIDATION MAY BE DURING THE WEEKEND, AS THE MOMENT AXIS SHIFTS
SLIGHTLY NORTHWARD AND WESTERLY FLOW IMPROVES.
EASTERN MICRONESIA UPDATE
THE INTRODUCTION OF INVEST 90W JUST SOUTH OF POHNPEI, IN ADDITION TO
THE EXTENSIVE MONSOON-LIKE TROUGH SPANNING MOST OF MICRONESIA, IS
EXPECTED TO CONTINUE TO BRING UNSETTLED WEATHER TO THE AREA. AS SUCH,
INTRODUCED HIGHER SHOWER COVERAGE TO POHNPEI, KOSRAE AND MAJURO FOR
TODAY. IN ADDITION, SOME OF THESE CELLS ARE LIKELY TO PRODUCE OUTFLOW
BOUNDARIES THAT MAY BRING FRESH GUSTS THIS AFTERNOON. APART FROM
THAT, THE MARINE FORECAST REMAINS UNCHANGED FOR ALL THREE COASTAL
WATERS.
WESTERN MICRONESIA UPDATE
ONLY MINOR CHANGES WERE MADE TO THE FORECAST. INTRODUCED THUNDERSTORMS
BUT KEPT COVERAGE MINIMAL FOR PALAU AND YAP TODAY, AS WESTERLIES AND
SOUTHWESTERLIES CONTINUE. PROXIMITY TO THE NEWLY LABELED INVEST 90W
IS BRINGING HEAVIER SHOWERS TO CHUUK, WITH JUST OVER AN INCH FALLEN
THE LAST FEW HOURS WITH MORE CELLS FORMING UPSTREAM. AS SUCH, KEPT
SHOWER COVERAGE HIGHER WITH LOCALLY HEAVY WORDING AND STRONG GUSTS
FOR THIS MORNING, WITH LESSER SHOWERS DELAYED TO THE AFTERNOON.
OTHERWISE, THE MARINE FORECAST REMAINS UNCHANGED FOR ALL THREE
COASTAL WATERS.
PREV DISCUSSION
/ISSUED 617 PM CHST WED JUL 15 2026/
MARIANAS SYNOPSIS...
ISOLATED SHOWERS ARE EXPECTED TO CONTINUE TONIGHT WITH ISOLATED
THUNDERSTORMS POSSIBLE FOR TINIAN AND SAIPAN, AND THEN ALL ISLANDS
AFTER MIDNIGHT. HOWEVER, THE MONSOON FLOW REMAINS LARGELY NORTH OF
THE MARIANAS LEAVING CONDITIONS DRY OVERALL. BUOY AND MODEL DATA
SUPPORT COMBINED SEAS OF AROUND 6 FEET TONIGHT.
DISCUSSION...
THE MONSOON TROUGH REMAINS NORTH AND HAS LEFT THE MARIANAS IN A DRY
SLOT WITH ONLY ISOLATED SHOWERS AND THUNDERSTORMS. THE MONSOON TROUGH
MAY SHIFT SLOWLY CLOSER BUT WILL LIKELY REMAIN OFFSHORE, SO ONLY AN
INCREASE TO SCATTERED SHOWERS LOOKS POSSIBLE THURSDAY NIGHT AND MAYBE
FRIDAY NIGHT. HOWEVER, THE MONSOON TROUGH IS EXPECTED TO SLOWLY
WEAKEN OVER THE NEXT FEW DAYS AS WHAT REMAINS OF INVEST 97W GETS
SHEARED APART AND THE TUTT CELL TO THE NORTH WEAKENS AND SHIFTS WEST.
SOUTHWEST WINDS WILL THEN DROP OFF AND ALLOW FOR AFTERNOON ISLAND
EFFECT SHOWERS AND ISOLATED THUNDERSTORMS AS SOON AS SATURDAY
AFTERNOON, POSSIBLY LASTING THROUGH THE REST OF THE FORECAST PERIOD
IF WINDS REMAIN LIGHT. OUTSIDE OF THE ISLAND EFFECT, SHOWER COVERAGE
IS EXPECTED TO STAY ISOLATED.
MARINE/SURF...
FOR THE COASTAL WATERS, SHOWERS MAY BECOME SCATTERED LATE TONIGHT.
GENTLE TO MODERATE SOUTHWEST WINDS ARE EXPECTED FOR THE NEXT TWO
NIGHTS WITH MODERATE TO FRESH WINDS THURSDAY. WINDS LOOK TO START
DECREASING FRIDAY AND INTO THE WEEKEND. THIS MAY ALLOW ISLAND EFFECT
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS TO DRIFT OVER THE
COASTAL WATERS NORTHEAST OF THE ISLANDS SATURDAY AFTERNOON. SEAS OF
AROUND 6 FEET TONIGHT WILL REMAIN STEADY BEFORE GRADUALLY DECREASING
SOMETIME FRIDAY OR FRIDAY NIGHT. SWELLS CONSIST OF MAINLY A MONSOONAL
SOUTHWEST SWELL AND A SMALL EAST TRADE SWELL. ISOLATED THUNDERSTORMS
ARE EXPECTED THROUGH AT LEAST SATURDAY AFTERNOON.
ALONG THE COASTLINE, THERE WILL BE A MODERATE RISK OF RIP CURRENTS
ALONG SOUTH AND WEST FACING REEFS OF THE MARIANAS. THERE WILL ALSO BE
A MODERATE RISK OF LIGHTNING THROUGH AT LEAST SATURDAY AFTERNOON.
OBSERVATIONAL DATA SHOWED SHOULDER TO HEAD HIGH SURF TODAY ON WEST
FACING REEFS WHICH SHOULD CONTINUE THROUGH TONIGHT.
TROPICAL SYSTEMS...
A WEAK CIRCULATION LOOKS TO BE IN THE EARLY STAGES OF LLCC
CYCLOGENESIS WEST-SOUTHWEST OF KOSRAE/SOUTHEAST OF POHNPEI NEAR 4.6N
160.3E. THIS CIRCULATION HAS BECOME A LITTLE "TIGHTER" SINCE THIS
MORNING, WITH A CORRESPONDING LESS BROAD CYCLONIC FLOW. ENSEMBLES
SUGGEST LITTLE TO NO DEVELOPMENT IS EXPECTED WITH THIS SYSTEM IN THE
SHORT TERM. HOWEVER, IT MAY AMPLIFY THE ONGOING MONSOON FLOW OVER
PALAU AND YAP TOWARDS THE END OF THE FORECAST PERIOD. THE KEY ITEM
TO WATCH WE THINK WILL BE THE CROSS EQUATORIAL FLOW, AS JTWC (THE
JOINT TYPHOON WARNING CENTER) NOTED. WE AGREE WITH THIS ASSESSMENT
AND WILL CONTINUE TO MONITOR BOTH OF THOSE ITEMS OF INTEREST. AT THE
VERY LEAST, IT'LL LIKELY REMAIN AS A LPA (LOW PRESSURE AREA) AND
INCREASE SHOWER AND THUNDERSTORM POTENTIAL AT KOSRAE AND POHNPEI OVER
THE NEXT 48 HOURS OR SO.
EASTERN MICRONESIA...
POHNPEI AND KOSRAE STAND THE BEST CHANCE OF SEEING SOME RAINFALL THE
NEXT FEW DAYS, WITH SOME THUNDERSTORMS MIXED IN FROM TIME TO TIME AS
WELL. THIS IS DUE TO A (SLOWLY) DEVELOPING AREA OF LOW PRESSURE
WEST-SOUTHWEST OF KOSRAE. THE MODELS LIFT THIS FEATURE UP OVER
POHNPEI THE NEXT FEW DAYS, EJECTING IT NORTH-NORTHWEST AFTER ITS
PASSAGE. THIS RAINFALL POTENTIAL WILL BE AIDED BY THE CROSS-
EQUATORIAL FLOW THAT DEVELOPED. HERE, SUSTAINED WINDS HAVE BEEN
MOSTLY IN THE 10 TO 15 KNOT RANGE, HELPING TO ADVECT A SOUTHEAST TO
SOUTHWESTERLY SWELL INTO THE REGION. HOWEVER, THE SWELL HAS BEEN TAME
ENOUGH TO NOT POSE ANY BEACH HAZARDS. OVERALL, LOOK FOR INCREASING
RAINFALL POTENTIAL WITH LIGHT TO GENTLE WINDS GRADUALLY VEERING FROM
SOUTHERLY TO A MORE WESTERLY DIRECTION BY THE WEEKEND. AFTER THE
CIRCULATION DEPARTS THE REGION, SOMEWHAT DRIER WEATHER WILL RETURN TO
BOTH POHNPEI AND KOSRAE.
MAJURO REMAINS A LITTLE MORE TRICKY OF A FORECAST AS A NEARBY SURFACE
TROUGH HAS ONLY MODEST CONVERGENCE. STILL, THIS CONVERGENCE IS
SUFFICIENT ENOUGH FOR LOW-END SCATTERED SHOWER DEVELOPMENT JUST TO
THE NORTH AND NORTHEAST. WITH THIS IN MIND, WENT WITH SCATTERED
SHOWERS (30 PERCENT PROBABILITIES) FOR TONIGHT, WITH SHOWER COVERAGE
DROPPING BACK TO ISOLATED FOR TOMORROW. THE ISOLATED SHOWER COVERAGE
WILL PERSIST THROUGH THE WEEKEND, WITH CURRENTLY, NO HIGHER RAINFALL
POTENTIAL IN SIGHT. THIS LOWER RAINFALL POTENTIAL, COMBINED WITH
LIGHT WINDS, WILL ALLOW AFTERNOON HIGH TEMPERATURES TO PUSH 90
DEGREES THROUGH THE WEEKEND, POSSIBLY LONGER.
VARIABLE WINDS IN THE LIGHT TO GENTLE RANGE CAN BE EXPECTED NEAR THE
CIRCULATION WEST-SOUTHWEST OF KOSRAE THE NEXT FEW DAYS, WITH LIGHT
EASTERLIES AT MAJURO. SEAS WILL REMAIN IN THE 4 TO 6 FOOT RANGE.
WESTERN MICRONESIA...
A BROAD, WEST-TO-EAST ELONGATED CIRCULATION REMAINS LOOSELY CENTERED
SOUTHEAST OF POHNPEI THIS AFTERNOON. CONVERGING NORTH TO
NORTHWESTERLY FLOW ACROSS MUCH OF CHUUK STATE IS EXPECTED TO PRODUCE
NUMEROUS TO WIDESPREAD LOCALLY HEAVY SHOWERS AND ISOLATED
THUNDERSTORMS ACROSS WENO TONIGHT. THERE IS SOME UNCERTAINTY ON THE
DEVELOPMENT AND MOVEMENT ON THIS CIRCULATION, BUT THERE IS SOME MODEL
CONSENSUS IN AN UNSETTLED PATTERN FOCUSED ACROSS SOUTHERN CHUUK
STATE AS THE CIRCULATION DRIFTS WESTWARD, WITH A PERIOD OF HIGH-END
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS WENO THURSDAY
THROUGH FRIDAY. DEPENDING ON HOW THE SYSTEM REORGANIZES AND LIFTS
NORTHWEST, SHOWERS LOOKS TO INCREASE BACK UP TO NUMEROUS ACROSS CHUUK
LAGOON STARTING LATE FRIDAY NIGHT. FOR YAP AND PALAU, THE MONSOON
TROUGH AND THE REMNANTS OF INVEST 97W REMAIN WELL TO THE NORTH.
STILL, A LINE OF PATCHY SHOWERS CONTINUES TO TRAIN OVER THE ISLANDS
THROUGH THURSDAY NIGHT, THEN SHOWERS LOOK TO INCREASE OVER THE
WEEKEND, ALONG CONVERGENT WESTERLIES LEADING INTO THE CIRCULATION
NEAR CHUUK. SINCE THERE IS SOME UNCERTAINTY ON THE ACTUAL DEVELOPMENT
AND MOVEMENT OF THE CIRCULATION, THIS MAY VARY THE TIMING OF
SCATTERED TO NUMEROUS SHOWERS LATE WEEK AND OVER THE WEEKEND.
ALTIMETRY SHOWS COMBINED SEAS OF 3 TO 5 FEET ACROSS THE REGION AND
ARE EXPECTED TO CONTINUE THROUGH EARLY NEXT WEEK. WEST SWELL
GRADUALLY WEAKENS, THEN LIGHT SOUTHEAST AND EAST SWELLS MIX IN OVER
THE NEXT FEW DAYS. FOR YAP AND PALAU, GENTLE TO FRESH SOUTHWEST TO
WEST WINDS PERSIST THROUGH SATURDAY, DECREASING TO GENTLE TO MODERATE
WESTERLIES EARLY NEXT WEEK. LIGHT TO GENTLE NORTH WINDS ARE EXPECTED
AT CHUUK THROUGH FRIDAY WITH OCCASIONAL GUSTS TO 20 KT NEAR HEAVIER
SHOWERS TONIGHT. THEN WINDS INCREASE TO LIGHT TO MODERATE FRIDAY
NIGHT AND SATURDAY, SHIFTING OUT OF THE NORTHWEST.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA/TROPICAL UPDATE: MONTVILA
MARIANAS: OGLE
EAST MICRONESIA/TROPICAL: DOLL
WEST MICRONESIA: CRUZ
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