200
FXPQ50 PGUM 170921
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
721 PM CHST FRI JUL 17 2026
MARIANAS SYNOPSIS
SATELLITE IMAGERY SHOWS MOSTLY CLOUDY SKIES, WHILE RADAR IMAGERY
SHOWS ISOLATED SHOWERS TO THE WEST OF THE COASTAL REGION. ALTIMETRY
SHOWS COMBINED SEAS OF 3 TO 5 FEET, WHILE TANAPAG BUOY SHOWS SEAS
CONTINUING TO TREND DOWN TO 4 TO 5 FEET.
DISCUSSION
A TRADE-WIND PATTERN OF ISOLATED TO LOW-END SCATTERED SHOWERS IS
EXPECTED THROUGH MONDAY. DURING THE AFTERNOON ON SATURDAY AND SUNDAY,
THE WINDS ARE EXPECTED TO BE LIGHT AND ISLAND-EFFECT SHOWERS MAY
BUILD IN. ISOLATED THUNDERSTORMS ARE POSSIBLE FOR SATURDAY AFTERNOON.
LOOKING FORWARD, A TROPICAL DISTURBANCE, INVEST 90W, IS CURRENTLY
LOCATED IN CHUUK STATE AND IS SOMETHING WE ARE CLOSELY MONITORING.
CURRENT MODEL GUIDANCE SUGGESTS A GENERAL TRACK NORTH-NORTHWESTWARD
OVER THE WEEKEND, GRADUALLY MOVING CLOSER TO THE MARIANAS AROUND
MIDWEEK. FOR NOW, A TREND TOWARDS A WETTER PATTERN IS EXPECTED NEXT
WEEK, WITH LOCALLY HEAVY SHOWERS AND STRONGER GUSTS POSSIBLE.
HOWEVER, AT THIS POINT IN TIME, THERE IS STILL A DEGREE OF
UNCERTAINTY TO SIGNIFICANT IMPACTS TO THE MARIANAS, BASED ON THE LACK
OF MODEL CONSENSUS. FURTHER UPDATES WITH POTENTIAL IMPACTS WILL BE
PROVIDED, BASED ON SUBSEQUENT MODEL RUNS AND THE OVERALL DEVELOPMENT
OF 90W IN THE COMING DAYS.
MARINE/SURF
GENTLE TO MODERATE SOUTHWESTERLIES WILL PREVAIL ACROSS THE MARIANAS
TONIGHT, BEFORE TAPERING DOWN THEREAFTER. COMBINED SEAS OF 4 TO 5
FEET WILL TAPER DOWN TO AROUND 3 TO 4 FEET BY SATURDAY NIGHT,
REMAINING FOR A DAY OR TWO BEFORE POSSIBLY BUILDING BY A FOOT OR SO
AROUND THE MIDDLE OF NEXT WEEK. AS WESTERLY SWELL GRADUALLY SUBSIDES,
A MODERATE RISK OF RIP CURRENTS REMAINS ALONG WEST FACING REEFS
THROUGH AT LEAST SATURDAY. AFTER WHICH, A LOW RISK OF RIP CURRENTS IS
EXPECTED ALONG ALL REEFS FOR A FEW DAYS. AROUND THE MIDDLE OF NEXT
WEEK, THE RIP RISK MAY INCREASE BACK UP TO MODERATE WITH AN INCREASE
IN SWELLS ASSOCIATED WITH THE DEVELOPING PATTERN AROUND 90W.
TROPICAL SYSTEMS
INVEST 90W, CURRENTLY REMAINS AT A "LOW" RATING FROM JTWC (THE
JOINT TYPHOON WARNING CENTER), MEANING TROPICAL CYCLONE
DEVELOPMENT IS NOT LIKELY WITHIN THE NEXT 24 HOURS. 90W CONTINUES
TO REMAIN QUASI-STATIONARY SOUTHEAST OF CHUUK, NEAR NAMOLUK. THIS
SYSTEM REMAINS IN A SOMEWHAT HOSTILE ENVIRONMENT, WITH WIND SHEAR
OF 15 TO 20 KNOTS NOTED.
HOWEVER, MORE FAVORABLE CONDITIONS (LESS WIND SHEAR) ARE LOCATED
JUST NORTH OF THE REGION. THE WIND SHEAR IS HELPING TO LIMIT
CONVECTIVE DEVELOPMENT, WITH POCKETS OF CONVECTION TRYING TO DEVELOP
AROUND THE LLCC (LOW-LEVEL CIRCULATION CENTER). THESE CONVECTIVE
ATTEMPTS ARE HAVING SOME SUCCESS IN DEVELOPING DEEPER/TALLER
UPDRAFTS, BUT, 90W IS STILL FIGHTING THE "WIND SHEAR BATTLE".
HOWEVER, AS IT LIFTS NORTH, THE IMPROVED CONDITIONS SHOULD ALLOW FOR
AN INCREASE IN CONVECTIVE COVERAGE AND STRENGTH.
THE OVERALL PATTERN WOULD FAVOR THIS "NORTHWARD JOG" STARTING
SOMETIME OVER THE NEXT 24 HOURS OR SO, WITH A GRADUAL CONTINUED
STRENGTHENING. THEN, ABOUT 60 TO 84 HOURS OUT THE SYSTEM LOOKS TO
MAKE MORE OF A NORTHWESTWARD TURN AND HEAD TOWARDS/THROUGH THE
MARIANAS. AS IT DOES SO, LOCALLY HEAVY RAINFALL AND GUSTY WINDS
ARE POSSIBLE TOWARDS THE MIDDLE OF NEXT WEEK.
EASTERN MICRONESIA
THE SOUTHWESTERLY WINDS AND CROSS-EQUATORIAL FLOW IS HELPING TO
GENERATE SOME SHOWERS THAT HAVE PUSHED ACROSS POHNPEI AND KOSRAE
THIS AFTERNOON, AND THIS WAS EXPECTED AS THE INFLOW INTO 90W SLOWLY
STRENGTHENS. AS SUCH, THERE'S NOT MUCH CHANGE FROM YESTERDAY WITH
REGARDS TO THE FORECAST OR FORECASTER THINKING AT ALL THREE
LOCATIONS (POHNPEI, KOSRAE, AND MAJURO). LOCALLY HEAVY RAINFALL AND
ISOLATED WINDS GUSTS TO 25 KNOTS REMAIN POSSIBLE AT POHNPEI AND
KOSRAE THROUGH SUNDAY NIGHT OR MONDAY, WITH MAJURO REMAINING ON THE
DRIER SIDE OF THINGS.
AS FOR MARINE CONDITIONS, SIMILAR TO YESTERDAY, POHNPEI WILL SEE
MODERATE TO FRESH WINDS THROUGH THE WEEKEND, AS YOU'RE CLOSER TO
INVEST 90W AND ITS EFFECTS, WITH WINDS DIMINISHING FOR DURING THE
FIRST HALF OF NEXT WEEK. KOSRAE WILL GENERALLY SEE LIGHT TO GENTLE
WINDS, BRIEFLY BECOMING MODERATE TO FRESH NEAR HEAVIER SHOWERS
THROUGH THE WEEKEND, THEN LIGHT TO GENTLE THEREAFTER. MAJURO REMAINS
IN THE LIGHT TO GENTLE WINDS. SEAS OF 4 TO 6 FEET WILL PERSIST AREA-
WIDE.
WESTERN MICRONESIA
A TROPICAL DISTURBANCE, INVEST 90W, IS NOW LOCATED SOUTHEAST OF CHUUK
LAGOON NEAR 7N153E. DEVELOPMENT INTO A TROPICAL DEPRESSION REMAINS
UNLIKELY WITHIN THE NEXT 24 HOURS. A SPECIAL WEATHER STATEMENT
REMAINS IN EFFECT FOR CHUUK STATE AND EASTERN YAP STATE FOR HEAVY
RAINFALL AND STRONGER GUST POTENTIALS. FLARING DEEP CONVECTION
REMAINS FOCUSED ALONG THE 90W'S SOUTHERN FLANK, WITH A GOOD BUILDUP
OF SHOWERS ENCOMPASSING EASTERN YAP STATE, ALONG CONVERGENT WESTERLY
FLOW. AS 90W DRIFTS NORTH TO NORTHWESTWARD, THE BULK OF CONVECTION
SHIFTS OVER CHUUK LAGOON LATE TONIGHT THROUGH SUNDAY. THIS IS WHEN
THE PEAK IN CONVECTIVELY-DRIVEN GUSTS ARE EXPECTED, WITH FRESH TO
STRONG, POSSIBLY NEAR-GALE GUSTS. THEN UNSETTLED WEATHER STILL
REMAINS THROUGH EARLY NEXT WEEK AS 90W SHIFTS NORTH OF CHUUK. THE
UNSETTLED PATTERN ACROSS EASTERN YAP STATE MAY EXPAND WESTWARD
ACROSS THE MAIN ISLANDS OF YAP AND PALAU, POSSIBLY BECOMING A MONSOON
SURGE EARLY NEXT WEEK. THE TIMING AND INTENSITY OF SHOWERS WILL STILL
DEPEND ON THE DEVELOPMENT AND TRACK OF 90W IN THE COMING DAYS.
ALTIMETRY AND BUOY DATA SHOW SEAS OF 3 TO 5 FEET ACROSS THE REGION.
SEAS LOOK TO BUILD TO 4 TO 6 FEET OVER THE WEEKEND, POTENTIALLY UP TO
7 FEET AT CHUUK WITH THE NEARBY TROPICAL DISTURBANCE. PERSISTENT,
GENTLE TO FRESH WESTERLIES ACROSS YAP AND PALAU WILL KEEP SEAS 3 TO 5
FEET, AT TIMES 4 TO 6 FEET THROUGH NEXT WEEK. HEAVY SHOWERS AND
STRONG GUSTS ACROSS CHUUK AND YAP STATE WILL CONTINUE TO POSE
CHALLENGES TO SMALL CRAFT OPERATIONS. THERE IS A POSSIBILITY FOR
SUSTAINED WINDS TO REACH HAZARDOUS LEVELS OF 22 KT OR MORE AT CHUUK
AND YAP, SO THIS MAY WARRANT A SMALL CRAFT ADVISORY.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: BOWSHER/CRUZ
EAST MICRONESIA: DOLL
WEST MICRONESIA: CRUZ
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