327
FXPQ50 PGUM 160901
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
701 PM CHST THU JUL 16 2026
MARIANAS SYNOPSIS
SATELLITE IMAGERY SHOWS MOSTLY CLOUDY SKIES, WHILE RADAR IMAGERY
SHOWS SCATTERED SHOWERS TO THE WEST OF THE COASTAL REGION. ALTIMETRY
SHOWS COMBINED SEAS OF 4 TO 5 FEET, WHILE TANAPAG BUOY SHOWS A
SEAS BEGINNING TO TREND DOWN FROM 5 TO 6 FEET.
DISCUSSION
TONIGHT THE SHOWERS JUST TO THE WEST ARE EXPECTED TO PROPAGATE EAST-
NORTHEASTWARD INTO OUR COASTAL WATERS AND LIKELY OVER THE ISLANDS.
OVER THE WEEKEND, WINDS ARE EXPECTED TO FALL TO LIGHT TO GENTLE AS
THE MARIANAS WILL BE BETWEEN TWO COMPETING WEATHER SYSTEMS, ONE TO
THE NORTH AND ONE TO THE SOUTH. WITH WINDS THIS LOW, ISLAND HEATING
MAY BE ENOUGH TO PRODUCE SCATTERED SHOWER AND ISOLATED THUNDERSTORMS
IN THE AFTERNOON FOR SATURDAY AND SUNDAY. SHOWERS AND WINDS MAY
RETURN AROUND TUESDAY.
MARINE
GENTLE TO MODERATE SOUTHWESTERLIES ARE EXPECTED THROUGH FRIDAY,
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED TONIGHT.
OVER THE WEEKEND, LIGHT TO GENTLE WINDS WILL PREVAIL, WINDS THIS LOW
MAY ALLOW FOR ISLAND EFFECT SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS TO POP UP SATURDAY AND SUNDAY AFTERNOON, DRIFTING OVER
THE COASTAL WATERS NORTHEAST OF THE ISLANDS. COMBINED SEAS OF 4 TO 5
FEET WILL TAPER DOWN TO AROUND 3 TO 4 FEET BY SATURDAY NIGHT AND MAY
REMAIN BENIGN THROUGH THE FIRST HALF OF NEXT WEEK.
TROPICAL SYSTEMS
INVEST 90W FROM JTWC CONTINUES TO SLOWLY ORGANIZE (IT WAS UPGRADED
TO "LOW" EARLIER THIS AFTENROON, MEANING ORGANIZED TROPICAL CYCLONE
DEVELOPMENT IS UNLIKELY WITHIN THE NEXT 24 HOURS). CONVECTION HAS
BECOME MORE WIDESPREAD NEAR THE DEVELOPING LLCC (LOW-LEVEL
CIRCULATION CENTER). LATEST POSITION IS SOUTH OF CHUUK, NEAR 4N152E.
WITH THAT SAID, THE CENTER IS STILL SOMEWHAT BROAD (ELONGATED) WITH
SLIGHTLY ELEVATED VORTICITY CENTERS (CIRCULATIONS JUST ABOVE THE
SURFACE), HELPING TO INFLUENCE THE WIND PATTERN NEAR THE SURFACE.
THIS SYSTEM IS EXPECTED TO REMAIN QUASI-STATIONARY THE NEXT 24 TO 36
HOURS OR SO, BEFORE IT STARTS TO LIFT OFF TO THE NORTH. THIS FAVORS
A WET PATTERN ACROSS MUCH OF THE FSM, FROM EASTERN YAP STATE THROUGH
POHNPEI AND KOSRAE, WITH LOCALLY HEAVY RAINFALL AND GUSTY WINDS
HIGHLY PROBABLE. A SPECIAL WEATHER STATEMENT WAS ISSUED LATE THIS
MORNING TO ADDRESS THIS, AND PREVIOUS FORECASTER THINKING HASN'T
CHANGED MUCH. THIS STATEMENT WILL GET UPDATED TOMORROW MORNING,
POSSIBLY SOONER IF CONDITIONS WARRANT IT.
THEN, THE 64,000 DOLLAR QUESTION IS WHERE WILL IT GO WHEN IT LIFTS
NORTH? THE OVERALL TREND HAS BEEN TO SHIFT THIS NORTH-NORTHWEST
TRAJECTORY WESTWARD WITH TIME, WITH THE LLCC LIKELY PASSING CLOSE TO
CHUUK AS IT BEGINS ITS TREK. THE MODELS ALSO SHOW 90W WILL TURN MORE
TO THE WEST-NORTHWEST AFTER CROSSING 10N. NOW, WHEN DOES IT TURN,
HOW ORGANIZED (STRONG) WILL IT BE, AND WHAT IMPACTS WILL IT HAVE?
THAT'S A GOOD QUESTION...AND TO BE HONEST...WE CAN'T ANSWER THAT YET.
SIMPLY PUT, IT'S STILL IN THE VERY EARLY STAGES OF FORMING, AND IT'S
ALREADY FURTHER WEST THAN EXPECTED 24 HOURS AGO. UNTIL THE CENTER
BECOMES BETTER-DEFINED, THE MODELS WILL CONTINUE TO STRUGGLE, WITH
OBSERVATIONAL TRENDS AND EXPERIENCE HELPING TO GUIDE US (ALONG WITH
CLIMATOLOGY).
EASTERN MICRONESIA
THE MAIN FORECAST CHALLENGES WERE RAINFALL POTENTIAL, WIND SPEEDS,
AND TEMPERATURES AT POHNPEI AND KOSRAE. INVEST 90W HAS DRIFTED
FURTHER WEST THAN EXPECTED TODAY, BUT, AN EAST-SOUTHEAST INFLOW WILL
LIKELY DEVELOP WITH THIS SYSTEM OVER THE WEEKEND, AIDED BY A NET
(NEAR-EQUATORIAL TROUGH) THAT IS LOCATED JUST SOUTH OF POHNPEI AND
MAJURO, WHILE PASSING THROUGH KOSRAE. OFTEN, THESE TWO FOCI ACT TO
INCREASE SHOWER AND THUNDERSTORM COVERAGE AND INTENSITY, WHICH ALSO
INCREASES WIND GUST SPEEDS. WITH THIS IN MIND, RAINFALL POTENTIAL WAS
INCREASED, WITH STRONGER WORDING FOR SUCH AND WITH REGARD TO WIND
GUSTS AT BOTH LOCATIONS, WHILE ALSO COOLING TEMPERATURES. THE
MAJORITY OF THE FORECAST (THROUGH MONDAY) WAS FOCUSED ON HOW WE
EXPECT THE PATTERN TO EVOLVE, WITH MAJURO NEEDING ONLY MINOR
UPDATES. ONE THING THAT LOOKS FAIRLY CERTAIN IS THE CROSS-EQUATORIAL
FLOW WILL CONTINUE, WITH SOUTHEAST TO SOUTHWEST SWELLS CONTINUING.
AS FOR MARINE CONDITIONS, SEAS WILL BE IN THE 4 TO 6 FOOT RANGE OVER
THE NEXT FEW DAYS. POHNPEI WILL SEE MODERATE TO FRESH WINDS THROUGH
THE WEEKEND, MAJURO WILL SEE LIGHT TO GENTLE WINDS, WITH KOSRAE IN
BETWEEN.
WESTERN MICRONESIA
A TROPICAL DISTURBANCE IN SOUTHERN CHUUK STATE, INVEST 90W, WAS
UPGRADED TO A LOW THIS AFTERNOON. IT IS STILL BEING MONITORED BY
JTWC, ALTHOUGH SIGNIFICANT DEVELOPMENT IS UNLIKELY WITHIN 24 HOURS.
A SPECIAL WEATHER STATEMENT WAS ISSUED EARLIER THIS MORNING FOR CHUUK
STATE AND EASTERN YAP STATE FOR HEAVY RAINFALL AND GUST POTENTIALS.
NUMEROUS TO WIDESPREAD LOCALLY HEAVY SHOWERS AND ISOLATED
THUNDERSTORMS REMAIN ACROSS MUCH OF CHUUK STATE TONIGHT. AS 90W
DRIFTS NORTHWARD, THE BULK OF CONVECTION SHIFTS OVER CHUUK LAGOON
LATE FRIDAY NIGHT THROUGH SATURDAY NIGHT. THIS IS WHEN THE PEAK IN
CONVECTIVELY-DRIVEN GUSTS ARE EXPECTED, WHICH LOOK TO BE FRESH TO
STRONG, POSSIBLY NEAR-GALE GUSTS. THEN UNSETTLED WEATHER STILL
REMAINS THROUGH EARLY NEXT WEEK AS 90W SHIFTS NORTH OF CHUUK.
LOCALLY HEAVY SHOWERS AND STRONG GUSTS ARE ALSO EXPECTED TO DEVELOP
ACROSS EASTERN YAP STATE, ALONG AN AREA OF CONVERGENT WESTERLIES
TRAILING 90W. THIS LOOKS TO EXPAND WESTWARD ACROSS THE MAIN ISLANDS
OF YAP AND PALAU, POSSIBLY BECOMING A MONSOON SURGE EARLY NEXT WEEK.
THE TIMING AND INTENSITY OF SHOWERS IS DEPENDING ON THE DEVELOPMENT
AND TRACK OF 90W.
ALTIMETRY AND BUOY DATA SHOW SEAS 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.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: BOWSHER
EAST MICRONESIA/TROPICAL: DOLL
WEST MICRONESIA: CRUZ
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