955
FXPQ50 PGUM 180847
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
647 PM CHST SAT JUL 18 2026
MARIANAS SYNOPSIS
SATELLITE AND RADAR IMAGERY THIS AFTERNOON SHOW ISOLATED SHOWERS
DRIFTING EAST-NORTHEAST ACROSS MARIANAS COASTAL WATERS, INCLUDING
THE REMNANTS OF ISLAND-EFFECT CONVECTION DIMINISHING WELL OFF THE
NORTHEAST SHORELINE OF GUAM. ALTIMETRY AND TANAPAG BUOY DATA INDICATE
COMBINED SEAS BETWEEN 3 AND 4 FEET, COMPRISED OF PRIMARY SWELL FROM
THE SOUTHWEST AND A SECONDARY NORTHEAST TRADE SWELL.
DISCUSSION
THE MARIANAS REMAIN WITHIN THE BROAD, WEST-TO-SOUTHWEST WIND FIELD
BETWEEN INVEST 90W TO THE SOUTHEAST, AND A LOW PRESSURE AREA LOCATED
FAR TO THE NORTH, NEAR IWO TO. THERE IS A COL AREA BETWEEN THESE TWO
FEATURES, LOCATED TO THE EAST OF THE COASTAL WATERS, WHICH MODELS
SUGGEST WILL HAVE MORE OF AN INFLUENCE ON SUNDAY AS LIGHTER, MORE
SOUTHERLY WINDS DEVELOP. THIS WOULD BETTER ALLOW FOR ISLAND-EFFECT
SHOWERS TO DEVELOP IN THE AFTERNOON, BUT THIS WOULD LARGELY DEPEND ON
THE WIND FIELD AROUND INVEST 90W AND ITS SLOW, SUBTLE MEANDERING. IF
90W, WHICH REMAINS VERY WEAK AND DISORGANIZED, IS FAIRLY STATIONARY
FOR THE NEXT DAY OR SO, THE NEARBY COL AREA WOULD LIKELY STAY FARTHER
EAST OF THE MARIANAS, WHICH WOULD SUPPORT A CONTINUATION OF MODERATE
WINDS AND FAIRLY DRY CONDITIONS TOMORROW. FOR TODAY, WINDS SUSTAINED
AT AROUND 10 TO 15 MPH WHICH KEPT MOST OF THE ISLAND CONVECTION OFF-
SHORE. FOR SUNDAY NIGHT THROUGH EARLY NEXT WEEK, ISOLATED TO LOW-END
SCATTERED SHOWERS ARE EXPECTED, ASSOCIATED WITH LOCALIZED
CONVERGENCE WITHIN THE SOUTHWESTERLY, THEN BECOMING EASTERLY TO
SOUTHEASTERLY, FLOW.
THE MAIN CONCERN IN THE FORECAST FOR THIS NEXT WEEK IS THE
DEVELOPMENT AND MOVEMENT OF INVEST 90W, CURRENTLY SITUATED EAST-
NORTHEAST OF WENO, CHUUK NEAR 8N156E. LATEST MODEL RUNS FAVOR A
SLOWER DEVELOPMENT AND MOVEMENT THAN PREVIOUS GUIDANCE INDICATED,
AND THE ASSOCIATED INCREASE IN SHOWERS WAS DELAYED IN THE FORECAST
UNTIL THE LATTER HALF OF THE COMING WEEK. HOWEVER, UNCERTAINTY
REMAINS HIGH. THE MAIN CONCERNS WITH INVEST 90W ARE THE FLOOD
POTENTIAL FROM NUMEROUS TO WIDESPREAD LOCALLY HEAVY SHOWERS, AS WELL
AS STRONG, GUSTY WINDS. EVEN IF 90W STRUGGLES TO ORGANIZE AND THE
WIND FIELD REMAINS LACKLUSTER, A WET PATTERN IS EXPECTED TO DEVELOP,
WITH INCREASING CERTAINTY FOR THE LATTER HALF OF THE COMING WEEK
THROUGH NEXT WEEKEND. THIS FAR OUT, THE PRECISE CERTAINTY IS LOW
REGARDING WHEN SHOWERS WILL BECOME NUMEROUS AS 90W APPROACHES, AND
SHOWERS WERE CAPPED AT 50 PERCENT FOR THURSDAY NIGHT THROUGH
SATURDAY, WITH WORDING INCLUDED FOR LOCALLY HEAVY SHOWERS POSSIBLE.
ADDITIONALLY, EXACT WIND SPEEDS AND TIMING REMAIN HIGHLY UNCERTAIN,
BUT INCLUDED WORDING FOR THE LIKELIHOOD OF BREEZY CONDITIONS
DEVELOPING AT TIMES LATER IN THE WEEK, ASSOCIATED WITH 90W.
MARINE/SURF
GENTLE TO MODERATE SOUTH TO SOUTHWEST WINDS WILL PREVAIL ACROSS
THE MARIANAS THROUGH THE REST OF THE WEEKEND, BECOMING LIGHT AT
TIMES, THEN GRADUALLY SHIFT TO THE NORTHEAST THROUGH MIDWEEK.
COMBINED SEAS OF 3 TO 4 FEET WILL PERSIST FOR MUCH OF THE COMING
WEEK. ALTHOUGH THE MAGNITUDE AND TIMING REMAINS UNCERTAIN, SEAS
LOOK TO BEGIN TO INCREASE TOWARD THE END OF THE WEEK FROM
INCREASING SWELLS ASSOCIATED WITH INVEST 90W. THE RISK OF RIP
CURRENTS REMAINS LOW ALONG ALL REEFS OF THE MARIANAS FOR THE NEXT FEW
DAYS, BUT MAY INCREASE TO MODERATE BY THE END OF THE WEEK AS SWELLS
START TO INCREASE.
TROPICAL SYSTEMS
INVEST 90W CONTINUES TO MEANDER DOWN ACROSS THE CHUUK/POHNPEI
STATES BORDER REGION, WITH THE LATEST UPDATES FROM JTWC PLACING THE
CENTER NEAR 8N156E, AND THIS LOOKS GOOD BASED ON VISIBLE IMAGERY AND
STREAMLINE ANALYSIS. THE SYSTEM CONTINUES TO STRUGGLE AS DRIER AIR
IS PUSHING AGAINST ITS NORTHERN FRINGES OF THE CIRCULATION ALOFT, AS
THE DRY AIR IS ASSOCIATED WITH THE TAIL END OF A MID-LATITUDE
TROUGH. ADDITIONALLY, 200MB ANALYSIS SHOWS ABOUT 20 TO 25 KNOTS OF
WIND SHEAR ALOFT, WHICH IS HINDERING ORGANIZATION/INTENSIFICATION.
WE EXPECT THIS DISTURBANCE TO MEANDER DOWN THERE FOR ANOTHER 48 TO
84 HOURS. THIS IS A CHANGE FROM PREVIOUS THINKING, AS WE HAD TO WAIT
FOR THE MID TO UPPER-LEVEL VORTICITY CENTERS TO DECIDE WHAT THEY
WANTED TO DO. THE ALPW (ALL LAYER PRECIPITABLE WATER) SHOWS ONE
CENTER IN THE 700-500MB AND 500-300MB LAYER HAS EJECTED WESTWARD TO
NEAR 5N143E. MEANWHILE, THE SFC-850MB AND 850-700MB LAYER VORTICITY
CENTER REMAINS WITH 90W, AS IT ALSO DOES 500MB AND ABOVE. SO
ESSENTIALLY, A "PIECE OF ENERGY" PINCHED OFF AND HEADED WEST. COULD
THIS BE TIED TO "FRINGE EFFECTS" OF THE INCOMING MJO (MADDEN-JULIAN
OSCILLATION)?
LOOKING AHEAD (PAST 84 HOURS), THE GENERAL THEME SEEN IN THE
MODELS AND HOW WE EXPECT THE PATTERN TO EVOLVE WOULD FAVOR ANY
NORTHEAST EJECTION OF 90W TO TURN MORE WESTWARD (WITH A FAIRLY
SHARP TURN) TOWARDS THE MARIANAS, BRINGING AT LEAST SOME GUSTY
WINDS AND LOCALLY HEAVY RAINFALL, ALBEIT DELAYED POTENTIALLY TO
THE LATTER HALF OF NEXT WEEK. UNTIL THEN, IT'LL (90W) CONTINUE TO
BRING INCREASED RAINFALL POTENTIAL TO LOCATIONS FROM EXTREME
EASTERN YAP STATE EASTWARD TO POHNPEI AND KOSRAE. PERIODS OF
LOCALLY HEAVY RAINFALL AND ISOLATED WIND GUSTS TO 25 KNOTS REMAIN
POSSIBLE. SPECIAL WEATHER STATEMENTS FOR EASTERN YAP STATE
THROUGH POHNPEI AND KOSRAE REMAIN IN EFFECT TO COVER THESE
CONCERNS.
EASTERN MICRONESIA
WIDESPREAD SHOWERS AND CLOUDY SKIES EARLIER TODAY HAVE DIMINISHED AT
POHNPEI AND KOSRAE THIS EVENING, AND THIS SHOULD PERSIST FOR A FEW
MORE HOURS. HOWEVER, WITH INVEST 90W REMAINING QUASI-STATIONARY
BETWEEN CHUUK AND POHNPEI, AND A SURFACE TROUGH EXTENDING EAST FROM
90W THROUGH POHNPEI AND MAJURO, LOOK FOR WIDESPREAD SHOWERS TO
REDEVELOP AT BOTH LOCATIONS AFTER MIDNIGHT, WITH A FEW THUNDERSTORMS
MIXED IN AS WELL. SOME LOCALLY HEAVY RAINFALL REMAINS POSSIBLE
THROUGH THE WEEKEND INTO MONDAY AS WELL, AS THE OVERALL WEATHER
PATTERN REMAINS UNCHANGED. SOUTHWEST TO WEST WINDS WILL ALLOW A
SOUTHERLY TO SOUTHWESTERLY SWELL OF 3 TO 4 FEET TO PERSIST THROUGH
MONDAY, POSSIBLY LONGER.
AT MAJURO, YOU REMAIN ON THE "BATTLE GROUND", BETWEEN A MOIST
SOUTHWEST FLOW TO YOUR SOUTHWEST, AND A DRIER AIRMASS TO YOUR NORTH
AND EAST, WITH LIGHT AND VARIABLE WINDS OVERHEAD. ADDING TO THE MIX,
IS ANOTHER CIRCULATION ALONG THE SURFACE TROUGH, THIS ONE BEING
LOCATED EAST OF MAJURO NEAR 8N178E. THE CIRCULATION HAS TIGHTENED
SOMEWHAT SINCE YESTERDAY, WITH INCREASED SHOWER DEVELOPMENT
CONTINUING TO ATTEMPT TO BECOME LONGER-LIVED IN DURATION. AS THIS
CIRCULATION MOVES WEST, YOUR RAINFALL POTENTIAL WILL START TO
INCREASE OVER THE WEEKEND OR EARLY NEXT WEEK. HOWEVER, RAINFALL
AMOUNTS LOOK TO REMAIN LIGHT, DESPITE THE INCREASED POTENTIAL. ALSO,
THE SOUTHWESTERLY SWELL AFFECTING POHNPEI AND KOSRAE IS TRYING TO
MAKE IT TO MAJURO, BUT THE ISLANDS IN THE RMI ARE DISRUPTING THE
FETCH LENGTH/STRENGTH, SO IT REMAINS UNCLEAR IF THIS WILL MAKE IT TO
MAJURO OR HAVE ANY EFFECTS.
WESTERN MICRONESIA
A TROPICAL DISTURBANCE, INVEST 90W, HAS MEANDERED NORTHWARD TO NEAR
8.2N 155.7E, NORTHEAST OF CHUUK. ALTHOUGH 90W HAS BEEN SLOW TO
DEVELOP, A WIDESPREAD, DISTURBED WEATHER PATTERN ENCOMPASSES THE
SYSTEM, WITH A DEVELOPING MONSOON-LIKE PATTERN BEGINNING TO ASSERT
ITSELF FURTHER WEST ACROSS YAP AND PALAU. A SPECIAL WEATHER STATEMENT
REMAINS IN EFFECT FOR CHUUK AND EASTERN YAP STATE REGARDING THIS
PROLONGED PERIOD OF DISTURBED WEATHER. AS 90W DRIFTS NORTH OF CHUUK
IN THE COMING DAYS, NUMEROUS TO WIDESPREAD HEAVY SHOWERS CONTINUE
THROUGH EARLY NEXT WEEK, THEN MAY SEE SHOWERS GRADUALLY TAPER DOWN
AROUND MIDWEEK AS 90W PULLS NORTHWESTWARD, AWAY FROM CHUUK STATE.
LOOKING WEST, AFTERNOON VISIBLE SATELLITE IMAGERY REVEALS SCATTERED
TO NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS TRACKING ACROSS YAP
AND PALAU THESE ARE RIDING ALONG MODERATE TO FRESH WESTERLIES AS THE
MONSOON-LIKE PATTERN CONTINUES TO LOCK INTO PLACE. SURFACE
OBSERVATIONS ACROSS THE REGION SHOW CONVECTIVE-DRIVEN GUSTS AROUND 25
KT. MODEL GUIDANCE CONTINUES TO DEPICT AN INCREASINGLY WET PATTERN
ACROSS YAP AND PALAU HEADING INTO NEXT WEEK.
ALTIMETRY AND YAP BUOY DATA REVEAL COMBINED SEAS CURRENTLY SITTING
AT 4 TO 6 FEET, LARGELY COMPRISED OF WESTERLY SWELL ACROSS THE
REGION, ALONG WITH LIGHT SOUTH-SOUTHEAST SWELL PUSHING INTO CHUUK
STATE. DEPENDING ON 90W'S DEVELOPMENT, THE MONSOONAL FLOW MAY
STRENGTHEN SLIGHTLY, BUILDING SEAS TO 5 TO 7 FEET NEXT WEEK. THIS
WILL ALSO MAINTAIN MODERATE TO ELEVATED SURF ALONG WEST-FACING REEFS
OVER THE NEXT SEVERAL DAYS. THE COMBINATION OF SUSTAINED MODERATE TO
FRESH WINDS AND SUDDEN, STRONG GUSTS WITH HEAVIER SHOWERS WILL
MAINTAIN CHOPPY SEAS AND CONTINUE TO PRESENT CHALLENGING CONDITIONS
FOR SMALL CRAFT OPERATIONS.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: DECOU
EAST MICRONESIA/TROPICAL: DOLL
WEST MICRONESIA: CRUZ
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