841
FXPQ50 PGUM 270823 CCA
AFDGUM
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE TIYAN GU
623 PM CHST FRI MAR 27 2026
CORRECTED MINOR TYPOS.
MARIANAS SYNOPSIS
SATELLITE SHOWS MOSTLY CLOUDY SKIES ACROSS MOST OF THE MARIANAS, BUT
CLOUD COVER HAS BEEN DECREASING OVER THE PAST COUPLE OF HOURS.
A BROAD TROUGH AND ELONGATED CIRCULATION TO THE WEST WILL HELP TO
KEEP WINDS LIGHT AND VARIABLE OVER THE ISLANDS WHICH IS EXPECTED
TO SUPPORT ISLAND-EFFECT SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS
SATURDAY. SEAS ARE AROUND 3 TO 5 FEET AND WILL START TO BUILD
TO AROUND 6 TO 8 FEET NEXT WEEK AS GENTLE TO MODERATE NORTHEAST WINDS
AND A PULSE OF NORTHERLY SWELL MOVE INTO THE REGION.
DISCUSSION
EARLIER TODAY SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS DEVELOPED
ALONG THE TROUGH AND EMBEDDED CIRCULATION TO THE WEST OF THE
MARIANAS AND THIS PROPAGATED EASTWARD, ESPECIALLY ACROSS TINIAN AND
SAIPAN, FOLLOWING A MID-LEVEL CIRCULATION. THIS BROUGHT AROUND 2
INCHES OF RAIN TO PARTS OF TINIAN AND SAIPAN, WHILE GUAM AND ROTA SAW
LESS RAINFALL OVERALL, THOUGH LIGHT WINDS DID BRING SOME SHOWERS TO
NORTHERN HALF OF GUAM AROUND NOON. SATELLITE AND RADAR IMAGERY SHOWS
THE REMAINS OF THE MID-LEVEL CIRCULATION BETWEEN ROTA AND TINIAN AS
IT SLOWLY DRIFTS EASTWARD AND DISSIPATES. THIS IS CAUSING CLOUD COVER
TO DECREASE ACROSS THE MARIANAS, HOWEVER, THERE APPEARS TO BE ENOUGH
INSTABILITY THAT SOME ISOLATED SHOWERS ARE DEVELOPING IN THE
REMNANTS OF THE MID-LEVEL CIRCULATION. THIS INSTABILITY COULD
TRIGGER AN ISOLATED THUNDERSTORM OVER THE FEW HOURS, SO MENTIONED A
SLIGHT RISK OF THUNDERSTORMS IN THE COASTAL FORECAST FOR THE EVENING.
OTHERWISE, HI-RES AND GLOBAL MODELS SHOW THE ATMOSPHERE STABILIZING
TONIGHT WHICH SHOULD SUPPORT PARTLY CLOUDY SKIES AND ISOLATED SHOWERS
FOR MOST OF THE NIGHT.
FOR SATURDAY, IF SKIES REMAIN PARTLY CLOUDY TO MOSTLY SUNNY OVER THE
ISLANDS DURING THE MORNING AND EARLY AFTERNOON HOURS AND WINDS ARE
LIGHT, THEN THIS COULD SETUP A FAVORABLE ENVIRONMENT FOR ISLAND-
EFFECT SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS. ALSO, AS THE
EMBEDDED CIRCULATION DISSIPATES AND THE TROUGH WEAKENS AND SHIFTS
SOUTH-SOUTHEAST, THIS WOULD ALSO SUPPORT THE POTENTIAL FOR SCATTERED
SHOWERS ACROSS THE MARIANAS. SATURDAY NIGHT AND INTO NEXT WEEK,
NORTHEAST TRADE-WINDS ARE EXPECTED TO PUSH BACK INTO THE REGION,
PROMOTING A DRIER WEATHER PATTERN OVERALL. THE EXTENDED FORECAST IS
STILL FAIRLY UNCERTAIN AS THE WEATHER PATTERN ACROSS MOST OF
MICRONESIA IS FAIRLY ATYPICAL FOR THIS TIME OF YEAR, WITH WEAK TRADE-
WINDS AND VARIABLE TO WESTERLY WINDS FOUND ACROSS PORTIONS OF THE
REGION. THIS PATTERN WILL INCREASE THE POTENTIAL FOR
CIRCULATIONS/DISTURBANCES TO DEVELOP SOMEWHERE IN THE REGION AND
AFFECTING THE LONG RANGE FORECAST.
MARINE
BENIGN MARINE CONDITIONS ARE EXPECTED WITH LIGHT TO GENTLE WINDS
AND COMBINED SEAS OF 3 TO 5 FEET EXPECTED THROUGH SATURDAY NIGHT.
THEN, A PULSE OF NORTHERLY SWELL IS EXPECTED TO INCREASE SEAS
BACK UP TO 6 TO 8 FEET BY TUESDAY. THIS PATTERN WILL SUPPORT A
MODERATE RISK OF RIP CURRENTS ALONG NORTH AND EAST FACING REEFS OVER
THE NEXT FEW DAYS. DEPENDING ON HOW THE STRONG THE NORTHERLY SWELL
NEXT WEEK IS, THERE COULD BE THE POTENTIAL FOR A PERIOD OF HAZARDOUS
SURF OF 9 FEET AND A HIGH RISK OF RIP CURRENTS ALONG NORTH FACING
REEFS. A BROAD TROUGH, WITH A WEAK EMBEDDED CIRCULATION TO THE WEST
OF THE REGION, WILL CAUSE SHOWERS TO BECOME SCATTERED AGAIN SATURDAY
AND ALSO SUPPORT A SLIGHT CHANCE OF THUNDERSTORMS THIS EVENING AND
SATURDAY. A DRIER TRADE-WIND PATTERN IS THEN EXPECTED TO PUSH INTO
THE REGION LATE THIS WEEKEND INTO EARLY NEXT WEEK.
TROPICAL SYSTEMS
A WEAK TROPICAL DISTURBANCE, JOINT TYPHOON WARNING CENTER'S (JTWC)
INVEST 99W, IS CENTERED NORTH-NORTHEAST OF KOSRAE NEAR 9.5N 163.9E.
OVER THE LAST 24 HOURS, 99W HAS DRIFTED WEST, WITH LITTLE CHANGE IN
INTENSITY. INVEST 99W IS NOT EXPECTED TO STRENGTHEN FOR AT LEAST THE
NEXT COUPLE OF DAYS. HOWEVER, THE EFFECTS OF THIS DISTURBANCE ARE
ALREADY OCCURRING ACROSS KOSRAE AND THE MARSHALL ISLANDS AND AS FAR
WEST AS POHNPEI. THIS SYSTEM IS ATYPICAL FOR THE REGION AND WILL
PRODUCE PERIODS OF WIDESPREAD SHOWERS, ISOLATED THUNDERSTORMS AND
STRONG WIND GUSTS ARE POSSIBLE ACROSS THE WESTERN MARSHALL ISLANDS,
INTO KOSRAE STATE OVER THE NEXT FEW DAYS. THERE WILL ALSO BE SEVERAL,
POSSIBLY LONG, PERIODS OF CALM TO LIGHT WINDS AND EXTENSIVE
SUNSHINE, OR STARRY SKIES AT NIGHT. CURRENTLY, NUMEROUS LOCALLY HEAVY
SHOWERS AND ISOLATED THUNDERSTORMS ARE FOUND OVER THE OUTLYING
ISLANDS OF THE MARSHALLS, INCLUDING AILINGLAPLAP AND NAMORIK, WITH
CONVECTION NOW NORTH OF JALUIT. HEAVY SHOWERS ARE ALSO SEEN TO THE
SOUTHEAST OF KWAJALEIN ATOLL. THE WESTERN OUTLYING ISLANDS SOUTH OF
10N WILL LIKELY SEE THE MOST CONVECTION THROUGH TONIGHT, THOUGH THERE
ARE SIGNS OF INCREASED SHOWERS JUST WEST OF MAJURO, AS WELL AS NEAR
WOTJE AND UTIRIK.
FARTHER WEST, THE NEAR-EQUATORIAL TROUGH (NET) EXTENDS SOUTHEASTWARD
FROM WEST OF THE MARIANAS INTO 99W, PASSING ACROSS POHNPEI. THE NET
IS PRODUCING A BAND OF HEAVY SHOWERS ACROSS POHNPEI AS IT IS FEEDING
MOISTURE INTO INVEST 99W. LATEST MODEL GUIDANCE NOW SHOWS INVEST 99W
CONTINUING TO DRIFT WEST AND WEAKENING OVER THE NEXT DAY OR TWO, WITH
ANOTHER CIRCULATION ALONG THE NET, CURRENTLY FOUND NEAR 7N179E,
MOVING IN AND BECOMING THE DOMINANT CIRCULATION. THIS SCENARIO WILL
ALSO PROMOTE INCREASED CONVECTION ACROSS THE MARSHALLS. THE
CONFIDENCE LEVEL WITH INVEST 99W REMAINS FAIRLY LOW AT THIS TIME,
HOWEVER, DUE TO THE RARITY OF THIS TYPE OF SETUP, 99W BEARS CLOSE
MONITORING OVER THE NEXT SEVERAL DAYS. JTWC AND THE NATIONAL WEATHER
SERVICE WILL CONTINUE TO MONITOR 99W CLOSELY THROUGH THE WEEKEND AND
INTO NEXT WEEK. RESIDENTS OF THE MARSHALL ISLANDS, KOSRAE AND POHNPEI
SHOULD CONTINUE TO MONITOR FORECASTS AND STATEMENTS FOR ANY CHANGES
OR UPDATES ON INVEST 99W.
EASTERN MICRONESIA
ALL THE ATTENTION CENTERS AROUND 99W DISCUSSED ABOVE AND AN
ANTICIPATED SECONDARY CIRCULATION THAT'S EXPECTED TO DEVELOP OVER THE
WEEKEND (POSSIBLY) OR EARLY TO THE MIDDLE OF NEXT WEEK (MORE LIKELY).
THIS NEW CENTER LOOKS TO DEVELOP ANYWHERE FROM NORTHEAST OF KOSRAE TO
EAST TO SOUTHEAST OF MAJURO. ALTHOUGH THIS IS A VERY LONG-RANGE
MENTION (WHICH WE TYPICALLY DON'T DO), SEVERAL MODEL RUNS OF BOTH THE
ECMWF AND GEFS ENSEMBLE MODELS SHOW THIS SCENARIO PLAYING OUT, AS DO
SOME NEW EXPERIMENTAL AI MODELS THAT SHOW WWBS (WESTERLY WIND
BURSTS) STRENGTHENING SIGNIFICANTLY BY THIS TIME. THE FACT THAT IT'S
ALREADY BEEN AN ACTIVE "DRY SEASON" ACROSS PORTIONS OF THE REGION,
THE PRESENCE OF A NET ALREADY EXTENDING FROM THE WESTERN EDGE OF
GUAM'S AOR (AREA OF RESPONSIBILITY) AT 130E, TO ITS EASTERN EDGE AT
THE DATE LINE, AND BEYOND, WITH WEAK WESTERLY FLOW ALREADY IN PLACE
TO AT LEAST 165E, GIVES SOME CREDENCE TO THIS. ADD INTO THE MIX, A
FAVORABLE MJO PHASE WILL AID IN THE POTENTIALS MENTIONED ABOVE.
SO WHAT DOES THIS ALL MEAN FOR THE REGION? IN GENERAL, AN UNSETTLED
WET PERIOD WILL CONTINUE TO AFFECT ALL OF THE REGION. WITH THE
FACTORS MENTIONED ABOVE, ANY SHOWER OR THUNDERSTORMS WILL HAVE THE
POTENTIAL TO FEATURE LOCALLY HEAVY RAINFALL AND WIND GUSTS IN THE 30
TO 40 MPH RANGE. THIS WILL BE VERY ISOLATED/PERIODIC OVER THE NEXT
SEVERAL DAYS, BUT, THE POTENTIAL IS SLIGHTLY HIGHER "THAN AVERAGE",
SO WE JUST WANTED TO GIVE FOLKS A HEADS UP. OTHERWISE, SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS WILL BE COMMON ACROSS THE AREA,
WITH LIGHT TO GENTLE WINDS AND SEAS IN THE 4 TO 6 FOOT RANGE
PREVAILING.
WESTERN MICRONESIA
THE MAIN FEATURE IN THE REGIONS REMAINS THE NEAR-EQUATORIAL TROUGH
(NET). THE NET ENTERS THE REGION NEAR 4N130E AND EXTENDS EAST-
NORTHEAST. THEN, EXITS THE WESTERN MICRONESIAN DOMAIN NEAR 9N155E AND
ENTERS THE EASTERN MICRONESIAN DOMAIN. THE EMBEDDED DISTURBANCE THAT
WAS LOCATED TO THE SOUTH-SOUTHWEST OF NGULU ATOLL HAS WASHED OUT.
THE PORTION OF THE NET IN WESTERN MICRONESIA HAS VERY LITTLE
CONVECTIVE ACTIVITY. THIS FEATURE IS EXPECTED TO REMAIN QUASI-
STATIONARY OVER THE NEXT SEVERAL DAYS WILL LITTLE CHANGE IN
CONNECTIVE.
OVERALL OF THE DOMAIN, A DRIER PATTERN HAS SET UP THE REGION. THIS
PATTERN IS ANTICIPATED TO REMAIN THROUGH THE WEEKEND WITH ONE CAVEAT.
A MID LEVEL CIRCULATION IS ANTICIPATED TO MOVE BETWEEN YAP PROPER AND
PALAU, THIS MAY CAUSE WINDS TO BUILD SLIGHTLY AND POSSIBLY BRING SOME
SHOWERS TO YAP PROPER, HOWEVER, CONFIDENCE IS LOW AT THIS TIME. AROUND
THE BEGINNING OF THE WORK WEEK NEXT WEEK, THE TRADE WIND PATTERN IS
ANTICIPATED TO RETURN TO THE REGION. THIS MAY BRING POCKETS OF
SCATTERED SHOWERS BACK TO THE REGION THROUGH THE MIDDLE OF NEXT WEEK.
MARINE CONDITIONS ARE FAIRLY BENIGN. ALTIMETRY SHOWS COMBINED SEAS OF
3 TO 4 FEET. WINDS ARE EXPECTED TO VARY OVER THE REGIONS. CHUUK IS
EXPECTED TO SEE VARIABLE LIGHT WINDS BECOMING NORTHEASTERLY NEXT
WEEK. PALAU IS EXPECTED TO SEE WEST WINDS THAT ARE LIGHT TO GENTLE.
THESE WINDS ARE EXPECTED TO BECOME NORTHERLY AND GRADUALLY CONTINUE
TO BECOME EASTERLY. FOR YAP, WINDS ARE EXPECTED TO BUILD SLIGHTLY
FROM LIGHT TO GENTLE FOR THE NEXT DAY OR SO TO GENTLE TO MODERATE FOR
ABOUT A DAY, THEN FALL BACK TO LIGHT TO GENTLE THROUGH THE MIDDLE OF
NEXT WEEK.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: SCHANK
TROPICAL: KLEESCHULTE
EAST MICRONESIA: DOLL
WEST MICRONESIA: BOWSHER
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