555
FXPQ50 PGUM 292014
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
614 AM CHST MON MAR 30 2026
MARIANAS UPDATE
SATELLITE AND RADAR IMAGERY EARLY THIS MORNING SHOW ISOLATED TO
SCATTERED SHOWERS ACROSS MARIANAS COASTAL WATERS ALONG THE EDGE OF A
SURFACE TROUGH AND FRAGMENTED SHEAR LINE. OVERNIGHT SCATTEROMETRY
SHOWS MODERATE TO FRESH NORTHEAST WINDS ACROSS THE NORTHERN CNMI,
NORTH OF THE SHEAR LINE BOUNDARY, AND LIGHT TO GENTLE EAST TO
EAST-NORTHEAST WINDS TO THE SOUTH. ALTHOUGH CONVERGENCE IS GREATER
TO THE NORTH NEAR TINIAN AND SAIPAN, PRECIPITABLE WATER AMOUNTS ARE
HIGHER TO THE SOUTH AROUND GUAM AND ROTA (2.2 - 2.5 INCHES AS OPPOSED
TO 1.6 TO 1.7 INCHES TO THE NORTH, FAIRLY DRY FOR THE TROPICS). FOR
GUAM AND ROTA, SHOWERS WERE INCREASED TO LOW-END SCATTERED (30
PERCENT) THIS MORNING, DECREASING TO ISOLATED IN THE AFTERNOON.
SHOWER CHANCES SHOULD DIMINISH OVER THE NEXT DAY AS THE SURFACE
TROUGH SHIFTS TO THE SOUTHWEST, AND THE NEARBY SHEAR LINE FRAGMENT
WEAKENS.
THERE WAS LITTLE CHANGE IN THE MARINE FORECAST. TANAPAG BUOY DATA
AND ALTIMETRY SHOW COMBINED SEAS AROUND 4 TO 7 FEET, COMPRISED
PRIMARILY OF NORTH SWELL WITH A SECONDARY EAST- NORTHEAST TRADE
SWELL. WINDS ARE EXPECTED TO BE GENTLE TO MODERATE OUT OF THE
NORTHEAST TO EAST THROUGHOUT THE WEEK. SEAS MAY INCREASE BY A FOOT OR
SO IN THE LATTER HALF OF THE WEEK AS THE TRADE SWELL STRENGTHENS
SLIGHTLY.
TROPICAL SYSTEMS UPDATE
THE JOINT TYPHOON WARNING CENTER (JTWC)'S INVEST 99W REMAINS
CATEGORIZED AS A SUB-LOW, MEANING DEVELOPMENT INTO A TROPICAL CYCLONE
IS NOT EXPECTED IN THE NEXT 24 HOURS AND REMAINS UNLIKELY IN THE NEXT
FEW DAYS. IT IS CURRENTLY CENTERED NEAR 8N161E, JUST NORTH TO
NORTHEAST OF POHNPEI, AND HAS BEEN DRIFTING WESTWARD WITH LITTLE
CHANGE IN INTENSITY OVER THE LAST 12 HOURS. AN AREA OF DEEP
CONVECTION HAS PERSISTED OVERNIGHT NEAR 99W WITH NEAR-CONSTANT
LIGHTNING AT ITS CENTER, PASSING JUST NORTH OF POHNPEI. UPPER-LEVEL
STREAMLINE ANALYSIS DEPICTS WEAKLY DIVERGENT FLOW ALOFT WHICH MAY BE
HELPING THE CONVECTIVE COMPLEX HOLD TOGETHER. OVERNIGHT SCATTEROMETRY
REVEALS AN AREA OF MODERATE TO FRESH EAST TO SOUTHEAST WINDS JUST
NORTH TO NORTHEAST OF 99W'S CENTER, WITH SOME STRONGER CONVECTIVE
GUSTS EMBEDDED. MODELS CONTINUE TO SHOW LITTLE TO NO DEVELOPMENT,
DIMINISHING 99W OVER THE NEXT DAY OR SO.
EASTERN MICRONESIA UPDATE
THERE WAS LITTLE CHANGE TO THE FORECAST, AFTER AN OVERNIGHT UPDATE
TO INCREASE SHOWERS FOR POHNPEI WITH NEARBY CONVECTION ASSOCIATED
WITH INVEST 99W. SHOWER CHANCES WERE MAINTAINED AT 50 PERCENT FOR
POHNPEI TODAY WITH THE PERSISTENT CONVECTIVE COMPLEX JUST NORTHWEST
OF COASTAL WATERS, AND SHOWERS BUILDING WITHIN THE CONVERGENCE JUST
TO THE EAST. SHOWERS DIMINISH FOR POHNPEI AND KOSRAE FOR TONIGHT AS
THE DISTURBANCE MOVES FURTHER WEST AND WEAKENS ALONG WITH THE BROAD
TROUGHING NEARBY. MAJURO CAN EXPECT HIGH-END SCATTERED SHOWERS (50
PERCENT CHANCE) TO BUILD AS A WEAK CIRCULATION NEAR THE DATE LINE
SHIFTS WEST TOWARD THE MARSHALLS, AND A TROUGH EXTENDING WEST-
NORTHWEST FROM IT BUILDS SHOWERS NEARBY.
WESTERN MICRONESIA UPDATE
THERE WAS LITTLE CHANGE TO THE FORECAST. A WEAK SURFACE CIRCULATION
REMAINS TO THE SOUTHEAST OF PALAU, ON THE WESTERN EDGE OF A BROAD
WEST-TO-EAST ORIENTED TROUGH. CONVERGENCE ALONG THE NORTHERN EDGE OF
THE CIRCULATION AND TROUGH, CONNECTED WITH ANOTHER TROUGH NOW
CENTERED JUST SOUTHWEST OF THE MARIANAS, WILL BE THE MAIN FOCUS OF
SHOWERS WITHIN THE REGION TODAY AND TONIGHT. MOST OF THE SHOWERS ARE
EXPECTED FOR PALAU, AS THE CIRCULATION GRADUALLY SHIFTS WESTWARD TO
THE SOUTH OF KOROR OVER THE NEXT DAY OR SO. FAIRLY DRY CONDITIONS
LOOK TO PERSIST FOR YAP AND CHUUK THROUGH TONIGHT.
PREV DISCUSSION
/ISSUED 527 PM CHST SUN MAR 29 2026/
MARIANAS SYNOPSIS...
A SURFACE TROUGH IS SLOWLY DRIFTING WESTWARD AND MOSTLY CLOUDY SKIES
AND SCATTERED SHOWERS ARE SHIFTING TOWARDS AND TINIAN AND SAIPAN AND
ARE EXPECTED TO MOVE TOWARDS ROTA AND GUAM LATER TONIGHT. A PULSE OF
NORTHERLY SWELL IS SUPPORTING SEAS AROUND 5 TO 7 FEET. A DRIER
PATTERN IS EXPECTED OVER THE NEXT FEW DAYS AS GENTLE TO MODERATE
NORTHEAST TO EASTERLY WINDS MOVE ACROSS THE REGION.
DISCUSSION...
SATELLITE IMAGERY SHOWS SHOWERS ARE FAIRLY SPOTTY AROUND GUAM AND
ROTA THIS EVENING WHILE SCATTERED SHOWERS ARE FOUND ALONG THE WESTERN
EDGE OF THE COASTAL WATERS AND JUST NORTH-NORTHWEST OF SAIPAN. THESE
SHOWERS ARE OCCURRING ALONG THE NORTHWESTERN EDGE OF THE SURFACE
TROUGH THAT IS SLOWLY SHIFTING SOUTHWARD AND EXTENDS UP TO A WEAK
COLD FRONT NORTHEAST OF THE MARIANAS. MODEL GUIDANCE SUPPORTS
SCATTERED SHOWERS SHIFTING SOUTHWARD ACROSS THE MARIANAS TONIGHT AND
THEN SHIFTING WESTWARD MONDAY AS THE TRADE-WINDS STRENGTHEN AND
SUPPORTING AN OVERALL DRIER PATTERN FOR MOST OF THE WEEK. THE WEATHER
PATTERN ACROSS MOST OF MICRONESIA IS STILL FAIRLY ATYPICAL FOR THIS
TIME OF YEAR, WITH WEAK TRADE-WINDS AND VARIABLE TO WESTERLY WINDS
FOUND ACROSS PORTIONS OF THE REGION, ESPECIALLY ACROSS CENTRAL AND
EASTERN MICRONESIA. THIS PATTERN WILL INCREASE THE POTENTIAL FOR
CIRCULATIONS/DISTURBANCES TO DEVELOP SOMEWHERE IN THE REGION SO HOW
LONG THIS DRIER-PERIOD WILL LAST IS UNCERTAIN.
MARINE...
ALTIMETRY AND BUOY DATA NEAR GUAM AND SAIPAN SHOW SEAS ARE AROUND
4 TO 7 FEET THIS EVENING, DRIVEN BY NORTH TO NORTHEAST SWELL AND
WEAK EASTERLY TRADE SWELL. LIGHT TO MODERATE NORTHEAST WINDS ARE
EXPECTED TO SHIFT EASTWARD OVER THE NEXT FEW DAYS. THIS PATTERN WILL
SUPPORT A MODERATE RISK OF RIP CURRENTS ALONG NORTH AND EAST FACING
REEFS OVER THE NEXT FEW DAYS AND MAY CAUSE THE RISK OF RIP CURRENTS
TO BECOME MODERATE ALONG WEST FACING REEFS AT TIMES BEFORE THE
NORTHERLY SWELL SLOWLY SUBSIDES. LOOKING TOWARDS THE END OF THE WEEK,
MODELS SHOW AN INCREASE IN THE EAST SWELL AND SUGGEST SEAS WILL
BUILD TO AROUND 5 TO 8 FEET.
TROPICAL SYSTEMS...
INVEST 99W CONTINUES TO BE RATED AS A "SUB-LOW" INVEST BY THE JOINT
TYPHOON WARNING CENTER. IT'S CENTER IS LOCATED NORTHEAST OF POHNPEI
THIS AFTERNOON, NEAR 8.6N 161.1E. A SLOW WESTWARD DRIFT IS EXPECTED
TO CONTINUE THE NEXT 24 TO 48 HOURS, BEFORE IT DISSOLVES AS ENERGY
FROM IT GETS ABSORBED INTO THE TROUGH EXTENDING SOUTHEAST FROM IT.
THIS TROUGH THEN INTERSECTS WITH A NEWLY-DEVELOPING CIRCULATION NEAR
4.7N180, WELL TO THE EAST-SOUTHEAST OF MAJURO, AND WELL EAST-
NORTHEAST OF MAKIN. THIS CIRCULATION LOOKS TO WOBBLE IN PLACE OVER
THE NEXT FEW DAYS, PERHAPS DRIFTING WEST TO SOUTHWEST AS IT
EVENTUALLY ABSORBS REMNANTS FROM 99W. THE OPERATIONAL AND ENSEMBLE
MEMBERS ALL SHOW THIS FEATURE MAY TAKE ANOTHER 5 TO 8 DAYS TO GET
BETTER ORGANIZED, BUT SOME OF THEM (THE MODELS) SUGGEST IT COULD
START TO OCCUR A LITTLE EARLIER. THE BULK OF THE GUIDANCE THEN TAKES
THIS TO MAKIN OR HALFWAY BETWEEN KOSRAE AND MAJURO IN A WEEK. AFTER
THAT, THEY (THE MODELS) HAVE A WIDE RANGE OF SOLUTIONS ON WHERE IT'LL
GO NEXT AND AT WHAT STRENGTH.
THE MAIN MESSAGING TO TAKE FROM THIS IS WE STILL EXPECT THE
CIRCULATION TO BECOME BETTER DEFINED, PERHAPS BRINGING LOCALLY HEAVY
RAINFALL TO LOCATIONS FROM MAJURO SOUTH FOR THE LATTER HALF OF THE
WEEK AND INTO NEXT WEEKEND. SOME LOCALLY HEAVY RAINFALL AND AT LEAST
CONVECTIVELY-AIDED STRONG WIND GUSTS WOULD BE A DISTINCT POSSIBILITY
IF THIS PAN OUT AS EXPECTED.
EASTERN MICRONESIA...
KOSRAE...
KOSRAE ENJOYED SOME PERSISTENT RAINFALL, SOME OF WHICH WAS HEAVY,
WITH A FEW THUNDERSTORMS MIXED IN TODAY. THIS HELPED KEEP AFTERNOON
HIGHS LIMITED TO THE LOWER 80S. A CONVERGENCE AXIS IS LOCATED EAST TO
NORTHEAST OF KOSRAE, AS THE WIND FIELD ROTATES AROUND THE 99W
CIRCULATION, GIVING KOSRAE RARE WESTERLY WIND. WITH THESE WINDS
INTERSECTING THE NORTHEAST TRADE WINDS, WIDESPREAD SHOWERS (SOME
LOCALLY HEAVY) WILL CONTINUE INTO THE EVENING, BEFORE POSSIBLE
DECREASING SLIGHTLY IN COVERAGE AND INTENSITY OVERNIGHT. THEN LOOKING
AHEAD, AT LEAST SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL
CONTINUE FOR MUCH OF THE WEEK. AFTERNOON HIGHS IN THE LOWER TO MID
80S ARE EXPECTED MONDAY, WARMING SOME FOR THE LATTER HALF OF THE
WEEK. OVERNIGHT LOWS WILL BE IN THE MID TO UPPER 70S.
POHNPEI...
THE MAIN FORECAST CHALLENGE HERE IS TRYING TO DETERMINE WHEN 99W MAY
START TO WEAKEN. THE MODEL TRENDS HAVE BEEN WEAKENING IT TOO FAST
THE PAST 36 HOURS, AND GIVEN FAVORABLE SEA SURFACE TEMPERATURES AND
LIGHT WINDS, IT WOULDN'T BE SURPRISING TO SEE 99W HOLD TOGETHER AS A
CIRCULATION WITH DECENT CONVECTION ASSOCIATED WITH IT, FOR ANOTHER
DAY OR TWO. AS SUCH, POPS (PROBABILITY OF PRECIPITATION) WERE
INCREASED FOR THE NEXT 36 HOURS. AFTER THAT, RAINFALL POTENTIAL WILL
DECREASE BRIEFLY FOR THE MIDDLE OF THE WEEK, BEFORE POSSIBLY TRENDING
BACK UP TOWARDS THE WEEKEND. TEMPERATURES WILL BE SLIGHTLY COOLER
THE NEXT DAY OR TWO WITH THE INCREASED CLOUD COVER AND RAINFALL.
MAJURO...
YOUR SANDWICHED INBETWEEN SYSTEMS WITH A TROUGH AXIS CONNECTING THE
TWO JUST SOUTH OF YOU. STILL, VISIBLE IMAGERY SHOWS WAVES OF SHOWERS
HEADING YOUR WAY, SOME OF WHICH HAVE HAD A FEW LIGHTNING STRIKES IN
THEM. LOOK FOR SHOWERS AND PERHAPS A THUNDERSTORM OR TWO TO INCREASE
IN COVERAGE TONIGHT, WITH SOME GUSTY WINDS NOT OUT OF THE QUESTION.
MORE OF THE SAME LOOKS PROBABLE FOR THE REMAINDER OF THE WEEK, WITH
YOUR WEATHER HEAVILY INFLUENCED BY THE NEWLY-DEVELOPING CIRCULATION,
WHICH MAY GET LABELED AS AN INVEST IN THE COMING DAYS. DEPENDING HOW
THE SYSTEM EVOLVED, LOCALLY HEAVY RAINFALL AND A BETTER POTENTIAL
FOR STRONGER WIND GUSTS MAY DEVELOP TOWARDS/DURING THE WEEKEND. STAY
TUNED!
MARINERS CAN EXPECT MAINLY LIGHT TO GENTLE WINDS, BUT THESE WINDS MAY
BECOME MODERATE AT TIMES FOR KOSRAE AND MAJURO FOR THE LATTER HALF OF
THE WEEK, DEPENDING HOW THE NEW CIRCULATION BEHAVES. SEAS OF 4 TO 6
FEET COULD INCREASE A FOOT IF THE CIRCULATION BECOMES BETTER
DEVELOPED. POHNPEI WILL LIKELY NOT SEE ANY INCREASE IN WINDS OR SEAS
UNTIL NEXT WEEK.
WESTERN MICRONESIA...
THE MAIN FEATURE IN THE REGIONS IS A BROAD SURFACE TROUGH. IT ENTERS
THE REGION NEAR 2N130E AND EXTENDS NORTHEAST INTO A NEWLY-FORMED
CIRCULATION NEAR 6N138E (TO THE SOUTH OF YAP PROPER AND EAST-
SOUTHEAST OF PALAU). THIS TROUGH CONTINUES TO EXTEND NORTHEAST TO
ABOUT 8N144E SPLITS WITH ONE SECTION GOING NORTH TO A CIRCULATION
NEAR GUAM, AND THE OTHER SECTION EXTEND EAST THROUGH CHUUK AND
CONTINUES INTO EASTERN MICRONESIA.
FOR YAP AND PALAU, THE BROAD SURFACE TROUGH IS EXPECTED TO BRING
PERIODS SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS TO BOTH
LOCATIONS. THE TROUGH IS CURRENTLY JUST OUTSIDE YAP PROPER'S
SOUTHERN COASTAL WATERS, AND PALAU'S SOUTHERN AND EASTERN COASTAL
WATERS. THIS TROUGH IS ANTICIPATED TO REMAIN OVER THIS PORTION OF THE
REGIONS THROUGH ABOUT TUESDAY. MODELS SUGGEST THAT THE TROUGH WILL
CONTINUE TO MOVE INTO OPEN WATERS TO SOUTHEAST OF THESE ISLANDS. FOR
THE LATTER HALF OF NEXT WEEK MODELS SUGGEST A SOMEWHAT DRY PATTERN
REGIME MAY SET UP.
FOR CHUUK, THIS REGION REMAINS NEAR A COL. THIS MEANS MORE BENIGN
WEATHER IS EXPECTED FOR WENO. THIS COL IS ANTICIPATED TO LINGER NEAR
CHUUK FOR THE NEXT SEVERAL DAYS. MODEL GUIDANCE SUGGESTS AROUND THE
MIDDLE OF NEXT WEEK, SHOWERS FROM EASTERN MICRONESIA ARE ANTICIPATED
TO MOVE INTO THE REGION. HOWEVER, THIS WILL ALL DEPEND ON WHAT AND
WHERE INVEST 99W AND ITS ASSOCIATED TROUGHS MOVE TO.
MARINE CONDITIONS ARE FAIRLY BENIGN. ALTIMETRY SHOWS COMBINED SEAS OF
3 TO 5 FEET. SEAS MAY RISE BY ABOUT A FOOT NEAR THURSDAY FOR CHUUK AS
A PULSE IN THE NORTH SWELL MAY ARRIVE. WINDS ARE EXPECTED TO LIGHT
TO MODERATE ACROSS THE DOMAIN. THESE ELEVATED WINDS AT YAP ARE DUE
THE SHOWERS NEAR BY.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS/EAST AND WEST MICRONESIA/TROPICAL UPDATE: DECOU
MARIANAS: SCHANK
EAST MICRONESIA/TROPICAL: DOLL
WEST MICRONESIA: BOWSHER
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