452
FXPQ50 PGUM 272017
AFDGUM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
617 AM CHST MON APR 28 2025
MARIANAS SYNOPSIS
SATELLITE SHOWS PARTLY SUNNY SKIES OVER THE MARIANAS THANKS TO HIGH
CLOUDS MOVING UP FROM THE SOUTH. THE BUOYS REVEAL COMBINED SEAS OF 3
TO 5 FEET, COMPOSED MAINLY OF SMALL TRADE-WIND SWELL, WIND WAVES, AND
A DECAYING NORTH SWELL.
DISCUSSION
VERY LITTLE CHANGE IN THE MARIANAS FORECAST FOR TODAY. CONTINUED
ISOLATED SHOWERS, JUST SOME THICKER THAN EXPECTED HIGH CLOUDS WAS THE
ONLY SURPRISE. THE EXTENDED WAVE FORECAST DOES GET A LITTLE MURKIER.
THE GFS IS SPINNING UP A TROPICAL CYCLONE TO OUR WEST. HAVING SEEN
THIS MANY TIMES AND KNOWING IT WILL JUST KEEP DELAYING IT AND
DELAYING IT UNTIL IT EITHER HAPPENS A MONTH FROM NOW, OR IT DOESN'T
HAPPEN AT ALL. EITHER WAY, THE SWELL FROM THAT SYSTEM IS MOST LIKELY
BOGUS, SO LEANED MORE ON THE ECMWF WAVE SOLUTION FOR TODAY. THIS
STARTS OUT WITH THE 3 TO 5 FEET WAVES WE SEE, INSTEAD OF RISING
SEVERAL DAYS FROM NOW THOUGH, THEY SINK TO BETWEEN 2 AND 4 FEET
INSTEAD. IT WILL BE INTERESTING TO SEE WHICH TURNS OUT TO BE TRUE.
TROPICAL SYSTEMS
JTWC INVEST 99W IS CURRENTLY LOCATED AT 4.8N AND 130E. THE LATEST
ASCAT DATA SHOWS A POORLY ORGANIZED SURFACE TROUGH. SIGNIFICANT
DEVELOPMENT REMAINS VERY LOW FOR THE NEXT 24 HOURS. INVEST 99W WILL
CONTINUE TO BRING SCATTERED TO NUMEROUS SHOWER TO PALAU AND YAP THE
NEXT FEW DAYS.
EASTERN MICRONESIA
ONLY CHANGE WITH THIS PACKAGE WAS TO DELAY THE START OF THE
SCATTERED SHOWERS FOR POHNPEI UNTIL THIS AFTERNOON. CURRENT
SATELLITE OBSERVATIONS SHOW A FEW SHOWERS JUST SOUTH OF POHNPEI
WHILE MORE ROBUST CONVECTION IS SEEN ALONG THE SOUTHERN EDGES OF
KOSRAE'S AND MAJURO'S COASTAL WATERS. INCREASED SHOWER ACTIVITY IS
STILL EXPECTED THROUGH THE FIRST HALF OF THE WEEK AS TRADE-WIND
CONVERGENCE INCREASES ACROSS EASTERN MICRONESIA.
NO CHANGES WERE MADE TO THE MARINE FORECAST. BENIGN SEAS AT OR BELOW
6 FEET ARE EXPECTED TO CONTINUE THROUGH THE PERIOD.
WESTERN MICRONESIA
THE ONLY CHANGE WAS TO BUMP UP SHOWER COVERAGE TO 50% FOR YAP
TODAY. CURRENT SATELLITE TRENDS SHOW CONVECTION MOVING ACROSS YAP
STATE AND JUST EAST OF YAP PROPER WITH NEW DEVELOPMENT FURTHER EAST.
OTHERWISE, THE FORECAST REMAINS CONSISTENT FROM THE PREVIOUS
PACKAGE.
NO CHANGES WERE MADE TO THE MARINE FORECAST. COMBINED SEAS WILL
GENERALLY BE BELOW 6 FEET FOR THE NEXT SEVERAL DAYS.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: STANKO
EAST/WEST MICRONESIA: WILLIAMS
PREVIOUS AFD, ISSUED AT 552 PM CHST SUN APR 27 2025:
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
552 PM CHST SUN APR 27 2025
MARIANAS SYNOPSIS
GENTLE TO MODERATE TRADES PREVAIL. SATELLITE IMAGERY AND DOPPLER
RADAR INDICATE A MINOR TROUGH MOVING IN UPSTREAM. BUOYS INDICATE SEAS
ARE ABOUT 5 FEET.
DISCUSSION
A MINOR SURFACE TROUGH UPSTREAM IS EXPECTED TO BRING LOW-END
SCATTERED SHOWERS TO GUAM MONDAY AND MONDAY NIGHT, FOLLOWED BY AN
EXTENDED PERIOD OF DRIER TRADES THAT MAY LAST FOR MUCH OF THE
FORECAST PERIOD.
MARINE
COMBINED SEAS OF 4 TO 6 FEET ARE EXPECTED THROUGH AT LEAST MONDAY
NIGHT, BEFORE TAPERING DOWN A FOOT OR TWO BRIEFLY BEFORE MIDWEEK. A
MODERATE RISK OF RIP CURRENTS IS EXPECTED ALONG NORTH AND EAST FACING
REEFS FOR AT LEAST THE NEXT SEVERAL DAYS. EXISTING SURF IS EXPECTED
TO PERSIST FOR MUCH OF THE WEEK AS THE SECONDARY NORTH SWELL WEAKENS,
BUT TRADE SWELL STRENGTHENS SLIGHTLY IN THE SECOND HALF OF THE WEEK.
FIRE WEATHER
SO FAR TODAY, 0.03 INCHES RAIN HAS FALLEN SINCE MIDNIGHT, WITH ONLY
ISOLATED SHOWERS EXPECTED OVERNIGHT AT GUAM. AS SUCH, THE KBDI IS
EXPECTED TO INCREASE FURTHER, WHICH IS AT 685 CURRENTLY (HIGH
CATEGORY). A MINOR TROUGH WILL BRINGER HIGHER RAINFALL AMOUNTS
TONIGHT, BUT NOT LIKELY TO BE WETTING RAINS, SO THE KBDI MAY CONTINUE
TO CREEP UPWARDS. EVEN SO, WINDS ARE EXPECTED TO REMAIN GENTLE TO
MODERATE, SO CONDITIONS CRITICAL TO FIRE WEATHER ARE NOT EXPECTED AT
LEAST OVER THE NEXT FEW DAYS.
TROPICAL SYSTEMS
THE MAIN VORTICITY FEATURE WITHIN THE NEAR-EQUATORIAL TROUGH (NET)
IS LOCATED NEAR 4N131E AND IS BEING MONITORED BY JTWC AS INVEST 99W.
THIS FEATURE LOOKS MORE LIKE AN MID-LEVEL CIRCULATION WITH ASCAT
WIND DATA SHOWING MORE OF A SHARP TROUGH OR WEAK CIRCULATION NEAR THE
SURFACE THIS AFTERNOON, SO WHILE IT IS AN AREA TO WATCH, THE OVERALL
POTENTIAL FOR DEVELOPMENT INTO A TROPICAL CYCLONE OVER THE NEXT 24
HOURS IS STILL VERY LOW. MULTI-MODEL CONSENSUS CONTINUES TO FAVOR A
BROAD CIRCULATION DEVELOPING SOMEWHERE WITHIN THE NET AND LIFT NORTH-
NORTHWEST OVER THE NEXT FEW DAYS, LIFTING SHOWERS AND THUNDERSTORMS
NORTHWARD TOWARDS YAP AND ESPECIALLY PALAU, WITH SOUTHERLY WINDS
ACROSS MOST OF THE REPUBLIC OF PALAU. THE ECMWF AND CANADIAN ENSEMBLE
FAVOR THE CIRCULATION DEVELOPING IN THE GENERAL LOCATION OF 99W,
LINGERING NEAR 130E FOR A COUPLE OF DAYS AND THEN MOVING NORTHWEST
TOWARDS THE PHILIPPINES. THE GFS FAVORS A CIRCULATION DEVELOPING
SLIGHTLY FARTHER EAST WITHIN THE NET AND LIFTING NORTHWARD THROUGH
PALAU, BEFORE MOVING NORTHWEST AND DEEPER INTO THE PHILIPPINE SEA.
CURRENTLY MODEL GUIDANCE KEEPS THIS CIRCULATION WEAK WHILE IT IS
WITHIN WESTERN MICRONESIA, BUT THE GFS SOLUTION WOULD LIKELY FAVOR
HEAVIER SHOWERS, THUNDERSTORMS, AND VARIABLE BUT GUSTY WINDS AROUND
THE MAIN ISLANDS OF PALAU MONDAY NIGHT THROUGH WEDNESDAY.
EASTERN MICRONESIA
MODEL GUIDANCE CONTINUES TO OVERESTIMATE THE POTENTIAL CONVECTION
ACROSS EASTERN MICRONESIA. UNFORTUNATELY, THE DEVELOPMENT REMAINS
LESS THAN EXPECTED AND FARTHER SOUTH. IT STILL APPEARS LIKELY THAT A
COMBINATION OF TRADE-WIND CONVERGENCE AND WEAK TROUGHS TRAVERSING
THE REGION WILL BRING PERIODS ENHANCED SHOWERS THROUGH THE COMING
WEEK. HOWEVER, BASED ON THE LATEST TRENDS AND HOW MUCH THE MODELS ARE
OVERDOING IT, IT IS MORE PRUDENT TO MAINTAIN A BIT OF PERSISTENCE
WITH THE FORECAST ALONG WITH DECREASING POPS (PROBABILITY OF
PRECIPITATION) A BIT. ALTHOUGH MODEL GUIDANCE CONTINUES VERY HIGH
POPS OVER THE NEXT SEVERAL DAYS (70 TO 90 PERCENT RANGE), TRENDS
INDICATE THIS IS RUNNING A LITTLE HOT, SO CAPPED THE POPS AT 50
PERCENT FOR NOW. MOSTLY CLOUDY SKIES WITH ISOLATED SHOWERS ARE
CURRENTLY IN PLACE OVER KOSRAE AND POHNPEI, WHILE LOW-END SCATTERED
SHOWERS ARE MOVING THROUGH MAJURO. THERE ARE A COUPLE OF WEAK BANDS
OF CONVERGENCE SEEN THROUGHOUT EASTERN MICRONESIA; A MUCH STRONGER
BAND, POSSIBLY A DEVELOPING INTER-TROPICAL CONVERGENCE ZONE (ITCZ),
SEEN JUST EAST OF THE DATE LINE, CONTINUES TO SHOW INCREASING POPS
OVER THE NEXT FEW DAYS ACROSS THE REGION. MAJURO WILL SEE THE
SHORTEST DURATION OF ANY CONVECTION AS MOST OF THE CONVERGENCE LOOKS
TO DRIFT MORE TOWARD THE SOUTH OF THE ATOLL. THEREFORE, A DRIER
TRADE-WIND PATTERN LOOKS TO BE ON TAP FOR MAJURO BY MIDWEEK. FOR
KOSRAE AND POHNPEI, AN OVERALL UNSETTLED PATTERN COULD EASILY
CONTINUE THROUGH THE COMING WEEKEND.
NO MAJOR CHANGES IN THE MARINE FORECAST. COMBINED SEAS WILL REMAIN AT
OR BELOW 7 FEET FOR MAJURO, AND AT OR BELOW 6 FEET FOR KOSRAE AND
POHNPEI. MOSTLY GENTLE TO MODERATE TRADE WINDS ARE EXPECTED THROUGH
THE PERIOD, THOUGH POHNPEI COULD SEE OCCASIONALLY LIGHT WINDS AFTER
MIDWEEK, AND MAJURO WILL SEE OCCASIONALLY FRESH WINDS TUESDAY INTO
TUESDAY NIGHT.
WESTERN MICRONESIA
THE NEAR-EQUATORIAL TROUGH (NET) CONTINUES TO SUPPORT NUMEROUS
SHOWERS AND ISOLATED THUNDESTORMS SOUTH OF PALAU AND ALONG THE
EQUATOR, AS IT EXTENDS FROM 5N130E TO NEAR THE EQUATOR AT 150E.
ACROSS THE OUTER ISLANDS OF YAP STATE AND THROUGH MOST OF CHUUK
STATE, A ZONE OF CONVERGENCE CREATED BY TRADE WINDS MEETING THE
SOUTH-TO-SOUTHWEST FLOW FOUND NEAR THE NET, IS CREATING ANOTHER BAND
OF NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS THAT EXTEND TOWARDS
POHNPEI STATE, WITH CHUUK LAGOON SITTING ON THE NORTHERN EDGE OF THIS
AREA OF CONVERGENCE. SATELLITE IMAGERY SHOWS A MID-LEVEL CIRCULATION
TO THE WEST-SOUTHWEST OF SONSOROL AND WELL SOUTHWEST OF KOROR NEAR
4N131E, WITH ASCAT WIND DATA SHOWING MORE OF A SHARP TROUGH OR WEAK
CIRCULATION NEAR THE SURFACE THIS AFTERNOON. THIS AREA IS CURRENTLY
BEING MONITORED AS INVEST 99W BY JTWC AS A SUB-LOW, SO WHILE IT IS AN
AREA TO WATCH THE OVERALL POTENTIAL, DEVELOPMENT INTO A TROPICAL
CYCLONE OVER THE NEXT 24 HOURS IS STILL VERY LOW. AS DISCUSSED IN THE
TROPICAL SYSTEMS SECTION ABOVE, MODELS BROADLY AGREE THAT THE NET
WILL LIFT NORTHWARD AS A BROAD CIRCULATION DEVELOPS WITHIN THE NET,
SO EXPECT A FAIRLY WET PATTERN ACROSS PALAU, YAP AND CHUUK THIS WEEK.
WHAT MODELS ARE NOT OVERLY CONSISTENT WITH IS THE EXACT LOCATION OF
THE CIRCULATION. THE ECMWF AND CANADIAN ENSEMBLE CONTINUE TO FAVOR
THE LOCATION NEAR 99W, WHICH WOULD FAVOR MORE OF A SOUTHEAST FLOW AND
POTENTIALLY LIMIT THE THREAT OF GUSTY WINDS AROUND YAP AND PALAU,
BUT THE GFS HAS THE MAIN CIRCULATION DEVELOPING FURTHER EAST, WHICH
COULD LEAD TO MORE VARIABLE WINDS AROUND PALAU ALONG WITH HEAVIER
SHOWERS AND GUSTY WINDS MONDAY NIGHT THROUGH WEDNESDAY.
SEAS ARE CURRENTLY AROUND 3 TO 5 FEET AND MODELS KEEP SEAS NEAR THIS
RANGE THROUGH THE WEEK, DRIVEN PRIMARILY BY THE NORTHEAST-TO-EAST
SWELL AND LOCAL WINDS. THE UNSETTLED WEATHER PATTERN ACROSS THE
REGION MAY PRODUCE LOCALLY GUSTY CONDITIONS, WHICH COULD LEAD TO
CHOPPY SEA CONDITIONS NOT CAPTURED BY THE MODELS, AND THEN THERE
ALWAYS IS THE POTENTIAL FOR LIGHTNING WITHIN HEAVIER SHOWERS AS THEY
DEVELOP INTO THUNDERSTORMS. MARINERS SHOULD CONTINUE TO MONITOR THE
LATEST FORECAST FOR ANY CHANGES TO MARINE CONDITIONS AND PRACTICE
CAUTION, ESPECIALLY IF PLANNING ANY INTER-ISLAND TRAVEL.
GUM WATCHES/WARNINGS/ADVISORIES
GU...NONE.
MP...NONE.
MARIANAS WATERS...NONE.
MARIANAS: MONTVILA
EAST MICRONESIA: KLEESCHULTE
WEST MICRONESIA: SCHANK
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