Area Forecast Discussion
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000
FXPQ60 PGUM 220627
AFDPQ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
427 PM CHST WED OCT 22 2014

.MARIANAS SYNOPSIS...
A SHEAR LINE ALONG WITH A DEFINED LINE OF SHOWERS AND
THUNDERSTORMS ARE PRESENT ACROSS THE FAR NORTHERN MARIANAS. A
WEAK CIRCULATION AND TROUGH ARE FOUND SOUTHEAST OF GUAM. SHOWERS
ASSOCIATED WITH THE TROUGH ARE APPROACHING EASTERN MARIANAS
COASTAL WATERS.

&&

.DISCUSSION...
THE CIRCULATION AND SURFACE TROUGH SOUTHEAST OF THE MARIANAS WILL
SLOWLY PUSH NORTHWARD...THEN WESTWARD THROUGH THURSDAY. WINDS
WILL VEER FROM THE EAST TO THE THURSDAY AND INTRODUCE DEEPER
TROPICAL MOISTURE TO THE MARIANAS. ADJUSTED SKY COVER TO MOSTLY
CLOUDY THURSDAY THROUGH FRIDAY NIGHT TO ACCOUNT FOR THE PASSAGE
OF THE CIRCULATION/TROUGH. SATELLITE AND RADAR IMAGERY INDICATE
ONLY ISOLATED SHOWER COVERAGE AT THE MOMENT. GFS AND NAVGEM ARE
STILL THE DRIER NWP SOLUTIONS WHILE THE ECMWF HOLDS OFF ON
INCREASED SHOWERS UNTIL FRIDAY NIGHT. UNCERTAINTY EXISTS
REGARDING THIS SYSTEM SINCE IT A SMALL FEATURE AND PROBABLY IS
NOT BEING HANDLED WELL BY MODELS. ONCOMING SHIFT SHOULD ASSESS IF
AN UPDATE IS NEEDED IF SHOWERS INCREASE FASTER THAN EXPECTED. FOR
NOW...ONLY ISOLATED SHOWERS ARE EXPECTED THU THROUGH FRI NIGHT
OWING TO AT LEAST SOME CONSISTENCY TO THE GFS AND NAVGEM RUNS
OVER THE LAST 24 HOURS. MODEL AGREEMENT BECOMES POOR AFTER THE
PASSAGE OF THE CIRCULATION/TROUGH OVER THE SOUTHERN MARIANAS WITH
ECMWF KEEPING THE AREA UNDER AMPLE MOISTURE AND WIDESPREAD SHOWER
ACTIVITY WHILE GFS AND NAVGEM CONTINUE TO BE THE LESS AGGRESSIVE
FORECAST...EVEN IN THE LONG TERM. THE FORECAST FOR NEXT WEEK IS
LARGELY PERSISTENCE WITH A DRY TRADE-WIND PATTERN EMERGING. A FEW
MORE MODEL RUNS WILL BE NEEDED BEFORE A CONSENSUS CAN BE MADE
REGARDING ANY CHANGES IN THE FORECAST FOR NEXT WEEK.

&&

.MARINE...
SAIPAN BUOY SHOWED A RAPID RISE IN SEAS OVERNIGHT AS THE NORTH-
NORTHEAST SWELL BUILT IN SAIPAN WATERS. SWELL HAS REACHED GUAM
AND HAS BEEN SLIGHTLY LARGER THAN WW3 OUTPUT WITH SAIPAN BUOY
INDICATING A 7 FT 12 SECOND NNE SWELL. THUS...A HIGH SURF
ADVISORY WAS ISSUED THIS MORNING WITH SURF HEIGHTS OF 8 TO 9 FEET
LIKELY CONTINUING OVERNIGHT. SURF IS EXPECTED TO FALL SLIGHTLY
THURSDAY BUT A SECONDARY LONG-PERIOD SWELL FROM THE NORTHEAST
WILL INCREASE FRIDAY BRINGING SURF TO ADVISORY LEVELS ONCE AGAIN.
SURF SHOULD FALL BELOW ADVISORY LEVELS LATE SATURDAY NIGHT OR
EARLY SUNDAY MORNING.

&&

.EASTERN MICRONESIA...
AN AREA OF SHOWERS AND THUNDERSTORMS PUSHED ACROSS POHNPEI TODAY.
SATELLITE IMAGERY SHOWED THAT THIS AREA WAS WEAKENING BUT
LINGERING SCATTERED SHOWERS ARE LIKELY FOR AT LEAST PART OF THE
NIGHT. WHILE THE CHANCE OF THUNDERSTORMS IS LOW A FEW MAY OCCUR
SO ADDED A SLIGHT CHANCE OF THUNDERSTORMS TO TONIGHT POHNPEI
FORECAST. LOW- LEVEL CONVERGENCE WILL KEEP SKIES MOSTLY CLOUDY
ACROSS POHNPEI THROUGH SATURDAY.

A SURFACE TROUGH IS STRETCHED ACROSS THE MARSHALL ISLANDS.
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS COULD BE FOUND SOUTH
OF MAJURO THIS AFTERNOON. WHILE THE BULK OF THE ACTIVITY WILL
REMAIN SOUTH OF MAJURO IT WILL PRODUCE ISOLATED SHOWERS AND A
SLIGHT CHANCE OF THUNDERSTORMS TONIGHT THROUGH THURSDAY NIGHT.

THIS SAME TROUGH WILL MOVE EAST AND CAUSE WINDS TO BECOME NORTHEAST
AT KOSRAE THURSDAY NIGHT. IT WILL BRING SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS TO KOSRAE FRIDAY AND FRIDAY NIGHT. HIGH
PRESSURE WILL BUILD ACROSS KOSRAE AND MAJURO SATURDAY AND SUNDAY.

&&

.WESTERN MICRONESIA...
A SURFACE TROUGH OF LOW PRESSURE CONTINUES TO STRETCH ACROSS THE
WESTERN HALF OF MICRONESIA. THE TROUGH AXIS WAS NORTH OF 10N.
CONVERGENCE SOUTH OF THE TROUGH BROUGHT A SOME PATCHES OF SHOWERS
AND THUNDERSTORMS ACROSS PALAU AND YAP THIS AFTERNOON. WHILE
ISOLATED SHOWERS ARE EXPECTED TO BE THE PREDOMINANT COVERAGE A
ISOLATED THUNDERSTORMS IS POSSIBLE ACROSS PALAU TONIGHT.

A CIRCULATION COULD BE FOUND ON THE TROUGH JUST SOUTH OF GUAM
THIS AFTERNOON. THIS TROUGH WILL PUSH SOUTHWEST TOWARD YAP.
MODELS SHOW IT CLOSE TO YAP ON THURSDAY. AT THIS TIME THE MODELS
KEEP THE WEATHER RATHER BENIGN NEAR THE CENTER OF THE
CIRCULATION. THE CIRCULATION LOOKS AS THOUGH IT WILL PUSH THE
SHOWERS NOW NEAR PALAU AND YAP FURTHER SOUTHWARD AS IT MOVES OVER
YAP. THE CIRCULATION WILL MOVE WEST TO 130E BY FRIDAY. IN THE
WAKE OF THE CIRCULATION EAST TRADE WINDS WILL BUILD ACROSS PALAU
AND YAP BY THE END OF THE WEEK.

THE SOUTHWEST WINDS AT CHUUK TODAY WILL GIVE WAY TO NORTHEAST
TRADE WINDS THURSDAY NIGHT. FAIR WEATHER WILL PREVAIL ACROSS
CHUUK THROUGH THURSDAY NIGHT. MODELS SHOW A CIRCULATION
DEVELOPING SOUTH OF CHUUK THIS WEEKEND. WHILE MOST OF THE
ACTIVITY WILL REMAIN SOUTH OF CHUUK...MOSTLY CLOUDY SKIES AND A
SLIGHT CHANCE THUNDERSTORMS WILL PREVAIL FRIDAY THROUGH MONDAY.

STRONG WINDS ASSOCIATED WITH A STORM SYSTEM IN THE NORTH PACIFIC
PRODUCED SWELLS THAT HAVE GENERATED HIGH SURF ACROSS THE MARIANAS
THIS AFTERNOON. MODELS SHOW LONG-PERIOD SWELL PUSHING ACROSS YAP
AND PALAU SOMETIME THIS WEEKEND. AT THIS TIME...THESE SWELL DO NOT
APPEAR TO BE HIGH ENOUGH TO GENERATE HAZARDOUS SURF AT THESE TWO
LOCATIONS. THIS SHOULD BE WATCHED AS THIS SWELL WAS NOT EXPECTED
TO PRODUCE HAZARDOUS SURF ACROSS THE MARIANAS. AT ANY RATE EVEN IF
HAZARDOUS SURF DOES NOT OCCUR THE LONG PERIOD SWELL...UP TO 14
SECONDS...MAY STILL PRODUCE A HIGHER RIP CURRENT RISK THIS
WEEKEND. THE SAME WAVE MODELS ALSO SHOW THE SURF POSSIBLY
APPROACHING HAZARDOUS AT CHUUK LATE FRIDAY NIGHT. AGAIN...EVEN IF
SURF DID NOT REACH HAZARDOUS THE RIP CURRENT RISK WOULD LIKELY
INCREASE.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...HIGH SURF ADVISORY UNTIL 4 PM CHST SUNDAY FOR GUZ001>004.

MARIANAS WATERS...NONE.
&&

$$

WILLIAMS/ZIOBRO





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