Area Forecast Discussion
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000
FXPQ60 PGUM 242159
AFDPQ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
759 AM CHST SAT APR 25 2015

.SYNOPSIS...EAST WINDS AND A FEW CLOUDS AND SHOWERS PREVAIL ACROSS
THE MARIANAS THIS MORNING.

&&

.DISCUSSION...
SCATTEROMETER DATA FROM FRIDAY NIGHT SHOWED A CIRCULATION CENTERED
SOUTHEAST OF YAP NEAR 4N142E. A SURFACE TROUGH EXTENDED NORTHEAST
FROM THE CIRCULATION TO 15N150E. AS THE CIRCULATION MOVES WEST IT
WILL DRAG THE TROUGH ACROSS THE MARIANAS TODAY. NORTHEAST WIND
PREVAIL ACROSS THE LOCAL AREA THIS MORNING. AS THE TROUGH AXIS
PROGRESSES ACROSS THE MARIANAS WINDS WILL BECOME EAST AROUND NOON
TIME.


THE PERCIPITABLE WATER INDEX FROM LAST NIGHTS SOUNDING WAS 1.64
INCHES...AT THE SAME TIME SATELLITE ESTIMATE OF THE PWI WAS 1.53
INCHES. BY SUNRISE THE SATELLITE ESTIMATE HAD INCREASED TO 1.92
INCHES. THIS INCREASE IN PWI IS INDICATIVE OF AN INCREASE IN DEEP
LAYER MOISTURE. THE SATELLITE DATA SHOWED HIGHER PWI VALES FURTHER
EAST. EXPECT THE PWI TO GO ABOVE 2 INCHES BY TONIGHT.

ONLY A FEW CLOUDS AND SHOWERS ARE EXPECTED WITH THE TROUGH PASSAGE
ITSELF. MODELS SHOW LOW-LEVEL CONVERGENCE IN THE WAKE OF THE
TROUGH. THIS CONVERGENCE WILL INCREASE THE CHANCES FOR SHOWERS
TONIGHT THROUGH MONDAY NIGHT. STILL NOT CERTAIN ON SHOWER COVERAGE
AS MODELS DEPICT SPOTTY COVERAGE IN RAINSHOWER ACTIVITY.
SATELLITE IMAGERY THIS MORNING DEPICTED SPOTTY COVERAGE OF SHOWERS
TO THE EAST OF THE TROUGH AXIS...ALTHOUGH SOME OF THE AREAS NEAR
155E WERE GETTING MORE CONCENTRATED.

FORECAST STILL ONLY HAS ISOLATED SHOWERS IN IT...BUT WITH THE INCREASE
IN MOISTURE AS EVIDENT BY THE PWI RISE AND SHOWER ACTIVITY NEAR
155E THIS MAY NEED TO BE WATCHED. AT THIS TIME FEEL THAT ISOLATED
SHOWERS WILL BE THE PREDOMINATE COVERAGE BUT THERE COULD BE
PERIODS OF SCATTERED SHOWERS FROM TONIGHT THOUGH MONDAY NIGHT. AS
THE MODELS SHOW A SPOTTY RAINFALL PATTERN IT IS HARD TO PINPOINT
THE TIMING OF ANY SCATTERED SHOWERS. MODELS DO AGREE WITH DRIER
WEATHER BY TUESDAY.

&&

.MARINE...
AN EAST TRADE-WIND SWELL WILL PERSIST THROUGH THE FORECAST. THIS
SWELL WILL NOT BECOME VERY LARGE AND A MODERATE RIP CURRENT RISK
WILL PREVAIL THROUGH THE FORECAST.

&&

.EASTERN MICRONESIA...
POHNPEI AND KOSRAE ARE SITUATED BETWEEN TWO WEATHER FEATURES...A
NEAR-EQUATORIAL TROUGH TO THE WEST AND A TROPICAL DISTURBANCE TO THE
EAST. THIS PATTERN SHOULD REMAIN SO THRU SUNDAY AFTERNOON. DURING
THIS TIME...ISOLATED SHOWERS EMBEDDED WITHIN GENTLE TO MODERATE
TRADES WILL PREVAIL BUT FAVORABLE UPPER-LEVEL DYNAMICS COULD SPARK
OFF A FEW THUNDERSTORMS FOR BOTH LOCALES. THE TROPICAL DISTURBANCE
CENTERED SOUTHEAST OF MAJURO NEAR 4N175E IS BEGINNING TO DRIFT WEST-
NORTHWESTWARD THIS MORNING. CONVECTION NORTH AND NORTHEAST OF THE
CENTER WILL SLOWLY BUT STEADILY APPROACH MAJURO TODAY AND SPREAD
OVER THE AREA BY LATE THIS AFTERNOON.

AS THE DISTURBANCE AND ASSOCIATED SURFACE TROUGH DRIFT WEST OF
MAJURO ON SUNDAY NIGHT...WEAKER SOUTHEAST WINDS SHOULD ALLOW SHOWER
COVERAGE TO DECREASE. ON ANOTHER HAND...CONVECTION WILL SPREAD
WESTWARD OVER KOSRAE AND POHNPEI. FAIR WEATHER WILL ARRIVE AT MAJURO
BY MONDAY AS SURFACE RIDGING SHIFTS WESTWARD ACROSS THE DATE LINE.
THIS SAME RIDGE MIGHT ALSO BRING DRIER WEATHER TO KOSRAE AND POHNPEI
TOWARD MIDWEEK AS WELL.

&&

.WESTERN MICRONESIA...
THE LEADING EDGE OF A TRADE-WIND SURGE HAS ARRIVED AT CHUUK THIS
MORNING. WITH THE SOUTHEASTERN END OF A NEAR-EQUATORIAL TROUGH STILL
LINGERING JUST TO THE SOUTHWEST...INCREASING SURFACE CONVERGENCE IS
COUPLING WITH DIVERGENT UPPER-LEVEL WINDS TO GENERATE POCKETS OF
DEEP CONVECTION NEAR THE ISLAND. THIS TREND SHOULD CONTINUE THRU
SUNDAY MORNING. AS THE TROUGH FINALLY MOVES FARTHER WEST AWAY FROM
CHUUK ON SUNDAY NIGHT...FAIRER WEATHER ALREADY OVER POHNPEI WILL
SPREAD WESTWARD OVER CHUUK. IN THE LONG TERM...THE TROPICAL
DISTURBANCE CURRENTLY SOUTHEAST OF MAJURO MIGHT BRING MORE WETNESS
TO CHUUK TOWARD MIDWEEK.

THE AXIS OF A NEAR-EQUATORIAL TROUGH RELATED TO A BROAD CIRCULATION
CENTERED SOUTHEAST OF YAP NEAR 7N143E IS INCHING CLOSER TO KOROR AND
YAP. AT THE UPPER-LEVELS...A RIDGE IS PERSISTING ACROSS THE REGION
NEAR 10N JUST NORTH OF BOTH PLACES. STRONG DIVERGENCE JUST SOUTH OF
THE RIDGE IS ENHANCING WIDESPREAD DEEP CONVECTION NEAR THE TROUGH
AXIS. ANTICIPATE THIS CONVECTION TO CONTINUE IMPACT KOROR UNTIL
SUNDAY NIGHT AND ENGULF YAP BY LATER THIS EVENING. AS THE
CIRCULATION GRADUALLY APPROACH YAP AND KOROR ON MONDAY...GENTLE
WINDS NEAR ITS CENTER WILL ALLOW CONVECTION TO WEAKEN. FURTHER
IMPROVEMENT SHOULD OCCUR BY MIDWEEK AS THE CIRCULATION PASSES WEST
OF THE AREA.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...NONE.
MARIANAS WATERS...NONE.
&&

$$

ZIOBRO/CHAN



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