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908
FXPQ60 PGUM 242018
AFDPQ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
618 AM CHST FRI APR 25 2014

.MARIANAS SYNOPSIS...
NEAR-EQUATORIAL TROUGH PASSES WELL TO THE SOUTH OF GUAM NEAR 5N.
JTWC LOW SUSPECT AREA 99W IS EMBEDDED IN THE TRADES NORTH OF THE
TROUGH NEAR 8N154E. CONVECTION ASSOCIATED WITH 99W REMAINS RATHER
LIMITED IN AREAL COVERAGE. A SURFACE TROUGH EXTENDING
NORTHWESTWARD FROM 99W BROUGHT SOME SHOWERS TO GUAM YESTERDAY
EVENING...BUT DRIER AIR HAS MOVED BACK IN FROM THE NORTHEAST.
WATER VAPOR LOOP SHOWS A TUTT JUST TO THE WEST OF THE FORECAST
ZONES OVER THE PHILIPPINE SEA. A FRONTAL ZONE IS SAGGING
SOUTHWARD FROM IWO TO TOWARD THE FAR NORTHERN CNMI.

&&

.DISCUSSION...
REDUCED POPS AND CLOUD COVER TODAY THROUGH SATURDAY BASED ON
MODEL AND SATELLITE TRENDS. UPPER-LEVEL CONVERGENCE IN THE
VICINITY OF THE TUTT IS SUPPORTING A SHORT TERM DRYING TREND.
BEYOND SAT...FORECAST CONFIDENCE RAPIDLY WANES. FUTURE COMPLEX
INTERACTION OF FRONT/SHEAR LINE AND 99W GUARANTEES SIGNIFICANT RUN
TO RUN DIFFERENCES IN THE MODELS. ALL THE MODELS AGREE ON THE
FRONT BECOMING A SHEAR LINE AND STALLING IN THE VICINITY OF SAIPAN
BY EARLY NEXT WEEK AS 99W DRIFTS SLOWLY NORTHWARD. FORECAST
REMAINS HIGHLY DEPENDENT ON THE EXACT TRACK AND EVOLUTION OF 99W.
FOR NOW...FORECAST COMPROMISES AND BRINGS 99W TO A POSITION SOUTH
OF GUAM ON SUNDAY...THEN FAVORS THE GFS40 SOLUTION WHICH TAKES 99W
SLOWLY NORTHWESTWARD AS A WEAK SYSTEM DURING THE FIRST HALF OF
NEXT WEEK. ECMWF AND UKMET TAKE 99W OVER OR EAST OF GUAM AND
SAIPAN...SO WIND FORECAST FOR EARLY NEXT WEEK MAY NEED SIGNIFICANT
REVISION. MAINTAINED ISOLATED THUNDER SATURDAY NIGHT THROUGH
MONDAY...BUT KEPT POPS ISOLATED BASED ON THE SMALL AREAL COVERAGE
SEEN IN THE CONVECTION ASSOCIATED WITH 99W. MAINTAINED DRY BIAS IN
THE LONG TERM FORECAST WHICH CALLS FOR PARTLY CLOUDY SKIES
BEGINNING NEXT WEDNESDAY. SLOW MOVEMENT OF 99W IN ALL THE MODELS
SUGGESTS UNSETTLED WEATHER COULD PERSIST BEYOND THE MIDDLE OF NEXT
WEEK.

&&

.MARINE...
ALTIMETRY AND BUOY READINGS INITIALIZE COMBINED SEAS BETWEEN 5
AND 7 FEET. HIGHEST SEAS WERE SEEN IN THE VICINITY OF GUAM. NO
ADVISORIES ARE FORESEEN THROUGH THE WEEKEND...BUT THEN THE PLOT
THICKENS. WAVE WATCH MODEL BRINGS LONG PERIOD SWELL IN FROM THE
NORTH-NORTHEAST EARLY ON MONDAY. CULPRIT APPEARS TO BE STRONG
FRONT CURRENTLY PUSHING SOUTHWARD FROM JAPAN. SWELL FROM THE
NORTH-NORTHEAST FOR GUAM AND ROTA WILL BE BLOCKED BY TINIAN AND
SAIPAN...SO USED SWELL BUNDLE TO REFRESH THESE GRIDS. AT
PRESENT...NORTH-NORTHEAST SWELL APPEAR TO BE HIGH ENOUGH TO
PRODUCE HIGH SURF ALONG NORTH FACING REEFS ON TINIAN AND SAIPAN
EARLY NEXT WEEK. FUTURE SHIFTS WILL NEED TO MONITOR THE FETCH
GENERATION AREA SOUTH OF JAPAN OVER THE WEEKEND FOR THE GENERATION
OF THESE SWELL.

&&

.EASTERN MICRONESIA...
THE EASTERN END OF THE NEAR-EQUATORIAL TROUGH HAS RETREATED
FARTHER TO THE SOUTHWEST OF POHNPEI AND KOSRAE THIS MORNING.
MODERATE TRADE WINDS NORTH OF THE TROUGH WILL MAINTAIN FAIR
WEATHER FOR POHNPEI UNTIL SATURDAY MORNING...AND FOR KOSRAE THRU
EARLY THIS EVENING. A FRESH TRADE-WIND SURGE IS VISIBLE ON THE
LATEST ASCAT SATELLITE IMAGERY. THE SURGE IS ARRIVING IN THE
MARSHALL ISLANDS THIS MORNING. THE LEADING EDGE OF THIS FEATURE
COULD SPARK OFF A FEW SHOWERS NEAR MAJURO TODAY. THEN MUCH DRYER
TRADES FOLLOWING BEHIND SHOULD USHER IN PLEASANT CONDITIONS FOR
THE CAPITAL BY THIS EVENING. AS THESE FRESH TRADES PUSH WEST OF
THE MARSHALLS TONIGHT...INCREASING SURFACE CONVERGENCE WILL BEGIN
TO TRIGGER SPORADIC CONVECTION NEAR KOSRAE AND POHNPEI. A ZONE OF
CONVERGING TRADES IS ALSO VISIBLE ALONG THE SOUTHERN EDGE OF THE
SURGE. IT LIES BETWEEN THE EQUATOR AND 5N AND STRETCHES EAST-
NORTHEASTWARD FROM NEAR TARAWA ATOLL TO WELL BEYOND THE DATE
LINE. WET WEATHER ASSOCIATED WITH THIS ZONE WILL SPREAD OVER
MAJURO BY SATURDAY NIGHT...AND COULD ALSO IMPACT KOSRAE AND
POHNPEI UNTIL EARLY NEXT WEEK.

&&

.WESTERN MICRONESIA...
THE TROPICAL DISTURBANCE EMBEDDED WITHIN THE NEAR-EQUATORIAL
TROUGH HAS DRIFTED NORTHWEST OF CHUUK OVERNIGHT. THIS HAS TAKEN
THE STRONGEST LOW-LEVEL CONVERGENCE AND ASSOCIATED CONVECTION
AWAY FROM CHUUK. ACCORDINGLY...GENTLER WINDS ON THE SOUTHEAST SIDE
OF THE DISTURBANCE SHOULD PROMOTE PARTLY CLOUDY SKIES NEAR CHUUK
THRU SATURDAY. BY SATURDAY NIGHT...INCREASING TRADE CONVERGENCE
FROM THE EAST COULD BRING BACK SHOWERY WEATHER LASTING INTO THE
FIRST PART OF NEXT WEEK.

A SURFACE TROUGH IS EXPECTED TO GENERATE SOME SHOWERS NEAR KOROR
TODAY. OTHERWISE...DRY WEATHER NORTH OF THE NEAR-EQUATORIAL
TROUGH WILL PREVAIL OVER KOROR THRU SATURDAY NIGHT AND OVER YAP
UNTIL SATURDAY MORNING. THE TROPICAL DISTURBANCE CURRENTLY
NORTHWEST OF CHUUK SHOULD CONTINUE TO MOVE NORTHWESTWARD AND PASS
NORTH OF YAP DURING THIS WEEKEND. IN RESPONSE...THE NEAR-
EQUATORIAL TROUGH RELATED TO IT WILL ALSO LIFT NORTHWARD OVER YAP
AND KOROR. THIS COULD INTRODUCE ISOLATED THUNDERSTORMS OVER BOTH
LOCALES...ESPECIALLY FOR YAP AS IT WOULD BE CLOSER TO THE
DISTURBANCE.

&&

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

$$

MCELROY/CHAN






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