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[Printable]
977
FXPQ60 PGUM 230725
AFDPQ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
525 PM CHST WED JUL 23 2014

MARIANAS SYNOPSIS...
VAPOR CHANNEL SAT IMAGERY SHOWS THE UPPER-LEVEL TROUGH STILL
ORIENTED NE-SW JUST EAST OF THE ISLANDS...AND STILL HELPING TO
TRIGGER ISOLATED THUNDERSTORMS. MEANWHILE...A BROAD AND WEAK
CIRCULATION ON THE MONSOON TROUGH IS CENTERED WEST OF CHUUK NEAR
7N148W...WITH THE CENTER EXPOSED AND DEEP CONVECTION ON THE
WESTERN AND EASTERN EXTREMITIES OF ITS LARGE CIRCULATION. THE
DISTURBANCE NORTH OF YAP HAS BEEN DOWNGRADED BY JTWC TO LOW
POTENTIAL FOR DEVELOPMENT...AND INDEED IT APPEARS FROM THE
SATELLITE LOOP THAT THE SURFACE CIRCULATION MAY HAVE OPENED BACK
UP INTO THE MONSOON TROUGH.

DISCUSSION...
WITH THE UPPER TROUGH SLOW TO MOVE WEST ACROSS THE ISLANDS...HAVE
EXTENDED ISOLATED THUNDERSTORMS THROUGH TONIGHT. OTHERWISE...NO
CHANGES MADE TO THE FORECAST AS SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS STILL LOOK GOOD FOR THE END OF THE WEEK--ONE WAY OR
THE OTHER. ECMWF AND GFS ARE STILL FAR APART...WITH THE HAWKISH
GFS AGGRESSIVELY DEVELOPING BOTH THE YAP AND CHUUK DISTURBANCES
AND BRINGING HEAVY RAIN AND STRONG WINDS TO THE MARIANAS AS THE
TWO SYSTEMS INTERACT. THE MORE-REALISTIC ECMWF BRINGS THE MONSOON
TROUGH NORTH INTO THE MARIANAS WITH SCATTERED LOCALLY HEAVY
SHOWERS FOR THE WEEKEND BUT RELATIVELY LITTLE WIND. STILL LEANING
HEAVILY TOWARD THE ECMWF AND WATCHING DEVELOPMENTS CAREFULLY.

MARINE...
FAIRLY STEADY MARINE CONDITIONS SHOULD PERSIST THE NEXT COUPLE OF
DAYS WITH GENTLE TO MODERATE WINDS AND 5-6 FT SEAS. AFTER THAT IT
ALL DEPENDS ON WHAT KIND OF WEATHER DEVELOPS OVER THE WEEKEND.

EASTERN MICRONESIA...
A QUIET WEATHER PATTERN WILL PERSIST OVER MAJURO THROUGH TONIGHT.
MODELS SUGGEST THE DEVELOPMENT OF A STRONG CONVERGENCE ZONE OVER THE
MARSHALL ISLANDS RELATED TO A MONSOON SURGE ALONG THE EQUATOR
SOUTH OF POHNPEI AND CHUUK AND AN APPROACHING SURFACE TROUGH FROM
THE EAST. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE
EXPECTED TO COMMENCE LATE THURSDAY AND LAST THROUGH FRIDAY NIGHT.
DRIER CONDITIONS AT MAJURO ARE INDICATED OVER THE WEEKEND. ACTIVE
WEATHER ASSOCIATED WITH THE MONSOON TROUGH WILL CONTINUE TO AFFECT
POHNPEI AND KOSRAE THROUGH THURSDAY. KOSRAE IS ON THE EASTERN EDGE
OF THE HEAVIEST SHOWERS BUT NEW CONVECTIVE DEVELOPMENT IS OBSERVED
IN VISIBLE SAT IMAGERY OVER KOSRAE WATERS. WEATHER WILL IMPROVE AS
RIDGING BUILDS OVER KOSRAE AND POHNPEI STATES. THE MONSOON SURGE
SOUTH OF CHUUK AND POHNPEI WILL GENERATE AN APPRECIABLE SOUTHWEST
SWELL THAT WILL IMPACT POHNPEI THURSDAY AND THURSDAY NIGHT.
HOWEVER...SURF PRODUCED BY THE SWELL AND WIND WAVES IS EXPECTED TO
REMAIN JUST BELOW HAZARDOUS THURSDAY NIGHT AND FRIDAY.

WESTERN MICRONESIA...
EXPANSIVE DEEP CONVECTION ASSOCIATED WITH THE MONSOON TROUGH IS
JUST TO THE SOUTHEAST OF CHUUK. SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS WILL MOVE OVER CHUUK THURSDAY AND THURSDAY NIGHT
THEN BEGIN TO LIFT NORTHWARD ALONG WITH THE MONSOON TROUGH FRIDAY.
A LESS ACTIVE PATTERN WILL BEGIN FRIDAY AND LIKELY LAST THROUGH
THE WEEKEND.

THE TROPICAL DISTURBANCE NORTH OF KOROR HAS BEEN HEAVILY SHEARED
OVER THE PAST 24 HOURS AND IS NO LONGER THE PRIMARY THREAT TO KOROR
AND PALAU. MODELS BRING THE MONSOON TROUGH SOUTHWARD OVER YAP FRIDAY
AND FRIDAY NIGHT. MODELS HAVE EXHIBITED RUN-TO-RUN CONSISTENCY
DISCREPANCIES REGARDING THE SYNOPTIC PATTERN AND MONSOON FEATURE.
MODELS DO BACK OFF QPF AND SEAS A BIT OVER THE WEEKEND SO TUNED
FORECAST DOWNWARD AT YAP AND KOROR FOR THE WEEKEND TIME FRAME.
NONETHELESS...A MONSOON SURGE EVENT IS STILL EXPECTED TO DEVELOP
OVER THE NEXT FEW DAYS BUT STRONGEST WINDS AND HIGHEST SEAS HAVE
BEEN DELAYED UNTIL THE WEEKEND. WIND DIRECTION AT YAP AND KOROR IS
STILL DIFFICULT TO DETERMINE AND DEPENDS ON EVENTUAL LOCATION OF
MONSOON TROUGH AXIS OVER THE NEXT FEW DAYS. LATEST ECMWF TAKES THE
TROUGH A BIT FARTHER SOUTH THAN PREVIOUS RUNS SO EAST WINDS COULD
OCCUR AT YAP FRIDAY AND FRIDAY NIGHT. SCATTEROMETER DATA SHOWS MORE
SIGNIFICANT BUT SMALL SWELL GENERATION REGION ORIENTED MORE TOWARD
YAP SO REDUCED SEAS FOR KOROR IN THE SHORT TERM. A SPECIAL WEATHER
STATEMENT WAS ISSUED THIS MORNING IN ADVANCE OF MONSOON EVENT.
HAZARDOUS SURF CRITERIA WILL LIKELY OCCUR CLOSER TO THE WEEKEND.

&&

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

$$

MIDDLEBROOKE/WILLIAMS






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