Area Forecast Discussion
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FXPQ60 PGUM 240857 AAA
AFDPQ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TIYAN GU
655 PM CHST THU JUL 24 2014

.MARIANAS SYNOPSIS...
WATER VAPOR SATELLITE IMAGERY SHOWS THE UPPER TROUGH MOVING WEST
OVER THE MARIANAS..WITH ISOLATED THUNDERSTORMS ASSOCIATED WITH IT
MAINLY WEST OF TINIAN AND SAIPAN. VISIBLE IMAGERY SHOWS AN ACTIVE
MONSOON TROUGH SOUTH OF THE REGION...ANCHORED BY WEAK CIRCULATIONS
BETWEEN YAP AND KOROR...AND WEST OF CHUUK.

&&

.DISCUSSION...
ECMWF AND GFS REMAIN FAR APART...WITH THE GFS STILL SPINNING UP
A PAIR A TROPICAL STORMS OR TYPHOONS NORTH OF YAP AND CHUUK...WITH
THE CHUUK STORM TURNING NW THROUGH THE MARIANAS NORTH OF SAIPAN
AROUND THE MIDDLE OF NEXT WEEK. THE MORE CONSISTENT AND REALISTIC
ECMWF STILL DEVELOPS THE WESTERN SYSTEM WHILE LIFTING THE MONSOON
TROUGH SLOWLY NORTHWARD THROUGH THE MARIANAS OVER THE WEEKEND...AND
THIS IS THE BASIS OF THE FORECAST FOR THE NEXT WEEK. HAVE EXTENDED
SCATTERED SHOWERS THROUGH MONDAY NIGHT...AND ISOLATED THUNDERSTORMS
THROUGH WEDNESDAY NIGHT. OF COURSE...WITH SUCH DISAGREEMENT
BETWEEN THE MODELS...FORECAST CONFIDENCE IN WINDS AND SEAS IS
RATHER LOW. IF A STRONG TROPICAL CYCLONE DOES INDEED FORM NORTH OF
CHUUK AS DEPICTED BY THE GFS...WINDS AND SEAS COULD BE MUCH HIGHER
THAN CURRENTLY FORECAST LATE THIS WEEKEND INTO NEXT WEEK.
CONFIDENCE IN THE RAIN FORECAST IS SOMEWHAT HIGHER...AS BOTH MODELS
WOULD BRING UP TO 7 INCHES OF RAIN BY NEXT WEDNESDAY.

&&

.MARINE...
HAVE CLOSELY FOLLOWED ECMWF WINDS...AND KEPT THE WEST-SOUTHWEST
SWELL AT 4 FEET THE NEXT 7 DAYS BASED ON PERSISTENT SOUTHWEST
MONSOON FLOW ACROSS YAP AND PALAU IN THE ECMWF. THIS BRINGS
COMBINED SEAS UP TO 7-8 FEET OVER THE WEEKEND INTO EARLY NEXT
WEEK. BUT AGAIN...IF A TROPICAL STORM FORMS AS IN THE GFS...WINDS
AND SEAS COULD BE HIGHER NEXT WEEK.

&&

UPDATED TO INCLUDE MICRONESIA DISCUSSION

.EASTERN MICRONESIA...
A MONSOON TROUGH MEANDERS EASTWARD FROM WESTERN MICRONESIA TO A WEAK
CIRCULATION CENTERED NORTH OF KOSRAE AT 9N163E AND THEN TURNS
SOUTHEASTWARD TO END AT EQ165E. WEAKER WINDS NEAR THE TROUGH AXIS
WILL TRIGGER ISOLATED CONVECTION NEAR POHNPEI AND KOSRAE THRU
TONIGHT. AS THE TROUGH SLOWLY LIFTS NORTHWARD ON FRIDAY...STRONGER
MONSOON WINDS SOUTH OF THE TROUGH WILL INCREASE SHOWER COVERAGE FOR
BOTH LOCALES. FARTHER EAST...MODERATE TO FRESH TRADES ARE FILTERING
WESTWARD ACROSS THE MARSHALL ISLANDS. A TRADE-WIND DISTURBANCE
EMBEDDED WITHIN THESE TRADES IS GOING TO PRODUCE A PERIOD OF SHOWERY
WEATHER FOR MAJURO UNTIL SATURDAY AFTERNOON. THIS SAME DISTURBANCE
WILL ALSO PROLONG WET WEATHER FOR KOSRAE AND POHNPEI THRU SATURDAY
EVENING. AFTER THE PASSAGE OF THIS DISTURBANCE THRU THE REGION BY
EARLY NEXT WEEK...DRIER MODERATE TRADES COULD BRING BACK FAIR
WEATHER ACROSS THE REGION FROM EAST TO WEST.

THE FIRST SET OF SWELL GENERATED BY MONSOON WINDS SOUTH OF THE
CIRCULATION NEAR CHUUK IS ARRIVING AT POHNPEI AND KOSRAE THIS
EVENING. ANTICIPATE THIS TO CAUSE HIGH SURF FOR THESE PLACES OVER
THE NEXT COUPLE OF DAYS.

&&

.WESTERN MICRONESIA...
A MONSOON TROUGH EXTENDS EAST-SOUTHEASTWARD FROM THE PHILIPPINE SEA
THRU A TROPICAL DISTURBANCE CENTERED NORTHWEST OF KOROR AT 10N133E
TO ANOTHER ONE CENTERED WEST OF WENO ISLAND IN CHUUK STATE NEAR
7N158E. LATEST ASCAT SATELLITE IMAGERY REVEALS FRESH MONSOON WINDS
DEVELOPING SOUTH OF BOTH DISTURBANCES ACROSS THE REPUBLIC OF PALAU
AND CHUUK STATE. THESE CONVERGING MONSOON WINDS ARE GENERATING
POCKETS OF DEEPER CONVECTION NEAR KOROR AND CHUUK. THEREFORE
INCLEMENT WEATHER IS ANTICIPATED FOR BOTH LOCATIONS FOR THE NEXT FEW
DAYS...ESPECIALLY CHUUK. HOWEVER IF THE CENTER OF THE SECOND
DISTURBANCE START TO SHIFT A BIT WESTWARD AWAY FROM CHUUK ON
FRIDAY...SHOWER COVERAGE AND WINDS COULD DECREASE FASTER THAN
EXPECTED. WITH YAP BEING RIGHT AT THE TROUGH AXIS...GENTLE WINDS
SHOULD MAINTAIN MAINLY ISOLATED SHOWERS THERE THRU FRIDAY.

AS THE FIRST DISTURBANCE AND TROUGH SHIFT NORTHWARD ON FRIDAY
EVENING...FRESH TO STRONG MONSOON WINDS WILL ALSO SPREAD HEAVY
SHOWERS AND GUSTY WINDS INTO YAP AS WELL. IT IS STILL A BIT TOO
EARLY TO DETERMINE HOW MUCH RAIN ALL THREE FORECAST POINTS WILL
RECEIVE FROM THIS MONSOON EPISODE...BUT 3 TO 5 INCHES SOUNDS
REASONABLE FOR THE TIME BEING. STARTING EARLY NEXT WEEK...THE
MONSOON TROUGH SHOULD BE FAR ENOUGH NORTH OF KOROR AND YAP SO THAT
SURFACE RIDGING WILL BEGIN TO TAKE OVER. FOR CHUUK...A TRADE
DISTURBANCE CURRENTLY APPROACHING THE MARSHALL ISLANDS COULD
GENERATE MORE SHOWERS FOR THE FIRST PART OF NEXT WEEK. MONSOON SWELL
IS BUILDING AND WILL CAUSE SEAS AND SURF TO REACH HAZARDOUS LEVELS
ACROSS THREE LOCALES BY LATE FRIDAY EVENING. A HIGH SURF ADVISORY
WILL BE NEEDED FOR THE ENTIRE REGION BY FRIDAY.

&&

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

$$

MIDDLEBROOKE/CHAN





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