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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
635 AM CHST FRI AUG 28 2015

.SYNOPSIS...LIGHT NORTHWEST WINDS AND A FEW SMALL SHOWERS PREVAIL
ACROSS THE MARIANAS THIS MORNING. LIGHT WINDS AND ISOLATED SHOWERS
ARE ALL THAT IS EXPECTED THROUGH THE WEEKEND AND INCLUDING MOST OF THE
COMING WEEK.

&&

.DISCUSSION...
ONLY A FEW TWEAKS MADE TO THE FORECAST. UPDATED WINDS HERE AND THERE 
TO REFLECT NEW MODEL DATA THAT APPEARS CLOSER TO CURRENT CONDITIONS.
LIGHT NORTHWEST WINDS NEAR A WEAK TROUGH WILL PREVAIL ACROSS THE
MARIANAS TODAY. WINDS WILL BECOME SOUTHWEST SATURDAY AS THE TROUGH
MOVES. WEAK HIGH PRESSURE WILL BUILD INTO THE AREA SUNDAY.

LIGHT WINDS ARE ONE OF THE USUAL INGREDIENTS THAT MAY PRODUCE AFTERNOON 
ISLAND SHOWERS AND THUNDERSTORMS. SOUNDING DATA AND WATER VAPOR IMAGERY
HOWEVER SHOW DRIER AIR IN PLACE ACROSS THE MARIANAS. MODELS SEEM TO
AGREE AS THEY KEEP DEEP LAYER MOISTURE AT A MINIMUM TODAY WITH A FURTHER
DECREASE THIS WEEKEND. SO EXPECT ONLY A FEW SHOWERS THROUGH THE NEXT
FEW DAYS.

&&

.MARINE...
RITIDIAN AND SAIPAN BUOY DATA SHOWS SEAS ARE AROUND 6 TO 8 FEET. THESE 
SAME BUOYS SHOW A NORTH SWELL OF BETWEEN 5 TO 6 FEET WITH A PERIOD
OF AROUND 13 SECONDS. THIS IS A BIT HIGHER THAN WW3 PREDICTIONS FOR
GUAM INDICATE BUT CLOSER TO SAIPANS PREDICTION. THIS NORTH SWELL IS
PROBABLY FROM THE REMAINS OF ATSANI WHICH HAS BECOME A LARGE LOW
PRESSURE SYSTEM EAST OF JAPAN.

CALCULATING SURF HEIGHT FROM THE SWELL YIELDS 7 TO 9 FEET. AT TIMES
THE BUOY DATA POINTS TOWARD 6 TO 8 FOOT SURF. FELT IT WAS TOO CLOSE
AND THAT IT WAS REASONABLE TO ISSUE A HIGH SURF ADVISORY FOR AT
LEAST TODAY. THE SAIPAN WW3 DATA HINT THAT THE HIGH SURF MAY PERSIST
THROUGH TONIGHT...WILL LET DAY SHIFT EVALUATE THIS.

&&

.EASTERN MICRONESIA...
PRESSURE GRADIENT BETWEEN A TROUGH OF LOW PRESSURE EXTENDING 
SOUTHEASTWARD FROM 20N160E TO 5N177E AND A RIDGE OF HIGH PRESSURE
NEAR 3N170E WILL CONTINUE TO CREATE MODERATE CONVERGING WINDS
ACROSS MUCH OF MICRONESIA FROM CHUUK STATE EASTWARD TO KOSRAE
STATE. COINCIDED WITH DIVERGENT FLOW WEST OF AN UPPER-LEVEL HIGH
NEAR 10N165E...SHOWERS AND THUNDERSTORMS ARE GOING TO LINGER NEAR
CHUUK...POHNPEI THRU SATURDAY AND KOSRAE UNTIL LATE THIS EVENING.
DESPITE WEAKER SURFACE WINDS NEAR MAJURO...AN UPPER TROUGH NEARBY
CAN ALSO TRIGGER A FEW THUNDERSTORMS THERE TODAY.

THE RIDGE OF HIGH PRESSURE NEAR 3N170E IS EXPECTED TO DRIFT WESTWARD 
OVER THE NEXT FEW DAYS. THIS WILL SHIFT THE STRONGEST PRESSURE 
GRADIENT WESTWARD...AWAY FROM KOSRAE BY SATURDAY AND POSSIBLY WEST 
OF POHNPEI AND CHUUK DURING THE WEEKEND. THEREFORE ANTICIPATE DRIER 
WEATHER TO SPREAD WESTWARD FROM MAJURO.

&&

.WESTERN MICRONESIA...
REASONING FOR THE CHUUK FORECAST IS INCLUDED IN THE EASTERN 
MICRONESIA SECTION DUE TO A SIMILAR WEATHER PATTERN.

A DEVELOPING MONSOON TROUGH PERSISTS JUST NORTH OF KOROR AND YAP 
NEAR 12N. GENTLE WEST TO SOUTHWEST WINDS SOUTH OF THIS FEATURE ARE 
GOING TO DOMINATE BOTH LOCATIONS WITH PARTLY CLOUDY SKIES THRU 
SATURDAY. AS A RIDGE OF HIGH PRESSURE CURRENTLY NEAR 3N170E IN 
EASTERN MICRONESIA SHIFTS WESTWARD...IT WILL GRADUALLY INCREASE THE 
WIND SPEED NEAR KOROR AND YAP. HEIGHTENING SURFACE CONVERGENCE WILL 
BRING A WETTER WEATHER PATTERN BY THIS WEEKEND.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...HIGH SURF ADVISORY UNTIL 6 PM CHST THIS EVENING FOR GUZ001>004.

MARIANAS WATERS...NONE.
&&

$$

ZIOBRO/CHAN

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