Subject: Western Pacific: Synoptic Discussion For The Marianas

From: LDM Weather <[email-masked]>
Date: Wed, 27 Oct 2010 15:56:01 -0500

321 
FXPQ60 PGUM 272055
AFDPQ 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
655 AM CHST THU OCT 28 2010

.SYNOPSIS...ISOLATED SHOWERS EXPECTED THE NEXT FEW DAYS. THERE
WILL BE A SLIGHT CHANCE OF THUNDERSTORMS ACROSS THE MARIANAS TODAY
AND TONIGHT. ISOLATED SHOWERS COULD BE SEEN ON RADAR OVER THE 
ISLANDS THIS MORNING. A FEW BRIEF THUNDERSTORMS DEVELOPED NEAR
GUAM AND ROTA BEFORE SUNRISE. AN UPPER-LEVEL LOW IS LOCATED TO THE
SOUTHEAST OF THE MARIANAS NEAR 11N148E.

&&

.DISCUSSION...
A FEW CHANGES MADE TO THE FORECAST. THE UPPER-LEVEL LOW SOUTHEAST
OF THE MARIANAS THIS MORNING WILL MOVE WEST DURING THE DAY. ALL
THE MODELS ARE CONSISTENT WITH LOCATING IT JUST SOUTH OF GUAM LATE
TONIGHT. THIS UPPER-LOW APPEARED TO HELP SPARK OFF A FEW
THUNDERSTORMS NEAR GUAM AND ROTA AFTER MIDNIGHT. EARLY MORNING
SATELLITE IMAGERY SHOWS MORE CONVECTION JUST NORTH OF THE UPPER
LOW. CONVECTION IS RATHER SPOTTY SO THE POSSIBILITY OF THUNDERSTORMS
IS ONLY SLIGHT. LOOKING AT THE POSITION OF CONVECTION IN RELATION
TO THE UPPER LOW...IT WOULD APPEAR THAT MOST IF NOT ALL OF THE
THUNDERSTORMS WOULD DEVELOP MOSTLY OVER ROTA AND GUAM. FELT THE
DIFFERENCE WAS TOO SMALL TO SPLIT THE ZONES...SO INCLUDED MENTION
OF THUNDER FOR ALL ISLANDS. MODELS KEEP THINGS FAIRLY QUIET WITH ONLY
ISOLATED SHOWERS EXPECTED THROUGH THE END OF THE FORECAST.

&&

.MARINE...TRADE-WIND SWELL WILL CONTINUE THROUGH THE END OF THE
FORECAST. THIS WILL GENERATE A MODERATE RISK OF RIP CURRENTS ON
NORTH AND EAST FACING REEFS. SWELL ASSOCIATED WITH DISTANT TYPHOON
CHABA IS SPREADING ACROSS THE PHILIPPINE SEA. THE MAIN PART OF THE
SWELL WILL PUSH DOWN TO PALAU AND YAP WHILE THE MARIANAS WILL ONLY
BE ON THE EDGE OF THE SWELL. EXPECT A NORTHWEST SWELL OF ABOUT 3 FEET
TO ENTER THE LOCAL AREA FRIDAY NIGHT AND CONTINUE INTO NEXT WEEK.
CURRENT CALCULATIONS GENERATE SURF OF 4 TO 6 FEET ON WEST FACING
REEFS THIS WEEKEND. AT THE PRESENT TIME THIS APPEARS REASONABLE BUT
ADJUSTMENTS EITHER UP OR DOWN MAYBE NEEDED SINCE THIS IS A MODEL
ESTIMATE. IF THE MODEL DID NOT ESTIMATE THE WIND FIELD ASSOCIATED
WITH THE TYPHOON CORRECTLY THAN THE PREDICTED SURF COULD BE IN
ERROR. 

&&

.EASTERN MICRONESIA...
A VIGOROUS LOW PRESSURE SYSTEM NORTHEAST OF WAKE ISLAND ALONG
WITH ITS ASSOCIATED SURFACE TROUGH EXTENDING SOUTHWARD TO NEAR
5N180 ARE RE-DIRECTING THE STRONGEST TRADE WINDS TO THE NORTH OF
EASTERN MICRONESIA. THEREFORE...WEAKER CONVERGENCE FROM LIGHT TO
GENTLE TRADES WILL PROMOTE RELATIVELY DRIER CONDITIONS FOR THE
REGION DURING THE NEXT FEW DAYS. AS THE LOW PRESSURE
SYSTEM/TROUGH COMBINATION CONTINUES TO MOVE WESTWARD...THE
SOUTHERN BRANCH OF THE TROUGH IS EXPECTED TO REACH THE MARSHALL
ISLANDS BY THE WEEKEND. INCREASING CONVERGENCE NEAR THE TROUGH
AXIS WILL LIKELY CAUSE SHOWERY WEATHER FOR MAJURO AND KOSRAE OVER
THE WEEKEND...AND EVENTUALLY FOR POHNPEI BY EARLY NEXT WEEK.
FINALLY...A MUCH DRIER TRADE SURGE FROM THE SOUTHERN HEMISPHERE
MIGHT INTRODUCE A DRYING TREND FOR MAJURO AND KOSRAE LATER NEXT
WEEK. BUILDING TRADE-WIND SWELL COULD RESULT IN HIGHER SURF ALONG
NORTH AND EAST FACING SHORES OF MAJURO OVER THE WEEKEND BUT
SHOULD BE BELOW ADVISORY LEVELS.

&&

.WESTERN MICRONESIA...
A WEAK SURFACE TROUGH ALONG WITH DIVERGENT WINDS SOUTH OF AN
UPPER TROUGH WILL KEEP SCATTERED CONVECTION OVER CHUUK THRU AT
LEAST THIS EVENING. THEN WEAKER TRADES FROM THE EAST ARE GOING TO
DECREASE SHOWER COVERAGE BY THE WEEKEND. THINGS COULD BECOME
WETTER AGAIN NEXT WEEK AS ANOTHER SURFACE TROUGH APPROACHES THE
ISLAND FROM THE EAST.

A SURFACE RIDGE TO THE SOUTHEAST OF DISTANT TYPHOON CHABA
PERSISTS OVER THE PHILIPPINE SEA JUST NORTHWEST OF KOROR AND YAP.
GENTLE TO MODERATE TRADES FLOWING ACROSS THE MARIANAS ARE MERGING
TOWARD THE RIDGE AXIS. AIDED BY AN UPPER TROUGH OVER THE
AREA...ISOLATED CONVECTIVE ACTIVITY CAN BE ANTICIPATED FOR YAP
THRU TODAY...AND KOROR INTO FRIDAY. SHOWER COVERAGE OVER KOROR
MIGHT INCREASE FURTHER BY THIS EVENING AS WELL. WITH THE SURFACE
RIDGE DISSIPATING OVER THE WEEKEND...THIS SHOULD ALLOW GENTLE
TRADES WITH ISOLATED PASSING SHOWERS TO FLOW ACROSS THE AREA.
LONG-PERIOD NW SWELLS FROM TYPHOON CHABA WILL CREATE A HIGH SURF
EVENT FOR BOTH PALAU AND YAP INTO THE WEEKEND. A HIGH SURF
ADVISORY HAD BEEN ISSUED ACCORDINGLY AND WILL NEED TO BE UPDATED
LATER THIS AFTERNOON.

&&

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

$$

ZIOBRO/CHAN

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