Subject: Western Pacific: Synoptic Discussion For The Marianas

From: LDM Weather <[email-masked]>
Date: Sat, 18 Sep 2010 15:19:54 -0500

033 
FXPQ60 PGUM 182019
AFDPQ 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
619 AM CHST SUN SEP 19 2010

.SYNOPSIS...
A WEAK UPPER TROUGH REMAINS EAST AND NORTH OF THE MARIANAS. EAST
OF THE ISLANDS...TROPICAL DISTURBANCE 90W CENTERED NEAR 15N152E IS
PRODUCING DEEP CONVECTION NEAR AND EAST OF THE CENTER. BUT IN THE
MARIANAS WATERS...ONLY ISOLATED SHOWERS ARE PRESENT.

&&

.DISCUSSION...
GFS...UKMET AND NOGAPS AGREE THAT 90W WILL MOVE NORTH...TAKING
MOST OF ITS WEATHER WITH IT. THE ECMWF TAKES 90W ON A MORE NW
TRACK...BUT STILL KEEPS THE HEAVIEST WEATHER NE OF THE MARIANAS.
NEITHER THE GFS NOR THE UKMET BRING MUCH QPF TO THE MARIANAS...SO
WILL KEEP FINGERS CROSSED AND MAINTAIN THE FORECAST OF ISOLATED
SHOWERS/THUNDER THROUGH TONIGHT...WHILE KEEPING A CLOSE EYE ON
90W.

&&

.EASTERN MICRONESIA...
LATEST ASCAT SATELLITE DATA REVEAL THE BROAD SURFACE TROUGH EAST OF 
THE MARIANAS IS NOW A LOW-LEVEL CIRCULATION AND JTWC INVEST AREA 
90W. THIS FEATURE IS RE-DIRECTING MODERATE TO FRESH TRADE WINDS 
ASSOCIATED WITH A SURGE CROSSING THE DATE LINE TO FLOW MORE 
EASTWARD...PASSING NORTH OF EASTERN MICRONESIA. IN RESPONSE...THE 
ITCZ HAS SHIFTED NORTHWARD TO ALONG 10N. THEREFORE...CURRENT 
FORECAST FOR THE REGION HAS IMPROVED SOMEWHAT FROM THE PREVIOUS ONE. 
HOWEVER...SURFACE WAVES EMBEDDED WITHIN THE WEAKER EAST TO SOUTHEAST 
TRADES SOUTH OF THE ITCZ CAN STILL PRODUCE PERIODS OF SHOWERS AND A 
FEW THUNDERSTORMS FROM THE MARSHALLS WESTWARD TO CHUUK STATE INTO 
EARLY NEXT WEEK. WITH EVEN LIGHTER TRADES FARTHER UPSTREAM EAST OF 
THE DATE LINE...SURFACE CONVERGENCE SHOULD GRADUALLY DECREASE TOWARD 
MIDWEEK. INSTEAD...AN UPPER TROUGH DRIFTING WESTWARD WILL PROVOKE 
WIDELY SCATTERED TRADE-WIND SHOWERS.

&&

.WESTERN MICRONESIA...
THE SURFACE RIDGE OVER THE PHILIPPINE SEA HAS MOVED NORTHWEST OF THE 
AREA...ALLOWING NORTHEASTERLY TRADES TO PENETRATE ACROSS YAP AND 
PALAU THIS MORNING. A WEAK SURFACE TROUGH MIGRATING ALONG IS 
ANTICIPATED TO PROVIDE A PERIOD OF WET WEATHER FOR YAP BY THIS 
AFTERNOON...AND POSSIBLY KOROR ON MONDAY. FORECAST AFTER MONDAY
CONTAINS UNCERTAINTY DEPENDING ON THE STATUS 90W EAST OF THE
MARIANAS. IF 90W REMAIN QUASI-STATIONARY...THERE WILL BE A BETTER
CHANCE FOR IT TO BECOME BETTER ORGANIZED AND FORMING A SURFACE
RIDGE NEAR CHUUK. THIS WILL BLOCK THE TRADE-WIND FLOW FROM THE
EAST AND CAUSE LIGHT AND VARIABLE WIND WITH FAIR WEATHER OVER
WESTERN MICRONESIA. ON THE OTHER HAND...IF IT BEGINS TO DRIFT
NORTHWESTWARD AS MOST MODELS SUGGEST...SURFACE WAVES OVER EASTERN
MICRONESIA WILL BE ABLE TO APPROACH WESTWARD AND TRIGGER MORE
SHOWERS. HAVE KEPT CLOUDS AND ISOLATED SHOWERS IN THE FORECAST
FOR NOW.

&&

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

$$

MIDDLEBROOKE/CHAN

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