Subject: Western Pacific: Synoptic Discussion For The Marianas

From: LDM Weather <[email-masked]>
Date: Wed, 15 Sep 2010 16:19:53 -0500

185 
FXPQ60 PGUM 152119
AFDPQ 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
719 AM CHST THU SEP 16 2010

.SYNOPSIS...
PGUA WSR-88D SHOWS ISOLATED SHOWERS AND THUNDERSTORMS MOVING
THROUGH THE MARIANAS WATERS. THESE ARE ASSOCIATED WITH A BROAD
AREA OF ACTIVITY BEING CAUSED BY AN UPPER-LEVEL LOW EXTENDING FROM
10N TO 25N FROM 139E TO 170E. FARTHER SOUTH TRADE-WIND CONVERGENCE
IS CREATING SCATTERED SHOWERS THROUGHOUT MICRONESIA...EXCEPT THEY
ARE A LITTLE SOUTH OF YAP.

&&

.DISCUSSION...
UPPER-LEVEL LOW MOVING THROUGH ALREADY TRIGGERED SOME THUNDER
EARLY THIS MORNING. MORE COULD ERUPT ANY TIME. FOR THE MOST PART
THE LOW ACTIVITY PORTION OF THE LOW SHOULD PASS OVER US...SO KEPT
THE ACTIVITY ISOLATED AT THIS TIME. GUAM MAY WELL HAVE SOME ISLAND
THUNDER TODAY...BUT WE COULD END UP HARD PRESSED TO TELL IT APART
FROM THE STUFF ASSOCIATED WITH THE TROPICAL UPPER TROPOSPHERIC
TROUGH /TUTT/. THEREFORE DID NOT MAKE ANY SPECIAL MENTION OR ZONE
SPLITS IN THE FORECASTS.

&&

.MARINE...
REDUCED EAST SWELL TO 2 FEET THE NEXT COUPLE OF PERIODS IN
RESPONSE TO UPDATED WAVE GUIDANCE AND THE IPAN BUOY. BENIGN
CONDITIONS WILL CONTINUE AS EVEN WHEN THE SWELLS RISE LATER IN THE
PERIOD...THEY SHOULD ONLY GET UP TO ABOUT 4 FEET.

&&

.EASTERN MICRONESIA...
THE SOUTHWESTERN END OF THE SUB-TROPICAL RIDGE IS PERSISTING OVER 
THE PHILIPPINE SEA JUST NORTH OF WESTERN MICRONESIA. THIS FEATURE IS 
CREATING A BLOCKAGE AGAINST THE TRADE-WIND FLOW OVER EASTERN 
MICRONESIA. IN RESPONSE...SURFACE IMPULSES ARE FORMING ALONG THE 
TRADE CONVERGENCE ZONE FROM CHUUK STATE EASTWARD TO THE DATE LINE. 
EXPECT PERIODS OF SHOWERS AND ISOLATED THUNDERSTORMS FOR CHUUK AND 
POHNPEI INTO THE WEEKEND...AND FOR KOSRAE AND MAJURO THRU TONIGHT. 
THEN A DRIER SOUTHEASTERLY TRADE SURGE WILL PROMOTE A BRIEF MOMENT 
OF FAIRER WEATHER FOR BOTH MAJURO AND KOSRAE FRIDAY AND SATURDAY. 
WITH THE SUB-TROPICAL RIDGE WEAKENING BY EARLY NEXT WEEK...GENTLE TO 
MODERATE TRADES SHOULD RETURN TO THE REGION FROM EAST TO WEST. 
HOWEVER...AN UPPER-LEVEL TROUGH DIGGING SOUTHWESTWARD FROM EAST OF 
WAKE ISLAND CAN ENHANCE TRADE-WIND SHOWER ACTIVITY FOR MAJURO AND 
KOSRAE. THIS SCENARIO WILL ALSO PROLONG SHOWERY CONDITIONS FOR 
POHNPEI AND CHUUK AS WELL. 

&&

.WESTERN MICRONESIA...
AN AREA OF SURFACE CONVERGENCE BETWEEN TRADE WINDS AND THE 
AFOREMENTIONED SUB-TROPICAL RIDGE IS CLEARLY VISIBLE ON BOTH ASCAT 
AND IR SATELLITE IMAGERY THIS MORNING. THE LEADING EDGE OF THIS AREA 
IS APPROACHING KOROR AND WILL SPREAD SCATTERED CONVECTION OVER THE 
ISLAND BY NOON TODAY. WITH THE CONVERGENCE ZONE EXTENDING 
NORTHEASTWARD FROM KOROR PASSING SOUTH OF YAP...ONLY ISOLATED 
SHOWERS ARE ANTICIPATED FOR YAP TODAY. AS A SURFACE TROUGH DEPARTS 
FROM CHUUK AND DRIFTS WESTWARD LATER TONIGHT...IT WILL CAUSE THE 
CONVERGENCE ZONE TO SHIFT NORTHWARD OVER YAP. TEAMING UP WITH AN 
UPPER TROUGH MOVING THROUGH THE AREA...SPORADIC CONVECTION WILL 
CONTINUE FOR BOTH LOCATIONS THRU FRIDAY. LATEST WV IMAGERY REVEALS 
AN AREA OF MUCH DRIER AIR TRAILING BEHIND THE SURFACE TROUGH 
SOUTHWEST OF CHUUK. THIS ELEMENT CAN BRIEFLY DECREASE SHOWER 
COVERAGE OVER THE WEEKEND BUT WET PATTERN WILL LIKELY RETURN BY NEXT 
WEEK AS MORE DISTURBANCES ARE PRESENT UPSTREAM.

&&

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

$$

STANKO/CHAN

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