Subject: Western Pacific: Synoptic Discussion For The Marianas

From: LDM Weather <[email-masked]>
Date: Mon, 21 Jan 2008 13:40:05 -0600

525 
FXPQ60 PGUM 211939
AFDPQ 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
539 AM CHST TUE JAN 22 2008

.SYNOPSIS...
SATELLITE AND RADAR IMAGERY CONFIRM TONIGHT WHAT THE MODELS HAVE 
ADVERTISED FOR DAYS...THAT A WEAKENING SHEAR LINE WOULD PASS THROUGH 
THE MARIANAS...FOLLOWED BY DRIER AIR IN ITS WAKE.

&&

.DISCUSSION...
NO BIG CHANGES TO THE GRIDS. MODELS STILL BRING IN THE TRADE-WIND 
SURGE BEHIND THE SHEAR LINE FOR THE MIDDLE OF THE WEEK. PRIMARY 
FORECAST CONCERN REMAINS WINDS...SEAS AND SURF. PLEASE SEE MARINE 
DISCUSSION SECTION FOR ADDITIONAL DETAILS.

&&

.EASTERN MICRONESIA...
BASED ON SATELLITE IMAGERY...A SURFACE WAVE IS MERGING INTO THE 
WEAK CIRCULATION SOUTHWEST OF POHNPEI. CONVERGENCE ALONG THE BACK 
SIDE OF THE WAVE WILL CONTINUE TO GENERATE SCATTERED SHOWERS OVER 
POHNPEI AND KOSRAE THROUGH THIS MORNING. ONCE THE WAVE HAS BEEN 
ABSORBED BY THE CIRCULATION...CONVERGENCE WILL EASE AND LEAD TO 
DECREASING SHOWER COVERAGE LATER THIS AFTERNOON. FRESH TRADES WILL 
THEN DOMINATE THE AREA WITH DRIER CONDITIONS INTO THE WEEKEND.
MAJURO IS ALREADY UNDER THE INFLUENCE OF FRESH TRADES AND WILL
REMAIN SO THROUGH THE FORECAST PERIOD.

LATEST COMPUTER WAVE GUIDANCE CONTINUES TO SHOW THAT SURF ALONG
NORTH FACING SHORES ON POHNPEI WILL REMAIN AT THE ADVISORY LEVEL
OF 9 FT THROUGH WEDNESDAY. THEREFORE THE HIGH SURF ADVISORY
REMAINS IN EFFECT FOR POHNPEI.

&&

.WESTERN MICRONESIA...
THE NEAR-EQUATORIAL TROUGH CONTINUES TO STAY WELL SOUTH OF
KOROR...YAP AND CHUUK. NO SIGNIFICANT CHANGES FROM THE PREVIOUS
FORECAST ARE EXPECTED THROUGH WEDNESDAY. LATEST GFS AND ECMWF
MODELS OUTPUT PRESENTS SOME DEVIATION FROM PREVIOUS RUNS. THE
CIRCULATION CURRENTLY SOUTHEAST OF CHUUK WILL DRIFT WEST-SOUTHWEST
AND CROSS THE EQUATOR AS A BUFFER NEAR 145E ON WEDNESDAY. A PIECE
OF THE ENERGY FROM THIS SYSTEM MIGHT PROPAGATE ALONG THE TROUGH
AXIS AND CREATE INSTABILITY FOR YAP AND PALAU ON THURSDAY. FOR THE
TIME BEING...CLOUDINESS HAS BEEN INTRODUCED FOR THESE LOCATIONS.
STRONG HIGH PRESSURE COMING OFF THE ASIAN CONTINENT IS STILL
EXPECTED TO STRENGTHEN TRADE WINDS ACROSS PALAU AND YAP BY FRIDAY.

TRADE WINDS CONVERGING INTO THE CIRCULATION TO THE SOUTHEAST WILL 
KEEP PRODUCING SCATTERED SHOWERS AND A FEW THUNDERSHOWERS OVER CHUUK 
THROUGH TONIGHT. FRESH TRADES FROM THE EAST ARE EXPECTED TO FINALLY
PUSH THE CIRCULATION WESTWARD AWAY FROM CHUUK DURING WEDNESDAY.
THIS WILL BRING IN MORE STABLE AIR AND REDUCE CLOUD COVER THROUGH
SATURDAY.

LATEST COMPUTER WAVE GUIDANCE INDICATES SURF ALONG NORTH-FACING
SHORES ON CHUUK WILL REMAIN AT THE ADVISORY LEVEL OF 9 FT AND WILL
PERSIST THROUGH WEDNESDAY. THEREFORE THE HIGH SURF ADVISORY
REMAINS IN EFFECT FOR CHUUK.

&&

.MARINE...
WILL USE THE IPAN BUOY TO INITIALIZE COMBINED SEAS ATTRIBUTABLE TO 
TRADE WINDS. WAVE WATCH TABULAR DATA SUGGEST FORECAST IS A BIT 
CONSERVATIVE REGARDING THE MARIANAS HIGH SURF ADVISORY END TIME. 
HOWEVER...IN LIGHT OF RECENT TRENDS EXTENDING THE END TIME OF THE 
CURRENT HIGH SURF EVENT...WILL MAINTAIN WEDNESDAY AFTERNOON END 
TIME. COMBINED SEAS RIGHT NOW APPEAR TO BE ABOUT A FOOT BELOW THE 
COMBINED SEAS THRESHOLD OF 10 FEET. HOWEVER...EXPECT IMMINENT 
TRADE-WIND SURGE WILL CAUSE SEAS TO REBUILD ONCE AGAIN IN A FEW 
HOURS SO LEFT BOTH THE HIGH SURF AND SMALL CRAFT ADVISORIES RIDE.

&&

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

MARIANAS WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6
PM CHST WEDNESDAY FOR PMZ151>154.

&&

$$

MCELROY/CHAN

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