Subject: Western Pacific: Synoptic Discussion For The Marianas

From: LDM Weather <[email-masked]>
Date: Sat, 26 Jan 2008 01:37:49 -0600

553 
FXPQ60 PGUM 260737
AFDPQ 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
537 PM CHST SAT JAN 26 2008

.SYNOPSIS...
VISIBLE SATELLITE IMAGERY SHOWS SHEAR LINE SHIFTING SOUTHWARD 
THROUGH THE MARIANAS. SHEAR LINE HAS SUBDIVIDED INTO SEVERAL BANDS 
ORIENTED FROM SOUTHWEST TO NORTHEAST. ONE OF THE BANDS HAS TRAINED
OVER GUAM EARLIER TODAY AND PRODUCED ABOUT A TENTH OF AN INCH OF
RAINFALL. THE LEADING EDGE OF MARINE STRATOCUMULUS WAS MOVING
SOUTHWARD NEAR SAIPAN...BUT WAS THINNING.

&&

.DISCUSSION...
MAIN WEATHER STORY INVOLVES WINDS AND THE MARINE ARENA. SEE
MARINE DISCUSSION SECTION FOR DETAILS. SHOWER COVERAGE LOOKS
RELATIVELY LOW IN THE WAKE OF THE SHEAR LINE. WILL LEAVE MOSTLY
CLOUDY WORDING IN THROUGH SUNDAY NIGHT BASED ON UPSTREAM
CLOUDINESS. GFS TIME-HEIGHT CROSS SECTION SHOWS SLIGHTLY DRIER
AIR ON MONDAY...WITH DEEPER MOISTURE RETURNING ON WEDNESDAY.
INVERSION MAY LIFT IN TANDEM WITH THE ADDED MOISTURE...SO WILL
LEAVE SKIES PARTLY CLOUDY FOR DAYS 3 THROUGH 7. BELIEVE WINDS
WILL ALSO INCREASE IN THE WAKE OF THE SHEAR LINE...AS PROGGED BY
THE MODELS. VAD GRADIENT-LEVEL WINDS HAVE INDEED TRENDED UPWARD
ABOUT 5 KNOTS DURING THE COURSE OF THIS SHIFT.

&&

.EASTERN MICRONESIA...
LEFT THE PREVIOUS FORECAST VIRTUALLY UNTOUCHED...DRY TRADES WILL 
PERSIST THROUGH NEXT WEEK AND MAINTAIN RELATIVELY DRY WEATHER. KEPT
MOSTLY CLOUDY WORDING DURING THE FIRST HALF OF THE WEEK. GFS
SEEMS TO BRING A STRONG SYSTEM THROUGH EASTERN MICRONESIA...BUT
GFS SOLUTION LOOKS TO ROBUST FOR ANYTHING ON SATELLITE NOW...SO
LEFT PREVIOUS FORECAST INTACT AND DID NOT INTRODUCE SCATTERED
SHOWERS. STILL...CONFIDENCE REMAINS LOW WITH HOW THIS SYSTEM WILL
IMPACT THE REGION...SO LEFT ISOLATED POPS IN THE FORECAST.

WW3 MODEL OUTPUT CONTINUES TO INDICATE LARGE AND LONG PERIOD 
NORTHWESTERLY SWELL ARRIVING TO THE REGION BY MONDAY NIGHT. THIS 
WILL LIKELY NECESSITATE HIGH SURF ADVISORIES FOR ALL LOCATIONS.

&&

.WESTERN MICRONESIA...
LITTLE CHANGE...KEPT PARTLY CLOUDY WORDING THROUGHOUT THE
FORECAST PERIOD FOR BOTH PALAU AND YAP. FARTHER TO THE EAST OVER
CHUUK...BROUGHT IN MOSTLY CLOUDY WORDING ON MONDAY TO COINCIDE
WITH THE AFOREMENTIONED SYSTEM OVER EASTERN MICRONESIA.

SURF HAS DIMINISHED BELOW HAZARDOUS LEVELS AT YAP AND PALAU. BY 
MONDAY NIGHT...HIGH SURF CRITERIA MAY ONCE AGAIN BE AN ISSUE AT 
CHUUK.

&&

.MARINE...
ONLY MINOR ADJUSTMENTS NEEDED TO MARINE SWELL GRIDS. LOOKS LIKE 
CURRENT NORTH SWELL EVENT WILL PEAK FROM NORTH TO SOUTH DURING THE 
DAY ON SUNDAY. COMBINED SEAS WILL REMAIN JUST BELOW THE SMALL CRAFT 
THRESHOLD DURING THE NEXT COUPLE OF DAYS. GFS AND ECMWF CALL FOR 
TRADE-WINDS TO STRENGTHEN FURTHER ON TUESDAY. MAY NEED A SMALL CRAFT 
ADVISORY AT THAT TIME. WILL INITIALIZE TRADE-WIND PORTION OF 
COMBINED SEAS USING THE IPAN BUOY.

&&

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

MARIANAS WATERS...NONE.
&&

$$

MCELROY/STANKO

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