Subject: Western Pacific: Synoptic Discussion For The Marianas

From: LDM Weather <[email-masked]>
Date: Wed, 20 Feb 2008 01:43:45 -0600

996 
FXPQ60 PGUM 200743
AFDPQ 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
543 PM CHST WED FEB 20 2008

.SYNOPSIS...
THE SHEAR LINE HAS MAINLY LOOSENED ITS GRIP ON THE MARIANAS...BUT
CURRENT RADAR AND SAT IMAGERY SHOWS A SOUTHWARD-PROPAGATING GRAVITY
WAVE SETTING OFF SCATTERED SHOWERS ALONG A SEGMENT OF THE SHEAR LINE
SOUTHEAST OF GUAM. THESE SHOWERS APPEAR TO BE DEVELOPING SOUTHWARD
WITH THE GRAVITY WAVE AND SHOULD STAY MAINLY S OF GUAM. ANOTHER
SHEAR LINE IS EVIDENT NORTH OF SAIPAN NEAR ANATAHAN...BUT IT APPEARS
TO BE STATIONARY.

&&

.DISCUSSION...
THE GRAVITY WAVE SHOULD CONTINUE TO TRIGGER SHOWERS FURTHER AND
FURTHER SOUTH AS IT RIPPLES THROUGH THE AREA THIS EVENING. THUS...
ITS ONLY EFFECT ON THE FORECAST PACKAGE IS IN THE COASTAL WATERS
FORECAST...WHICH HAS SCT SHWRS OVER THE SOUTHEASTERN GUAM WATERS
TONIGHT. 

MEANWHILE...GFS SHOWS THE SHEAR LINE N OF THE ISLANDS REMAINING UP
NORTH FOR THE NEXT FEW DAYS. IT LOOKS PRETTY DRY THROUGH AT LEAST
FRIDAY. IN FACT...THE GFS KEEPS THE MARIANAS IN STRONG SUBSIDENCE
THROUGH FRIDAY NIGHT...SO HAVE DROPPED POPS TO 10 PCT AND HAVE
ONLY A SLT CHC OF SHOWERS FOR THU NITE THROUGH FRI NITE.

THE NEXT FORECAST ISSUE INVOLVES THIS WEEKEND...WHEN THE GFS AND
NOGAPS BOTH TRY TO BRING A TRADE-WIND DISTURBANCE THROUGH THE
MARIANAS. ON THE PLUS SIDE...THE DISTURBANCE ACTUALLY EXISTS AND
IS NOW BRINGING SHOWERS TO KWAJALEIN AND MAJURO. ON THE MINUS
SIDE...THE UKMET AND THE 12Z ECMWF TAKE IT SOUTH OF GUAM SATURDAY.
SO WILL KEEP ISOLATED SHOWERS FOR NOW OVER THE WEEKEND...BUT WE
WILL KEEP AN EYE ON THE SITUATION.

&&

.FIRE WEATHER...
AFTER YESTERDAY'S COPIOUS RAINS...THE KBDI FELL TO 463. THUS...NO
THREAT OF RED FLAG CONDITIONS FOR AT LEAST THE REST OF THE MONTH.

&&

.MARINE/SURF...
THE PERSISTENT NORTH SWELL SHOULD FINALLY DECLINE OVERNIGHT AND
THURSDAY. BY EARLY MORNING...BOTH THE HIGH SURF AND SMALL CRAFT
ADVISORIES SHOULD BE COMING DOWN.

&&

.EASTERN MICRONESIA...
NO MAJOR CHANGES COMPARED TO THE PREVIOUS FORECAST. POHNPEI IS 
DRYING OUT THIS EVENING AS CONVERGENCE MOVES ON. KOSRAE IS INSIDE AN 
AREA OF NORTHEASTERLIES BUT THE NEXT DISTURBANCE IS CLOSING IN FROM 
THE EAST. PERIODS OF SHOWERS AND A FEW THUNDERSTORMS WILL CONTINUE 
OVER MUCH OF THE MARSHALL ISLANDS THRU THURSDAY EVENING. KOSRAE WILL 
GET ITS NEXT SHARE OF WEATHER BY THURSDAY NIGHT...AND POHNPEI BY 
FRIDAY.

HIGH SURF ADVISORY IS LIKELY TO REMAIN IN EFFECT FOR POHNPEI AND 
KOSRAE INTO FRIDAY. LATEST ALTIMETRY AND WW3 MODEL GUIDANCE SUGGESTS 
5 TO 6 FEET NNW SWELLS OF 13 TO 14 SECONDS...WILL BARELY PRODUCE 
SURF HEIGHTS BTW 10 AND 11 FEET ALONG NORTHERN EXPOSURES ON MAJURO. 
THEREFORE NO ADVISORY IS NEEDED FOR THIS PARTICULAR EVENT.

&&

.WESTERN MICRONESIA...
THINGS LOOK BASICALLY IDENTICAL AS BEFORE. SURFACE TROUGH WILL 
DEPART CHUUK THURSDAY MORNING AND REACH YAP AND PALAU BY FRIDAY. 
ADDED SLIGHT CHANCE OF THUNDER FOR BOTH STATES SINCE UPPER-LEVEL
HIGH TO THE NORTHEAST MIGHT SUPPORT DIFFLUENT FLOW IN THE
VICINITY.

HIGH SURF ADVISORY WILL REMAIN IN EFFECT FOR PALAU AND YAP INTO 
SATURDAY...AND CHUUK INTO FRIDAY.

&&

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

MARIANAS WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 
6 AM CHST THURSDAY FOR PMZ151>154.

&&

$$

MIDDLEBROOKE/CHAN

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