Subject: Western Pacific: Synoptic Discussion For The Marianas

From: LDM Weather <[email-masked]>
Date: Sun, 17 Feb 2008 01:52:25 -0600

811 
FXPQ60 PGUM 170752
AFDPQ 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
552 PM CHST SUN FEB 17 2008

.SYNOPSIS...
SHEAR LINE IS PASSING SLOWLY OVER GUAM NOW...WITH 88D IMAGERY 
REVEALING ISOLATED SHOWERS IN THE WAKE OF THE SHEAR LINE BEFORE THE 
RADAR WENT DOWN AT 425 PM. AS A RESULT...WILL COMBINE ALL THE 
MARIANAS ZONES BASED ON CONGRUENT SHORT-TERM WEATHER. SATELLITE AND 
QUIKSCAT IMAGERY SHOW A SECOND SHEAR LINE BEGINNING TO FORM IN THE 
CNMI AROUND AGRIHAN.

&&

.DISCUSSION...
GFS DID NOT INITIALIZE WIND FIELDS WELL WITH RESPECT TO THE 
AFOREMENTIONED SHEAR LINES...SO HAVE GONE WITH THE UKMET THROUGH 72 
HOURS...THEN THE GFS75 FOR DAYS 4 AND 5. GFS AND ECMWF KEEP THE LEAD 
SHER LINE SOUTH OF GUAM THROUGH TUESDAY NIGHT...THEN CONSOLIDATE 
BOTH SHEAR LINES NORTH OF SAIPAN ON WEDNESDAY. IF THIS TRANSITION IS 
NOT SMOOTH OR TAKES SOME TIME...MAY NEED TO RE-DIVIDE THE FORECAST 
ZONES. LATEST UKMET SUGGESTS THE LEAD SHEAR LINE WILL BECOME THE 
DOMINANT ONE. HAVE FOLLOWED THE GFS/ECMWF THROUGH WEDNESDAY...BUT 
CONFIDENCE IS LOW. FRONTAL BOUNDARY MERGERS USUALLY FAVOR THE 
SOUTHERNMOST BOUNDARY. IF SHEAR LINE BEHAVIOR IS ANALOGOUS...FUTURE 
SHIFTS MAY NEED TO CHANGE THE FORECAST PARADIGM. ALSO...GFS GUIDANCE 
SHOWS QPF ENHANCING NORTH OF THE SHEAR LINE MONDAY AND TUESDAY... 
APPARENTLY IN RESPONSE TO MID AND UPPER-LEVEL TROUGHING ALOFT. IF 
THE SHEAR LINE SETS UP FARTHER SOUTH...MAY NEED TO ADD SCATTERED 
POPS AND LOWER TEMPS ON MONDAY AND TUESDAY. IN ANY CASE...THURSDAY 
THROUGH SUNDAY LOOK SEASONABLY DRY AS THE SHEAR LINE DISSIPATES AND 
RETREATS NORTHWARD.

&&

.MARINE...
STILL LOOKS LIKE PERSISTENT LONG PERIOD NORTH SWELL WILL MAINTAIN 
THE HIGH SURF ADVISORY THROUGH AT LEAST WEDNESDAY. TAKING INTO 
ACCOUNT RECENT EVENTS...WOULD NOT BE SURPRISED TO SEE THIS ONE LAG 
ONWARD THROUGH THURSDAY. TRADE-WIND SURGE IN THE WAKE OF THE 
NORTHERNMOST SHEAR LINE MAY BRING SMALL CRAFT ADVISORY CONDITIONS TO 
THE MARINE ZONES MONDAY AND TUESDAY. BEST CHANCES WILL BE IN TINIAN AND 
SAIPAN WATERS. CAN SEE AN OUTSIDE CHANCE THAT A HIGH SURF ADVISORIES 
MAY BE NEEDED FOR EAST-FACING EXPOSURES AS WELL IN CONJUNCTION WITH 
THIS SURGE.

&&

.EASTERN MICRONESIA...
A WELL-ORGANIZED CLUSTER OF LOW TO MID-LEVEL CLOUDS ASSOCIATED
WITH A TRADE-WIND DISTURBANCE IS LOCATED ABOUT 150 MILES EAST OF
POHNPEI...AND IS MOVING WEST AT 15 TO 20 MPH. GFS IS BRINGING
SCATTERED SHOWERS OVER POHNPEI EARLY MONDAY...WHILE UKMET DELAYS
BRINGING SCATTERED POPS OVER POHNPEI UNTIL MONDAY MID-MORNING.
SATELLITE IMAGERY DOES NOT REVEAL A LOW-LEVEL CIRCULATION BUT
MODELS SUGGEST A WEAK SURFACE LOW PRESSURE ASSOCIATED WITH THIS
ACTIVITY. FARTHER EAST...TRAILING SHOWER BANDS OVER MAJURO ARE
TRADE-WIND DRIVEN AND SCATTERED POPS ARE EXPECTED OVER MAJURO
TONIGHT. KOSRAE WAS SURROUNDED BY SHOWERS TODAY...AND MORE
SCATTERED SHOWERS FROM THE EAST ARE EXPECTED TO MOVE OVER KOSRAE
TONIGHT.

UPDATED THE HIGH SURF ADVISORY TO INCLUDE KOSRAE. INCREASING NNW
SWELLS ARE EXPECTED TO REACH KOSRAE WATERS LATE TONIGHT...AND THIS
EVENT MAY LAST FOR THE NEXT SEVERAL DAYS.

&&

.WESTERN MICRONESIA...
TRADE-WIND REGIME WILL DOMINATE LOCAL CONDITIONS OVER THE NEXT 
COUPLE OF DAYS. MODEL GUIDANCE ENHANCES THE TRADE-WIND DISTURBANCE
CURRENTLY EAST OF CHUUK BEFORE IT PASSES CHUUK ON WEDNESDAY. WILL
HAVE TO MONITOR THIS SYSTEM DURING THE NEXT 36 HOURS.

HAZARDOUS SURF ON CHUUK WILL CONTINUE THROUGH MONDAY...AND THE
COASTAL HAZARD MESSAGE WAS UPDATED LATE THIS AFTERNOON. LARGE
NORTH SWELLS OF 6 TO 7 FEET WILL ARRIVE ALONG THE SHORES OF KOROR
AND YAP BY TUESDAY...AND THIS EVENT WILL PROBABLY REQUIRE A HIGH
SURF ADVISORY FOR BOTH ISLANDS.

&&

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

MARIANAS WATERS...NONE.
&&

$$

MCELROY/BAQUI

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