Storm Surge in Guam, December 9 to 15, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
700 PM CHST MON DEC 8 2008

.SYNOPSIS...
A RELATIVELY INTENSE SURFACE LOW IS PASSING SOUTH OF WAKE ISLAND
AROUND 16N. A WEAK SURFACE TROUGH CURVES WESTWARD FROM THE LOW...
THEN TURNS NORTHWARD ALONG 150E. A LARGE FIELD OF COLD AIR STRATOCU
CAN BE SEEN NORTH OF THE LOW IN VISIBLE SATELLITE IMAGERY...IN THE
SAME AREA WHERE A LONG FETCH OF GALES FROM THE NORTHEAST HAS SET UP.
A SHEAR LINE IS HOVERING NORTH OF THE MARIANAS AROUND 22N.
&&

.DISCUSSION...
PRIMARY FORECAST CONCERN REVOLVES AROUND POTENT NORTHEAST SWELL
EVENT ALREADY IN PROGRESS. SEE MARINE DISCUSSION SECTION.
OTHERWISE...WILL ACCOUNT FOR TROUGHING AND CLOUDINESS CURRENTLY
AROUND 150E WITH A PERIOD OF MOSTLY CLOUDY SKIES DURING THE PREDAWN
HOURS. WEAKNESS OF THIS FEATURE AND MODEL QPF ARGUE FOR MAINTAINING
ISOLATED SHOWER COVERAGE DURING THIS TIME. EXCEPT FOR EARLY TOMORROW
MORNING...HAVE REDUCED SHOWER COVERAGE TO SLIGHT CHANCE AS SATELLITE
IMAGERY AND MODEL QPF FIELDS SUGGEST ASSOCIATED AIR MASS IS QUITE
DRY. BEYOND WEDNESDAY...MODELS STILL REMAIN IN GENERAL AGREEMENT ON
ADVECTING THE LOW SE OF WAKE ISLAND IN THE GENERAL DIRECTION OF THE
MARIANAS. CURRENT FORECAST CALLS FOR SCATTERED COVERAGE BETWEEN
THURSDAY MORNING AND FRIDAY AFTERNOON...WHICH STILL AGREES WELL WITH
THE LATEST SUITE OF MODEL GUIDANCE. TIMING OF INVERTED SURFACE
TROUGH WITH THIS SYSTEM STILL LOOKS GOOD...SO WILL GO WITH EXISTING
WIND GRIDS. GFS BRINGS IN AN AREA OF TRADE-WIND SHOWERS ON SATURDAY
AND SUNDAY. WILL WAIT A COUPLE OF MORE MODEL RUNS BEFORE ADDING ANY
DETAINS TO THE GRIDS REGARDING THIS FEATURE.
&&

.MARINE...
NAVO ALTIMETRY SHOWS COMBINED SEAS IN THE 12 TO 15 FOOT RANGE NEAR
AND UPSTREAM OF THE MARIANAS...WHILE WAVE WATCH GUIDANCE ALSO
CARRIES COMBINED SEAS IN THIS RANGE. HOWEVER...SURF OBS ON NORTHERN
AND EASTERN EXPOSURES ARE COMING IN ON THE LOW SIDE CONSIDERING THE
AFOREMENTIONED WAVE WATCH GUIDANCE AND ALTIMETRY. WILL CLOSELY
FOLLOW THE STORY WE HAVE ON THE STREET WITH THE EXCEPTION OF
EXTENDING THE SMALL CRAFT AND HIGH SURF ADVISORIES THROUGH THURSDAY
AFTERNOON...WITH MENTION THAT HIGH SURF WARNING MAY BE NEEDED
TUESDAY AND TUESDAY NIGHT IF SURF OBSERVED ON NORTH AND EAST FACING
REEFS IS HIGHER THAN FORECAST.
&&

.EASTERN MICRONESIA... A HIGH SURF WARNING REMAINS IN EFFECT FOR
POHNPEI WITH SURF OF 14 TO 17 FEET TONIGHT. CONTINUED WITH PREVIOUS
FORECAST TRENDS ALONG WITH HIGH SURF ADVISORY FOR BOTH KOSRAE AND
MAJURO. WW3 SWELL HEIGHTS AND PERIODS FOR KOSRAE AND MAJURO ARE
SLIGHTLY BELOW BUT NEAR WARNING THRESHOLDS FOR HIGH SURF WARNING.
QUIKSCAT AND SATELLITE IMAGES SHOW AN UNUSUAL PATTERN CHANGING TO A
MORE CHARACTERISTIC ONE. FAIRLY INTENSE CLOSED CIRCULATION SOUTHEAST
OF WAKE ISLAND IS MOVING SOUTHWESTWARD. THIS CIRCULATION IS TAKING
ON MORE TROPICAL CHARACTERISTICS AS IT MOVES SOUTHWARD. A TROUGH
EXTENDS FROM 15N168 TO ABOUT 9N157E AND BECOMES A SHEARLINE AT SOME
POINT AND CONTINUES NORTHWESTWARD. SHOWERS ACROSS EASTERN MICRONESIA
ARE ISOLATED IN COVERAGE THIS EVENING EXCEPT FOR AN AREA OF INTENSE
SHOWERS NORTHEAST OF MAJURO. THESE SHOWERS ARE ABOUT 150 MILES
NORTHEAST OF MAJURO AND ARE ASSOCIATED WITH ANOTHER SURFACE TROUGH
AND ARE MOVING SLOWLY SOUTHWEST BUT LESSENING IN INTENSITY. THE
FORECAST FOR MAJURO MAY NEED TO BE UPDATED IF THIS THESE SHOWERS
HOLD TOGETHER AND REACH MAJURO. MEANWHILE WW3 INDICATES THAT STRONG
NORTHERLY SWELLS WILL PEAK FOR THE AREA TUESDAY NIGHT.
&&

.WESTERN MICRONESIA...HIGH SURF WARNING CONTINUES FOR CHUUK WHERE
WW3 COMPUTER MODELS AND ONE SURF REPORT INDICATE SURF SHOULD BE
AROUND 16 FEET. CONTINUED PREVIOUS FORECAST TRENDS EXCEPT FOR
SCATTERED SHOWERS ON TUESDAY AND TUESDAY NIGHT FOR PALAU...CONTINUED
PREVIOUS FORECAST TRENDS FOR HIGH SURF FOR WESTERN MICRONESIA. WW3
INDICATES NORTHERLY SWELL SUBSIDING AFTER TUESDAY FOR PALAU AND
YAP...AND AFTER WEDNESDAY FOR CHUUK.
&&

.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.
&&

MCELROY/DEVITA