Area Forecast Discussion
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000
FXPQ60 PGUM 030628 RRA
AFDPQ

AREA FORECAST DISCUSSION...RETRANSMITTED
NATIONAL WEATHER SERVICE TIYAN GU
420 PM CHST TUE MAR 3 2015

RETRANSMITTED TO PLACE ON THE WEB

.SYNOPSIS...
THE LEADING EDGE OF A TRADE-WIND SURGE IS MOVING OVER THE
MARIANAS...BRINGING ISOLATED SHOWERS TO THE REGION THIS AFTERNOON.
THE MOST RECENT SCATTEROMETER PASS EAST OF THE MARIANAS SHOWS A
SWATH OF AT LEAST 20 KT SUSTAINED EAST-NORTHEAST WINDS. 00Z
SOUNDING SHOWED SOME DESTABILIZATION AND INCREASED MOISTURE SINCE
LAST NIGHT AS THE EFFECTS FROM THE TRADE-WIND SURGE BEGIN.

&&

.DISCUSSION...
THE LEADING EDGE OF THE TRADE-WIND SURGE AND ACCOMPANYING SHOWER
ACTIVITY WILL PASS OVER THE MARIANAS THIS AFTERNOON AND EVENING.
WINDS WILL INCREASE BEHIND THE BAND OF CLOUDS AND SHOWERS BUT
DRIER WEATHER WILL RESUME LATER THIS EVENING. MODELS HANDLE THE
TRADE-WIND SURGE EVENT WELL WITH WINDS INITIALIZING CLOSELY WITH
SCATTEROMETER DATA NORTHEAST OF THE MARIANAS. EAST-NORTHEAST WINDS
WILL PEAK AT FRESH TO OCCASIONALLY STRONG LEVELS WEDNESDAY BEFORE
FALLING SLIGHTLY WEDNESDAY NIGHT AND THURSDAY. ONLY WEAK TRADE-
WIND DISTURBANCES ARE EXPECTED TO AFFECT THE MARIANAS THIS
WEEK. ONE IS EXPECTED TO ARRIVE THURSDAY AND ANOTHER BY THE
WEEKEND. HOWEVER...EFFECTS ON THE MARIANAS WILL BE MINIMAL WITH
EXPANDED CLOUD COVER AND A MARGINAL INCREASE IN SHOWERS.
OVERALL...A TYPICAL DRY SEASON REGIME WILL CONTINUE THROUGH EARLY
NEXT WEEK.

&&

.MARINE...
SCATTEROMETER PASS EAST OF THE MARIANAS SHOWS AN AREA OF WINDS
CLOSE TO SMALL CRAFT ADVISORY SPEEDS. THE STRONGER WINDS HAVE
ALREADY PUSHED INTO SAIPAN WATERS WITH SAIPAN OBSERVATIONS
SHOWING WIND GUSTS EVERY HOUR FOR THE LAST SEVERAL HOURS ABOVE 22
KT. THIS WILL BE A SHORT LIVED EVENT. RITIDIAN BUOY IS STILL
SHOWING SIGNIFICANT WAVE HEIGHTS AROUND 7 FEET. THE SWATH OF
ADVISORY LEVEL WINDS IS SMALL ENOUGH TO DELAY SEA HEIGHTS
REACHING 10 FEET IN THE NEAR TERM. HOWEVER...WAVE MODEL GUIDANCE
INDICATES THAT SEAS MAY RISE TO NEAR 10 FEET BY WEDNESDAY
AFTERNOON SO FURTHER ASSESSMENT WILL BE NEEDED AS THE EVENT
UNFOLDS. IN ADDITION...SURF COULD RISE TO HAZARDOUS LEVELS ON EAST
FACING REEFS TOMORROW AFTERNOON IN RESPONSE TO BUILDING TRADE-WIND
SWELL AND WAVES.

&&

.FIRE WEATHER...
SHOWERS ASSOCIATED WITH THE TRADE-WIND SURGE EVENT ARE ONGOING
ACROSS THE MARIANAS. HOWEVER...IT IS UNLIKELY THAT ALL OF GUAM
WILL SEE A WETTING RAINFALL. BENEFICIAL RAIN HAS FALLEN ACROSS
SOUTHERN GUAM SINCE THIS MORNING. DRIER CONDITIONS ARE ANTICIPATED
LATER THIS EVENING AS THE THE LEADING EDGE OF THE TRADE-WIND SURGE
AND ASSOCIATED SHOWER ACTIVITY MOVES WEST OF THE MARIANAS.
ASSESSMENT OF THE RAINFALL TODAY AND THIS AFTERNOON WILL DICTATE
THE DECISION ON WHETHER TO CONTINUE THE FIRE WEATHER WATCH OR
TEMPORARILY SUSPEND THE WATCH.

&&

.EASTERN MICRONESIA...
SCATTERED SHOWERS WILL MOVE ACROSS MAJURO OVERNIGHT. SATELLITE
AND ASCAT WIND ANALYSIS SHOW A SURFACE TROUGH MOVING INTO THE
MARSHALL ISLANDS THIS AFTERNOON. SCATTERED SHOWERS ARE ALSO
SPREADING ACROSS THE NORTHERN ATOLLS OF THE RMI WHERE AN UPPER-
LEVEL TROUGH IS PROVIDING DIVERGENT FLOW ALOFT. THE SURFACE
TROUGH IS MOVING VERY SLOWLY AND SHOWERY WEATHER WILL BE WELCOME
FOR THOSE NORTHERN ATOLLS THIS TIME OF YEAR. DRIER WEATHER SHOULD
GRADUALLY DEVELOP ACROSS THE RMI FROM EAST TO WEST LATER THIS
WEEK.

HAZARDOUS SEA CONDITIONS ARE EXPECTED NEAR MAJURO. EARLIER
ALTIMETRY DATA SHOWED COMBINED SEAS OF 9 TO 12 FEET NORTHEAST OF
THE MARSHALL ISLANDS AND ASCAT ANALYSIS NOW SHOWS 20 TO 25 KT
TRADE WINDS IN THAT AREA. THE WAVE WATCH MODEL INDICATES COMBINED
SEAS WILL BUILD TO AT LEAST 9 FT TONIGHT...WHICH IMPLIES A
FORECAST RANGE OF 8 TO 10 FEET. AT THIS TIME...THE SURF IS
EXPECTED TO REMAIN JUST BELOW HAZARDOUS LEVELS.

MAINLY DRY TRADE WINDS WILL PREVAIL ON BOTH KOSRAE AND POHNPEI
FOR THE NEAR TERM AT LEAST. MODELS INDICATE THE MONSOON TROUGH
SHOULD REMAIN JUST SOUTH OF BOTH LOCATIONS...WHILE THE SURFACE
TROUGH OVER THE RMI TODAY MOVES VERY SLOWLY TOWARD THE WEST.

&&

.WESTERN MICRONESIA...
THE NEAR-EQUATORIAL TROUGH REMAINS ALONG 2N-3N AND MODERATE TO
FRESH TRADE WINDS PREVAIL FOR KOROR...YAP AND CHUUK. THE WEATHER
WILL BE UNSETTLED OVER KOROR AND YAP IN THE COMING DAYS...SINCE
MODEL GUIDANCE INDICATES THAT WINDS AND SEAS WILL INCREASE AS A
SHEAR LINE REFORMS AND SAGS SOUTHWARD ACROSS THE YAP AND KOROR
AREAS BY ABOUT THURSDAY OR FRIDAY. FAIRLY DRY WEATHER SHOULD
PREVAIL ON CHUUK UNTIL AT LEAST FRIDAY WHEN SHOWERS ALONG THE
NEAR-EQUATORIAL TROUGH COULD SPREAD NORTHWARD.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...FIRE WEATHER WATCH THROUGH THURSDAY AFTERNOON FOR GUZ001.

MARIANAS WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 6 PM THURSDAY
     FOR PMZ151>154.

&&

$$

WILLIAMS/SIMPSON



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