Area Forecast Discussion
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FXPQ60 PGUM 230604
AFDPQ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
404 PM CHST TUE SEP 23 2014

.MARIANAS SYNOPSIS...
LATEST ASCAT/WINDSAT IMAGERY...AS WELL AS ANIMATED RADAR AND
VISIBLE SATELLITE IMAGERY SUGGEST JTWC HIGH INVEST AREA 98W IS
CENTERED ABOUT 200 MILES EAST OF SAIPAN NEAR 15N147E. 98W IS AN
ELONGATED AND POORLY DEFINED SYSTEM...SO CONFIDENCE ON THE EXACT
LOCATION OF THE CENTER IS LOW. 98W IS A LARGE SYSTEM. A TUTT CELL
IS CENTERED ON THE NORTH SIDE OF 98W NEAR 20N151E. THESE TWO
FACTORS BOTH SUGGEST 98W WILL NOT RAPIDLY DEVELOP.

&&

.DISCUSSION...
ASCAT/WINDSAT STREAMLINE ANALYSIS INDICATED WINDS ON THE
PERIPHERY OF 98W WERE QUITE A BIT HIGHER THAN THEY WERE IN THE
FORECAST GRIDS. HAVE ACCORDINGLY UPDATED WIND GRIDS FOR DAYS 1
THROUGH 4 TO MORE CLOSELY ALIGN WITH MODEL CONSENSUS AS WELL.
LARGE SIZE AND PROXIMITY OF 98W BOTH ARGUE FOR ADDING SCATTERED
SHOWERS TO THE FORECAST FOR TONIGHT. CONSIDERED ADDING SCATTERED
SHOWERS FOR WEDNESDAY AND WEDNESDAY NIGHT AS WELL...BUT HELD OFF
ON THIS BASED ON THE LATEST GFS40 RUN...WHICH BEST INITIALIZES THE
DRY AIR AND LACK OF CONVECTION ON THE NORTHWEST SIDE OF 98W. 98W
SHOULD DEPART THE FORECAST ZONES BY THURSDAY AFTERNOON...BUT IT
WILL LEAVE THE MONSOON TROUGH BEHIND. KEPT MOSTLY CLOUDY AND
ISOLATED THUNDERSTORM WORDING IN THE FORECAST THROUGH DAY 7. NEXT
POSSIBLE WEATHER MAKER IS A SYSTEM CENTERED BETWEEN KOSRAE AND
KWAJALEIN. IF THIS SYSTEM DEVELOPS AND MOVES TOWARD THE
MARIANAS...SCATTERED SHOWERS MAY BE NEEDED IN THE FORECAST FOR
THIS WEEKEND.

&&

.MARINE...
MADE SIGNIFICANT UPDATES TO THE MARINE FORECAST GRIDS. INCREASED
WINDS AND SEAS FOR DAYS 1 THROUGH 4. LATEST ASCAT AND WINDSAT
IMAGERY INDICATED WINDS OF 20 TO 25 KT ON THE PERIPHERY OF
98W...WITH LIGHTER WINDS TOWARD THE CENTER OF THE SYSTEM. DID GO
WITH A LARGER RANGE IN SWELL AND SURF BASED UPON BLOCKING OF THE
PRIMARY NORTHEAST SWELL BY SAIPAN AND TINIAN. LATEST FORECAST
UPDATE STOPS JUST SHORT OF ADVISORY CONDITIONS FOR THURSDAY AND
FRIDAY. IF 98W DEVELOPS FURTHER...ADVISORIES MAY BE REQUIRED
DURING THIS TIME FRAME.

&&

.EASTERN MICRONESIA...
ASCAT ANALYSIS SHOWS A MONSOON TROUGH RUNS SOUTHEASTWARD FROM THE
CIRCULATION JUST EAST OF SAIPAN INTO A WEAK CIRCULATION CENTERED
BETWEEN KWAJALEIN AND KOSRAE NEAR 8N165E. SATELLITE SHOWS PATCHY
AREAS OF SCATTERED SHOWERS ACROSS POHNPEI AND KOSRAE STATES.
MODELS GENERALLY INDICATE THE MONSOON TROUGH WILL SLOWLY LIFT
TOWARD THE NORTHWEST...SO THERE SHOULD BE A GRADUAL DRYING TREND
FOR POHNPEI AND KOSRAE THROUGH THIS WEEK. FAIRLY DRY WEATHER
PREVAILS ON MAJURO THROUGH THE NEAR TERM...BUT THE GFS IN
PARTICULAR INDICATES MORE SHOWERS COULD MOVE ACROSS THE RMI THIS
WEEKEND AS ANOTHER TRADE DISTURBANCE ARRIVES FROM THE EAST.

&&

.WESTERN MICRONESIA...
ASCAT ANALYSIS SHOWS MONSOON WEST TO SOUTHWEST WINDS PREVAIL
ACROSS THIS WHOLE AREA...AND A DEVELOPING CIRCULATION JUST EAST
OF SAIPAN THIS AFTERNOON SEEMS TO BE MOVING SLOWLY TOWARD THE
NORTH- NORTHWEST. WIND FLOW ACROSS CHUUK...YAP AND KOROR WILL
CONTINUE TO BE UNSTABLE BUT THE BULK OF SHOWER ACTIVITY IS
EXPECTED TO REMAIN NORTH OF THESE FORECAST POINTS. MONSOONAL
WINDS ACROSS YAP AND KOROR COULD INCREASE FURTHER IN THE COMING
DAYS AND FUTURE SHIFTS WILL NEED TO MONITOR FOR POSSIBLE HIGHER
SEA CONDITIONS OR GREATER SHOWER COVERAGE. CHUUK WILL BE AT RISK
FOR MORE SHOWERS ARRIVING WITH A DISTURBANCE FROM EASTERN
MICRONESIA BY ABOUT SATURDAY OR SUNDAY.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...NONE.
MARIANAS WATERS...NONE.
&&

$$

MCELROY/DEVITA/SIMPSON





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