Area Forecast Discussion
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000
FXPQ60 PGUM 070709
AFDPQ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
509 PM CHST TUE JUL 7 2015

.SYNOPSIS...
TYPHOON NANGKA IS ABOUT 650 MILES EAST OF GUAM AND MOVING WEST-
NORTHWEST ABOUT 13 MPH TOWARD THE NORTH MARIANA ISLANDS. TYPHOON
CHAN-HOM IS ABOUT 650 MILES NW OF GUAM AND MOVING AWAY. RADAR SHOWS
ISOLATED SHOWERS ACROSS THE COVERAGE AREA AND VAD WINDS SOUTHWEST AT
15 TO 20 KT. SAIPAN/TANAPAG BUOY SHOWS COMBINED SEAS OF 9 TO 11 FEET
MAINLY FROM WEST-SOUTHWEST.

&&

.DISCUSSION...
TYPHOON NANGKA WILL BE A SEVERE THREAT ACROSS NORTHERN PARTS OF THE
REGION THIS WEEK. SOME CHANGES WERE MADE TO THE FORECAST...MAINLY
REGARDING BEEFING UP THE FORECAST WIND FIELDS AS TYPHOON NANGKA
MOVES BY TO OUR NORTH. ISOLATED SHOWERS AND A FEW THUNDERSTORMS ARE
EXPECTED ACROSS OUR LOCAL FORECAST ZONES AS NANGKA APPROACHES THE
ISLANDS TO THE NORTH OF SAIPAN BY THURSDAY. LATER FORECASTS WILL BE
SUBJECT TO CHANGE AND THERE COULD BE SCATTERED SHOWERS ACROSS THE
SAIPAN AND TINIAN AREAS DURING SOME TIME PERIODS FROM WEDNESDAY
NIGHT THROUGH FRIDAY. IN THE LONGER TERM...MUCH BETTER WEATHER IS
EXPECTED ACROSS THE REGION NEXT WEEK.

&&

.MARINE...
COMPLEX MARINE CONDITIONS WILL PERSIST DURING THE COMING DAYS. WINDS
AND WAVES WILL INCREASE ACROSS THE REGION. GFS MODEL WINDS SEEMED
REASONABLE FOR THE SITUATION AND WERE RELOADED INTO THE GRIDS WHILE
THE WAVE GRIDS CURRENTLY ACCOUNT DECENTLY FOR TYPHOON NANGKA PASSING
ACROSS TO THE NORTH OF SAIPAN ON THURSDAY. THE SMALL CRAFT AND HIGH
SURF ADVISORIES REMAIN IN EFFECT THROUGH THURSDAY AND WILL LIKELY BE
EXTENDED...PERHAPS INTO THE WEEKEND. HIGH SURF LINGERS ALONG WEST
AND SOUTH FACING SHORES AND TYPHOON NANGKA WILL CAUSE HIGH SURF ON
NORTH AND EAST FACING REEFS BY THURSDAY.

&&

.TROPICAL SYSTEMS...
TYPHOON NANGKA IS ABOUT 650 EAST OF GUAM WITH A WELL-DEVELOPED EYE
AND CONTINUES TO INTENSIFY. NANGKA IS GAINING LATITUDE SLOWLY AND
THE JTWC TRACK TAKES IT CLOSE TO PAGAN AND AGRIHAN BY 4PM THURSDAY
AS A CATEGORY 4 TYPHOON. MEANWHILE...TYPHOON CHAN-HOM IS 650 MILES
NORTHWEST OF GUAM AND MOVING AWAY...BUT IF CHAN-HOM SLOWS ITS
NORTHWEST MOVEMENT THEN THE DOWNSTREAM CONDITIONS NEAR NANGKA
COULD BE SLOWED ALSO. NANGKA WILL NEED TO BE WATCHED VERY CLOSELY
DURING THE NEXT 24 HOURS IN CASE WATCHES OR WARNING MAY EVENTUALLY
BE NEEDED FARTHER SOUTH FOR SAIPAN AND TINIAN.

&&

.EASTERN MICRONESIA...
TYPHOON NANGKA CENTERED ALMOST 500 MILES NORTHWEST OF POHNPEI IS
STEADILY MOVING AWAY FROM THE REGION TOWARDS THE WEST-NORTHWEST.
SWELL GENERATED BY TYPHOON NANGKA WILL IMPACT THE NORTH AND WEST
EXPOSURES BUT WILL NOT BE SUFFICIENT TO CAUSE HAZARDOUS SURF.
CONVERGENT FLOW INTO NANGKA IS TRIGGERING SCATTERED SHOWERS AND A
FEW THUNDERSTORM MAINLY NORTH OF POHNPEI. THIS ACTIVITY IS
EXPECTED TO SHIFT FARTHER NORTH AND WEST AS THE NIGHT PROGRESSES
AS NANGKA MOVES FARTHER AWAY. OTHERWISE...QUIET CONDITIONS ARE
FOUND ACROSS KOSRAE STATE AND THE MARSHALL ISLANDS WITH NO MAJOR
WEATHER FEATURE EXPECTED TO IMPACT THESE LOCATIONS THROUGH THE
REST OF THE WEEK. SIMILARLY...ONCE CONVECTION MOVES OUT OF POHNPEI
WATERS TONIGHT EXPECT PLEASANT CONDITIONS TO SETTLE IN OVER THE
ISLAND FOR THE NEXT SEVERAL DAYS.

&&

.WESTERN MICRONESIA...
SATELLITE IMAGERY SHOWS MOST OF THE SHOWER ACTIVITY ASSOCIATED WITH
TYPHOON NANGKA NORTH OF CHUUK WATERS. CLOUD COVER OVER CHUUK IS
PRIMARILY CIRRUS WITH DEEP CONVECTION NORTH OF 9N. MODELS INDICATE
SUBSEQUENT SHOWER DEVELOPMENT WILL BE NORTH OF CHUUK THROUGH
WEDNESDAY AS NANGKA MOVES WEST-NORTHWESTWARD WELL NORTH OF CHUUK.
RIDGING WILL KEEP QUIET WEATHER OVER CHUUK STATE THROUGH THE
WEEKEND. LARGE SCALE RIDGING SOUTH OF TYPHOON CHAN-HOM AND TYPHOON
NANGKA WILL ALLOW DRY CONDITIONS TO CONTINUE AT YAP AND KOROR FOR THE
NEXT SEVERAL DAYS.

SWELL GENERATED BY TYPHOON NANGKA SHOULD BE INSUFFICIENT TO CAUSE
HAZARDOUS SURF TO DEVELOP ON CHUUK FOR THE NEXT COUPLE OF DAYS.
MONSOON GENERATED SWELL AND WIND WAVES WILL CONTINUE TO PRODUCE
HAZARDOUS SURF ON SOUTH AND WEST FACING SHORES OF YAP AND KOROR AT
LEAST THROUGH TONIGHT. SCATTEROMETER DATA SHOWS WINDS HAVE SUBSIDED
CONSIDERABLY OVER THE LAST COUPLE OF DAYS ALLOWING SOUTHWEST SWELL
TO DIMINISH. AS A RESULT...SURF SHOULD FALL BELOW HAZARDOUS LEVELS
AT YAP AND KOROR SOONER THAN EXPECTED...LIKELY BY EARLY WEDNESDAY
AFTERNOON. SWELL FROM CHAN-HOM SHOULD NOT CAUSE HAZARDOUS SURF ON
NORTH FACING REEFS OF YAP AND KOROR.

&&

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

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

&&

$$

SIMPSON/WILLIAMS



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