Flash Flood Warning 4, NWS Guam

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
735 AM CHST FRI SEP 20 2013

.MARIANAS SYNOPSIS... A DEVELOPING TROPICAL CYCLONE IS BRINGING
SCATTERED SHOWERS AND GUSTY WINDS TO THE MARIANAS THIS MORNING.
THE BULK OF THE SHOWERS AND WINDS WERE OBSERVED NEAR GUAM.

&&

.DISCUSSION...
MAIN FORECAST PROBLEM IS THE DEVELOPING TROPICAL DEPRESSION OVER
THE LOCAL AREA. WINDS ACROSS GUAM WERE FROM THE WEST-NORTHWEST
THIS MORNING. SAIPAN WAS FROM THE SOUTHEAST AND ROTA FROM THE
NORTH. THIS ADDS UNCERTAINTY TO LOCATING THE CENTER OF THE
CIRCULATION. JTWC IN THEIR TCFA MENTIONED A LOCATION NEAR 15.5N
AND 148.5E. THIS SEEMS TOO FAR EAST. ARE THERE MULTIPLE
CIRCULATIONS EMBEDDED IN THE LARGER FLOW OR IS THE CIRCULATION
ELLIPTICAL SINCE IT IS IN THE FORMATIVE STAGES. AT ANY RATE
SPLIT THE FORECAST ZONES WITH GUAM SEPARATE FROM THE OTHER THREE
ZONES. NOT ONLY IS THE SPLIT FOR WIND DIRECTION BUT RAIN. GUAM IS
CLOSER TO A BAND OF SHOWERS SOUTH OF THE CIRCULATION CENTER.
THIS BAND MOVED ACROSS THE ISLAND JUST AFTER MIDNIGHT. FEEL THAT
IT WILL REMAIN SOUTH OF THE ISLAND THROUGH THE MORNING BUT MAY
MOVE BACK NORTHWARD THIS AFTERNOON. WHILE SCATTERED SHOWERS
ARE EXPECTED OVER ALL OF THE ISLANDS SHOWERS MAY BE HEAVIER
OVER GUAM.

MODELS SHOW THAT WHATEVER DEVELOPS WILL MOVE NORTHWARD. WHILE
THIS MAY MEAN THAT THE HIGHER WINDS WILL OCCUR NORTH OF THE
ISLANDS WITH THE TROPICAL CYCLONE IT MAY NOT BE THE WHOLE STORY.
IF THE BAND OF HEAVY SHOWERS THAT IS SOUTH OF GUAM STAYS TOGETHER
IT MAY MOVE NORTHWARD WITH WHATEVER CIRCULATION DEVELOPS. THIS
MAY EQUAL ANOTHER ROUND OF ON AND OFF HEAVY RAINFALL FOR ALL THE
ISLANDS AND A PERIOD GUSTY WINDS FOR AT LEAST TONIGHT. WILL HAVE
TO MONITOR THIS SITUATION AS THINGS MAY CHANGE IF THE CIRCULATION
DECIDED TO DEVELOP QUICKER THAN ANTICIPATED.

MODELS CONTINUE TO KEEP THE MONSOON FLOW OVER THE AREA THROUGH
THE WEEK. SO EXPECT PERIODS OF SCATTERED SHOWERS THROUGH AT LEAST
THURSDAY.

&&

.MARINE...
SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR THE LOCAL AREA. A SHIP
JUST WEST OF GUAM...THE MSC FIRENZE...OBSERVED SEAS AT 10 FEET.
THIS FITS WELL WITH THE COMBINED SEAS IN THE MARINE FORECAST. THE
RITIDIAN BUOY DID HAVE A FEW MAX WAVES ABOVE 20 FEET DURING THE
HIGH WINDS THIS MORNING BUT THESE HAVE DECREASED. EXPECT COMBINED
SEAS TO AVERAGE BETWEEN 9 TO 11 FEET THROUGH THE WEEKEND. THE
WEST SWELL WILL GENERATE HAZARDOUS SURF ON WEST AND NORTH FACING
REEFS THROUGH AT LEAST MONDAY. IF THE CIRCULATING DOES DEVELOP
QUICKER THAN ANTICIPATED AND CLOSER TO THE LOCAL AREA THESE SEA
HEIGHTS AND SURF HEIGHTS MAY NEED TO BE REVISED.

&&

.EASTERN MICRONESIA...
SHOWERS AND THUNDERSTORMS CONTINUE TO DEVELOP ALONG A TRADE-WIND
CONVERGENCE ZONE OVER THE MARSHALL ISLANDS. SATELLITE IMAGERY
SHOWS DEEP CONVECTION REDEVELOPING EAST OF MAJURO THAT WILL
LIKELY SPREAD WESTWARD OVER MAJURO WATERS TODAY. WET CONDITIONS
ARE EXPECTED TO CONTINUE THROUGH AT LEAST TONIGHT BEFORE CALMER
WEATHER SETTLES IN FROM THE SOUTHEAST SATURDAY. SHOWERS AND
POSSIBLE TSTMS ARE ALSO EXPECTED AT KOSRAE LATER TODAY AND
EVENTUALLY POHNPEI LATE TONIGHT AS THE CONVERGENCE ZONE AND
SHOWER ACTIVITY SHIFT WESTWARD. ACTIVE WEATHER WILL PUSH MOSTLY
NORTHWARD OF POHNPEI AND KOSRAE EARLY NEXT WEEK.

&&

.WESTERN MICRONESIA...
STRONG MONSOONAL FLOW INTO TROPICAL DISTURBANCE 98W NEAR THE
MARIANAS IS ALLOWING SHOWERS AND TSTMS TO DEVELOP OVER AND NEAR
YAP. AN ACTIVE MONSOON PATTERN IS EXPECTED TO CONTINUE THROUGH AT
LEAST SATURDAY BEFORE THE MONSOON TAIL AND ASSOCIATED SHOWER
ACTIVITY PUSH NORTH OF YAP LATE SATURDAY OR EARLY SUNDAY. KOROR
WILL REMAIN RELATIVELY DRY OVER THE WEEKEND WITH WIDESPREAD
SHOWERS DEVELOP MAINLY TO THE NORTHEAST. SOUTHWEST MONSOON WINDS
WILL BECOME FRESH TO STRONG BEGINNING EARLY NEXT WEEK BUT MODELS
INDICATE BULK OF SHOWER ACTIVITY SHOULD REMAIN NORTH OF 10N. FOR
CHUUK...EXPECT QUIET WEATHER TODAY AND SATURDAY WITH RIDGING IN
PLACE ACROSS CHUUK STATE. SHOWER ACTIVITY ASSOCIATED WITH TRADE-
WIND CONVERGENCE AFFECTING THE EASTERN MICRONESIA MAY NOT REACH
CHUUK UNTIL SUNDAY. MODELS SHOW SHOWERS STALLING JUST EAST OF
CHUUK ON SUNDAY.

NORTHWEST SWELL GENERATED BY NOW SUPER TYPHOON USAGI CONTINUES TO
INCREASE AT YAP AND KOROR. SURF HEIGHTS WILL PEAK THIS AFTERNOON
AT 9 TO 11 FEET ON KOROR AND 10 TO 13 FEET ON YAP. SURF WILL FALL
SATURDAY BUT INCREASE ONCE AGAIN EARLY NEXT WEEK AS A REINFORCING
WNW SWELL FROM INCREASED MONSOON WINDS AND NORTHEAST SWELL
GENERATED BY TROPICAL DISTURBANCE 98W NEAR THE MARIANAS ARRIVE ON
THE ISLANDS. SURF MAY BRIEFLY FALL BELOW ADVISORY CRITERIA AT
KOROR ON SATURDAY AND SUNDAY BUT WILL RISE TO HAZARDOUS LEVELS
AGAIN ON MONDAY AS WEST AND NORTHEAST SWELL INCREASE.

&&

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

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

&&

ZIOBRO/WILLIAMS