AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TIYAN GU 720 AM CHST THU JUL 17 2014 .MARIANAS SYNOPSIS... AN INVERTED TROUGH HEADS NORTHWARD FROM A CIRCULATION EMBEDDED IN THE MONSOON SOUTH OF GUAM NEAR 10N145E. A TUTT CELL IS CENTERED JUST SOUTH OF IWO TO AT 23N142E. A TUTT IS PUSHING SOUTHWESTWARD FROM MINAMI TORI SHIMA TOWARD THE MARIANAS. && .DISCUSSION... LATEST FORECAST ISSUANCE INCORPORATES SOME NEAR TERM UNCERTAINTY. LATEST MODEL GUIDANCE AND SATELLITE IMAGERY FROM EARLIER IN THE SHIFT SUPPORTED THE INHERITED FORECAST OF MOSTLY CLOUDY SKIES AND ISOLATED SHOWERS AND THUNDERSTORMS. HOWEVER...SURFACE TROUGH TO THE EAST OF THE FORECAST ZONES HAS BECOME MORE AMPLIFIED AND SHIFTED A BIT FARTHER EAST. THIS HAS CAUSED WINDS TO BACK MORE THAN EXPECTED FROM EAST TO NORTHEAST DURING THE PAST SEVERAL HOURS OVER ALL THE FORECAST ZONES. AT THE SAME TIME...AN MCS HAS DEVELOPED JUST TO THE EAST OF THE ROTA...SAIPAN AND TINIAN MARINE ZONES. IF THIS MCS HOLDS TOGETHER AND PROPAGATES WESTWARD...A FORECAST UPDATE WILL BE REQUIRED. TROUGH IS STILL EXPECTED TO PASS TO THE WEST AND ALLOW WINDS TO VEER FROM THE SOUTHEAST. TRANSITION TO SOUTHEAST WINDS EXPECTED FOR THIS AFTERNOON MAY TAKE LONGER THAN NEAR TERM MODEL GUIDANCE SUGGESTS. OTHERWISE... FORECAST ASSUMES CIRCULATION SOUTH OF GUAM WILL REMAIN WEAK AND CONTINUE ON A CLIMATOLOGICAL TRACK TOWARD THE WEST-NORTHWEST. DEPTH OF LOW-LEVEL MOISTURE SHOULD DECREASE BY EARLY NEXT WEEK AS THE TUTT ARRIVES FROM THE NORTHEAST. && .MARINE... NO CHANGES TO THE ONGOING NARRATIVE. MARINE SWELL GRIDS INITIALIZED WELL. STILL EXPECT SURF ALONG EAST FACING REEFS WILL HOVER JUST ABOVE THE MODERATE RIP CURRENT RISK THRESHOLD BEFORE FALLING TO LOW RIP CURRENT RISK LEVELS FOR THE REMAINDER OF THE WEEK. && .EASTERN MICRONESIA... AN ACTIVE PATTERN HAS SET UP OVERNIGHT WITH THREE DISTINCT AREAS OF WEATHER DEPICTED IN IR SATELLITE IMAGERY. SHOWERS AND THUNDERSTORMS ARE SEEN NEAR A CIRCULATION CENTERED NORTH OF THE MARSHALL ISLANDS...AND NEAR ANOTHER CIRCULATION CENTERED BETWEEN KOSRAE AND POHNPEI. TRADE-WIND SHOWERS ARE SPREADING ACROSS THE CENTRAL AND SOUTHERN MARSHALLS. SHORT TERM TWEAKS WERE MADE TO PUT SCATTERED SHOWERS IN THE FORECAST TODAY FOR ALL 3 LOCALES. WET PATTERN WILL CONTINUE THROUGH FRIDAY NIGHT UNTIL SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THE CIRCULATION NEAR KOSRAE MOVES WEST. AN ACTIVE TRADE-WIND PATTERN WILL BUILD IN BEHIND THIS CIRCULATION... MAINTAINING SHOWERY CONDITIONS ACROSS THE REGION. LIGHTER WINDS AND DRIER WEATHER ARE DEPICTED IN THE MODELS SUNDAY AND MONDAY FOR MAJURO AND KOSRAE. && .WESTERN MICRONESIA... A VERY TRICKY WEATHER PATTERN REMAINS IN PLACE OVER YAP AND PALAU. FORECAST WAS UPDATED YESTERDAY EVENING FOR DETERIORATING WEATHER OVER KOROR ASSOCIATED WITH THE MONSOON TAIL SOUTH OF A DEVELOPING CIRCULATION. THIS CIRCULATION...STILL CENTERED NORTHWEST OF YAP...HAS DRIFTED SLOWLY TOWARDS THE WEST AND IS NOW THE SUBJECT OF A TROPICAL CYCLONE FORMATION ALERT ISSUED BY THE JOINT TYPHOON WARNING CENTER. ASSOCIATED MONSOON BAND RAPIDLY FILLED IN LAST NIGHT OVER KOROR...ACCOMPANIED BY GUSTY WINDS AND HEAVY RAIN. ANOTHER BAND OF CONVECTION IS SETTING UP OVER AND UPSTREAM OF KOROR THIS MORNING. DRIER WEATHER IS SEEN ON YAP THIS MORNING. THEREFORE...YAP SHOWER COVERAGE WAS REDUCED TO ISOLATED FOR TODAY. SCATTERED SHOWERS REMAIN IN THE FORECAST FOR BOTH LOCATIONS TONIGHT THROUGH FRIDAY NIGHT. HOWEVER...SHORT TERM ADJUSTMENTS OR UPDATES MAY BE NEEDED FOR CHANGING WEATHER CONDITIONS. MODELS STILL INDICATE THE YAP CIRCULATION WILL CONTINUE TO DEVELOP AS IT MOVES WEST-NORTHWEST. FRESH SOUTHWEST WINDS WILL PERSIST THE NEXT FEW DAYS ON BOTH ISLANDS. BY SUNDAY...RIDGING WILL BUILD IN OVER YAP AND PALAU...BRINGING IN DRIER WEATHER. OVERALL WEATHER PATTERN WILL REMAIN COMPLICATED AS THE CIRCULATION DEVELOPS DURING THE NEXT FEW DAYS...SO CONFIDENCE IN THE MID AND LONG RANGE FORECAST IS LOW. CHUUK RESIDES JUST SOUTH OF THE MONSOON TROUGH AXIS. DRY WEATHER STRETCHES TO THE EAST AND SOUTH...BUT SHOWERS AND THUNDERSTORMS LOOM TO THE WEST AND NORTH. SATELLITE SHOWS A CLUSTER OF SHOWERS THAT HAS PERSISTED JUST NORTHWEST OF WENO...AND HAS DROPPED SLOWLY TOWARDS THE SOUTH. FORECAST MAINTAINS ISOLATED SHOWERS AND THUNDERSTORMS WITH THE EXPECTATION THIS CLUSTER WILL STAY JUST WEST THIS MORNING. MONSOON TROUGH WILL KEEP UNSETTLED WEATHER IN PLACE THROUGH FRIDAY NIGHT BEFORE RIDGING USHERS IN DRIER WEATHER FOR THE WEEKEND. A HIGH SURF ADVISORY WAS ISSUED LAST NIGHT FOR BUILDING WEST SWELL CAPABLE OF PRODUCING HAZARDOUS SURF ACROSS PALAU. THAT SURF ADVISORY WAS EXPANDED TO INCLUDE YAP THIS MORNING. WAVE MODELS STILL SHOW COMBINED SEAS OF 7 TO 8 FEET FOR BOTH LOCATIONS THROUGH TONIGHT. WEST SWELL WILL GRADUALLY TAPER AS THE CIRCULATION NORTHWEST OF YAP PULLS FARTHER TOWARDS THE WEST- NORTHWEST. SURF COULD REMAIN HAZARDOUS UNTIL SATURDAY. WAVE MODELS SHOW A LONG PERIOD WEST SWELL REACHING BOTH LOCATIONS SUNDAY NIGHT THAT COULD BRING SURF BACK TO ADVISORY LEVELS THEN. WILL HAVE TO WATCH HOW THIS EVOLVES.
Posted on: Thu, 17 Jul 2014 00:48:11 +0000
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