Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
537 PM CHST SAT JUL 26 2014

.MARIANAS SYNOPSIS...
THE MONSOON TROUGH MIGRATED NORTHWARD THROUGH THE FORECAST ZONES
TODAY AND HAS PASSED TO THE NORTH OF SAIPAN. BEST LOW-LEVEL
CONVERGENCE SOUTH OF THE TROUGH AXIS WAS NEAR GUAM THIS MORNING.
SHOWERS HAVE DIMINISHED OVER THE FORECAST ZONES FOR NOW...BUT A
REINFORCING SURGE OF MONSOON WINDS CAN BE SEEN APPROACHING THE
GUAM MARINE ZONE FROM YAP. JTWC LOW INVEST AREA 90W IS CENTERED
JUST NORTHWEST OF POHNPEI. DEEP CONVECTION HAS BEEN REDEVELOPING
NEAR THE CENTER DURING THE PAST COUPLE OF HOURS.

&&

.DISCUSSION...
FORECAST FOR SHOWER COVERAGE CLOSELY FOLLOWS PERSISTENCE. STILL
EXPECT SHOWER COVERAGE/QPF TO FAVOR THE OVERNIGHT HOURS TONIGHT
AND SUNDAY NIGHT...THEN MODEL GUIDANCE SUGGESTS A MORE PERSISTENT
BAND OF MONSOONAL CONVECTION WILL SET UP OVER THE FORECAST ZONES.
THE BAND OF CONVECTION IS PROGGED BY THE MODELS TO FEED INTO 90W
AS IT APPROACHES THE MARIANAS. MODELS GENERALLY AGREE IN BRINGING
90W THROUGH THE FORECAST ZONES AROUND MID WEEK. FELT ECMWF
SOLUTION FOR TUESDAY NIGHT WAS TOO FAST...SO FAVORED THE GFS
SOLUTION WHICH BRINGS 90W THROUGH ON WEDNESDAY NIGHT. UPDATED
WIND FIELDS FOR DAYS 1 THROUGH 7 TO FACTOR IN STRONG MONSOONAL
WINDS OVER THE GUAM WATERS TONIGHT AND SUNDAY...AS WELL AS THE
WIND FIELD FROM 90W AS IT PASSES THROUGH TUESDAY THROUGH
THURSDAY. IF CONFIDENCE IMPROVES ON THE LOCATION AND TIMING OF THE
PASSAGE OF 90W...LATER SHIFTS WILL NEED TO INCREASE POPS DURING
THE TIME 90W WILL PASS THROUGH THE MARIANAS.

&&

.MARINE...
LATEST ASCAT IMAGERY SHOWS SOUTHWEST WINDS HAVE ALREADY INCREASED
TO BETWEEN 15 AND 25 KNOTS OVER GUAM WATERS. MODEL GUIDANCE
SUGGESTS THESE WINDS WILL NOT MAKE INROADS MUCH FARTHER TOWARD
THE NORTH...BUT LARGE SWELL WILL BEGIN ARRIVING FROM THE FETCH
GENERATION REGION IN YAP STATE ON SUNDAY. ISSUED SMALL CRAFT
ADVISORY FOR GUAM WATERS TONIGHT BASED ON WINDS/WIND WAVES...BUT
EXPECT SMALL CRAFT ADVISORY FOR ALL MARINE ZONES BY SUNDAY NIGHT
AS COMBINED SEAS FOR ALL MARINE ZONES EVENTUALLY BUILD TO
ADVISORY LEVELS. HIGH SURF SHOULD AFFECT SOUTH AND WEST FACING
REEFS BY SUNDAY EVENING. CURRENTLY HAVE SMALL CRAFT ADVISORY IN
EFFECT THROUGH TUESDAY MORNING...BUT IF 90W INTENSIFIES...THE
ADVISORY WILL NEED TO BE EXTENDED.

&&

.EASTERN MICRONESIA...
ASCAT ANALYSIS INDICATES TWO CIRCULATIONS EMBEDDED IN THE MONSOON
TROUGH. THE TROUGH IS STRETCHED ACROSS NORTHERN PARTS OF EASTERN
MICRONESIA TO BEYOND THE DATE LINE. ONE CIRCULATION...INVEST AREA
90W...IS NEAR 9.5N158E AND A WEAKER CIRCULATION IS NEAR 10.5N169E.
MODELS INDICATE THE MOST SIGNIFICANT WEATHER WILL MOVE NORTHWEST
OF THESE FORECAST POINTS AS INVEST 90W CONTINUES TO DEVELOP AND
LIFTS TOWARD THE NORTHWEST IN THE COMING DAYS. MEANWHILE...WEATHER
AND WIND CONDITIONS ACROSS THIS AREA WILL BE CHANGEABLE AND
UNSTABLE DURING THE NEXT FEW DAYS...BUT GRADUALLY IMPROVING
WEATHER IS EXPECTED FOR EASTERN MICRONESIA DURING THE COMING WORK
WEEK AS A TRADE-WIND PATTERN RETURNS.

THE HAZARDOUS SURF ADVISORY REMAINS IN EFFECT FOR POHNPEI AND THE 
SPECIAL WEATHER STATEMENT FOR MICRONESIA WAS RE-ISSUED.

&&

.WESTERN MICRONESIA...
ASCAT ANALYSIS INDICATES THE LOW-LEVEL CIRCULATION ASSOCIATED WITH 
INVEST 96W IS NEAR 10.5N134E AND EDGING TOWARD THE NORTHWEST.
MODERATE TO STRONG SOUTHWEST WINDS WILL CONTINUE ACROSS KOROR AND
YAP THROUGH THE NEAR TERM...THEN GRADUALLY DECREASE THIS COMING
WEEK. INVEST 96W WILL NEED TO BE WATCHED CLOSELY BECAUSE IT WILL
SIGNIFICANTLY AFFECT THE WEATHER...WINDS AND SEA CONDITIONS FOR
YAP AND KOROR.

NEWLY DEVELOPED INVEST AREA 90W IS CENTERED NORTHEAST OF CHUUK AT
9N158E. MOST MODELS ARE AGGRESSIVE IN DEVELOPING 90W AS IT MOVES
TOWARD THE NORTHWEST THE NEXT FEW DAYS. MONSOON-TYPE WEATHER WILL
CONTINUE ON CHUUK AND CONDITIONS WILL BE VERY CHANGEABLE THERE...
DEPENDING ON HOW ACTIVE THE WEATHER ASSOCIATED WITH 90W BECOMES IN
THE COMING DAYS.

HAZARDOUS SURF ADVISORY REMAINS IN EFFECT FOR KOROR...YAP...AND 
CHUUK. CONDITIONS COULD DETERIORATE EVEN MORE IF INVEST 96W QUICKLY 
BECOMES MORE INTENSE. THE SPECIAL WEATHER STATEMENT FOR MICRONESIA 
WAS RE-ISSUED.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...NONE.
MARIANAS WATERS...SMALL CRAFT ADVISORY UNTIL 6 AM CHST TUESDAY FOR
PMZ151.

&&

$$

MCELROY/SIMPSON

National Weather Service Glossary of Abbreviations