Area Forecast Discussion
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000
FXPQ60 PGUM 210634
AFDPQ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
434 PM CHST MON APR 21 2014

.MARIANAS SYNOPSIS...
SATELLITE IMAGERY SHOWS THE WEAK CIRCULATION THAT MOVED SOUTH OF
GUAM EARLIER IN THE WEEKEND TO BE WEST OF YAP NEAR 10N135E.
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS EXTEND NORTHEASTWARD
FROM THE CIRCULATION ALONG A SURFACE TROUGH WEST OF THE MARIANAS.
MORE CLOUDS AND SHOWERS ARE FOUND OVER THE FAR NORTHERN CNMI
ALONG A SHEAR LINE THAT EXTENDS EAST-NORTHEASTWARD FROM NEAR
20N145E TO WELL NORTH OF WAKE ISLAND. CLOSER TO THE MARIANAS
THOUGH... SATELLITE AND RADAR SHOW SHOWERS AND THUNDERSTORMS WEST
OF THE MARINE ZONES THAT HAVE BEEN SLOWLY BACK-BUILDING CLOSER TO
THE WESTERN COASTAL WATERS TODAY. TO THE EAST IS DRIER WEATHER
WITH THE EXCEPTION OF A TROPICAL DISTURBANCE OVER EASTERN
MICRONESIA.

&&

.DISCUSSION...
DECIDED TO ADD IN A SMALL CHANCE OF THUNDERSTORMS FOR THE WESTERN
COASTAL WATERS OF THE MARIANAS FOR TONIGHT BASED ON SATELLITE
IMAGERY. ISOLATED SHOWERS...SOME HEAVY...HAVE CONTINUED TO PASS
THROUGH LOCAL WATERS WITH LIGHTNING DETECTION NETWORKS SHOWING
LIGHTNING WITHIN THE CELLS AS THEY PASS WELL WEST OF THE
MARIANAS. THE LARGER CLUSTER OF SHOWERS WEST OF THE AREA HAS
SHOWED A BACKING TREND TOWARD THE MARIANAS SO THERE IS THAT SMALL
CHANCE OF THUNDERSTORMS UNTIL AROUND MIDNIGHT. LATER TONIGHT...
ACTIVITY IS EXPECTED TO DIE DOWN. LOWERED POPS AND REDUCED CLOUD
COVER FOR MIDWEEK AS MODELS STRONGLY AGREE ON DRIER CONDITIONS UP
UNTIL AROUND THURSDAY. BY FRIDAY...THE FORECAST BECOMES SOMEWHAT
TRICKY. THROUGH THURSDAY...MODELS GENERALLY AGREE IN THE GRADUAL
WEST- NORTHWESTWARD MOVEMENT OF THE WEAK CIRCULATION CURRENTLY
NEAR KOSRAE. AS A RESULT HAVE KEPT INCREASED CLOUDINESS IN THE
FORECAST BEGINNING FRIDAY. FRIDAY AND SATURDAY IS WHEN MODELS
BEGIN TO GREATLY DIVERGE. ECMWF CONTINUES TO SEND THE CIRCULATION
IN A GENERAL WESTWARD TRACK BETWEEN YAP AND GUAM...SIMILAR TO THE
CIRCULATION THAT PASSED BY GUAM JUST A FEW DAYS AGO. HOWEVER...GFS
SHOWS THE CIRCULATION STALLING NEAR GUAM IN RESPONSE TO A PASSING
FRONTAL SYSTEM TO THE NORTH...THEN BEING PULLED NORTHWARD EAST OF
THE ISLANDS BY THAT FRONTAL SYSTEM LATER IN THE WEEKEND. FOR
NOW...HAVE ADJUSTED THE WIND GRIDS USING GFS IN THE SHORT TERM AND
A BLEND OF ECMWF AND GFS FOR THE LONG TERM TO ALIGN MORE WITH THE
ECMWF IN SHOWING THE CIRCULATION PASSING BY SOUTH OF GUAM YET WITH
A SURFACE TROUGH PASSING OVER THE MARIANAS. TIMING FOR SCATTERED
SHOWERS WILL LIKELY NEED TO BE BETTER FINE TUNED... ESPECIALLY
ONCE MODELS COME INTO A LITTLE BETTER AGREEMENT...BUT AT THIS
POINT IT LOOKS LIKE THE BEST CHANCE OF INCREASED SHOWERS WILL COME
OVER THE WEEKEND.

&&

.MARINE...
FEW CHANGES MADE TO THE MARINE GRIDS. TRADE-WIND SWELL AND A
SMALL NORTH SWELL WILL PERSIST FOR THE WEEK AND MAINTAIN A
MODERATE RISK OF RIP CURRENTS ON EAST FACING REEFS THE NEXT
SEVERAL DAYS. WAVE MODELS INDICATE A BUILDING NORTH SWELL LATE IN
THE WEEKEND FROM A DEVELOPING FRONTAL SYSTEM THAT WILL PUSH OFF
OF JAPAN IN THE COMING DAYS.

&&

.EASTERN MICRONESIA...
ONLY MINOR CHANGES NEEDED FOR FORECASTS IN THE SHORT-TERM. ALL 3
LOCALES WILL SEE SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS. A
DISTURBANCE CENTERED SOUTH OF KOSRAE WILL MAINTAIN UNSETTLED
WEATHER ACROSS THE REGION AT LEAST THROUGH TUESDAY NIGHT. VIS
SATELLITE SHOWS WIDESPREAD SHOWERS FARTHER EAST...NEAR AND EAST
OF THE DATE LINE. MODELS INDICATE THESE SHOWERS WILL GRADUALLY
TAPER THROUGH TUESDAY...BUT WILL HAVE TO WATCH THIS THROUGH THE
NEXT 12 TO 24 HOURS JUST IN CASE. SHOWERS ASSOCIATED WITH THE
DISTURBANCE SOUTH OF KOSRAE WILL SLOWLY LIFT TOWARDS THE
NORTHWEST BY WEDNESDAY. DESPITE THE EVENTUAL PASSING OF THIS
DISTURBANCE... MODELS HINT AT A CONTINUATION OF UNSETTLED WEATHER
INTO THE WEEKEND.

&&

.WESTERN MICRONESIA...
ALL SITES IN WESTERN MICRONESIA CURRENTLY ARE ENJOYING FAIRLY DRY
CONDITIONS. LATEST OBSERVATIONS AT YAP SHOW SOME SHOWERS HAVE
BEEN TRAINING OVER THE ISLAND...PART OF THE LARGER LOW-LEVEL FLOW
INTO INVEST AREA 98W CENTERED WEST OF YAP AT 10N135E. LOW-LEVEL
CLOUDS ARE BEGINNING TO DRIFT IN OVER CHUUK FROM THE EAST BUT DRY
WEATHER WILL PERSIST THERE AT LEAST THROUGH TONIGHT. MODELS
INDICATE SHOWERS ASSOCIATED WITH THE DISTURBANCE NEAR KOSRAE WILL
REACH CHUUK BY TUESDAY EVENING. MOISTURE WILL SHIFT NORTHWESTWARD
ON THURSDAY WITH A RETURN TO DRIER CONDITIONS. AS FOR YAP AND
KOROR...DRY CONDITIONS WILL PERSIST AT LEAST THROUGH TUESDAY
NIGHT OR WEDNESDAY MORNING. SHOWERS OVER YAP AND KOROR ULTIMATELY
DEPEND ON WHAT TRACK THE DISTURBANCE NEAR KOSRAE TAKES. MOST
MODELS CURRENTLY MOVE THE DISTURBANCE WEST-NORTHWEST DURING THE
NEXT COUPLE OF DAYS TO NEAR GUAM BY LATE WEEK...THEN CURVE IT
NORTHWARD. WITH THIS SCENARIO...FORECAST WILL MAINTAIN A DRY BIAS
FOR BOTH LOCATIONS THROUGH THE WEEKEND. DUE TO CURRENT LIGHT
WINDS ON KOROR...WILL KEEP A SLIGHT CHANCE OF THUNDERSTORMS IN
THE AFTERNOON FORECAST FOR TUESDAY.

&&

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

$$

W. AYDLETT/M. AYDLETT





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