Subject: Western Pacific: Synoptic Discussion For The Marianas

From: LDM Weather <[email-masked]>
Date: Sat, 16 Oct 2010 16:50:21 -0500

407 
FXPQ60 PGUM 162150
AFDPQ 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
750 AM CHST SUN OCT 17 2010

.SYNOPSIS...
PGUA WSR-88D SHOWS ISOLATED SHOWERS MOVING THROUGH THE MARIANAS
WATERS. CONVERGING FLOW INTO TYPHOON MEGI IS PRODUCING SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS BETWEEN 5N AND 23N FROM 130E TO
135E WHICH IS JUST WEST OF KOROR PALAU. A SURFACE TROUGH IS
CREATING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WEST OF CHUUK
AND SOUTHEAST OF YAP BETWEEN 1N AND 8N FROM 139E TO 151E. TRADE-
WIND CONVERGENCE IS GENERATING SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS OVER MUCH OF THE MARSHALL ISLANDS BETWEEN 7N AND 12N
FROM 160E TO 180. AN UPPER-LEVEL LOW IS SPARKING SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS BETWEEN 15N AND 25N FROM 148E TO 166E.
THIS IS JUST EAST OF THE MARIANAS AND JUST WEST OF WAKE ISLAND.

&&

.DISCUSSION...
GFS40 HAS BACKED OFF A BIT ON THE AMOUNT OF RAIN IT IS BRINGING IN
TO THE MARIANAS OVER THE NEXT 10 DAYS. SO FOR NOW AM LEAVING THE
GRIDS RELATIVELY DRY AS ECMWF-HIRES HAS BEEN SAYING ALL ALONG AND
IT NOW SEEMS THE GFS40 IS TRENDING THAT WAY ALSO. THERE WILL STILL
BE SOME SHOWERS OF COURSE...AM JUST THINKING THAT ISOLATED WILL
COVER IT. THE UPPER-LEVEL LOW MOVING OUR WAY HAS BECOME MUCH MORE
CONVECTIVELY ACTIVE IN THE PAST 24 HOURS. NONETHELESS...MOST OF
THE ACTIVITY LOOKS LIKE IT WILL SLIDE NORTH OF SAIPAN. INHERITED
GRIDS HANDLED THIS DRY SCENARIO WELL...SO NO CHANGES WERE NEEDED.

&&

.MARINE...
WEST TYPHOON SWELL WAS REMOVED YESTERDAY...WHICH WITH NEW DATA AND
ON FARTHER REFLECTION SEEMS TO BE A FINE IDEA. MEGI IS MOVING TO
THE WEST-NORTHWEST AT A FAIRLY HIGH SPEED. THIS IS NOT ONLY
WEAKENING THE WEST WINDS THAT MIGHT GIVE US A SWELL BUT ALSO
INDUCES A REVERSE DYNAMIC FETCH...LOWERING THE SWELL RATHER THAN
RAISING IT. WE STILL MIGHT GET SOME 1 OR 2 FOOT SWELLS...BUT THEY
WILL BARELY BE NOTICEABLE.

&&

.EASTERN MICRONESIA...
CONVECTION HAS RAPIDLY DISSIPATED NEAR POHNPEI ALLOWING FOR CLOUD 
COVER TO QUICKLY DIMINISH. LATEST SURFACE ANALYSIS INDICATES AN 
ELONGATED TROUGH STRETCHING FROM NORTH OF KOSRAE...ACROSS KWAJALEIN 
AND MAJURO...THEN PASSING THROUGH 10N180. MAJURO CONTINUES TO SIT 
WITHIN A SMALL AREA FREE OF DEEP CONVECTION. MODELS GUIDANCE 
SUGGESTS THAT MAJURO MAY ONLY SEE ISOLATED SHOWERS THE NEXT FEW DAYS 
AS CONVECTION PASSES BY TO THE NORTH. POHNPEI AND KOSRAE WILL LIKELY 
NOT SEE ANY SIGNIFICANT RAINFALL EITHER WITH CONVECTION STAYING 
NORTH OF BOTH LOCATIONS. THE PRIMARY FORECAST UNCERTAINTY IS THE 
SURFACE WIND. GFS40...GFSE AND UKMET ALL DEPICT A BROAD LOW-LEVEL 
CIRCULATION FORMING ALONG 10N-11N NORTH OF KWAJALEIN BY TUESDAY... 
WHILE ECMWF JUST SHOWS AN OPEN TROUGH. EITHER WAY...WINDS ARE 
EXPECTED TO REMAIN UNDER 15 KT. DEPENDING ON THE DEGREE OF 
DEVELOPMENT THIS SYSTEM EXPERIENCES OVER THE NEXT COUPLE OF DAYS... 
EAST OR SOUTHEAST WINDS COULD SWING TO THE SOUTH...BUT WINDS WOULD 
REMAIN LIGHT TO GENTLE. 

&&

.WESTERN MICRONESIA...
WITH CONVECTION QUICKLY DEPARTING CHUUK...DECIDED TO DROP TO 
ISOLATED FOR TODAY BUT KEPT THE SLIGHT CHANCE FOR THUNDERSTORMS 
BASED ON PLACEMENT OF UPPER-LEVEL TROUGH. THE EXPANDING DRY SLOT 
OVER POHNPEI AND KOSRAE WILL CONTINUE TO ENVELOP CHUUK FOR THE NEXT 
SEVERAL DAYS SUPPRESSING SHOWER ACTIVITY. THE PRIMARY CONTRIBUTOR TO 
SCATTERED SHOWERS AT PALAU THROUGH MONDAY NIGHT WILL BE LOW-LEVEL 
CONVERGENCE OF SOUTH AND SOUTHWEST WINDS FLOWING NORTHWARD TOWARD 
TYPHOON MEGI. FOR YAP...MODELS MAY BE DOWNPLAYING THE TROUGH WEST OF 
CHUUK...BUT FOR NOW...DECIDED TO STICK WITH THEM AND CONTINUE 
ISOLATED SHOWERS AT YAP. DECIDED TO INCREASE SEAS SLIGHTLY FOR BOTH 
YAP AND PALAU FOR THE NEXT COUPLE DAYS DUE TO THE EFFECTS OF 
TYPHOON-GENERATED SWELL. WAVEWATCH MODEL DOES NOT YET SHOW ANY 
EFFECT FROM THE TYPHOON...BUT ALTIMETRY DATA DOES INDICATE THAT SEAS 
HEIGHTS ARE INCREASING SOME ACROSS MUCH OF THE PHILIPPINE SEA.

&&

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

$$

STANKO/W. AYDLETT

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