Subject: Western Pacific: Synoptic Discussion For The Marianas

From: LDM Weather <[email-masked]>
Date: Thu, 16 Sep 2010 03:13:15 -0500

885 
FXPQ60 PGUM 160813
AFDPQ 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
613 PM CHST THU SEP 16 2010

.SYNOPSIS...LATEST SATELLITE AND RADAR SHOW THE MARIANAS...
ESPECIALLY IN THE GUAM AND ROTA ZONES...ARE STILL UNDER THE
INFLUENCE OF A SLOW MOVING UPPER TROUGH...NOW WEST OF THE ISLANDS.
POSSIBILITY OF THUNDERSTORMS REMAINS FOR THE NEXT SEVERAL DAYS...
AND THE ADDITION OF SCATTERED SHOWERS BY SUNDAY INTO MONDAY FOR A
WEAK WESTERLY-MOVING DISTURBANCE CURRENTLY JUST EAST OF 150E.

&&

.DISCUSSION...YET TO SEE HOW MUCH RAIN WE GET FROM THE WEAKLY
DEFINED DISTURBANCE NOW LOCATED BETWEEN 150E AND 160E THAT WAS FORMERLY
DESCRIBED BY JTWC AS 98W. EVIDENCE OF A CIRCULATION NO LONGER
EXIST BUT MODELS ARE CONSISTENT WITH BRINGING SOMETHING IN ON
SUNDAY. THE EXACT TIMING AND THE AMOUNT OF MOISTURE DEPENDS ON THE
MODEL WITH THE ECMWF THE MOST AGGRESSIVE...AS ALWAYS. WATER VAPOR
IMAGERY SHOWS PLENTY OF MOISTURE CONVERGENCE ALONG THE SOUTHERN
AND EASTERN PERIPHERY OF THE UPPER TROUGH LEADING INTO THE DISTURBANCE
THAT I THINK IT A GOOD BET FOR THE MARIANAS WATERS IN GENERAL AND GUAM...
WITH ITS ISLAND HEATING...IN PARTICULAR TO HAVE A CHANCE OF THUNDERSTORMS
EACH OF THE NEXT 3-4 DAYS.  IF THE SCENARIO GOES AS PLANNED...WEATHER
SHOULD GO BACK TO THE RAINY SEASON VERSION OF TRADE-WIND SHOWERS BY
TUESDAY. NO SIGNIFICANT FEATURE IS INDICATED AFTER THIS TIME FRAME BY
ANY NWP MODEL. WAVES AND SEAS ARE EXPECTED TO REMAIN LOW DURING
THIS FORECAST PERIOD. LITTLE TO NO INFLUENCE IS EXPECTED FROM TYPHOON
FANAPI...TOO SMALL AND TOO FAR AWAY.

&&

.EASTERN MICRONESIA...
LITTLE CHANGE TO PRIOR FORECAST AND REASONING. THE SOUTHWESTERN
END OF THE SUB-TROPICAL RIDGE IS PERSISTING OVER THE PHILIPPINE
SEA JUST NORTH OF WESTERN MICRONESIA. THIS FEATURE IS CREATING A
BLOCKAGE AGAINST THE TRADE-WIND FLOW OVER EASTERN MICRONESIA. IN
RESPONSE... SURFACE IMPULSES ARE FORMING ALONG THE TRADE
CONVERGENCE ZONE FROM CHUUK STATE EASTWARD TO THE DATE LINE.
EXPECT PERIODS OF SHOWERS AND ISOLATED THUNDERSTORMS FOR POHNPEI
INTO THE WEEKEND...AND FOR KOSRAE AND MAJURO THRU TONIGHT. THEN A
DRIER SOUTHEASTERLY TRADE SURGE WILL PROMOTE A BRIEF MOMENT OF
FAIRER WEATHER FOR BOTH MAJURO AND KOSRAE FRIDAY AND SATURDAY.
WITH THE SUB-TROPICAL RIDGE WEAKENING BY EARLY NEXT WEEK...GENTLE
TO MODERATE TRADES SHOULD RETURN TO THE REGION FROM EAST TO WEST.
HOWEVER...AN UPPER-LEVEL TROUGH DIGGING SOUTHWESTWARD FROM EAST
OF WAKE ISLAND CAN ENHANCE TRADE-WIND SHOWER ACTIVITY FOR MAJURO
AND KOSRAE. THIS SCENARIO WILL ALSO PROLONG SHOWERY CONDITIONS
FOR POHNPEI AND CHUUK AS WELL.

&&

.WESTERN MICRONESIA...
AN AREA OF SURFACE CONVERGENCE BETWEEN TRADE WINDS AND THE
AFOREMENTIONED SUB-TROPICAL RIDGE IS VISIBLE ON BOTH ASCAT AND
SATELLITE IMAGERY. THIS AREA IS NOW WEST OF KOROR WITH KOROR
TEMPORARILY IN THE CLEAR...BUT WITH A TROUGH APPROACHING BUT
BLOCKED BY THE RIDGE TO THE WEST. YAP IS NORTH OF MOST OF THE
ACTIVITY THIS EVENING. AS A SURFACE TROUGH MOVES WESTWARD IT WILL
CAUSE THE CONVERGENCE ZONE TO SHIFT NORTHWARD AND BRING WIDELY
SCATTERED SHOWERS OVER YAP. TEAMING UP WITH AN UPPER TROUGH
MOVING THROUGH THE AREA...SPORADIC CONVECTION WILL CONTINUE FOR
BOTH LOCATIONS THRU FRIDAY. LATEST WV IMAGERY REVEALS AN AREA OF
MUCH DRIER AIR TRAILING BEHIND THE SURFACE TROUGH SOUTHEAST OF
YAP AND KOROR. THIS ELEMENT CAN BRIEFLY DECREASE SHOWER COVERAGE
OVER THE WEEKEND BUT A WETTER PATTERN WILL LIKELY RETURN BY NEXT
WEEK AS MORE DISTURBANCES ARE PRESENT UPSTREAM.

&&

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

$$

EDSON/DEVITA

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
To unsubscribe from WX-TROPL send e-mail to [email-masked] with
"unsub wx-tropl" in the body of your message. For help with WX-TROPL
write to [email-masked]. For more information on tropical weather products, see the NHC Homepage at http://www.nhc.noaa.gov.