474
FXSA20 KWBC 061555
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1154 AM EDT MON OCT 06 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z OCTOBER 06). EXCELLENT AGREEMENT
OVER THE CONTINENT AND WESTERN ATLANTIC THROUGH DAY 05...WITH
SUBTLE DIFFERENCES OVER THE EASTERN PACIFIC GRADUALLY BECOMING
MORE PRONOUNCED BY 132-144 HRS. OVERALL...CONFIDENCE IN THE
FORECAST IS HIGH...AS THE ENSEMBLE MODELS CLUSTER IN FAVOR OF A
SIMILAR SOLUTION.
AT 500 HPA...A RIDGE OVER THE EASTERN PACIFIC GRADUALLY MOVES
INTO THE SOUTHERN CONE BY 54-60 HRS...TO THEN SETTLE OVER THE
WESTERN ATLANTIC BY 72-84 HRS. IT WILL THEN PERSIST THROUGH 120
HRS. NORTHERN STREAM VORTICES WILL ERODE/WEAKEN AS THEY PUSH
AGAINST THIS AXIS...WITH ONE TO ENTER CENTRAL/NORTHERN CHILE BY
42-48 HRS. BY 60-72 HRS THIS VORTEX IS TO RAPIDLY DECAY AS IT
MOVES ACROSS PARAGUAY TO SOUTHEAST BRASIL. AS IT ENTERS THE
CONTINENT...THIS VORTEX WILL SUSTAIN ISOLATED TO SCATTERED
CONVECTION...WITH MOST INTENSE BETWEEN SALTA-NORTHERN MENDOZA IN
ARGENTINA WHERE IT WILL FAVOR RAINFALL AMOUNTS OF 05-10MM ON DAY
02. THIS...HOWEVER...WILL SET THE STAGE FOR A STRONGER VORTEX TO
FOLLOW. THE LATTER WILL ENTER CENTRAL/NORTHERN CHILE BY 78-84
HRS....AND IT IS TO ENTER NORTHWEST ARGENTINA/SOUTHERN BOLIVIA BY
96 HRS. BY 120 HRS IT WILL CONTINUE ACROSS SOUTHERN
BRASIL/URUGUAY. IN CONTRAST TO THE FORMER...THE LATTER WILL BE
MORE ACTIVE AS IT MOVES ACROSS MESOPOTAMIA VALLEY AND SOUTHEAST
BRASIL. IN THIS AREA MOISTURE WILL BE PLENTIFUL...AND CONDITIONS
WILL TEND TO FAVOR ORGANIZED DEEP CONVECTION. AS A RESULT...WE
PROJECT RAINFALL AMOUNTS OF 20-40MM/DAY TO AFFECT THE SOUTHERN
STATES OF BRASIL...AND AS FAR NORTH AS SAO PAULO.
ON THE SOUTHERN STREAM...THE AFOREMENTIONED MID LEVEL RIDGE WILL
GENERALLY FORCE SOUTHERN STREAM PERTURBATIONS TO STREAK ACROSS
THE DRAKE PASSAGE AND TIERRA DEL FUEGO. THIS PATTERN IS TO HOLD
TRUE DURING THE NEXT THREE DAYS. ON DAY 04...HOWEVER...A STRONGER
VORTEX WILL ENTER THE DOMAIN...AND IT WILL MOVE ACROSS THE
ANTARCTIC PENINSULA AND INTO THE SOUTHERN CONE BY 120 HRS. THE
ASSOCIATED FRONT ENTERS SOUTHERN CHILE BY 108 HRS...AND NORTH
INTO PATAGONIA THROUGH 120 HRS. SCATTERED CONVECTION WILL
CONCENTRATE OVER CHILE SOUTH OF TEMUCO/CONCEPCION...WITH RAINFALL
MAXIMA OF 10-15MM/DAY.
OVER THE WESTERN ATLANTIC...ON THE NORTHERN STREAM FLOW...A MID
LEVEL TROUGH IS ANALYZED OFF THE COAST OF ARGENTINA...WITH AXIS
TRAILING TO BUENOS AIRES PROVINCE/RIO DE LA PLATA. THE TROUGH IS
SLOW TO EVOLVE...WITH AXIS TO DRIFT BETWEEN 50-W20W AND SOUTH OF
25S BY 72 HRS. AFTER 84 HRS IT WILL GAIN MOMENTUM...TO ACCELERATE
ACROSS 25W BY 96 HRS...AND ACROSS 05W/10W BY 120 HRS. THE
ASSOCIATED FRONT WILL EXTEND ACROSS RIO DE LA PLATA/LA PAMPA TO
PATAGONIA IN ARGENTINA BY 24 HRS...AND THROUGH 48 HRS IT WILL
PUSH NORTH ACROSS RIO GRANDE DO SUL/LOWER MESOPOTAMIA TO CORDOBA
IN ARGENTINA. UNDER INFLUENCE OF A BUILDING RIDGE OVER THE
WESTERN ATLANTIC/SOUTHERN CONE...THE FRONT WILL THEN MOVE FARTHER
NORTH INTO SAO PAULO IN BRASIL...WHERE IT IS TO GRADUALLY MERGE
WITH/REINFORCE AND OLD BOUNDARY. THE LATTER IS TO MEANDER ACROSS
THE SOUTH ATLANTIC TO RIO DE JANEIRO/NORTHERN SAO PAULO...THEN
NORTHWEST ACROSS MATO GROSSO TO RONDONIA/NORTHERN BOLIVIA-CENTRAL
PERU. THE BOUNDARY REMAINS QUASISTATIONARY WHILE GRADUALLY
WEAKENING OVER THE CONTINENT THROUGH 72-84 HRS. HOWEVER...IT IS
TO PERSIST/REMAIN WELL ORGANIZED OVER THE WESTERN ATLANTIC AND
INTO RIO DE JANEIRO/SOUTHERN ESPIRITO SANTO THROUGH AT LEAST 120-
132 HRS. MOST ACTIVE CONVECTION IS EXPECTED EARLY IN THE
CYCLE...WHEN IT WILL SUSTAIN SCATTERED CONVECTION ACROSS CENTRAL
BRASIL WITH MAXIMA OF 20-35MM/DAY. AFTER 36-48 HRS CONVECTION
WILL CONCENTRATE OVER RIO DE JANEIRO/SOUTHERN MINAS GERAIS WITH
DAILY MAXIMA OF 10-15MM. A SURGE IN ACTIVITY IS EXPECTED LATER IN
THE PERIOD WHEN A MID/UPPER LEVEL SHORT WAVE TROUGH FAVORABLY
INTERACTS WITH THIS BOUNDARY TO SUSTAIN MAXIMA OF 20-40MM. OTHER
CONVECTION IS EXPECTED ON THE CENTRAL/SOUTHERN JUNGLE OF PERU
EARLY THIS CYCLE...WITH MAXIMA OF 30-60MM. THIS IS TO GRADUALLY
DECREASE TO 10-15MM/DAY BY 60 HRS. OVER NORTHERN JUNGLE OF PERU
AND NORTHERN AMAZONAS IN BRASIL MAXIMA OF 40-80MM/DAY IS FORECAST
THROUGH 36 HRS...TO DECREASE TO 25-50MM/DAY BY 60 HRS.
AFTERWARDS...MAXIMA IN THIS REGION WILL PEAK AT 20-35MM/DAY.
AT 200 HPA...THE SUBTROPICAL RIDGE DIVIDES IN TWO CELLS...WITH
ONE OVER THE EASTERN TROPICAL PACIFIC AND THE OTHER OVER THE
TROPICAL ATLANTIC. AS CONVECTION OVER PERU/WESTERN BRASIL BECOMES
MORE ACTIVE...THE SUBTROPICAL RIDGE OVER THE ATLANTIC WILL
GRADUALLY BUILD INLAND ACROSS NORTHERN BRASIL ALONG 10S TO
PARA/AMAZONAS IN BRASIL...WITH A CLOSED HIGH TO CENTER NEAR 06S
55W. BUT BY 84-96 HRS IT WILL EVOLVE INTO AN OPEN RIDGE. AREAS OF
MOST ACTIVE CONVECTION WILL ASSOCIATE WITH FRONTAL INCURSION OVER
BRASIL EARLY IN THE PERIOD. BY MID CYCLE...TROPICAL CONVECTION IS
TO GENERALLY CONFINE TO AREA NORTH OF 05S...WITH CLUSTERS OF DEEP
CONVECTION TO SUSTAIN RAINFALL MAXIMA OF 20-35MM/DAY. OTHER
CONVECTION IS EXPECTED ACROSS ILHA DE MARAJO...WITH MAXIMA OF 10-
15MM/DAY THROUGH DAY 03.
URRA...DMC (CHILE)
MOREYRA...SENAMHI PERU
DAVISON...HPC (USA)
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