531
FXSA20 KWBC 081642
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1241 PM EDT WED OCT 08 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z OCTOBER 08). THE MODELS MADE
MINOR CORRECTIONS TO PREVIOUS CYCLE...AS THEY GENERALLY
REMAIN IN EXCELLENT AGREEMENT THROUGH 120 HRS. VARIABILITY
AMONG THE ENSEMBLE MODELS IS SMALL...SO CONFIDENCE IN THE
FORECAST REMAINS HIGH.
AT 500 HPA...A LONG WAVE RIDGE EXTENDS OVER THE SOUTHERN CONE/
WESTERN ATLANTIC...AND IT IS TO MOVE EAST INTO THE WESTERN
ATLANTIC EARLY THIS CYCLE...WHERE IT WILL PERSIST THROUGH 84-96
HRS. AT LOW LEVELS IT WILL REFLECT AS A BROAD SURFACE RIDGE...
WITH MODELS SHOWING A MASSIVE 1033-1035 HPA HIGH CLOSING OVER THE
WESTERN ATLANTIC BY 48-72 HRS. THIS WILL ESTABLISH/SUSTAIN A
WARM/MOIST NORTHERLY FLOW ACROSS PARAGUAY TO NORTHERN/CENTRAL
ARGENTINA LATER IN THE CYCLE.
ON THE NORTHERN STREAM...SHORT WAVE VORTICES CONTINUE TO PUSH
EAST AGAINST THIS RIDGE. ONE ENTERED CENTRAL/NORTHERN CHILE...AND
THROUGH 24 HRS IT WILL MOVE ACROSS CHACO ARGENTINO/PARAGUAY...BUT
AS IT ENTERS SOUTHERN BRASIL BY 30-36 HRS...THIS TROUGH IS
FORECAST TO WEAKEN/FILL. CONVECTION...IF ANY...WILL LIMIT TO
NORTHWEST ARGENTINA EARLY THIS PERIOD. THIS PERTURBATION...
HOWEVER...SET THE STAGE FOR A STRONGER VORTEX TO FOLLOW. THE
LATTER WILL ENTER CENTRAL/NORTHERN CHILE BY 36 HRS. IT WILL MOVE
INLAND ACROSS 65W TO NORTHWEST ARGENTINA/SOUTHERN BOLIVIA BY 54-
60 HRS. THROUGH 72 HRS IT WILL CONTINUE EAST ACROSS SOUTHERN
BRASIL/URUGUAY...TO MOVE OFF THE SOUTHERN COAST OF BRASIL BY 96-
108 HRS. 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 PARAGUAY-THE
SOUTHERN STATES OF BRASIL...AND AS FAR NORTH AS SAO PAULO.
PROGRESSIVE SOUTHERN AND NORTHERN STREAM PERTURBATIONS WILL
CONTINUE TO ENTER SOUTHERN CHILE/PATAGONIA OVER THE NEXT COUPLE
OF DAYS...WITH A STRONG/HIGH AMPLITUDE TROUGH TO MOVE ACROSS 90W
BY 36-48 HRS. THE TROUGH WILL CONTINUE ACROSS 80W BY 72 HRS...
WITH A LOW FORMING/CLOSING NEAR 42S 78W. THIS LOW WILL EJECT
ACROSS PATAGONIA BY 96-108 HRS. A SECONDARY VORTEX WILL FOLLOW...
WITH MODELS FORECASTING A LOW TO MOVE NEAR 40S 85W BY 96 HRS.
THIS IS SLIGHTLY DEEPER/STRONGER THAN WHAT THE MODELS PREVIOUSLY
INDICATED...AND IT IS LIKELY TO STALL OFF THE COAST OF CHILE JUST
WEST OF PUERTO MONTT/TEMUCO. THE COMBINATION OF THESE
PERTURBATIONS WILL HELP SUSTAIN A BROAD/LOW AMPLITUDE TROUGH OVER
THE FAR EASTERN PACIFIC AND THE SOUTHERN CONE. AT LOW LEVELS
EXPECT A PROGRESSIVE FRONT TO ENTER SOUTHERN CHILE BY 48-60
HRS...AND TO EJECT ACROSS PATAGONIA TO LA PAMPA/CENTRAL CHILE BY
72 HRS...TO CONTINUE NORTH ACROSS BUENOS AIRES PROVINCE/CORDOBA
BY 96 HRS...AND INTO URUGUAY/RIO GRANDE DO SUL-NORTHWEST
ARGENTINA BY 120 HRS. ACROSS SOUTHERN CHILE THIS WILL FAVOR
SCATTERED CONVECTION WITH ACCUMULATION OF 15-30MM/DAY... WHILE
OVER LA PAMPA/NORTHERN PATAGONIA MAXIMA WILL PEAK AT 10-20MM. AS
IT MOVES NORTH ACROSS CENTRAL ARGENTINA...SCATTERED DEEP
CONVECTION WILL PRECEDE/ACCOMPANY THIS FRONT...WITH MAXIMA OF 20-
35MM ON DAY 04 AND 30-60MM/DAY ON DAY 05. ALTHOUGH STABILITY
INDICES DO NOT SUGGEST POSSIBILITY OF SEVERE CONVECTION...IN A
STRONG SHEARED ENVIRONMENT...THERE IS A GOOD CHANCE OF SEVERE
THUNDERSTORMS FORMING AHEAD OF THIS FRONT.
OVER THE WESTERN ATLANTIC...ON THE NORTHERN STREAM FLOW...A MID
LEVEL TROUGH REMAINS OFF THE COAST OF ARGENTINA...WITH AXIS
TRAILING TO SOUTHERN BRASIL. THE TROUGH IS TO SLOWLY EVOLVE OVER
THE NEXT FEW DAYS...WITH AXIS TO DRIFT BETWEEN 50W-20W AND SOUTH
OF 25S BY 24 HRS. AFTER 36 HRS IT WILL GAIN MOMENTUM...TO
ACCELERATE ACROSS 25W BY 48 HRS...AND ACROSS 05W/10W BY 72 HRS.
THE ASSOCIATED FRONT WILL PUSH NORTH ACROSS SOUTHEAST BRASIL...TO
THEN MERGE WITH AN OLD BOUNDARY OVER NORTHERN SAO PAULO/SOUTHERN
MINAS GERAIS TO MATO GROSSO DO SUL. THIS BOUNDARY REMAINS
QUASISTATIONARY WHILE GRADUALLY WEAKENING OVER THE CONTINENT
THROUGH 24-36 HRS. HOWEVER...IT IS TO PERSIST/REMAIN WELL
ORGANIZED OVER THE WESTERN ATLANTIC AND INTO RIO DE
JANEIRO/SOUTHERN ESPIRITO SANTO THROUGH AT LEAST 96 HRS.
SCATTERED CONVECTION WILL AFFECT NORTHERN SAO PAULO-SOUTHERN
MINAS GERAIS...WHERE IT WILL SUSTAIN MAXIMA OF 10-15MM/DAY. A
SURGE IN ACTIVITY...HOWEVER...IS EXPECTED BY 36-60 HRS...WHEN
MAXIMA WILL INCREASE TO 20-35MM. OTHER CONVECTION IS EXPECTED ON
THE CENTRAL/SOUTHERN JUNGLE OF PERU...WITH MAXIMA OF 05-15MM/DAY.
MOST ACTIVE WILL FALL FARTHER NORTH...ACROSS NORTHERN PERU-
SOUTHERN COLOMBIA-NORTHERN AMAZONAS BRASIL...WITH MAXIMA OF 25-
50MM/DAY THROUGH 36 HRS...AND 20-40MM/DAY AT 36-60 HRS.
AT 200 HPA...THE SUBTROPICAL RIDGE ESTABLISHED OVER THE
CONTINENT...TO CENTER/ANCHOR ON A CLOSED HIGH NEAR 08S 57W. BUT
THIS WILL BE SHORT LIVED...WITH THE HIGH TO COLLAPSE TO AN OPEN
RIDGE BY 24-48 HRS. THIS THEN BECOMES NARROW AND ELONGATED DURING
THE SECOND HALF OF THE CYCLE. 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 01...AND AGAIN LATER THIS CYCLE.
URRA...DMC (CHILE)
MOREYRA...SENAMHI PERU
DAVISON...HPC (USA)
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