SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1159 AM EST FRI FEB 10 2012
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
 
NOTE: MODELS SHOWING DEEP LOW FORMING OFF THE COAST OF URUGUAY
EARLY IN THE CYCLE. THIS IS NOW EXPECTED TO RETAIN EXTRATROPICAL
CYCLONE CHARACTERISTICS. AS IT DEEPENS...IT WILL SUSTAIN STRONG
BOUNDARY LAYER WINDS THAT ARE TO PEAK AT 35-45KT. THE GOVERNMENT
OF BRASIL WILL ISSUE MARINE ADVISORIES ON THIS SYSTEM.

MODEL COMPARISON (VALID FROM 00 UTC FEB 10): MODELS AGREE ON
PATTERN EVOLUTION THROUGH 168 HRS. CONFIDENCE IN THE FORECAST IS
HIGH.

A MID LEVEL TROUGH ON THE NORTHERN STREAM WILL GRADUALLY DEEPEN
AS IT MEANDERS OFF THE COAST OF URUGUAY/RIO GRANDE DO SUL. A
LOW NEAR 33S 50W IS TO ANCHOR THIS SYSTEM DURING THE NEXT COUPLE
OF DAYS...EXTENDING A TROUGH NORTH TO THE SOUTHERN STATES OF
BRASIL. BY 72-84 HRS IT IS TO THEN FILL TO AN OPEN TROUGH WHILE
IT BEGINS TO PULL TO THE EAST-SOUTHEAST AHEAD OF AN AMPLIFYING
POLAR TROUGH TO THE SOUTH. AT LOW LEVELS...THE TROUGH ALOFT IS
INTERACTING WITH A SURFACE FRONT...SUSTAINING A FRONTAL LOW THAT
QUICKLY DEEPENS/OCCLUDES THROUGH 12UTC TOMORROW MORNING. THIS IS
TO EXTEND A FRONT ACROSS PARANA/SOUTHERN SAO PAULO TO MATO GROSSO
DO SUL IN BRASIL EARLY IN THE PERIOD...WITH BOUNDARY TO GRADUALLY
WEAKEN TO AN OPEN TROUGH. AS UPPER WIND SHEAR IS FORECAST TO
PERSIST...THE RISK OF THIS SYSTEM THEN EVOLVING INTO A
SUBTROPICAL CYCLONE IS SMALL. STRONG WINDS ON THE PERIPHERY OF
THE SURFACE LOW WILL AFFECT URUGUAY-RIO GRANDE DO SUL IN BRASIL
DURING THE NEXT 36 HRS...TO FAVOR SCATTERED CONVECTION WITH
ACCUMULATION OF 10-15MM/DAY. MOST ACTIVE CONVECTION IS EXPECTED
ACROSS PARANA-SAO PAULO...AS UPPER TROUGH IN INTERACTION WITH
SURFACE FRONT/TROUGH SUSTAINS HEAVY CONVECTION WITH ACCUMULATION
OF 25-50MM/DAY. THIS WILL PERSIST THROUGH 60-72 HRS. LOCALLY
HIGHER AMOUNTS ARE HIGHLY LIKELY ALONG THE COAST/SERRA DO MAR IN
BRASIL.

AT MID/UPPER LEVELS...A BROAD/LOW AMPLITUDE TROUGH DOMINATES THE
FLOW ACROSS THE SOUTHEAST PACIFIC/DRAKE PASSAGE. SHORT WAVE
PERTURBATIONS REVOLVE AROUND THIS AXIS...WITH A STRONG ONE
FORECASTED TO ENTER SOUTHERN CHILE/PATAGONIA IN ARGENTINA
BY 54-60 HRS. THIS WILL THEN PULL ACROSS 50W BY 72 HRS...TO REACH
30W AT 96 HRS. THE TROUGH WILL SUSTAIN A POLAR FRONT ACROSS
PATAGONIA IN ARGENTINA/SOUTHERN CHILE EARLY IN THE CYCLE...WITH
BOUNDARY TO UNDULATE NORTH ACROSS LA PAMPA TO SOUTHERN BUENOS
AIRES PROVINCE IN ARGENTINA BY 48-72 HRS...WHERE IT IS TO THEN
STALL THROUGH 96-108 HRS. THIS IS TO SUSTAIN STRONG BOUNDARY
LAYER WINDS AND MODERATE TO HEAVY RAINFALL AMOUNTS. DAILY MAXIMA
ACROSS SOUTHERN CHILE WILL PEAK AT 10-15MM/DAY. OVER LA
PAMPA/SOUTHERN BUENOS AIRES IN ARGENTINA EXPECTING RAINFALL
AMOUNTS OF 05-10MM/DAY IN SCATTERED CONVECTION.

AT 200 HPA...THE BOLIVIAN HIGH IS TO MEANDER OVER NORTHERN
CHILE/WESTERN BOLIVIA EARLY IN THE CYCLE. THIS WILL ANCHOR A
RIDGE OVER THE CONTINENT THAT IS TO EXTENDS BETWEEN 30S-15S. THE
HIGH IS TO THEN MEANDER BETWEEN NORTHERN CHILE-SOUTHERN PERU-
WESTERN BOLIVIA THROUGH 120-132 HRS. MODELS NOW SHOW GRADUAL
INTENSIFICATION OF THIS RIDGE...AND DURING THE SECOND HALF OF THE
FORECAST IT IS TO EXTEND ACROSS THE CONTINENT TO THE NORTH OF 35S
AND WEST OF 50W. AS IT MEANDERS ACROSS MID SECTIONS OF SOUTH
AMERICA...THE RIDGE ALOFT WILL VENT LATE AFTERNOON CONVECTION
ACROSS NORTHWEST ARGENTINA...WHERE IT IS TO GENERALLY FAVOR
RAINFALL AMOUNTS OF 10-15MM/DAY. AS IT SUSTAINS AN EASTERLY FLOW
ACROSS BRASIL...THIS WILL ENHANCE MOISTURE CONVERGENCE ACROSS
WESTERN BRASIL-PERUVIAN JUNGLE/SIERRA. IN THIS AREA ACTIVITY
BECOME MORE ACTIVE/BETTER ORGANIZED THROUGH 48-72 HRS...WITH
RAINFALL MAXIMA TO PEAK AT 30-60MM/DAY. AS THE RIDGE OVER THE
CONTINENT BUILDS/INTENSIFIES...A DEEP LOW ALOFT IS TO ESTABLISH
OFF THE NORTHEAST COAST OF BRASIL. THROUGH 72-96 HRS THE
LOW/TROUGH WILL DRIFT EAST TOWARDS NORTHEAST BRASIL. AS THE
TROUGH MEANDERS ACROSS NORTHEAST BRASIL...IT WILL ENHANCE
CONVECTIVE ACTIVITY...TO SUSTAIN MAXIMA OF 20-35MM/DAY.

GONZALEZ...SHIN (ARGENTINA)
VILLELA...INMET (BRASIL)
DAVISON...HPC (USA)