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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1613Z May 21, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1213 PM EDT MON MAY 21 2018

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM MAY 21 AT 0000 UTC): A BROAD
MID/UPPER LEVEL TROUGH IS INITIALIZED ACROSS ARGENTINA TO THE
WESTERN ATLANTIC...WITH AXIS TO MEANDER EAST ACROSS 40W LATER ON
WEDNESDAY. THIS IS TO GRADUALLY DEEPEN AS IT CONTINUES EAST ACROSS
20W ON FRIDAY EVENING. AT LOW LEVELS THE MID LEVEL TROUGH SUSTAINS
A DEEPENING LOW OFF THE COAST OF URUGUAY/BUENOS AIRES. BUILDING
POLAR RIDGE OVER MID SECTIONS OF SOUTH AMERICA WILL THEN DISPLACE
THIS AXIS FARTHER OFFSHORE THROUGH WEDNESDAY EVENING. UNDER
INFLUENCE OF THE LOW LEVEL RIDGE A DRYER AIR MASS IS TO THEN
ADVECT ACROSS MID SECTIONS OF SOUTH AMERICA...A PATTERN THAT HOLDS
TROUGH THE END OF THE WEEK.

AN OLD FRONT TO THE EAST AND NORTH EXTENDS ACROSS THE SOUTH
ATLANTIC TO BAHIA-CENTRAL BRASIL. PORTION OF THIS BOUNDARY OVER
THE CONTINENT IS LOSING ITS UPPER LEVEL SUPPORT...AND THROUGH
TUESDAY IT IS EXPECTED TO FRONTOLIZE. REMAINING SEGMENT OVER THE
ATLANTIC IS EXPECTED TO PERSIST THROUGH THE END OF THE WEEK. AS IT
MEANDERS ALONG THE COAST OF BAHIA THIS IS TO ENHANCE LOW LEVEL
MOISTURE CONVERGENCE...TO FAVOR MODERATE RAINFALL AMOUNTS. EARLY
IN THE CYCLE EXPECTING ACCUMULATION OF 10-15MM/DAY. THROUGH
WEDNESDAY THIS INCREASES TO 20-40MM...WITH POTENTIAL FOR LOCALLY
HIGHER RAINFALL AMOUNTS.

DURING MEDIUM RANGE PERIOD...THE GLOBAL MODELS AGREE ON AN
ENHANCED RISK OF EXPLOSIVE CYCLOGENESIS ACROSS THE EASTERN
PACIFIC...WITH A LOW TO THE WEST-NORTHWEST OF ARCHIPELAGO DE JUAN
FERNANDEZ ON WEDNESDAY TO RAPIDLY DEEPEN AS IT NEARS SOUTHERN
CHILE EARLY ON FRIDAY MORNING. AS IT MOVES ACROSS THE SOUTHERN
CONE THIS WILL BE ACCOMPANIED BY TROPICAL STORM INTENSITY WINDS OF
40-60KT. UNDER FAVORABLE JET DYNAMICS THIS IS TO SUSTAIN MODERATE
TO HEAVY RAINFALL AMOUNTS BETWEEN PUERTO MONTT AND ISLA DE
CHILOE...WITH MAXIMA OF 20-35MM ON THURSDAY AND 20-40MM ON FRIDAY.
NOTE THAT THE STABILITY INDICES SHOW PROBABLE THUNDERSTORMS AS IT
MAKES LANDFALL EARLY ON FRIDAY.

NORTH OVER THE CONTINENT...AT 200 HPA...A BROAD/LOW AMPLITUDE
RIDGE IS TO DOMINATE THE FLOW TO THE NORTH OF 10S. THIS IS TO VENT
DIURNAL CONVECTION ALONG THE NORTH COAST OF BRASIL...PARA/RORAIMA
AND AMAZONAS-SOUTHERN COLOMBIA/NORTHERN PERU-EASTERN ECUADOR.
ACROSS PARA EXPECTING MAXIMA OF 20-40MM OVER THE NEXT COUPLE OF
DAYS...WITH POTENTIAL FOR HIGHER AMOUNTS LATER IN THE WEEK.
LIKEWISE ACROSS AMAZONAS-SOUTHERN COLOMBIA/NORTHERN PERU...WHERE
THE MAXIMA INCREASES FROM 15-20MM/DAY EARLY IN THE CYCLE TO
30-60MM BY THE END OF THE WEEK.

BALBINO...INMET (BRASIL)
DIAZ...INUMET (URUGUAY)
DAVISON...WPC (USA)