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South American Forecast Discussion
 
(Latest Discussion - Issued 1704Z Mar 22, 2019)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
104 PM EDT FRI MAR 22 2019

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

MODEL DISCUSSION FROM MAR 22/00 UTC: GLOBAL MODELS AND ENSEMBLE
MEMBERS ARE IN GENERAL GOOD AGREEMENT ON THE EVOLUTION OF THE
FORECAST THROUGH 120 HRS. AN EXCEPTION ARE PROBLEMS IN THE
ATLANTIC BY 72 HRS WITH REGARD TO THE EVOLUTION OF AN
EXTRATROPICAL CYCLONE NEAR/TO THE SOUTHEAST OF THE RIO DE LA
PLATA. ALSO...MODELS ARE IN LESS AGREEMENT THAN YESTERDAY
REGARDING THE POTENTIAL TROPICAL CYCLOGENESIS OFF THE COAST OF
BAHIA/ESPIRITO SANTO ON SUNDAY AND MONDAY. THE GFS IS THE WEAKEST
MODEL WITH THIS EVOLUTION WHILE THE UKMET CONTINUES BEING THE MOST
AGGRESSIVE.

A PROGRESSIVE SHORT WAVE TROUGH IS ENTERING THE SOUTHERN CONE ON
FRIDAY/EARLY SATURDAY. THE TROUGH IS FORECAST TO LIFT TO THE
NORTHEAST ALONG THE COAST OF PATAGONIA INTO THE SOUTHERN BUENOS
AIRES PROVINCE THROUGH EARLY SUNDAY. AT LOW-LEVELS...THE TROUGH
WILL INDUCE CYCLOGENESIS OFF THE COAST OF PATAGONIA...AND A
PROGRESSIVE FRONT THAT WILL RAPIDLY MOVE FROM NORTHERN PATAGONIA
ON SATURDAY MORNING...TO THE CENTRAL BUENOS AIRES PROVINCE AND
WEST INTO SOUTHERN MENDOZA BY SATURDAY EVENING...TO NORTHERN
URUGUAY...CORDOBA BY SUNDAY MORNING. INITIALLY...AS THE SYSTEM
ENTERS SOUTHERN CHILE...IT WILL SUSTAIN SCATTERED CONVECTION WITH
ACCUMULATIONS OF 05-10MM/DAY. IN ARGENTINA AND URUGUAY...GIVEN THE
LIMITED AMOUNTS OF AVAILABLE MOISTURE...EXPECTING ALSO MAXIMA
CONSTRAINED TO THE 05-10MM/DAY IN ASSOCIATION WITH THIS SYSTEM.

THE MOST ACTIVE CONVECTION AND ASSOCIATED PRECIPITATION IS
CLUSTERING IN TROPICAL PORTIONS OF SOUTH AMERICA. THE SUBTROPICAL
UPPER RIDGE LIES ELONGATED FROM A HIGH OVER/OFF THE COAST OF BAHIA
IN BRASIL...ALONG MATO GROSSO...NORTHERN BOLIVIA AND INTO SOUTHERN
PERU. THIS IS INTERACTING WITH THE SUBEQUATORIAL RIDGE THAT
EXTENDS ALONG THE EQUATORIAL ATLANTIC...TO SUSTAIN AN ENHANCED
VENTILATION PATTERN ACROSS NORTHEASTERN AND NORTH-CENTRAL BRASIL.
AT LOW-LEVELS...THE MOST SIGNIFICANT FEATURE IS THE SOUTH ATLANTIC
CONVERGENCE ZONE THAT HAS FORMED ACROSS NORTHERN ESPIRITO SANTO
INTO NORTHERN MATO GROSS AND RONDONIA IN BRASIL. THE PERSISTENCE
OF THE SACZ AND ENHANCED UPPER VENTILATION IN EASTERN BRASIL WILL
SUSTAIN A VERY WET PATTERN IN THESE REGIONS...WHERE EXPECTING
MAXIMA IN THE 40-80MM/DAY RANGE. LARGER AMOUNTS
ARE...HOWEVER...EXPECTED IN NORTHERN ESPIRITO SANTO AND BAHIA. IN
THESE REGIONS...PERSISTENT 25-30KT SOUTHEASTERLY TRADES WILL
ENHANCE MOISTURE CONVERGENCE TO SUSTAIN ISOLATED MAXIMA OF
75-150MM/DAY ON FRIDAY-SATURDAY...MAXIMA OF 40-80MM/DAY BY
SUNDAY-MONDAY. ALSO...WARM SEA SURFACE TEMPERATURE ANOMALIES HAVE
SET THE SSTS OVER 29C OFF THE COASTS OF BAHIA AND ESPIRITO SANTO.
UNDER THE INFLUENCE OF THE SACZ TROUGH...ENHANCED DEEP
CONVECTION...AND LIMITED UPPER SHEAR...THE ENVIRONMENT IS APPEARS
FAVORABLE FOR FORMATION OF A TROPICAL CYCLONE OFF THE COASTS OF
BAHIA AND NORTHERN ESPIRITO SANTO BY THE LATE WEEKEND/EARLY NEXT
WEEK. IF A CYCLONE FORMS...THE HYDROGRAPHIC CENTER OF THE
BRAZILIAN NAVY WILL ISSUE THE REQUIRED ADVISORIES.

ALSO IN TROPICAL SOUTH AMERICA...ACTIVE CONVECTION WILL CONTINUE
ALONG THE EXTREME WESTERN AMAZON. EXPECTING ACCUMULATIONS OF
25-50MM/DAY ON FRIDAY INCREASING TO MAXIMA OF 30-60MM/DAY BY
SATURDAY-SUNDAY...DECREASING TO MAXIMA OF 15-30MM/DAY
SUNDAY-MONDAY.

A SYSTEM OF INTEREST IS A SHORT WAVE MID/UPPER LEVEL TROUGH
APPROACHING THE ALTIPLANO FROM THE WEST ON SUNDAY THROUGH TUESDAY.
THIS WILL STIMULATE MOISTURE CONVERGENCE ALONG INTERIOR PORTIONS
OF NORTHERN ARGENTINA AND SOUTHERN BOLIVIA TO TRIGGER MAXIMA OF
15-20MM/DAY BY SUNDAY-MONDAY...INCREASING TO MAXIMA OF 30-60MM/DAY
BY MONDAY-TUESDAY. BY TUESDAY-WEDNESDAY EXPECTING MAXIMA OF
30-60MM/DAY IN NORTHERN BOLIVIA/SOUTHERN PERU. ISOLATED MODERATE
AMOUNTS ARE ALSO EXPECTED IN THE EASTERN CORDILLERA OD THE
ALTIPLANO...WHERE LOCALIZED MAXIMA OF 15-20MM/DAY IS POSSIBLE ON
SUNDAY THROUGH TUESDAY.

MONCADA...DMC (CHILE)
DIAZ... DMC (CHILE)
GALVEZ...WPC (USA)