323  
FXSA20 KWBC 111730  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
130 PM EDT WED OCT 11 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM OCT 11 AT 0000 UTC): MODEL CONFIDENCE  
REMAINS HIGH THROUGH THE CYCLE...AS MODELS AGREE ON THE TRANSITION  
INTO A LONG-WAVE PATTERN.  
 
AN UPPER LOW MEANDERING OFF THE COAST OF CENTRAL CHILE IS  
STIMULATING PRECIPITATION IN THE CUYO REGION IN ARGENTINA. AT  
LOW-LEVELS...THIS IS INTERACTING WITH A LOW-LEVEL JET FROM THE  
EAST THAT IS ENHANCING MOISTURE CONVERGENCE. THIS WILL BE  
SUFFICIENT TO TRIGER INTERMITTENT RAINFALL WITH MAXIMUM  
ACCUMULATIONS OF 20-30MM/DAY THROUGH EARLY THURSDAY. AMOUNTS WILL  
DECREASE RAPIDLY AFTER.  
 
ALSO IN THE SOUTHERN CONE...A TROUGH WILL RAPIDLY ARRIVE FROM THE  
WEST LATE ON THURSDAY AND CROSS THE SOUTHERN CONE ON FRIDAY. THIS  
SYSTEM WILL ARRIVE ACCOMPANIED WITH 40-45KT WINDS TO THE SOUTH OF  
ISLA CHILOE...AND WITH A SUBTROPICAL MOISTURE CONNECTION. THE  
LIMITATION FOR HEAVY RAINFALL ACCUMULATIONS WILL BE THE FAST  
PROPAGATION OF THE SYSTEM. ACCORDINGLY...WE HAVE DECREASED THE  
EXPECTED RAINFALL MAXIMA TO 15-20MM/DAY ON FRIDAY-SATURDAY BETWEEN  
ISLA CHILOE AND MOST OF THE AYSEN REGION. TO THE SOUTH...EXPECTING  
MAXIMA OF 10-15MM/DAY. A SECOND BURST OF PRECIPITATION IS EXPECTED  
ON CHILE ON SUNDAY INTO MONDAY. THIS IN ASSOCIATION WITH A  
SUBTROPICAL MOISTURE CONNECTION FROM THE NORTHWEST. THIS WILL LEAD  
TO MAXIMA OF 15-20MM/DAY CONSTRAINED TO THE COAST.  
 
IN MID-SECTIONS OF THE CONTINENT...A SURFACE FRONT CONTINUES TO  
CONTINUE BEING THE FOCUS FOR MOISTURE CONVERGENCE THROUGH LATE  
SATURDAY. PRECIPITABLE WATER WILL LINGER BETWEEN 45 AND 50MM  
THROUGH THE CYCLE...WHICH WILL SUSTAIN PERIODS WITH MODERATE  
RAINFALL AMOUNTS...MODULATED BY THE PASSAGE OF UPPER TROUGHS AND  
UPPER JETS. INITIALLY...EXPECTING CONVECTION TO PRODUCE MAXIMA OF  
35-70MM IN SOUTHERN RIO GRANDE DO SUL AND CORRIENTES. BY  
THURSDAY-FRIDAY MAXIMA WILL DECREASE TO 25-50MM/DAY IN SOUTHERN  
RIO GRANDE DO SUL. AS A SHORT WAVE TROUGH APPROACHES FROM THE  
WEST...EXPECTING A NEW BURST IN CONVECTION IN PARAGUAY TO PRODUCE  
AMOUNTS OF 15-25MM/DAY. BY FRIDAY-SATURDAY...LARGEST ACCUMULATIONS  
WILL DECREASE TO MAXIMA OF 15-20MM STRETCHING FROM EASTERN  
PARAGUAY SOUTH INTO SANTA CATARINA AND RIO GRANDE DO SUL IN  
BRASIL. BY SATURDAY-SUNDAY EXPECTING A BURST IN PRECIPITATION  
ALONG THE EASTERN SLOPES OF THE SERRA DO MAR IN SANTA  
CATARINA-PARANA-SAO PAULO...WHERE POST-FRONTAL SOUTHERLIES WILL  
ENHANCE LOW-LEVEL MOISTURE CONVERGENCE TO SUSTAIN MAXIMA OF  
20-40MM/DAY. FRONTAL CONVECTION WILL THEN FOCUS IN SOUTHERN  
ESPIRITO SANTO AND EASTERN RIO DE JANEIRO...WHERE EXPECTING  
10-15MM/DAY ON SUNDAY-MONDAY.  
 
NORTH ACROSS THE CONTINENT...IN THE AMAZON BASIN...SCATTERED  
DIURNAL CONVECTION IS FORECAST TO INCREASE AS THE CYCLE PROGRESSES  
AND MAXIMA IS FORECAST TO MEANDER WESTWARD. FROM THURSDAY AND  
ON...EXPECTING MAXIMA INCREASING TO 20-35MM/DAY. BY SATURDAY...A  
DEVELOPING SOUTHEASTERLY SURGE IN THE WESTERN AMAZON WILL ENHANCE  
LOW-LEVEL MOISTURE CONVERGENCE TO ENHANCE ACCUMULATIONS TO MAXIMA  
OF 30-60MM. ANDEAN CONVECTION IN THE CENTRAL ANDES IS ALSO  
ACTIVATING TWO PERIODS ARE FAVORABLE FOR MODERATE  
AMOUNTS...WEDNESDAY...WHEN EXPECTING MAXIMA OF 05-10MM/DAY FROM  
NORTHERN PERU INTO BOLIVIA...AND SATURDAY...WHEN EXPECTING  
ISOLATED MAXIMA OF 10-15MM/DAY IN THE ALTIPLANO. A NEW BURST IN  
ANDEAN CONVECTION IS EXPECTED DURING MONDAY AS AN UPPER TROUGH  
APPROACHES FROM THE WEST. THIS WILL SUSTAIN MAXIMA OF 10-15MM/DAY.  
 
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENMAHI (PERU)  
GALVEZ...WPC (USA)  

 
 
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