989  
FXSA20 KWBC 121738  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
138 PM EDT THU OCT 12 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM OCT 12 AT 0000 UTC): MODEL CONFIDENCE  
CONTINUES HIGH THROUGH THE CYCLE. IT STARTS DECREASING IN REGIONS  
TO THE SOUTH OF 50S AFTER 120 HRS.  
 
IN SOUTHERN CHILE...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 LARGE 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  
MAGALLANES IN EXTREME SOUTHERN 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 ON SUNDAY-MONDAY...AND MAXIMA OF 20-30MM/DAY ON  
MONDAY-TUESDAY.  
 
IN MID-SECTIONS OF THE CONTINENT...A SURFACE FRONT CONTINUES TO  
CONTINUE BEING THE FOCUS FOR MOISTURE CONVERGENCE THROUGH LATE  
SATURDAY. UNDER THE INFLUENCE OF AN UPPER TROUGH CROSSING THE  
ANDES OF CENTRAL CHILE AND ARGENTINA ON FRIDAY-SATURDAY...THE  
FRONT WILL PROPAGATE NORTHWARD THROUGH SATURDAY...ACCOMPANIED BY A  
PRE=FRONTAL SOUTHERLY SURGE THAT WILL REACH NORTHERN PERU/ECUADOR  
ON SATURDAY-SUNDAY. THIS WILL LEAD TO MODERATE RAINFALL IN THE  
WESTERN AMAZON DURING THE WEEKEND. INITIALLY...DURING  
THURSDAY...LARGEST ACCUMULATIONS ARE EXPECTED IN RIO GRANDE DO  
SUL-BRASIL...WHERE CONVECTION AHEAD OF A FRONTAL WAVE WILL LEAD TO  
ACCUMULATIONS OF 25-50MM. ANOTHER REGION WITH ENHANCED  
PRECIPITATION WILL BE THE BOLIVIAN YUNGAS/SOUTHEASTERN  
PERU...WHERE EXPECTING MAXIMA OF 20-35MM. BY FRIDAY EXPECTING A  
DECREASE IN ACCUMULATIONS TO MAXIMA OF 15-20MM/DAY IN SANTA  
CATARINA/PARANA IN BRASIL. BY SATURDAY-SUNDAY...AS THE SOUTHERLY  
WIND SURGE DEVELOPS...EXPECTING ENHANCED MOISTURE CONVERGENCE IN  
WESTERN BRASIL/CENTRAL AND SOUTHERN PERU...TO PRODUCE  
ACCUMULATIONS OF 40-80MM/DAY. ALSO DURING  
SATURDAY-SUNDAY...INTERACTIONS BETWEEN THE SURFACE COLD FRONT AND  
THE SERRA DO MAR IN PARANA/SAO PAULO WILL LEAD TO MAXIMA OF  
20-30MM. BY SUNDAY-MONDAY...LARGEST ACCUMULATIONS ARE EXPECTED IN  
NORTHERN PERU/ECUADOR/SOUTHERN COLOMBIA...AS THE WANING SOUTHERLY  
SURGE LEADS TO MAXIMA OF 25-50MM. ALSO DURING SUNDAY-EARLY  
MONDAY...FRONTAL CONVECTION IN RIO DE JANEIRO AND ESPIRITO SANTO  
WILL LEAD TO MAXIMA OF 10-15MM/DAY. BY MONDAY-TUESDAY...ENHANCED  
TRADES IN ASSOCIATION WITH THE SURFACE FRONT WILL STIMULATE  
PRECIPITATION IN ESPIRITO SANTO...WHERE EXPECTING MAXIMA OF  
15-20MM/DAY.  
 
ALSO LATE IN THE FORECAST CYCLE...ON TUESDAY-WEDNESDAY...THE  
INTERACTION OF TWO MID-UPPER TROUGHS CROSSING THE ANDES OF CENTRAL  
CHILE AND ARGENTINA...WILL INTERACT WITH A MOIST AND UNSTABLE AIR  
MASS BREWING IN PORTIONS OF NORTHEASTERN ARGENTINA. THIS WILL POSE  
THE RISK FOR SEVERE CONVECTION IN NORTHEASTERN ARGENTINA/SOUTHERN  
BRASIL ON TUESDAY-WEDNESDAY...YET IT IS STILL A BIT EARLY FOR  
CONFIDENCE ON THE DETAILS.  
 
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENMAHI (PERU)  
GALVEZ...WPC (USA)  

 
 
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