500
FXSA20 KWBC 031632
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1232 PM EDT THU MAY 03 2012
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00 UTC MAY 02): MODELS AND ENSEMBLE
MEMBERS SHOW GENERALLY GOOD AGREEMENT THROUGH THE CYCLE. FORECAST
CONFIDENCE DECREASES GRADUALLY AFTER 108-120 HRS SOUTH OF 45S.
THE GFS MODEL ADJUSTED ITS PREVIOUS FAST TREND LATE IN THE CYCLE.
THERE IS MORE CONFIDENCE NOW ON TIMING OF SYSTEM ARRIVING IN
CHILE ARGENTINA MY MID-LATE CYCLE.
A TROUGH THAT EXTENDS INTO RIO DO JANEIRO-EASTERN MINAS GERAIS IS
RAPIDLY PULLING EASTWARD INTO THE SOUTH ATLANTIC. AT LOW
LEVELS...A FRONT IS TO REMAIN STATIONARY OFFSHORE ESPIRITO SANTO
WHILE WEAKENING. PERSISTENT EASTERLY ALONG THE BOUNDARY IS TO
FAVOR OROGRAPHIC UPLIFT ALONG THE EASTERN SLOPES OF SIERRA DO
ESPINACO THROUGH THE CYCLE. EXPECT ACCUMULATIONS OF 10-15MM/DAY
EARLY IN THE CYCLE TO INCREASE TO 15-20MM/DAY BY 36-84
HRS....WHILE THE AREA OF HEAVIEST PRECIPITATION SLOWLY EXTENDS
INTO SOUTHERN BAHIA. RAINFALL IS FORECAST TO DECREASE AFTERWARDS
WITH LINGERING SHOWERS ALONG THE COAST OF BRASIL NORTH OF SANTA
CATARINA AND HEAVIEST REMAINING ALONG ESPIRITO SANTO/BAHIA.
A STRONG MID/UPPER IS FORECAST TO CROSS INTO THE SOUTH ATLANTIC
BY 24-36 HRS WHILE FLATTENING. BEHIND THE TROUGH...A RIDGE IS
FORECAST TO BUILD ALONG SOUTHERN CHILE BY 36-60 HRS TO THEN
SLOWLY PROGRESS EASTWARD. TO THE WEST OF THE RIDGE...A MID/UPPER
TROUGH IS AMPLIFYING OVER THE EASTERN PACIFIC. THE TROUGH IS
FORECAST TO ENTER IN PHASE WITH A TROUGH DEVELOPING IN THE
NORTHERN STREAM. MODELS NOW AGREE ON TROUGH ARRIVING BY 72-96
HRS. AS THE TROUGH ARRIVES...MODELS ARE FORECASTING HEIGHT FALLS
OVER WESTERN SOUTH AMERICA SOUTH OF COQUIMBO. OVER
CHILE...ALTHOUGH DYNAMIC FORCING IS GOOD...BOUNDARY-LAYER
MOISTURE WILL NOT BE SUFFICIENTLY HIGH TO SUPPORT RAINS AS HEAVY
AS THOSE OBSERVED EARLIER THIS WEEK. NEVERTHELESS...EXPECT
PRECIPITATION TO DEVELOP AS FAR NORTH AS RANCAGUA/SANTIAGO DE
CHILE WITH LIGHT ACCUMULATIONS. HEAVIEST RAINFALL IS FORECAST TO
PRODUCE ACCUMULATIONS OF 10-15MM/DAY...AND IS EXPECTED SOUTH OF
ISLA CHILOE BY 48-78 HRS TO THEN MIGRATE NORTHWARDS AND AFFECT
AREAS NORTH OF CHILOE AND SOUTH OF CONCEPCION/ANGOL BY 78-90 HRS.
BETWEEN CONCEPCION AND RANCAGUA...EXPECT SHOWERS AND LIGHT RAIN
WITH LIGHT ACCUMULATIONS TO BECOME THE MOST NUMEROUS BY 84-96
HRS.
TO THE EAST OF THE ARGENTINA...MOISTURE IS EXPECTED TO RETURN
GRADUALLY THROUGH THE CYCLE...AS LOW-LEVEL NORTHERLY FLOW TO THE
EAST OF THE ARRIVING TROUGH TRANSPORTS MOIST AIR FROM THE
PANTANAL/CENTRAL-EASTERN BRASIL. A SURFACE FRONT IS FORECAST TO
ARRIVE FROM THE WEST BY 84-90 HRS AND RUSH NORTHEASTWARD ACROSS
NORTHERN PATAGONIA INTO CENTRAL ARGENTINA...WHERE IT IS TO STALL.
THE FRONT IS EXPECTED TO EXTEND ACROSS NORTHERN PATAGONIA-SAN
LUIS-NORTHERN NEUQUEN BY 96 HRS...TO NORTHERN BUENOS AIRES
PROVINCE-MENDOZA BY 120 HRS. LOW-LEVEL MOISTURE AHEAD OF THE
SURFACE COLD FRONT WILL BE SUFFICIENTLY LARGE TO SUSTAIN
CONVECTIVE DEVELOPMENT. EXPECT LOCALIZED MAXIMA OF 15-30MM/DAY TO
AFFECT NORTHEASTERN PATAGONIA AND SOUTHERN BUENOS AIRES PROVINCE
BY 90-108 HRS. THESE ARE TO DECREASE TO 15-25MM/DAY BY THE END OF
THE CYCLE OVER EXTREME EASTERN BUENOS AIRES PROVINCE...WHILE MUCH
LIGHTER ACCUMULATIONS ARE EXPECTED INLAND AS BOUNDARY-LAYER
MOISTURE IS TO REMAIN SOMEWHAT LIMITED AND DYNAMIC FORCING
DECREASES.
NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE IS
TO REMAIN OVER NORTHERN AMAZONIA THROUGH THE CYCLE. FAVORABLE
AREAS FOR UPPER DIVERGENCE ARE FORECAST TO REMAIN GENERALLY NORTH
OF 05S TO VENT CONVECTION OVER THE REGION. MODELS ARE NOT SHOWING
ANY PARTICULAR TREND THROUGH THE CYCLE...THUS...EXPECT MAXIMUM
ACCUMULATIONS OF 20-35MM/DAY ACROSS NORTHERN BRASIL TO PERSIST
THROUGH 120 HRS IN SCATTERED DEEP CONVECTION. TO THE WEST OVER
WESTERN ECUADOR...CONVECTION IS GRADUALLY BECOMING MORE ACTIVE AS
TROUGH ESTABLISHES OFFSHORE AND NORTHWESTERLY FLOW ADVECT A
MOISTER AIR MASS PERPENDICULARLY INTO THE WESTERN ANDES. ITCZ
REMAINS WELL TO THE NORTH...YET...THIS FLOW PATTERN IS TO ENHANCE
LOW-LEVEL CONVERGENCE OVER COASTS/WESTERN SLOPES OF ECUADOR TO
PRODUCE LOCALIZED MAXIMA OF 15-30MM/DAY IN AREAS AS FAR SOUTH AS
GUAYAQUIL/MACHALA PEAKING BY 36-108 HRS. TO THE EAST...LIMITED
BOUNDARY-LAYER MOISTURE AND SUBSIDENCE INVERSION ARE TO FAVOR
GENERALLY FAIR WEATHER OVER NORDESTE AND EAST/CENTRAL BRASIL.
STRONGEST CONVECTION IS TO REMAIN ALONG COASTAL REGIONS OF PARA
AND AMAPA WITH MAXIMUM ACCUMULATIONS OF 15-30MM/DAY INCREASING TO
LOCALIZED MAXIMA OF 20-35MM/DAY AFTER 84 HRS.
PARRENO...INAMHI (ECUADOR)
VILLELA...INMET (BRASIL)
GALVEZ...HPC (USA)
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