SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1125 AM EST FRI JAN 16 2009
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
 
LAST NO AMENDS...NEXT BULLETIN JANUARY 21.

MODEL COMPARISON (VALID FROM 00Z JANUARY 16). EXCEPT FOR SUBTLE
CORRECTIONS...THE MODELS MAINTAIN GOOD CONTINUITY WITH THE
GENERAL EVOLUTION DURING THE NEXT FIVE TO SEVEN DAYS. STRONG
POLAR SURGES ARE TO CONTINUE STREAMING ACROSS THE SOUTH
PACIFIC...AND ARE TO AMPLIFY OVER THE SOUTHERN CONE/WESTERN
ATLANTIC...WITH THE MODELS SUSTAINING A HIGH AMPLITUDE SINUSOIDAL
PATTERN. THE GLOBAL ENSEMBLES CORRELATE QUITE WELL THROUGH 132
HRS...WITH UPSTREAM DIFFERENCES RAPIDLY CRESTING BY 144-168 HRS.

AT 200 HPA...AND CONSISTENT WITH THE PREVIOUS FORECASTS...A CELL
OF THE SUBTROPICAL RIDGE SETTLES OVER THE EASTERN PACIFIC EARLY
THIS CYCLE...WHERE IT IS TO TAKE ADVANTAGE OF ABOVE NORMAL SEA
SURFACE TEMPERATURES. THIS CELL WILL ANCHOR ON A HIGH THAT
MEANDERS NEAR 25S 90W. ANOTHER CELL THEN ESTABLISHES/BUILDS OVER
TROPICAL SOUTH AMERICA BY MID CYCLE...WITH A HIGH TO CENTER
NEAR 17S 50W BY 84-96 HRS...WHICH ANCHORS A BUILDING RIDGE
ACROSS BRASIL-BOLIVIA AND SOUTHERN PERU. AS THE RIDGE PATTERN
EVOLVES...IT WILL ALLOW NORTHERN STREAM PERTURBATIONS TO PUSH
ACROSS NORTHERN CHILE INTO NORTHWEST ARGENTINA/SOUTHERN BOLIVIA
TO PARAGUAY. THE PERTURBED PATTERN PERSISTS THROUGH 60-72
HRS...THEN RAPIDLY WEAKENS BY 84-96 HRS AS THE NEW CELL OF THE
SUBTROPICAL RIDGE ESTABLISHES OVER BRASIL. THE SHORT WAVE
PERTURBATIONS WILL SUSTAIN ORGANIZED CONVECTION OVER MID SECTIONS
OF SOUTH AMERICA...WHERE THEY ARE FORECAST TO INTERACT WITH THE
SACZ AS IT EXTENDS ACROSS BOLIVIA-EL PANTANAL TO SOUTHEAST
BRASIL. OTHER CONVECTION IS EXPECTED FROM SOUTHERN BOLIVIA TO
JUJUY/SALTA IN NORTHWESTERN ARGENTINA...WHERE THE PERTURBATIONS
ARE TO ENHANCE DIURNAL CONVECTION TO FAVOR MAXIMA OF 20-35MM.
OVER BOLIVIA-CHACO PARAGUAYO-MATO GROSSO/MATO GROSSO DO SUL (EL
PANTANAL)...THE MAXIMA WILL PEAK AT 40-80MM/DAY THROUGH 36 HRS...
AND 25-50MM/DAY THEREAFTER THROUGH 72-84 HRS. ANOTHER SURGE IN
ACTIVITY IS EXPECTED ON DAY 04...WITH MAXIMA TO INCREASE TO 30-
60MM/DAY...WHILE EXPANDING WESTWARD INTO SOUTHERN JUNGLE OF PERU
AND RONDONIA IN BRASIL. HEAVY CONVECTION ALONG THE SACZ IS TO
ALSO AFFECT SAO PAULO/RIO DE JANEIRO-MINAS GERAIS IN BRASIL...
WITH ACTIVITY TO EXPAND NORTHWARD INTO GOIAS BY 72-96 HRS...WITH
DAILY MAXIMA IN THIS AREA ALSO TO PEAK AT 25-50MM. OTHER
CONVECTION IS EXPECTED ACROSS THE SIERRA/JUNGLE OF PERU WHERE
DAILY MAXIMA IS TO PEAK AT 20-40MM DURING THE NEXT 36 HRS...AND
15-30MM/DAY THEN EXPECTED ON DAYS 02-05. 

THE EVOLVING PATTERN OVER NORTHERN SOUTH AMERICA IS ALLOWING AN
UPPER TROUGH TO EXPAND ACROSS NORTHERN BRASIL...ORIGINATING ON A
200 HPA LOW NEAR FORTALEZA BRASIL AND EXTENDING WESTWARD TO
RORAIMA/THE GUIANAS. THE TROUGH PATTERN WEAKENS LATER IN THE
CYCLE AS THE SUBTROPICAL HIGH OVER BRASIL IS TO ONCE AGAIN BUILD/
STRENGTHEN. MEANWHILE...THE PERSISTENT TROUGH WILL ENHANCE SEA
BREEZE RELATED CONVECTION...AS WELL AS IT IS TO INTERACT WITH THE
DIURNAL CYCLE TO FAVOR FORMATION OF CLUSTERS OF DEEP CONVECTION.
ALONG THE NORTHERN COAST...WEST OF PERNAMBUCO/ILHA DE MARAJO IT
WILL FAVOR MAXIMA OF 15-30MM/DAY...FORECAST TO INCREASE TO 20-
40MM/DAY BY 60-84 HRS. ACTIVITY IS TO ALSO BUILD WESTWARD INTO
PARA-AMAZONAS IN WESTERN BRASIL...WHERE DAILY MAXIMA WILL PEAK AT
15-30MM/DAY. BUT THROUGH 72-84 HRS THIS IS TO ALSO
INCREASE/BECOME BETTER ORGANIZED.

OVER THE FAR EASTERN PACIFIC-SOUTHERN CONE-WESTERN ATLANTIC...IN
A TIGHT BELT OF WESTERLIES...PROGRESSIVE MID/UPPER LEVEL
PERTURBATIONS ARE TO RACE ACROSS THE DOMAIN. A PROGRESSIVE TROUGH
MOVES ACROSS PATAGONIA/LA PAMPA IN ARGENTINA EARLY THIS CYCLE. AS
THE TROUGH EJECTS ACROSS THE SOUTHERN CONE...AND AS A RIDGE
BUILDS ON THE NORTHERN STREAM OVER THE FAR EASTERN PACIFIC...THE
TROUGH WILL THEN AMPLIFY TO THE NORTH-NORTHWEST...WITH AXIS TO
EXTEND ACROSS BUENOS AIRES PROVINCE/CENTRAL ARGENTINA BY 60-72
HRS. THE LONG WAVE TROUGH MOVES OFF THE COAST ALONG 45W/50W BY
84-96 HRS...NEARING 40W BY 120 HRS. AT LOW LEVELS THE TROUGH
SUPPORTS A FRONT ACROSS PATAGONIA/LA PAMPA-TO THE EASTERN
PACIFIC. THE FRONT IS FORECAST TO PUSH NORTH ACROSS LA
PAMPA/BUENOS AIRES PROVINCE THROUGH 30-36 HRS. AT 48 HRS IT WILL
MOVE ACROSS RIO DE LA PLATA...TO STALL OVER SOUTHERN BRASIL-
NORTHERN PROVINCES OF ARGENTINA BY 72-84 HRS. THIS BOUNDARY IS TO
THEN RAPIDLY WEAKEN OVER THE CONTINENT...WHILE A WANING FRONT
REMAINS OVER THE ATLANTIC/OFF THE COAST OF BRASIL. THE BEST
CHANCE FOR CONVECTION WITH THIS BOUNDARY WILL BE ON DAY 02...WHEN
IT MOVES ACROSS RIO DE LA PLATA BASIN. THE FRONT WILL TRIGGER
MODERATE CONVECTION ACROSS URUGUAY/SOUTHERN MESOPOTAMIA AND
PORTIONS OF BUENOS AIRES PROVINCE WITH MAXIMA OF 10-15MM. MOST
ACTIVE WILL BE ON THE TAIL END OF THE FRONT...FROM NORTHERN
MENDOZA TO JUJUY/SALTA...WHERE IT WILL TRIGGER MAXIMA OF 20-35MM.
AFTER 60 HRS MOST ACTIVE CONVECTION WILL BE FAR TO THE NORTH
ALONG THE SACZ...AFFECTING CHACO PARAGUAYO-EL PANTANAL-
BOLIVIA...WITH MAXIMA TO PEAK AT 30-60MM. 

AS PREVIOUSLY MENTIONED...A MID/UPPER LEVEL RIDGE WILL BUILD OVER
THE EASTERN PACIFIC ALONG 80W/100W TO 55S/60S. THIS WILL AID WITH
THE NORTHWARD AMPLIFICATION OF THE AFOREMENTIONED TROUGH OVER THE
WESTERN ATLANTIC. IT WILL ALSO FAVOR A TIGHT GRADIENT ON THE
SOUTHERN STREAM FLOW...WITH PROGRESSIVE SHORT WAVE PERTURBATIONS
TO STREAM TOWARDS THE DRAKE PASSAGE/TIERRA DEL FUEGO. STARTING ON
DAY 02...AND PERSISTING INTO DAY 05...ELONGATED FRONTS WILL THEN
ENTER EXTREME SOUTHERN CHILE/SOUTHERN PATAGONIA...TO FAVOR A
RELATIVELY WET/ACTIVE PATTERN WITH RAINFALL AMOUNTS OF 10-
15MM/DAY...AND STRONG BOUNDARY LAYER WINDS OF 35-50KT.

PEREZ...SENAMHI (BOLIVIA)
MOREYRA...SENAMHI (PERU)
DAVISON...HPC (USA)q-