716
FXSA20 KWBC 071600
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1159 AM EDT TUE OCT 07 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z OCTOBER 07). GLOBAL MODELS
GENERALLY AGREE THROUGH 120 HRS...WITH BOTH EUROPEAN MODELS
MAKING PATTERN CORRECTIONS IN SUPPORT OF THE GFS SOLUTION.
CONFIDENCE IN THE FORECAST REMAINS HIGH...WITH THE ENSEMBLE
MODELS CLUSTERING IN FAVOR OF A SIMILAR SOLUTION.
AT 500 HPA...A LONG WAVE RIDGE IS INITIALIZED ACROSS THE FAR
EASTERN PACIFIC...WITH MEAN AXIS SOUTH ALONG 75W/78W. THROUGH 24-
30 HRS THIS RIDGE IS TO GRADUALLY MOVE EAST INTO THE SOUTHERN
CONE/WESTERN ATLANTIC. AFTER 48-60 HRS IT WILL MOVE FARTHER
EAST...TO EXTEND BETWEEN 65W-40W...WHERE IT WILL REMAIN/PERSIST
THROUGH 108-120 HRS. AT LOW LEVELS IT WILL REFLECT AS A BROAD
SURFACE RIDGE...WITH MODELS SHOWING A MASSIVE 1033-1035 HPA HIGH
CLOSING OVER THE WESTERN ATLANTIC BY 72-96 HRS. THIS WILL
ESTABLISH/SUSTAIN A WARM/MOIST NORTHERLY FLOW ACROSS PARAGUAY TO
NORTHERN/CENTRAL ARGENTINA.
NORTHERN STREAM VORTICES WILL PUSH AGAINST THIS AXIS...WITH ONE
TO ENTER CENTRAL/NORTHERN CHILE BY 24 HRS. BY 36-48 HRS THIS
VORTEX IS TO RAPIDLY DECAY/WEAKEN AS IT MOVES ACROSS PARAGUAY TO
SOUTHEAST BRASIL. BUT...AS IT ENTERS THE CONTINENT...THIS VORTEX
WILL SUSTAIN ISOLATED TO SCATTERED CONVECTION...WITH MOST INTENSE
BETWEEN SALTA-NORTHERN MENDOZA IN ARGENTINA. THIS PERTURBATION
WILL SET THE STAGE FOR A STRONGER VORTEX TO FOLLOW. THE LATTER
WILL ENTER CENTRAL/NORTHERN CHILE BY 48-60 HRS. IT WILL MOVE
INLAND ACROSS 65W TO NORTHWEST ARGENTINA/ SOUTHERN BOLIVIA BY 72
HRS. AT 96 HRS IT WILL CONTINUE ACROSS SOUTHERN
BRASIL/URUGUAY...TO MOVE OFF THE SOUTHERN COAST OF BRASIL BY 108
HRS. IN CONTRAST TO THE FORMER...THE LATTER WILL BE MORE ACTIVE
AS IT MOVES ACROSS MESOPOTAMIA VALLEY AND SOUTHEAST BRASIL. IN
THIS AREA MOISTURE WILL BE PLENTIFUL...AND CONDITIONS WILL TEND
TO FAVOR ORGANIZED DEEP CONVECTION. AS A RESULT...WE PROJECT
RAINFALL AMOUNTS OF 20-40MM/DAY TO AFFECT THE SOUTHERN STATES OF
BRASIL...AND AS FAR NORTH AS SAO PAULO.
PROGRESSIVE SOUTHERN AND NORTHERN STREAM PERTURBATIONS WILL
CONTINUE TO ENTER SOUTHERN CHILE/PATAGONIA OVER THE NEXT COUPLE
OF DAYS...WITH A STRONGER/HIGHER AMPLITUDE TROUGH TO MOVE ACROSS
90W BY 60-72 HRS. THE TROUGH WILL CONTINUE ACROSS 80W BY 96
HRS...WITH A LOW FORMING/CLOSING NEAR 43S 80W. THIS LOW WILL
EJECT ACROSS PATAGONIA BY 120 HRS. A SECONDARY VORTEX IS TO
CLOSELY FOLLOW...WITH MODELS NOW AGREEING ON A CLOSED LOW NEAR
43S 85W BY THE END OF THE PERIOD. THIS WILL HELP SUSTAIN A BROAD/
LOW AMPLITUDE TROUGH OVER THE FAR EASTERN PACIFIC AND THE
SOUTHERN CONE. AT LOW LEVELS EXPECT A PROGRESSIVE FRONT TO ENTER
SOUTHERN CHILE BY 72-84 HRS...AND TO EJECT ACROSS PATAGONIA TO LA
PAMPA/CENTRAL CHILE BY 96 HRS. ACROSS SOUTHERN CHILE THIS WILL
FAVOR SCATTERED CONVECTION WITH ACCUMULATION OF 15-30MM/DAY...
WHILE OVER LA PAMPA/NORTHERN PATAGONIA MAXIMA WILL PEAK AT 10-
20MM.
OVER THE WESTERN ATLANTIC...ON THE NORTHERN STREAM FLOW...A MID
LEVEL TROUGH REMAINS OFF THE COAST OF ARGENTINA...WITH AXIS
TRAILING TO URUGUAY/RIO GRANDE DO SUL BRASIL. THE TROUGH IS TO
SLOWLY EVOLVE OVER THE NEXT FEW DAYS...WITH AXIS TO DRIFT BETWEEN
50W-20W AND SOUTH OF 25S BY 48 HRS. AFTER 60 HRS IT WILL GAIN
MOMENTUM...TO ACCELERATE ACROSS 25W BY 72 HRS...AND ACROSS
05W/10W BY 96 HRS. THE ASSOCIATED FRONT WILL PUSH NORTH ACROSS
RIO GRANDE DO SUL/LOWER MESOPOTAMIA TO CORDOBA IN ARGENTINA EARLY
THIS PERIOD. UNDER INFLUENCE OF A BUILDING RIDGE OVER THE WESTERN
ATLANTIC/SOUTHERN CONE...THE FRONT WILL THEN MOVE FARTHER NORTH
INTO SAO PAULO IN BRASIL...WHERE IT IS TO GRADUALLY MERGE
WITH/REINFORCE AND OLD BOUNDARY. THE LATTER IS TO MEANDER ACROSS
THE SOUTH ATLANTIC TO RIO DE JANEIRO/NORTHERN SAO PAULO...THEN
NORTHWEST ACROSS MATO GROSSO TO RONDONIA/NORTHERN BOLIVIA-CENTRAL
PERU. THE BOUNDARY REMAINS QUASISTATIONARY WHILE GRADUALLY
WEAKENING OVER THE CONTINENT THROUGH 48-60 HRS. HOWEVER...IT IS
TO PERSIST/REMAIN WELL ORGANIZED OVER THE WESTERN ATLANTIC AND
INTO RIO DE JANEIRO/SOUTHERN ESPIRITO SANTO THROUGH AT LEAST 96-
108 HRS. ORGANIZED CONVECTION WILL AFFECT NORTHERN SAO PAULO-
SOUTHERN MINAS GERAIS...WHERE IT WILL SUSTAIN MAXIMA OF 25-
50MM/DAY THROUGH 36 HRS...AND 10-15MM/DAY AT 36-60 HRS. A SURGE
IN ACTIVITY IS EXPECTED BY 60-84 HRS...WHEN MAXIMA WILL INCREASE
TO 20-35MM. OTHER CONVECTION IS EXPECTED ON THE CENTRAL/SOUTHERN
JUNGLE OF PERU...WITH MAXIMA OF 05-15MM/DAY. MOST ACTIVE WILL
FALL FARTHER NORTH...ACROSS NORTHERN PERU-SOUTHERN COLOMBIA-
NORTHERN AMAZONAS BRASIL...WITH MAXIMA OF 25-50MM/DAY THROUGH
48-60 HRS.
AT 200 HPA...THE SUBTROPICAL RIDGE IS TO BUILD OVER THE CONTINENT
THROUGH 24-36 HRS...TO CENTER/ANCHOR ON A CLOSED HIGH NEAR 08S
58W. BUT THIS WILL BE SHORT LIVED...WITH THE HIGH TO COLLAPSE
TO AN OPEN RIDGE BY 48-72 HRS. THIS THEN BECOMES NARROW AND
ELONGATED DURING THE SECOND HALF OF THE CYCLE. AREAS OF MOST
ACTIVE CONVECTION WILL ASSOCIATE WITH FRONTAL INCURSION OVER
BRASIL EARLY IN THE PERIOD. BY MID CYCLE...TROPICAL CONVECTION IS
TO GENERALLY CONFINE TO AREA NORTH OF 05S...WITH CLUSTERS OF DEEP
CONVECTION TO SUSTAIN RAINFALL MAXIMA OF 20-35MM/DAY. OTHER
CONVECTION IS EXPECTED ACROSS ILHA DE MARAJO...WITH MAXIMA OF 10-
15MM/DAY THROUGH DAY 02.
URRA...DMC (CHILE)
MOREYRA...SENAMHI PERU
DAVISON...HPC (USA)!*
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page