Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4
000
FXSA20 KWBC 231627
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1226 PM EDT WED MAY 23 2018

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM MAY 23 AT 0000 UTC): MID/UPPER LEVEL
RIDGE OFF THE COAST OF CHILE IS INDUCING THE NORTHWARD
AMPLIFICATION OF A TROUGH OVER THE WESTERN ATLANTIC. EARLY IN THE
CYCLE THE MID LEVEL TROUGH IS TO EXTEND NORTH BETWEEN 55W-30W TO
25S. THROUGH FRIDAY EVENING THE TROUGH IS TO DRIFT EAST ACROSS
20W...THEN ACCELERATE ACROSS 10W LATER ON SATURDAY. AT LOW LEVELS
THIS SUSTAINS A DEEPENING TROUGH OFF THE SOUTH COAST OF
BRASIL-ARGENTINA...WITH AIS TO SLOWLY MIGRATE TO THE
EAST-SOUTHEAST. ASSOCIATED FRONT IS TO TRAIL ACROSS SAO PAULO TO
SANTA CATARINA IN SOUTHERN BRASIL...WHERE IT IS TO ENHANCE LOW
LEVEL MOISTURE CONVECTION. OVER THE NEXT FEW DAYS THIS SI TO FAVOR
LIGHT RAINFALL AMOUNTS WITH ACCUMULATION OF 05-10MM/DAY.

THE MID LEVEL TROUGH IS TO ALSO INTERACT WITH AN OLD FRONT TO THE
NORTH...AS THE LATTER EXTENDS WEST ACROSS THE SOUTH ATLANTIC TO
ESPIRITO SANTO IN BRASIL. THE FRONT IS TO REMAIN NEARLY STATIONARY
DURING THE NEXT FEW DAYS...MEANWHILE SUSTAINING A PREFRONTAL SHEAR
LINE ACROSS BAHIA. THIS WILL ENHANCE LOW LEVEL MOISTURE
CONVERGENCE ALONG THE COAST...TO FAVOR MODERATE RAINFALL AMOUNTS
WITH MAXIMA OF 25-50MM. THROUGH FRIDAY THIS IS TO GRADUALLY
DECREASE TO 15-30MM/DAY...SURGING AGAIN DURING THE WEEKEND.
LOCALLY HIGHER AMOUNTS ARE HIGHLY PROBABLE DUE TO STRONG
TOPOGRAPHICAL FORCING.

UPSTREAM OVER THE EASTERN PACIFIC...DEEPENING MID LEVEL TROUGH IS
TO AMPLIFY BETWEEN 120W-90W TO 20S LATER TODAY. UNDER INFLUENCE OF
A RIDGE TO THE EAST...THE TROUGH IS TO ACCELERATE ACROSS 90W TO
80W EARLY ON FRIDAY MORNING...THEN MOVE ACROSS THE SOUTHERN ANDES
TO PATAGONIA IN ARGENTINA DURING THE LATE AFTERNOON/EVENING HOURS.
AS IT ENTERS SOUTHERN CHILE ON FRIDAY THIS IS TO SUSTAIN HEIGHT
FALLS OF 250-300 GPM. AT 250 HPA COUPLED JETS ARE TO ACCOMPANY
THIS TROUGH AS IT REACHES THE SOUTH COAST OF CHILE...TO FAVOR A
BROAD AREA OF DIVERGENCE THAT IS TO VENT DEEP CONVECTION. UNDER
FAVORABLE JET DYNAMICS THE ASSOCIATED SURFACE LOW IS TO FORECAST
TO RAPIDLY INTENSIFY ON THURSDAY TO FRIDAY...WITH DEEP SURFACE LOW
TO TRACK ACROSS EXTREME SOUTHERN PORTIONS OF CHILE TO
PATAGONIA/TIERRA DEL FUEGO LATER ON FRIDAY. AS IT ENTERS SOUTHERN
CHILE THIS IS TO SUSTAIN TROPICAL STORM INTENSITY WINDS OF 40-60KT
ON FRIDAY AND SATURDAY...WHILE ACROSS SOUTHERN PATAGONIA THIS
INCREASES TO HURRICANE INTENSITY WINDS OF 70-80KT. OVER THE NEXT
FEW DAYS EXPECTING MODERATE RAINFALL AMOUNTS OVER CHILE SOUTH OF
PUERTO MONTT...WITH MAXIMA OF 15-20MM ON WEDNESDAY AND 20-35MM ON
THURSDAY. ON FRIDAY THIS INCREASES TO 20-40MM WHILE BUILDING NORTH
ACROSS TEMUCO TO CONCEPCION IN CENTRAL CHILE. SOUTH OF ISLA DE
CHILOE THE MAXIMA IS TO PEAK AT 15-20MM ON FRIDAY.

THE NEXT MID LEVEL TROUGH WILL RACE ACROSS THE SOUTHEAST PACIFIC
TO SOUTHERN REGIONS OF CHILE EARLY ON SUNDAY MORNING. AT LOW LEVEL
THIS WILL SUSTAIN A DEEPENING LOW OFF THE SOUTH COAST OF CHILE AND
A PROGRESSIVE SURFACE FRONT. STRONG WESTERLY WINDS ARE TO
ACCOMPANY THIS FEATURE...TO RESULT IN TOPOGRAPHICAL LIFTING AND
MODERATE RAINFALL AMOUNTS BETWEEN CONCEPCION AND PUERTO MONTT IN
SOUTHERN CHILE.

THE FLOW OVER NORTHERN SOUTH AMERICA SPLITS AT 200 HPA BETWEEN A
CELL OF THE SUBEQUATORIAL RIDGE TO THE NORTH AND A WEAK CELL OF
THE SUBTROPICAL RIDGE TO THE SOUTH. THE LATTER WILL CONFINE TO
NORTHERN BRASIL-PERU. AS THE FLOW DIVERGES BETWEEN THESE RIDGE
THIS IS TO VENT DIURNAL CONVECTION ACROSS EQUATORIAL SOUTH
AMERICA. ACTIVITY IS TO GRADUALLY BUILD WEST ACROSS THE
CONTINENT...WITH MODERATE TO HEAVY CONVECTION ACROSS THE
GUIANAS-AMAPA/NORTHERN PARA IN BRASIL TO INITIALLY FAVOR MAXIMA OF
25-50MM. THIS DECREASES TO 20-30MM ON THURSDAY...AND 15-20MM ON
FRIDAY. OVER AMAZONAS-SOUTHERN COLOMBIA/NORTHERN PERU-EASTERN
ECUADOR CONVECTION IS TO INTENSIFY ON THURSDAY-FRIDAY...WITH
MAXIMA IN THIS AREA INCREASING TO 30-60MM/DAY IN SCATTERED DEEP
CONVECTION.

BALBINO...INMET (BRASIL)
DIAZ...INUMET (URUGUAY)
DAVISON...WPC (USA)
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.