Title: The South American Monsoon System: Recent Evolution and Current Status
1The South American Monsoon System Recent
Evolution and Current Status
Update prepared by Climate Prediction Center /
NCEP 13 December 2008
For more information, visit http//www.cpc.ncep.
noaa.gov/products/Global_Monsoons/American_Monsoon
s
2Outline
- Highlights
- Recent Evolution and Current Conditions
- NCEP/GFS Model Forecasts
- Climatology
3Highlights
- During the last 30 days, rainfall deficits
decreased over Central and Southeast Brazil, as
an enhanced South Atlantic Convergence Zone
(SACZ) brought above normal rainfall to the
region.
4Rainfall Anomaly Patterns
Last 90 Days
Last 30 Days
Last 7 Days
Long-term rainfall deficits over the southern
Amazon, central and southeastern Brazil
decreased during the last 30 days. Much above
normal rainfall was observed over coastal
southeastern Brazil. During the last 7 days
below-normal rainfall was observed over
southeastern and central-western Brazil.
Long-term (90 30 days) rainfall deficits are
evident over Uruguay and eastern Argentina.
NOTE Due to a lack of station reports, the
rainfall deficits over northern Colombia and
southern Venezuela are not real (red circle).
5Recent Evolution Rainfall
- 90-day rainfall totals are below normal in the
southern Amazon (deficits between 100-180 mm). - 90-day rainfall totals are near normal over
portions of the Brazilian Planalto (BP) and
southeastern Brazil (near Rio de Janeiro)
BP
6Atmospheric Circulation Recent 7 days
- During 5-11 Dec an anomalously strong 200-hPa
trough (heavy dashed line) was located over the
western Atlantic, with anomalous downward motion
(positive omega) observed to the west of the
trough axis from the southern Amazon basin to
southeastern Brazil. These features are
consistent with dry conditions observed in that
region (see slide 4).
7925-hPa Temperature
Recent 90 Days
Recent 30 Days
Recent 7 Days
- During the last 7 days (5-11 Dec 2008),
near-normal temperatures were observed over most
of South America, with the exception of slightly
below-normal temperatures over the southeastern
Brazil coast.
8NCEP/GFS Model Forecasts Bias-Corrected
Precipitation
Forecasts from 13 December 2008
Week 1
Week 2
Note Bias correction based on last 30-day
forecast error.
9NCEP/GFS MODEL FORECASTS
- For week 1 (13-19 Dec2008), above normal rainfall
is forecasted for central and southeastern
Brazil, associated with an enhanced South
Atlantic Convergence Zone (SACZ). Below-normal
rainfall is predicted for the western Amazon
basin, southern Brazil, Paraguay, northern
Argentina and Uruguay. - For week 2 (20-26 Dec 2008) below-normal rainfall
is predicted over most of the Amazon Basin and
central-western Brazil and Paraguay.
NOTE See forecast verification in the next slide.
10Forecast Verification
Forecast from 5 Dec 2008 Valid 5-11 Dec 2008
Observed 6 Nov 12 Dec 2008
Forecast from 28 Nov 2008 Valid 5-11 Dec 2008
11ClimatologyRainy Season Dates
ONSET
DEMISE
12Precipitation Climatology