The South American Monsoon System Recent Evolution and

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The South American Monsoon System: Recent Evolution and Current Status Update prepared by Climate

The South American Monsoon System: Recent Evolution and Current Status Update prepared by Climate Prediction Center / NCEP 17 October 2008 For more information, visit: http: //www. cpc. ncep. noaa. gov/products/Global_Monsoons/American_Monsoons

Outline • Highlights • Recent Evolution and Current Conditions • NCEP/GFS Model Forecasts •

Outline • Highlights • Recent Evolution and Current Conditions • NCEP/GFS Model Forecasts • Summary • Climatology

Highlights ONSET DATES • As shown in the rainfall climatology onset dates, by this

Highlights ONSET DATES • As shown in the rainfall climatology onset dates, by this time of the year the monsoon should be active over the Amazon basin and central Brazil. • Slide 5 shows that the monsoon rainfall is lagging behind the long-term average over the monsoon core region, and rainfall deficits between 5080 mm remain in that region.

Rainfall Anomaly Patterns: Last 90 Days Last 30 Days Last 7 Days During the

Rainfall Anomaly Patterns: Last 90 Days Last 30 Days Last 7 Days During the last 90 days rainfall was below normal over the southern Amazon, central and southeastern Brazil. In the last 30 days rainfall was near normal over the northern Amazon, but below normal over the southern Amazon. During the last 7 days below-normal rainfall was observed over central Brazil (South American monsoon core region). NOTE: Due to a lack of station reports, the rainfall deficits over northern Colombia and southern Venezuela are not real (red circle).

Recent Evolution: Rainfall - 90 -day rainfall totals are below normal in the central

Recent Evolution: Rainfall - 90 -day rainfall totals are below normal in the central Amazon. - The lack of rainfall during this past week increased the longterm deficits over the Brazilian Planalto (BP) (50 -80 mm). BP

Atmospheric Circulation Recent 7 days • During 9 -15 October anomalous 200 -h. Pa

Atmospheric Circulation Recent 7 days • During 9 -15 October anomalous 200 -h. Pa cyclonic circulation was observed over tropical South America, and at mid-latitudes near the coast of Chile. • Anomalous downward motion (positive omega) was observed over the eastern third of Brazil. This pattern is consistent with belownormal rainfall over that region during the last 7 days (slide 4). C C

925 -h. Pa Temperature Recent 90 Days Recent 30 Days Recent 7 Days •

925 -h. Pa Temperature Recent 90 Days Recent 30 Days Recent 7 Days • During the last 7 days (9 -15 October 2008), abovenormal temperatures were observed over central Brazil. These positive temperature departures were associated with drier-than-normal conditions over the region during that period.

NCEP/GFS Model Forecasts Bias-Corrected Precipitation Forecasts from 17 October 2008 Week 1 Week 2

NCEP/GFS Model Forecasts Bias-Corrected Precipitation Forecasts from 17 October 2008 Week 1 Week 2 Note: Due to a wet bias in CMORPH the area of wetter-than-normal conditions is likely to be greater and the area of drier-than-normal conditions is likely to be less than depicted in the maps above.

Summary • The lack of rainfall during the last 7 days increased the long-term

Summary • The lack of rainfall during the last 7 days increased the long-term deficits over the monsoon core region. Rainfall deficits are now between 50 - 80 mm in that region. • Note: Due to a lack of station reports over Colombia and Venezuela, the long-term rainfall deficits over those regions are not real. NCEP/GFS MODEL FORECASTS • For week 1 (18 -24 Oct 2008), above-normal rainfall is predicted for the western Amazon and southern Brazil. Below-normal rainfall is predicted over the South American monsoon core region. • For week 2 (25 -31 Oct 2008) below-normal rainfall is predicted to continue over the South American monsoon core region. NOTE: See forecasts verification in the next slide.

Forecast Verification Period: 10 -17 OCT 2008 Forecast from 2 October 2008 10 October

Forecast Verification Period: 10 -17 OCT 2008 Forecast from 2 October 2008 10 October 2008 Observed Valid 10 -17 October 2008

Information About the NCEP/GFS Model Forecasts 1. The forecast uses four operational NCEP/GFS forecast

Information About the NCEP/GFS Model Forecasts 1. The forecast uses four operational NCEP/GFS forecast runs from 00 Z, 06 Z, 12 Z, and 18 Z initial conditions. 2. PDF (Probability Density Function) correction is made for each forecast: - For each individual forecast and each grid point, cumulative PDFs for both forecasts and observations (CMORPH) are defined using values of the past 35 days within 15°X 15° boxes. - GFS forecasts are replaced by observations at the same percentile level of the cumulative PDFs. 3. Forecast anomalies are taken as the differences of the bias-corrected ensemble mean from the 2003 -2006 CMORPH average. 4. Week-1 forecast is at 1 -day lead and week-2 forecast is at 8 -day lead.

Climatology Rainy Season Dates ONSET DEMISE

Climatology Rainy Season Dates ONSET DEMISE

Precipitation Climatology

Precipitation Climatology