Forecasting the complex precipitation and circulation characteristics of the South Asian Monsoon (SAM) in Global Numerical Weather Prediction (NWP) models still remains a challenging problem. Observing system experiments (OSE) for predicting the onset of SAM has been carried out to analyze the contribution of high impact observing systems on the Global Forecasting System (GFS) model. The Global Data Assimilation System (GDAS) and GFS model are used to quantify the impacts of two remotely sensed satellite sensors and in-situ radiosonde data to 1-7 day forecasts of the SAM. These forecast experiments are compared to their own analyses as well as to the operational GFS model (control) that uses all conventional and nonconventional data sources. The instruments that are removed from each experiment are the Advanced Microwave Sounding Unit-A (AMSUA), Global Positioning System Radio Occultation (GPSRO), and radiosonde observations. The experimental evaluation period of 168-hr forecasts is from 22 May through 25 June 2011 for a 35-day analysis interval. In 2011, the Indian Meteorological Department (IMD) defined the onset of SAM as 29 May 2011. Anomaly correlation and precipitation statistics are analyzed for all experiments within the SAM region. Results show that the monsoon onset with its circulation characteristics is reasonably simulated in the control but the precipitation maxima around 10N – 15N show displacement errors to the west over the Arabian Sea. Data denial experiments, in general, show diminished precipitation amounts and displacement errors compared to the control. Future results, using statistics, will show the performance of the operational GFS model compared to the experimental runs.