<p>The Indian Summer Monsoon (ISM) is one of the most significant weather phenomena. The monsoon arrives in Kerala around 1st June, then gradually covers the entire country. The monsoon onset is associated with changes in both large-scale circulation patterns and local rainfall. Therefore, it is crucial to predict the monsoon's onset quite accurately. Various observation-based analyses have provided the methodology to define the monsoon onset over Kerala (MOK), using different objective and subjective criteria, including an increase in daily rainfall, the abrupt strengthening of the low-level westerly winds, and moisture transport. However, a detailed study of dynamical model fidelity in capturing the MOK still needs to be explored. Few studies have focused on the forecast of MOK using dynamical models in extended range and medium range; however, the fidelity of the short to medium-range forecast model operationally used by the India Meteorological Department (IMD) remains elusive. Thus, in the present work, we have studied the high-resolution global forecast system model (GFS-T1534) fidelity in capturing the MOK in the backdrop of observation-based objective criteria developed by earlier studies. The analysis reveals that the GFS-T1534 model has good fidelity in capturing the increased rainfall associated with the MOK. Some other features, such as a decrease in outgoing long wave radiation (OLR) and the reversal of the tropospheric temperature index, are also captured well. The model can reasonably capture the low-level southwesterly wind structure, but the amplitude is underestimated, and the underestimation increases as we approach the MOK. The increase in the 600&#xa0;hPa westerly winds is a signature of the depth of westerly wind reaching up to 600&#xa0;hPa in and around the MOK date. The model has good fidelity in capturing the increased wind speed at 600&#xa0;hPa with reasonable accuracy. Thus, the GFS-T1534 model has reasonable fidelity in capturing the observed features associated with the MOK.</p>