By February 2021, the overall impact of the COVID-19 pandemic in India had been relatively mild in terms of total reported cases and deaths. Surprisingly, the second wave in early April becomes devastating and attracts worldwide attention. On April 30, 2021, India became the first country reporting over 400,000 daily new cases. Multiple factors drove the rapid growth of the epidemic in India and caused a large number of deaths within a very short period. These factors include a new variant with increased transmissibility, a lack of preparations exists national wide, and health and safety precautions poorly implemented or enforced during festivals, sporting events, and state/local elections. Moreover, India's cases and deaths are vastly underreported due to poor infrastructure, and low testing rates. In this paper, we use the COVID-19 mortality data in India and a mathematical model to calculate the effective reproduction number and to model the wave pattern in India. We propose a new approach to forecast the epidemic size and peak timing in India with the aim to inform mitigation in India. Our model simulation matched the reported deaths accurately and is reasonably close to results of serological study. We forecast that the IAR could reach 43% by June 13, 2021 under the current trend, which means 532,629 reported deaths with a 95% CI (552,445, 513,194) ie., double the current total deaths. Our approach is readily applicable in other countries and with other type of data (e.g. excess deaths).