A physical model, based on modeling of the near wall velocity fluctuations, is used for prediction of transition in an attached boundary layer. The near wall velocity fluctuations are assumed to develop into turbulent spots when their amplitudes exceed a threshold value. In this work, the relevant physical correlations are developed and incorporated into a conventional boundary layer computer code for prediction of transitional flows. Test cases include transitional flat plate boundary layer flows under zero and non-zero pressure gradients with various high free stream turbulence intensities. The results show close agreements with available the experimental data.