The strong flows of relativistic electrons, encountered in high power short pulse laser plasma interaction, have the potential to drive Weibel instability producing short wavelength magnetic fields. The presence of a Langmuir wave couples the Weibel instability to two electrostatic wave sidebands. The density perturbations due to the sidebands couple with the oscillatory electron velocity due to the pump to produce a current that enhances the growth rate of Weibel instability. The thermal spread of the energetic (drifting) electrons, however, reduces the growth rate.