Which trigonometric function I should use to generate the temperature with two peaks (i.e.one strong and one moderate peak)? I want to generate seasonal temperature of Bay of Bengal. I want to do this with a trigonometric function. Seasonal temperature of Bay of Bengal has two peaks. One major peak during April and another moderate peak in November. Which trigonometric function I should use to do this? !enter image description here

The standard way to model periodic function is with Fourier series (though in your case the function seems approximately periodic only).

A simple second order approximation would be

$$a+b\cos\omega t+c\sin \omega t+d\cos 2\omega t+e\sin 2\omega t$$ where $\omega=\dfrac{2\pi}{12}$ if $t$ is in months.

You can find the extrema by canceling the derivative,

$$-b\sin\omega t+c\cos\omega t-d\sin2\omega t+e\cos2\omega t=0.$$

The coefficient $a$ will be the annual average and the remaining coefficients can be found by giving the positions and amplitudes of the two maxima, and solving a linear system of equations.