Harmonic analysis converts periodic function into waves of primary frequency and higher harmonics. Analytical schemes, in the past, were developed to determine the harmonic coefficients. As all the waves at a time pass through each of the ordinates which are at their respective positions along the primary period, the arithmatic sum of the amplitudes put together at the time of passing through an ordinate is made equal to that ordinate, or at least in the practical way, the sum of the amplitudes at each ordinate tends to be equal to that ordinate. This view makes it possible to find the harmonic coefficients from the selected ordinates. And thus, the coefficients could be directly determined without adopting any analytical scheme. The new method of determining harmonic coefficients is applied to SST observations of the Bay of Port Blair. The SST observations were conducted from on board FORV Sagar Sampada during September 29^th (18 Hrs) to 24 Hrs. on 30^th September, 1988 at hourly intervals. The theoretically evaluated SST values from harmonic coefficients were found to be closer to the observed values.