Predicting the Shape of Solar Cycle 25 Using a Similar-Cycle Method

A similar-cycle method is applied in predicting the shape of Solar Cycle 25, through a more scientific definition to select similar cycles. Using the current solar minimum $R_{\mathrm{min}}(25)$ as a reference, the six most similar cycles to Solar Cycle 25 are found to be Cycles 24, 15, 12, 14, 17, and 10 (in that order). The monthly values of sunspot-number series for the whole of Cycle 25 are predicted by weighted averaging the corresponding ones in the six similar cycles. As a result, Solar Cycle 25 is predicted to peak around October 2024 with an amplitude of about $R_{\mathrm{m}}=137.8\pm 31.3$ and to end around September 2030. As a by-product, there might be a secondary peak eight months earlier. The similar-cycle method considers only the solar cycles with similar parameters rather than all ones as for regression methods. It has an advantage that it does not depend so much on the accuracy of the observation.