  A phenomenological model is presented for the quantitative description of
individual solar cycles' features, such as onset, intensity, evolution, in
terms of the number of M and X-class solar flares. The main elements of the
model are the relative ecliptic motion of the planets Jupiter and Saturn, and
its synergy with a quasi-periodic component of solar activity. Using as input
the temporal distribution of flares during cycle 21, the general evolution of
cycles 22-24 is reproduced in notable agreement with the observations,
including the resurgence of activity in the last months of 2017, and further
predictions are provided for cycle 25. This deterministic description could
contribute to elucidating the responsible physical mechanisms and forecasting
space weather.
