  A new formula for predicting solar cycles based on the current theoretical
understanding of the solar cycle from flux transport dynamo is presented. Two
important processes---fluctuations in the Babcock-Leighton mechanism and
variations in the meridional circulation, which are believed to be responsible
for irregularities of the solar cycle---are constrained by using observational
data. We take the polar field near minima of the cycle as a measure of the
randomness in the Babcock-Leighton process, and the decay rate near the minima
as a consequence of the change in meridional circulation. We couple these two
observationally derived quantities into a single formula to predict the
amplitude of the future solar cycle. Our new formula suggests that the cycle 25
would be a moderate cycle. Whether this formula for predicting the future solar
cycle can be justified theoretically is also discussed using simulations from
the flux transport dynamo model.
