We present a nonparametric method to forecast a seasonal time series, and propose four dynamic updating methods to improve point forecast accuracy. Our forecasting and dynamic updating methods are data-driven and computationally fast, and they are thus feasible to be applied in practice. We will demonstrate the effectiveness of these methods using monthly El Niño time series from 1950 to 2008 (http://www.cpc.noaa.gov/data/indices/sstoi.indices).Let {Z w , w ∈ [0, ∞)} be a seasonal univariate time series which has been observed at N equispaced time. Aneiros-Pérez & Vieu (2008) assume that N can be written as N = np, where n is the number of samples and p is dimensionality. To clarify this, in the El Niño time series from 1950 to 2008, we have N = 708, n = 59, p = 12. The observed time series {Z 1 , · · · , Z 708 } can thus be divided into 59 successive paths of length 12 in the following setting: y t = {Z w , w ∈ (p(t − 1), pt]}, for t = 1, · · · , 59. The problem is to forecast future processes, denoted as y n+h,h>0 , from the observed data.