There is a class of model under the name Transfer Function Model
This class of models expect that you have a series of Y (your outcome at all time points), and series of inputs (your a, b, c, d, e measure at all time points).
E.g. your have y[0], y[1], ..., y[n], y[n+1], and a[0], a[1], ... a[n], a[n+1], etc.
This class of models can help you to predict Y at a future time t, using past values of Y and past-AND/OR-current values of your inputs.
E.g. predict y[n+1], using y[0], y[1], ..., y[n], and a[0], a[1], ... a[n], a[n+1], and so on.
If you have a[n+1], at a future time, great, things just work out.
If you don't have a[n+1], a technique is to put your predicted value of a[n+1] in the place. To have your predicted value for a[n+1], you need a separate model on the series a, to get a[n+1].
The model is under a modeling framework known as ARIMA (autoregressive integrated moving average). But the steps can be applied to other general modeling approaches if the normality assumption is terribly violated, as long as you can formulate the prediction of future values using the past ones..