Great question! The simple answer is never. Once we issue our long range forecasts 11-months in advance, we do not make any changes to them. This is due to the way we forecast. Our long range forecasts do not use the traditional physics-based methods for forecasting, but rather are formed based on a combination of the 24 oceanic climate cycles (such as El Nino), historical weather, and statistics.
Once the date in question is less than 15 days away, it becomes part of our short range forecast that is updated daily using the more traditional physics-based methods of forecasting.
All dates that have passed are now considered historical data and are actual values of what occurred that day. These values have no relationship to our forecasts.