The sixteen parameters are calibrated using historical precipitation and streamflow values. A few locations report precipitation every 6 hours, and even fewer on an hourly basis. This is accomplished by using stations which are able to report precipitation on an hourly or 6-hourly basis. These reports provide the key to when the rainfall occurred. Once the data is in 6-hour intervals, the reporting stations located within a river basin, and some that are nearby, are averaged.
Theissen weighting is used to produce the basin average rainfall.
Table 2 displays an example of a QPF product from Puerto Rico. Example of a QPF Product from Puerto Rico. Hurricane Georges was the first excessive rainfall event to effect the island since this duty was implemented. Forecasting precipitation amounts for a land falling hurricane is a very difficult undertaking. Differences in forward speed and storm track could significantly affect the amount of heavy rain on the island.