Weather Underground is a site that provides excellent local weather information in the form of graphs, tables and csv files. You can use the data very easily in SWMM 5 by copying from Excel to a time series in SWMM 5. Here is the rainfall for a storm event in Tampa, Florida in September, 2010
Export from WeatherUnderground using the CSV File Export Option
The data imported from the csv file to Excel and after the text to columns tool is used looks like this in Excel. The data is now ready to be imported into SWMM 5 after the time column is adjusted to fall on even 5 minute intervals. In Excel you can use the formula @ROUND((B2)/"0:05:00",0)*"0:05:00" to round all of the time values to 5 minutes. If you do not do this step then you will have problems in SWMM 5 due to the rainfall interval not being equal to the defined raingage interval.
You will need to format the new rounded time as a time format for import into SWMM 5
Open up and make a new time series in SWMM 5 and then copy and paste the date, rounded time column and rainfall column into the SWMM 5 time series columns.