How to perform precipitation data analysis?
Date/timestamps are tricky to convert without further information; are the values you show days (unlikely, if 990555 is your date/time value), hours, seconds? See if you can figure out the system used (either by knowing which date your timestamp is supposed to represent, or looking at the step sizes for the data); this will generally give you an idea of what is being represented, and how to convert to an actual date.
Coordinate and long/lat are basically the same thing, only built up from decimals or hours/minutes (e.g. 0.5 representing 30 minutes). Conversion can be found http://transition.fcc.gov/mb/audio/bickel/DDDMMSS-decimal.html, for instance. Mind that other coordinate systems are also possible, which will make the conversion different; again, this is important to figure out before you can convert your data.
Comparison options will depend on: 1) whether your data corresponds (do you have measurements on the same date/time, as well as the same location?), 2) what you are interested in.