mydataMinTempKTaMia =
WeatherData["KTMB",
"MinTemperature", {{2005, 1, 1}, {2012, 12, 31}, "Day"}]
Export["MinTempKTaMia.xlsx", mydataMinTempKTaMia // Values, "XLSX"]
This will get the values out of the timeseries object and get them in 1 column in XLS.
Is that what you needed?