score:1
The simplest way, aside from forecasts, is to look at historical climate models that will indicate the historically most likely results.
For Ella - from weather and climate.com:
It looks like May gets average sun, is part of the rainy season, and the temperature is starting to drop. Precipitation is over 150mm, usually, for the month, over 16-17 rainy days.
For Nuwara Eliya from ClimateData.org:
Also definitely into the wetter seasons, with average high around 18 deg C.