Not a great time, summers would be at the peak and in case of rain the road accessibility would be reduced.
The best time would be Sep onwards and Dec Jan for the peak winter experience
Travelling Kerala in summers is really not good time to visit. If you really want to enjoy beauty of Kerala you must visit either early monsoon or end of the monsoon. or else during winter, Kerala can be visited
Munnar in Winter (September to November and January to March)- Best Season to visit Munnar. The best time to visit Munnar would be October to November and from January to May when it is comfortably cold. There may be occasional rains which will give a misty experience of Munnar.