Most of the sensors overheat in hot climate. In fact the recommended upper limit for ambient temperature is 40 degrees centigrade (page 350 of D3300 manual, check you manual under Technical Notes), and 85% humidity. Thus in hot and humid climate like India, especially the Southern Region in general and the Northern Region in summers, the camera is operating well beyond recommended specifications.
With long exposures, the sensor heat builds up, and in hot Indian summers may damage it self. The only recourse is to cool the sensor some how. For long exposures on tripods here is what can be done to cool the camera
. A fan to blow air across the camera - basic cooling
. A fan blowing through a peltier cooler - best as now you are blowing cold air
. A fan blowing across a bag of ice - same as above, but requires no power
As the camera is weather sealed, any air blown will not get inside to cool the electronics, so you have to cool the camera casing. In case the rear LCD is on during long exposures, it will not only eat up batteries, but also heat up. So cooling the LCD will help.