In his Tuesday message, Mousavi also sympathized with the nations and governments of the three countries as well as the bereaved families of the victims.
Flooding and mudslides have killed at least 97 people in the Indian states of Karnataka, Maharashtra and Gujarat.
Flooding downpours have also struck northern India with at least 34 deaths reported in the state of Uttarakhand.
In Kerala at least 76 deaths have been reported in the past week, and more than 290,000 people have been affected by the flooding.
Nearly 227,000 people are seeking shelter from the flooding in Karnataka, where 60 people have been killed. Chief Minister B.S. Yeddyurappa told Reuters that the flooding was the worst the state had endured in 45 years.
Southern Pakistan has also endured deadly weather with at least 17 deaths reported thus far.
Also a typhoon wreaked havoc in southern China over the weekend killing at least 33 people. Rescue workers used rubber dinghies to evacuate people left stranded as swift currents swept through villages.
Among the dead were 23 people killed when a landslide blocked a river and then engulfed a village in Yongjia county.
Heavy monsoon rainfall has also been deadly in Myanmar where more than 50 people have lost their lives in the past week. Monsoon rainfall will continue across Myanmar this week; however, downpours are not expected to be as widespread as last week.
Climate scientists in 2015 ranked Myanmar at the top of a global list of nations hardest hit by extreme weather. That year more than 100 people died in floods that also displaced hundreds of thousands.
Every year monsoon rains hammer Myanmar and other countries across south-east Asia, submerging homes, displacing residents and triggering landslides.