April marks a turn around season in much of South East Asia when there is a switch in the prevailing monsoon systems, brining drier more settled weather to some regions and wetter, less settled weather to others.
The West coasts of Thailand and Malaysia are coming to the end of the 'dry' season and the 'rainy' season is knocking on the door. So April can see extended periods of rain-free days, but equally can be humid and may have some unsettled weather (usually in the form of short, sharp late afternoon downpours rather than incessant rainfall).
Over on the East coast of Malaysia similarly, the wetter months are drawing to a close and drier weather is becoming predominant. April is a good time to visit Borneo.
April is a good time of year to visit Bali and Lombok and much of Indonesia.
April marks the end of the high season for touring in Cambodia, Laos and Myanmar. Central Vietnam has a good climate at this time of year making Hoi An a great choice for a beach holiday to Vietnam in April.
In the Indian Ocean, Sri Lanka (with the exception of the west coast) is a great choice in April, as is the Maldives, which is a great Winter Sun destination. Mauritius is a year-round destination and April is a good time to visit. April is one of the best times to visit the Seychelles as the climate is usually calm and windless.
April is still a good time of year to visit Oman and the UAE, as temperatures are still tolerable.