The rainy season will officially start on Monday with less rain forecast this year due to the El Nino weather phenomenon, the Meteorological Department announced on Friday.
TMD director-general Chomparee Chompurat said the seasonal climatic change would also see a shift in general wind direction.
According to Ms Chomparee, the El Nino weather phenomenon could mean a dry spell from mid-June to mid-July, leading to water shortages in several agricultural areas.
Rainfall is expected to peak in August and September with one or two tropical storms moving across the North and the Northeast, bringing heavy rain and triggering flash floods, she said.
According to the TMD chief, the rainy season is due to end in the middle of October but rainfall is expected to continue in the southern region, especially on the eastern side, until January next year.
Meanwhile, the Department of Royal Rainmaking and Agricultural Aviation said it is preparing for droughts. Department chief Supit Pitaktham said the country has experienced little rain since January, and about 116 million rai of farmland outside the irrigation system faces water shortages.
From May 1-14, there were 1,387 requests for rain-making operations from 459 districts in 64 provinces, including those from the Royal Irrigation Department, to increase water reserves in 70 reservoirs.
Bangkok governor Chadchart Sittipunt said City Hall had drawn a map of flood-prone areas and is well-equipped to handle any flooding.
He expressed concern about possible drought affecting several large public parks under its care, including Benjakitti Park, which requires a particularly large amount of water to maintain.
Mr Chadchart said waste management also needs to be addressed, especially in the outer districts of Sai Mai, Min Buri and Nong Chok, where populations have increased.