The cool season is over, the department's director, Chomphari Chomphurat, told a press conference. Summer starts in Thailand on March 5 and will end in mid-May when the rain arrives.
The temperature will rise to 35 degrees Celsius or higher in upper parts of the country from Sunday, and remain high until the end of summer, Chomphari said.
“The average [summer] temperature will be 35.5 degrees Celsius this year, which is higher than last year,” she said.
Temperatures will soar to as high as 40-43 degrees Celsius in the northern provinces of Sukhothai, Tak, Lampang and Mae Hong Son in summer this year, Chomphari said.
Bangkok and its satellite provinces will see a maximum temperature of 38-39 degrees Celsius, she said.
Summer in the upper parts of Thailand is characterised by shifting winds – from northeasterly to southeasterly.
Thunderstorms are expected to continue in the North, Northeast, Central and East regions until the middle of this month, as a cold mass from China clashes with increasing hotter air in Thailand, Chomphari said.
Weather will be erratic between late April and mid-May, with sudden shifts from sweltering heat to thunderstorms and high winds, she said, adding that hailstorms are a possibility.
The North and Northeast will see thick morning mist till the middle of this month, as well as summer storms in some areas.
Thunderstorms are expected to hit 20 to 30% of southern Thailand between late March and late April. Rainfall will be heavier and more frequent from mid-May, with downpours hitting 60-80% of the region.
Waves in Andaman coastal areas are expected to be two to three metres high, while those in the Gulf of Thailand will be one to two metres high.
Chomphari said the amount of rainfall will be average in upper parts of the country, while the South will see “slightly higher than usual levels”.
There may be a pause in the rainy season in late June and early July, she said, suggesting that farmers should store water for the period.