From today until Tuesday, sudden summer storms, gusty winds and even hail are expected in the Northeast, East, North, Central and upper South.
The Meteorological Department (TMD) said it feared the damage caused by the storms would be felt far and wide.
The storms are being brought by a moderate high-pressure system from China, moving over upper Thailand and the South China Sea.
It is expected to enter the Northeast and Eastern regions today, before moving into the North and Central Plains, including Bangkok, and finally down to the upper South.
The TMD warned people to avoid open areas, to not shelter near big trees or large advertising boards during the storm while farmers are advised to take precautions against crop damage.
People in the South should prepare for heavy rain and strong winds, with waves 2-3 metres high in the Andaman Sea and even higher waves during thunderstorms.
Shipping in the Andaman should proceed with caution during this period and small boats should remain ashore.
Firefighters and volunteers in Chiang Mai province were already busy on Friday, battling a bush fire for five hours at Doi Suthep-Pui National Park in Chiang Mai that destroyed 120 rai of forest, Maj Gen Thanudpol Kosaisewee, deputy commander of the Third Army Region, told media on Friday.
A further 100 officers in the army’s northern fire control department, plus staff from the Protected Areas Regional Office 16, Doi Suthep-Pui National Park and villager volunteers have been battling a bush fire in the national park since Thursday. By late Friday they said 90% of fire had been brought under control.
The fire also sent PM2.5 levels soaring. Air Visual, an app that monitors air quality, recorded a level of 156 microgrammes per cubic metre (µg/m3) near Chiang Mai University on Friday evening, far above the so-called “safe” level of 50 µg/m3.