Thailand warns of heavy rain across multiple regions

The Thai Meteorological Department has issued a nationwide weather forecast warning of alternating periods of heavy rain and reduced rainfall across Thailand between 18 and 24 June 2026, as the southwest monsoon continues to influence conditions over the Andaman Sea, Thailand and the Gulf of Thailand.

During 18–20 June, most regions are expected to experience widespread thunderstorms, with heavy rain in some areas. This is linked to a moderate southwest monsoon combined with a low-pressure cell covering northern Vietnam, increasing atmospheric instability across the region.

From 21–24 June, rainfall is expected to decrease in most parts of the country. However, isolated heavy rain is still likely in the eastern region, where monsoon conditions remain active.

Sea conditions will remain moderately rough in places. In the upper Andaman Sea, waves are forecast at around 1–2 metres, while the lower Andaman Sea and the Gulf of Thailand will generally see waves of around 1 metre. During thunderstorms, wave heights may exceed 2 metres, and mariners are advised to exercise caution throughout the period.

Authorities have urged the public, particularly in the northern, upper north-eastern and eastern regions, to remain vigilant for hazards associated with accumulated rainfall, including flash floods, forest runoff and river overflows. People living in foothill areas, waterways and low-lying zones are advised to take extra precautions during periods of heavy rain.

Small boat operators in the Andaman Sea and the Gulf of Thailand have also been warned to avoid sailing during thunderstorms due to rapidly changing sea conditions and potentially dangerous wave activity.

Regional forecast outlook

• In the northern region, thunderstorms are expected across 40–60% of areas during 18–20 June, with heavy rain in some locations. Between 21–24 June, rainfall is forecast to ease to 30–40% coverage, with south-westerly winds of 10–20 km/h. Temperatures will range from 22–26°C at night to 31–36°C during the day.
• In the north-eastern region, thunderstorms will affect 40–60% of areas in the first period, with heavy rain in some places. Rainfall will reduce to 20–30% of areas in the later period, with similar wind conditions. Temperatures are expected between 23–27°C and 33–37°C.
• The central region will see thunderstorms across 40–60% of areas during 18–20 June, decreasing to 30–40% afterwards, with light to moderate south-westerly winds of 10–20 km/h. Temperatures will range from 23–28°C to 31–37°C.
• In the eastern region, thunderstorms will cover 60–70% of areas early in the period, with heavy rain in some locations. This will ease to 40–60% later, but heavy rainfall remains possible. Winds are expected at 15–30 km/h, with sea waves around 1 metre, rising above 2 metres during thunderstorms. Temperatures will range from 24–28°C to 31–36°C.

• For the southern eastern coast, thunderstorms will affect 40–60% of areas initially, easing to 30–40% later. South-westerly winds of 15–30 km/h are expected, with wave heights around 1 metre and exceeding 2 metres during storms. Temperatures will range from 23–27°C to 33–36°C.
• On the western southern coast, thunderstorms will also cover 40–60% of areas during 18–20 June, easing to 30–40% afterwards. From Phuket northwards, winds will reach 15–35 km/h with waves of 1–2 metres, while areas from Krabi southwards will see winds of 15–30 km/h and lower wave heights. Temperatures will range from 23–27°C to 32–36°C.
• Bangkok and surrounding provinces are expected to experience thunderstorms across 40–60% of areas during 18–20 June, easing to 30–40% later in the forecast period. Winds will remain south-westerly at 10–20 km/h, with temperatures between 24–27°C and 33–36°C.