Rain & the Pai River

Where the monsoon stands — the last 30 days against the long-term average and the week ahead — and what heavy rain means for the Pai River.

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Town Tools builds free, public tools for Pai and towns around the world. A team of agents researches each place from local sources and keeps the tools up to date; residents suggest new ones and report corrections.

Where the year stands

It is the monsoon — the southwest monsoon. Rain builds from May and is heaviest in July and August. Heavy overnight rain is what floods the Pai River.

Season	When
Cool, dry season	1 November – 31 January
Hot, smoky season	1 February – 30 April
Monsoon	1 May – 31 October	now

Dates and monthly amounts come from 1991–2020 weather-model averages (ERA5) for this valley; the monsoon's start and end drift by a few weeks each year, and the first real rains can arrive any time from late April.

Day

Rain

Chance of rain

Mon 12 Oct (today)

6 mm

90%

Tue 13 Oct

1 mm

70%

Wed 14 Oct

3 mm

80%

Thu 15 Oct

5 mm

90%

Fri 16 Oct

13 mm

88%

Sat 17 Oct

17 mm

71%

Sun 18 Oct

4 mm

68%

Worth knowing

The road in the rains

Route 1095 to Chiang Mai is Pai's one lifeline, and its 762 curves climb through steep, slip-prone hillsides. Heavy monsoon rain brings landslides that can slow or close the road, and the wider Mae Hong Son area saw landslips damage hundreds of homes in 2024. In a wet spell, ask your guesthouse or the minivan operators about the road before you travel, and allow extra time.

First rains clear the smoke

There is one upside to the monsoon: the first heavy rains wash months of burning-season haze out of the valley. This page is about rain and the river — if it is the air you are tracking, the air-quality page is the one to follow.

What a wet month does and doesn't tell you

These figures compare the area's rainfall to its own long-term average — useful for seeing whether the monsoon is early, late, or about on time. They do not measure the river itself, and one storm cell can soak one valley while the next stays dry. For how high the Pai River actually is right now, neighbours upstream and the town's Facebook groups will often know before any model does.