Quick answer: September is the transition from monsoon to autumn in Nepal. Kathmandu sits around 26°C by day and 19°C at night, the lowland Terai is hot at 36–38°C, and high trekking altitudes range from roughly 10–20°C by day down toward freezing at night. The first half of the month is still wet; skies clear progressively through late September, opening the autumn trekking season.
September straddles two seasons. Early in the month, the monsoon is still winding down — expect humidity, afternoon showers, and clouds that can hide the peaks. By the last week, the rains retreat, the air clears, and visibility of the Himalaya improves dramatically. That's why late September into October is considered the start of Nepal's prime trekking season.
If you're choosing dates, the second half of September is noticeably better than the first for clear mountain views and drier trails.
Temperature in Nepal in September by region
Nepal's weather changes sharply with altitude, so a single "Nepal temperature" figure is misleading. Here's what to expect across the main regions:
| Region | Daytime | NIghttime | Notes |
| Kathmandu | 26-30°C | 15-19°C | Warm, humid, occasional showers |
| Pokhara | 28-32°C | 18-22°C | Warm and wet |
| Terai / Chitwan (lowlands) | 32-38°C | 24-26°C | Hot and Humid |
| Mid-hills / trekking trails 2000-3500m | 15-20°C | 5-10°C | Pleasant trekking temperatures |
| High altitude (4000m+, base camps | 5-15°C | 0°C or below | Chill nights, layers essential |
Rainfall and humidity in September
September is still officially a monsoon month, and this is the detail most guides understate. Rainfall is heaviest in the first 10–15 days and tapers toward the end.
Kathmandu: roughly 200 mm of rain spread across about 15 rainy days.
Pokhara: the rainiest major destination, often 550–640 mm — most of it early in the month.
Terai (Chitwan): around 300 mm, but spread across many gloomy, humid days.
Humidity: high across the country, typically 80–86%.
Most rain falls as short, heavy afternoon or evening downpours rather than all-day drizzle, so mornings are often the clearest part of the day, a good reason to start trekking early.
Early September vs. late September: the difference that matters
| Expect | Early September | Late September |
| Rain | Frequent, heavier in rainy weather areas | Tapering off |
| Mountain Views | Nice view in the morning, daytime is often cloud-covered | Increasingly clear |
| Trails | Wetter, it can be slippier on some trails | Drying out |
| Crowds | Very quiet | Picking up |
| Verdict | Green and peaceful, but gamble on a perfect view | Best balance of clear skies and solitude |
Weather at popular trekking altitudes
If you're heading up, here's roughly what conditions look like in September:
Everest Base Camp region (up to ~5,500 m): Days mild, nights cold. Lukla flights can be delayed by clouds, especially early in the month. Trails mostly free of snow.
Annapurna Base Camp / Circuit: Warm, green, fewer crowds than October. Higher passes are generally clear of snow.
Rain-shadow regions (Upper Mustang, Dolpo, Jomsom): Stay relatively dry even in early September — these are the safest bets if you want to trek early in the month.
Yes, with the right expectations. If you want guaranteed clear skies, October is safer. But September rewards you with lush green landscapes, full waterfalls, far fewer crowds, major festivals (Teej, Indra Jatra, sometimes Dashain), and steadily improving weather. For trekkers who don't mind some early-month rain and want quiet trails, it's one of the most underrated months of the year.
Planning to trek? See our guide to the 10 best treks in Nepal in September for specific routes, costs, and itineraries.
Frequently asked questions
What is the temperature in Nepal in September?
Kathmandu averages about 26°C during the day and 19°C at night. The lowland Terai is hotter (30–32°C), while high trekking altitudes range from around 10–20°C by day to near freezing at night.
Does it rain in Nepal in September?
Yes, especially in the first half of the month — it's the tail end of the monsoon. Rain usually comes as short afternoon or evening showers and tapers off significantly by late September.
Is September a good month to trek in Nepal?
Late September is excellent: clearing skies, green scenery, and quiet trails before the October peak. Early September is wetter, and views can be cloudy, so rain-shadow regions like Mustang and Dolpo are the better early-month choices.
Which part of Nepal is driest in September?
The rain-shadow regions north of the Himalaya, Upper Mustang, Dolpo, and the Jomsom area stay relatively dry even when the rest of the country is still getting monsoon showers.
What should I pack for Nepal in September?
Waterproofs (jacket and pack cover), quick-dry layers, a warm layer for cold high-altitude nights, grippy waterproof boots, and insect repellent.
