El Niño and Southeast Asia, and what it means for our weather scores

El Niño is a warming of the surface of the central and eastern Pacific that recurs every few years. Its effect on Southeast Asia is fairly consistent: rainfall shifts east, toward the open Pacific, and much of the region gets less rain than usual. For someone planning a month in Bali, Chiang Mai or Da Nang, that usually means drier weeks, hotter months before the monsoon and, in some places, smoke.

This post covers what tends to change, when it changes, and how it interacts with the weather numbers NomadNext shows. Those numbers describe a typical recent year, and an El Niño year is not typical.

What tends to change, and where

Indonesia, Malaysia and Singapore. The dry season, roughly June to October, tends to be drier and to last longer, and the rains often arrive late. Dry peatland in Sumatra and Kalimantan then burns more easily. Smoke from those fires is the main cause of the haze that drifts across Singapore, Peninsular Malaysia and southern Thailand. The bad haze years of 1997 and 2015 were both El Niño years.

Thailand, Vietnam, Cambodia and Laos. The strongest effect often comes the spring after El Niño peaks. The hot months of March to May can be hotter than usual, and the southwest monsoon can start late or bring less rain. In northern Thailand, a drier spring can make the smoke from the seasonal burning last longer. In the Mekong Delta, low river levels let seawater push further inland.

The Philippines. Rainfall tends to be below normal, especially from late in the year into the next spring.

These are tendencies, not forecasts. Every El Niño is different, and other climate patterns, notably the Indian Ocean Dipole, can strengthen or offset them. For example, the bad 2019 haze season came in a year when the Indian Ocean Dipole was strongly positive, not in a strong El Niño year.

When it matters

El Niño usually develops in the northern summer and peaks around December. For Southeast Asia, that gives two periods to watch:

• August to November of the year El Niño develops, for a dry, long dry season and haze in Indonesia and Malaysia.
• March to May of the following year, for heat on the mainland and in the Philippines.

Meteorological agencies such as NOAA's Climate Prediction Center and Australia's Bureau of Meteorology publish El Niño outlooks several months ahead. If your stay falls in one of these periods, check the outlook before you commit to a long booking.

How our weather data is built

Weather on NomadNext comes from hourly historical weather records. We use the two most recent complete calendar years for each city, which in 2026 means 2024 and 2025, and average each month across those two years.

We define rain around how a day feels, not the standard meteorological measure:

• A rainy day is one with more than two hours of rain between 07:00 and 23:00 local time. An hour counts as rainy if it records at least 0.1 mm. A short shower at 3am does not count. An afternoon of rain does.
• A heavy-rain day is one with at least 10 mm in total.

The monthly weather score combines four parts:

In search ranking, only temperature and rainy days are used, and they count equally. Weather is one of three signals in the ranking:

What that means in an El Niño year

The averages lag a little. Two years is a short window, so one unusual year moves the average a lot. Our current window starts with the end of the 2023–24 El Niño. Southeast Asia had a severe heatwave in April 2024, so our March to May temperatures for mainland cities may run warmer than a longer average would show. As the window moves forward each year, that year will drop out.

Drier usually scores better. Fewer rainy days lift the score, so in a dry El Niño season the conditions will often be better than our average suggests, as far as rain goes.

Heat costs more than it looks. Above 27 °C, the temperature part drops by about 0.09, on a scale from 0 to 1, for every additional degree. As an illustration from the formula, not from any city's data: a month averaging 29 °C scores 0.82 on temperature, and the same month at 30 °C scores 0.73.

If your dates fall in an El Niño year