UV and heat in Hanoi
In Hanoi, the average daily peak UV index stays at 3 or above in every month of the year, from 3.9 in January to 9.3 in July.
The warmest month is June, with average highs of 35°C, and the air is most humid in August, at around 87% relative humidity. UV figures come from five years of NASA satellite data, 2020 to 2024, and temperatures from the nearest long-running weather station.
- 9.3Average daily peak UV in July, very high
- 12Months with an average peak of UV 3 or more
- 35°CAverage high in June
- 7.5 hA day at UV 3 or more in July, on average
When is the UV index highest in Hanoi?
The sun is strongest all year round, with the highest average peak in July. In July, about 81% of days reach a UV index of 8 or more, which the World Health Organization calls very high.
How hot and humid does Hanoi get?
Average highs range from 21°C to 35°C through the year. Relative humidity averages 79% to 87%. Day length ranges from 10.9 to 13.4 hours.
Month by month
| Month | Peak UV | Days UV 8+ | Hours UV 3+ | High | Low | Humidity | Daylight |
|---|---|---|---|---|---|---|---|
| January | 3.9 | 0% | 3.3 | 21°C | 15°C | 82% | 11.0 h |
| February | 4.8 | 4% | 4.5 | 22°C | 16°C | 83% | 11.5 h |
| March | 4.8 | 8% | 4.7 | 25°C | 20°C | 83% | 12.0 h |
| April | 5.8 | 21% | 5.4 | 28°C | 22°C | 82% | 12.6 h |
| May | 8.0 | 61% | 6.9 | 33°C | 25°C | 84% | 13.1 h |
| June | 8.3 | 71% | 7.4 | 35°C | 27°C | 85% | 13.4 h |
| July | 9.3 | 81% | 7.5 | 34°C | 27°C | 86% | 13.3 h |
| August | 8.9 | 79% | 7.3 | 33°C | 26°C | 87% | 12.8 h |
| September | 8.3 | 67% | 6.7 | 32°C | 25°C | 87% | 12.3 h |
| October | 7.0 | 48% | 5.7 | 30°C | 23°C | 85% | 11.7 h |
| November | 5.7 | 13% | 4.9 | 27°C | 20°C | 83% | 11.1 h |
| December | 4.1 | 0% | 3.7 | 22°C | 15°C | 79% | 10.9 h |
When should you protect your skin in Hanoi?
The World Health Organization advises sun protection whenever the UV index is 3 or above, and the advice gets stronger from 8. In Hanoi, that means every month of the year, for about 7.5 hours around midday in July. The forecast on any day can be higher or lower than these averages, so check it each morning.
How do you protect yourself?
Cancer Council Australia recommends five steps together when the UV index is 3 or higher: slip on covering clothing, slop on SPF 50 or SPF50+ broad-spectrum, water-resistant sunscreen, slap on a hat, seek shade and slide on some sunglasses.
Clothing covers skin all day without reapplying. Sleeves usually stop at the wrist and the collar, so the backs of your hands and your neck are easy to miss; the Meriggio · Italian · say it “meh-REED-joh”The shady spot where you rest through the midday heat. has hand covers and a neck shade for those two places. Women’s fit, men’s fit.
Other cities in Vietnam
UV and heat across Vietnam. All cities.
Sources and data
- UV index: NASA POWER Hourly API, NASA Langley Research Center, CERES SYN1deg (UV index), MERRA-2 (temperature, humidity). Hourly values for 2020 to 2024, around 21.03, 105.85. Satellite and reanalysis grid values for the area around the city, not a single weather station. Peak UV is the mean of each day’s highest hourly UV index. Fetched 18 October 2026.
- Temperature: NOAA NCEI Global Surface Summary of the Day, weather station HA DONG (48825099999), 11.1 km from the city centre, 2012 to 2024. Highs and lows are the average of each month’s mean daily maximum and minimum.
- Relative humidity is an area average from NASA POWER for a grid square about 55 km wide.
- Day length calculated from latitude for the 15th of each month.
- World Health Organization: Radiation, the ultraviolet (UV) index, 20 June 2022
- Cancer Council Australia: Be SunSmart