Where fog days matter in Vietnam: Sa Pa, Ha Giang, Ha Long

Fog days peak in different months across Sa Pa, Ha Giang, Ha Long, and Ninh Binh. We use the station tables from Vietnam's construction regulation, where averages describe a typical month, not a forecast.

The monthly fog table

The figures below keep the four records together. Each value is the station's number of fog days for that month.

The table shows why one national "fog season" would be too simple. Sa Pa begins the year with the largest values. Ha Giang's values build toward December. Ha Long peaks in March, while Ninh Binh's highest value is December.

Where each place peaks

Sa Pa's highest fog value is January at 17.4 fog days. February follows at 16.9, and March records 15.3. The value is still 13.3 in December. That winter pattern sits beside Sa Pa's lower winter rain totals, which is why a low millimeter figure does not automatically mean clear views. Our article on Sa Pa in winter keeps the rain, drizzle, fog, and sun columns together.

Ha Giang's peak is December at 6.4 fog days, followed by November at 4.6 and October at 3.5. The station's highest fog values arrive later in the year than Sa Pa's. February is its driest month by rainfall, but the fog table is a different measure.

Ha Long Bay reaches 4.2 fog days in March. February records 2.5, and April 1.4. Ninh Binh reaches 2.6 in December, with January at 2.1 and February at 1.5. The smaller values do not mean that a particular boat trip or mountain view will have the same visibility as the station average.

The Ha Giang place page, Ha Long Bay page, and Ninh Binh page identify the place records. They are useful for keeping a station's location separate from a general regional label.

Why the peaks need context

The four stations sit in different settings and elevations. Sa Pa's station is 1,570 m above sea level and 2 km from its map pin. Ha Giang's station is 118 m above sea level and 1 km from its pin. Ha Long Bay uses the Bãi Cháy station at 87 m and 13 km from the pin. Ninh Binh's station is 2 m above sea level and 2 km from its pin.

A mountain station, a town station and a coastal station can have different fog patterns, so one pattern should not be applied to every road or viewpoint.

Da Lat and Ho Chi Minh City have no fog data. That means no figure exists, not that there are zero fog days.

The four complete rows also show that fog does not follow the rainfall extreme in a simple way. Sa Pa's wettest month is July, but its largest fog value is in January. Ha Giang's wettest month is July, while its largest fog value is in December. Ha Long Bay's wettest month is August, while its fog peak is March. Ninh Binh's wettest month is September, while its fog peak is December.

If your trip depends on a view, treat the peak month as a reason to check the weather closer to the date. A monthly fog count can't tell you whether a specific lookout, boat route or mountain road will be visible when you arrive.

What this does not tell you

The regulation does not define a fog day, so we cannot say how thick the fog must be or how long it must last. The table also does not measure visibility, cloud height, road safety, wind, or a mountain loop's conditions.

The station distance and altitude matter. Ha Giang's record is from the town station at 118 m, not from the mountain loop. Sa Pa's record is from a high station, not every trail. The regulation does not state the observation period of these tables, so we do not name a period. The figures are monthly context, not a daily forecast.

References

• QCVN 02:2022/BXD, National technical regulation on natural physical and climatic data for construction: https://datafiles.chinhphu.vn/cpp/files/vbpq/2022/10/02-bxd.pdf. Checked 2026-09.

Photo: Mã Pí Lèng, Vietnam.jpg, Hoach Le Dinh, CC0, https://commons.wikimedia.org/wiki/File:M%C3%A3_P%C3%AD_L%C3%A8ng,_Vietnam.jpg

Data checked: September 2026.