Climate and average weather in Cát Bà
In Cát Bà, the summers are oppressive, hot, wet, and mostly cloudy and the winters are mild and mostly cloudy.
Over the course of the year, the temperature in Cát Bà typically varies from 16°C to 30°C, and is rarely below 12°C or above 32°C. July is the hottest month of the year, while January is the coldest.
Based on the travel score, the best times of year to visit Cát Bà for warm-weather activities are from early January to early May and mid October to late December.
- Hottest
- Jul
- 30°
- Coldest
- Jan
- 16°
- Wettest
- Aug
- 399 mm
- Driest
- Feb
- 23 mm
- Rain / yr
- 1792 mm
- 152 wet days
- Daylight
- 10.7–13.3 h
- shortest–longest
- Elevation
- 24 m
- 20.7°N
- Clearest
- Oct
- 48% cloud
Cát Bà is town in Vietnam.
Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.
Cát Bà weather by month, at a glance
The whole year in one picture — sky, rain, humidity, temperature and travel score. Click any band to jump to its full chart.
Each stripe is one measure across the whole year, stacked so a single day reads top to bottom. The sky band runs overcast grey on top down to clear blue at the base — more blue means sunnier — followed by the rainfall curve, the humidity band, a temperature strip that tints each stretch of the year by how warm its average high is, and the travel-score line at the foot. Scan straight down any date to read that day across every measure at once; the score climbs highest around early January to early May.
Temperature through the year
Daily average highs and lows in Cát Bà, from 1991–2020 of climate data. The shaded bands show the range most days fall in — 10th to 90th percentile.
The hot season lasts 5.4 months, from May 7 to October 17, with daily high temperatures above 27°C. The hottest month of the year in Cát Bà is July, with an average high of 30°C and low of 28°C.
The cool season lasts 2.7 months, from December 15 to March 7, with daily high temperatures below 21°C. The coldest month of the year in Cát Bà is January, with an average low of 16°C and high of 19°C.
Days typically run about 3°C warmer than nights year-round.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°C) | 19 | 19 | 21 | 25 | 28 | 30 | 30 | 30 | 29 | 28 | 24 | 21 |
| Avg low (°C) | 16 | 17 | 19 | 23 | 26 | 28 | 28 | 27 | 26 | 25 | 21 | 18 |
| Avg high (°C) | Avg low (°C) | |
|---|---|---|
| Jan | 19 | 16 |
| Feb | 19 | 17 |
| Mar | 21 | 19 |
| Apr | 25 | 23 |
| May | 28 | 26 |
| Jun | 30 | 28 |
| Jul | 30 | 28 |
| Aug | 30 | 27 |
| Sep | 29 | 26 |
| Oct | 28 | 25 |
| Nov | 24 | 21 |
| Dec | 21 | 18 |
How hot and cold Cát Bà really feels
The felt-temperature range through the year — heat index on the day's high (summer humidity), wind chill on the night's low (winter wind). The dashed lines are the plain thermometer; the gap is how much hotter or colder it really feels.
On the hottest afternoons, once humidity is folded in, Cát Bà feels like about 38°C (around June 25). About 142 days a year carry some heat stress, peaking in June.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Feels-like high (°C) | 19 | 19 | 21 | 25 | 32 | 37 | 38 | 37 | 35 | 29 | 24 | 21 |
| Air high (°C) | 19 | 19 | 21 | 25 | 28 | 30 | 30 | 30 | 29 | 28 | 24 | 21 |
| Feels-like low (°C) | 16 | 17 | 19 | 23 | 26 | 28 | 28 | 27 | 26 | 25 | 21 | 18 |
| Air low (°C) | 16 | 17 | 19 | 23 | 26 | 28 | 28 | 27 | 26 | 25 | 21 | 18 |
| Feels-like high (°C) | Air high (°C) | Feels-like low (°C) | Air low (°C) | |
|---|---|---|---|---|
| Jan | 19 | 19 | 16 | 16 |
| Feb | 19 | 19 | 17 | 17 |
| Mar | 21 | 21 | 19 | 19 |
| Apr | 25 | 25 | 23 | 23 |
| May | 32 | 28 | 26 | 26 |
| Jun | 37 | 30 | 28 | 28 |
| Jul | 38 | 30 | 28 | 28 |
| Aug | 37 | 30 | 27 | 27 |
| Sep | 35 | 29 | 26 | 26 |
| Oct | 29 | 28 | 25 | 25 |
| Nov | 24 | 24 | 21 | 21 |
| Dec | 21 | 21 | 18 | 18 |
Average hourly temperature in Cát Bà
A compact picture of the whole year, hour by hour: each column is a day, each row an hour, and the color is the modeled average temperature. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
Read left to right for the day of the year and top to bottom for the hour of the day; the color is the modeled temperature, cool blues through to hot reds on the same scale as the other charts. A vertical slice is a single day's swing — coolest just before dawn, warmest in the mid-afternoon — while a horizontal slice follows one hour across the seasons. The darker overlay marks night and the lighter one the twilight around sunrise and sunset. Colors run warmest on July afternoons, near 30°C, and coldest before dawn in January, near 16°C.
Cát Bà weather by month
Every month at a glance. Click a month for its detailed page.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|
| Jan | 19° / 16° | 40 | 7.6 | 10.9 | 6.2 |
| Feb | 19° / 17° | 23 | 5.7 | 11.3 | 6.4 |
| Mar | 21° / 19° | 40 | 7.6 | 11.9 | 6.6 |
| Apr | 25° / 23° | 52 | 7.7 | 12.5 | 7.0 |
| May | 28° / 26° | 185 | 15.5 | 13 | 5.1 |
| Jun | 30° / 28° | 215 | 17.8 | 13.2 | 3.7 |
| Jul | 30° / 28° | 303 | 19.8 | 13.1 | 3.6 |
| Aug | 30° / 27° | 399 | 24 | 12.7 | 3.3 |
| Sep | 29° / 26° | 305 | 20 | 12.1 | 4.0 |
| Oct | 28° / 25° | 134 | 11.6 | 11.5 | 6.2 |
| Nov | 24° / 21° | 56 | 8.4 | 11 | 7.2 |
| Dec | 21° / 18° | 39 | 6.3 | 10.8 | 6.9 |
Chance of rain
How likely it is to rain on a typical day, and how that shifts across the wetter and drier seasons.
Cát Bà gets about 1792 mm of precipitation a year. On a typical day the chance of rain is often wet, but that rises and falls sharply with the seasons.
The wetter season lasts 5.2 months, from around May 5 to Oct 10, peaking in August at about 80% chance on a given day. The drier stretch runs the rest of the year, bottoming out around Dec 18.
August is the wettest month by volume, with 399 mm over about 24 wet days; February is the driest, with 23 mm.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rain on a day (%) | 24 | 21 | 24 | 27 | 49 | 59 | 64 | 77 | 66 | 38 | 28 | 21 |
| Rain days | 8 | 6 | 8 | 8 | 16 | 18 | 20 | 24 | 20 | 12 | 8 | 6 |
| Rain on a day (%) | Rain days | |
|---|---|---|
| Jan | 24 | 8 |
| Feb | 21 | 6 |
| Mar | 24 | 8 |
| Apr | 27 | 8 |
| May | 49 | 16 |
| Jun | 59 | 18 |
| Jul | 64 | 20 |
| Aug | 77 | 24 |
| Sep | 66 | 20 |
| Oct | 38 | 12 |
| Nov | 28 | 8 |
| Dec | 21 | 6 |
Monthly rainfall
Over a full year, Cát Bà collects about 1792 mm of rain across 152 wet days — roughly 149 mm in an average month.
It doesn’t fall evenly. August is the wettest month with 399 mm, while February is the driest at just 23 mm. The three wettest months alone bring about 56% of the year’s total.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rainfall (mm) | 40 | 23 | 40 | 52 | 185 | 215 | 303 | 399 | 305 | 134 | 56 | 39 |
| Rain days | 8 | 6 | 8 | 8 | 16 | 18 | 20 | 24 | 20 | 12 | 8 | 6 |
| Rainfall (mm) | Rain days | |
|---|---|---|
| Jan | 40 | 8 |
| Feb | 23 | 6 |
| Mar | 40 | 8 |
| Apr | 52 | 8 |
| May | 185 | 16 |
| Jun | 215 | 18 |
| Jul | 303 | 20 |
| Aug | 399 | 24 |
| Sep | 305 | 20 |
| Oct | 134 | 12 |
| Nov | 56 | 8 |
| Dec | 39 | 6 |
Clouds and sunshine
How often the daytime sky is clear, partly cloudy or overcast.
In Cát Bà, the average share of the sky covered by clouds shows significant seasonal variation over the course of the year.
The clearer part of the year begins around September 13 and lasts for 3.7 months, ending around January 4. The clearest month is October, when the sky is clear, mostly clear, or partly cloudy 63% of the time on average.
The cloudier part of the year begins around May 16 and lasts for 3.9 months, ending around September 12. The cloudiest month is June, when it is overcast or mostly cloudy 85% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Clearer (%) | 32 | 30 | 29 | 42 | 35 | 15 | 20 | 23 | 41 | 63 | 61 | 46 |
| Cloudier (%) | 68 | 70 | 71 | 58 | 65 | 85 | 80 | 77 | 59 | 37 | 39 | 54 |
| Clearer (%) | Cloudier (%) | |
|---|---|---|
| Jan | 32 | 68 |
| Feb | 30 | 70 |
| Mar | 29 | 71 |
| Apr | 42 | 58 |
| May | 35 | 65 |
| Jun | 15 | 85 |
| Jul | 20 | 80 |
| Aug | 23 | 77 |
| Sep | 41 | 59 |
| Oct | 63 | 37 |
| Nov | 61 | 39 |
| Dec | 46 | 54 |
Daylight, sunrise and sunset
Hours of daylight through the year, with sunrise and sunset times.
The gold band is daylight — sunrise runs along its lower edge, sunset along the upper — so it widens toward summer and pinches toward winter, with night the dark area above and below. The longest day, around June 16, brings about 13 h 18 min of light; the shortest, around December 16, only 10 h 42 min — a swing of roughly 2 h 36 min.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daylight (h) | 10.9 | 11.3 | 11.9 | 12.5 | 13.0 | 13.2 | 13.1 | 12.7 | 12.1 | 11.5 | 11.0 | 10.8 |
| Sunrise (AM) | 6:35 | 6:28 | 6:06 | 5:38 | 5:19 | 5:15 | 5:23 | 5:34 | 5:43 | 5:51 | 6:07 | 6:26 |
| Sunset (PM) | 5:27 | 5:45 | 5:57 | 6:06 | 6:18 | 6:30 | 6:32 | 6:17 | 5:50 | 5:22 | 5:07 | 5:10 |
| Daylight (h) | Sunrise (AM) | Sunset (PM) | |
|---|---|---|---|
| Jan | 10.9 | 6:35 | 5:27 |
| Feb | 11.3 | 6:28 | 5:45 |
| Mar | 11.9 | 6:06 | 5:57 |
| Apr | 12.5 | 5:38 | 6:06 |
| May | 13.0 | 5:19 | 6:18 |
| Jun | 13.2 | 5:15 | 6:30 |
| Jul | 13.1 | 5:23 | 6:32 |
| Aug | 12.7 | 5:34 | 6:17 |
| Sep | 12.1 | 5:43 | 5:50 |
| Oct | 11.5 | 5:51 | 5:22 |
| Nov | 11.0 | 6:07 | 5:07 |
| Dec | 10.8 | 6:26 | 5:10 |
Sunny days
How many genuinely sunny days each month brings — days the sky stays clear or mostly clear — banded into plain-language zones.
Cát Bà averages about 7 sunny days a month — counting the days the sky stays clear or mostly clear — with a clear seasonal swing between 2 and 16 days.
The sunnier stretch runs 3.8 months, from around Sep 12 to Jan 5. The sunniest month is October, with roughly 15 sunny days (mixed).
The greyest month is June, down near 3 sunny days — about 81% fewer than the October peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sunny days | 6 | 5 | 5 | 7 | 6 | 3 | 4 | 4 | 8 | 15 | 14 | 10 |
| Sky | Gloomy | Gloomy | Gloomy | Gloomy | Gloomy | Gloomy | Gloomy | Gloomy | Mixed | Mixed | Mixed | Mixed |
| Sunny days | Sky | |
|---|---|---|
| Jan | 6 | Gloomy |
| Feb | 5 | Gloomy |
| Mar | 5 | Gloomy |
| Apr | 7 | Gloomy |
| May | 6 | Gloomy |
| Jun | 3 | Gloomy |
| Jul | 4 | Gloomy |
| Aug | 4 | Gloomy |
| Sep | 8 | Mixed |
| Oct | 15 | Mixed |
| Nov | 14 | Mixed |
| Dec | 10 | Mixed |
Humidity comfort
Share of days at each humidity comfort level, based on the dew point — the measure that tracks how muggy it actually feels.
Humidity comfort is graded by the dew point — the temperature at which the air would be fully saturated — because it tracks how muggy it actually feels far better than relative humidity does. A low dew point feels dry and crisp; a high one feels sticky and oppressive no matter the reading on a humidity gauge.
In Cát Bà, how humid it feels changes dramatically over the year.
The more humid part of the year lasts 7.5 months, from around March 19 to October 31. The muggiest month is May, when the air feels humid, muggy or worse about 100% of the time.
The most comfortable stretch runs from around November 1 to March 18, and January is the most comfortable month — the air is dry or comfortable 61% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry (%) | 41 | 28 | 11 | 2 | 0 | 0 | 0 | 0 | 0 | 2 | 13 | 37 |
| Comfortable (%) | 20 | 19 | 12 | 4 | 0 | 0 | 0 | 0 | 0 | 5 | 17 | 20 |
| Humid (%) | 24 | 29 | 24 | 10 | 2 | 0 | 0 | 0 | 2 | 12 | 20 | 21 |
| Muggy (%) | 15 | 22 | 39 | 23 | 8 | 1 | 0 | 0 | 8 | 25 | 22 | 16 |
| Oppressive (%) | 1 | 1 | 14 | 49 | 24 | 5 | 1 | 2 | 21 | 40 | 24 | 5 |
| Miserable (%) | 0 | 0 | 0 | 13 | 66 | 94 | 99 | 98 | 69 | 17 | 3 | 0 |
| Dry (%) | Comfortable (%) | Humid (%) | Muggy (%) | Oppressive (%) | Miserable (%) | |
|---|---|---|---|---|---|---|
| Jan | 41 | 20 | 24 | 15 | 1 | 0 |
| Feb | 28 | 19 | 29 | 22 | 1 | 0 |
| Mar | 11 | 12 | 24 | 39 | 14 | 0 |
| Apr | 2 | 4 | 10 | 23 | 49 | 13 |
| May | 0 | 0 | 2 | 8 | 24 | 66 |
| Jun | 0 | 0 | 0 | 1 | 5 | 94 |
| Jul | 0 | 0 | 0 | 0 | 1 | 99 |
| Aug | 0 | 0 | 0 | 0 | 2 | 98 |
| Sep | 0 | 0 | 2 | 8 | 21 | 69 |
| Oct | 2 | 5 | 12 | 25 | 40 | 17 |
| Nov | 13 | 17 | 20 | 22 | 24 | 3 |
| Dec | 37 | 20 | 21 | 16 | 5 | 0 |
Wind
Average wind speed through the year, banded into plain-language speed zones so a number reads as 'breezy' or 'calm' without knowing the scale.
This is the average sustained wind speed at the standard 10 metres above open ground — the steady flow a weather station reports, not the sharper gusts that come and go, which can run half again as fast. It's the number that says whether a place is generally breezy or calm.
Across the year, average wind speed in Cát Bà is typically light breeze, near 16 km/h, and varies moderately with the seasons.
The windier part of the year lasts 2.9 months, from around May 3 to Jul 28. The windiest month is July, averaging about 17 km/h (light breeze).
The calmer part of the year runs from around Jul 29 to Oct 7, with August the calmest month at about 14 km/h.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wind speed (km/h) | 16 | 15 | 15 | 15 | 16 | 17 | 17 | 14 | 14 | 16 | 16 | 17 |
| Feels | light breeze | light breeze | light breeze | light breeze | light breeze | light breeze | light breeze | light breeze | light breeze | light breeze | light breeze | light breeze |
| Wind speed (km/h) | Feels | |
|---|---|---|
| Jan | 16 | light breeze |
| Feb | 15 | light breeze |
| Mar | 15 | light breeze |
| Apr | 15 | light breeze |
| May | 16 | light breeze |
| Jun | 17 | light breeze |
| Jul | 17 | light breeze |
| Aug | 14 | light breeze |
| Sep | 14 | light breeze |
| Oct | 16 | light breeze |
| Nov | 16 | light breeze |
| Dec | 17 | light breeze |
Hazard calendar for Cát Bà
When the seasonal hazards worth planning around — the rainy season, tropical-cyclone risk and dust haze — are active through the year.
Cát Bà sits in the Pacific typhoon belt; the season peaks July–October.
Cát Bà's monsoon runs May–September, when most of the year's rain falls.
Best time to visit Cát Bà
To characterize how pleasant the weather is in Cát Bà throughout the year, we compute two travel scores — one for general sightseeing, one for beach and pool weather.
Around mid January, Cát Bà is still near the start of its best-weather window — great conditions with the peak-season crowds not yet at full swing.
Inferred from the travel-score curve; month-by-month visitor numbers are a planned addition.
The travel score favors clear, rainless days with daytime highs between 18°C and 28°C. Based on this score, the best time of year to visit Cát Bà for general outdoor tourist activities is from mid October to early May, with a peak score in the third week of November.
The travel score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Travel score (0–10) | 6.2 | 6.4 | 6.6 | 6.9 | 5.1 | 3.7 | 3.5 | 3.3 | 4.1 | 6.2 | 7.2 | 6.9 |
| Rating | good | good | good | good | fair | fair | fair | poor | fair | good | good | good |
| Travel score (0–10) | Rating | |
|---|---|---|
| Jan | 6.2 | good |
| Feb | 6.4 | good |
| Mar | 6.6 | good |
| Apr | 6.9 | good |
| May | 5.1 | fair |
| Jun | 3.7 | fair |
| Jul | 3.5 | fair |
| Aug | 3.3 | poor |
| Sep | 4.1 | fair |
| Oct | 6.2 | good |
| Nov | 7.2 | good |
| Dec | 6.9 | good |
The beach/pool score favors clear, rainless days with daytime highs between 24°C and 34°C. Based on this score, the best times of year to visit Cát Bà for hot-weather activities run from early April to early June and again from mid September to late November, with a peak score in the last week of October.
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
What to pack for Cát Bà, by month
Month by month, what's worth putting in the bag — from the temperature range, rain chance, sun and wind. Tap a month for a quick packing note.
For a warm-season trip around July (highs near 30°C), the essentials are light clothes, rain gear and sun protection. In the cold season around January (highs near 19°C), pack a light layer.
In July, Cát Bà sees daytime highs around 30°C and nights near 28°C. Pack light clothes and rain gear. Worth having: sun protection. About 20 days see rain.
Sea temperature near Cát Bà
Average ocean temperature at the nearest coast, month by month, banded into swim-comfort zones — the other half of the beach question.
The sea at the nearest coast (about 14 km away) is warmest in August at about 30°C and coldest in February near 20°C.
It's comfortable for a long swim from Mar 6 to Jan 18 — about 10.5 months when the water holds above 20°C.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 20 | 20 | 20 | 23 | 27 | 29 | 30 | 30 | 29 | 28 | 25 | 22 |
| Comfort | Refreshing | Cool | Refreshing | Refreshing | Warm | Tropical | Tropical | Tropical | Tropical | Warm | Warm | Refreshing |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 20 | Refreshing |
| Feb | 20 | Cool |
| Mar | 20 | Refreshing |
| Apr | 23 | Refreshing |
| May | 27 | Warm |
| Jun | 29 | Tropical |
| Jul | 30 | Tropical |
| Aug | 30 | Tropical |
| Sep | 29 | Tropical |
| Oct | 28 | Warm |
| Nov | 25 | Warm |
| Dec | 22 | Refreshing |
UV index (midday) in Cát Bà by month
Clear-sky midday UV index through the year, shaded by the WHO exposure levels — how much sun protection each month calls for.
Under clear skies, the midday UV index in Cát Bà peaks around July 12 at about 12 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 19 at about 6 (high).
The index reaches 3 or more — the level where the WHO recommends sun protection — every month of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 7 | 8 | 9 | 8 | 10 | 12 | 12 | 9 | 9 | 9 | 7 | 6 |
| Level | High | Very high | Very high | Very high | Extreme | Extreme | Extreme | Very high | Very high | Very high | High | High |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 7 | High |
| Feb | 8 | Very high |
| Mar | 9 | Very high |
| Apr | 8 | Very high |
| May | 10 | Extreme |
| Jun | 12 | Extreme |
| Jul | 12 | Extreme |
| Aug | 9 | Very high |
| Sep | 9 | Very high |
| Oct | 9 | Very high |
| Nov | 7 | High |
| Dec | 6 | High |
Average hourly UV index in Cát Bà
Modeled clear-sky UV for every hour of every day — when in the day sun protection actually matters.
The whole year hour by hour: each column is a day, each row an hour, and the color is the modeled clear-sky UV index — the midday peak scaled down as the sun sits lower in the sky. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
UV falls off far faster than brightness as the sun drops, so even in July the burn window is concentrated in the middle of the day: about 8.5 hours a day reach index 3 (protection recommended), and 6.5 hours reach 6 or more. Mornings and late afternoons stay comparatively gentle year round.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV ≥ 3 (h/day) | 6 | 6.5 | 7 | 7 | 8 | 8.5 | 8.5 | 7.5 | 7.5 | 6.5 | 6 | 5.5 |
| UV ≥ 6 (h/day) | 2.5 | 4 | 4.5 | 4 | 5.5 | 6 | 6.5 | 4.5 | 5 | 4.5 | 2.5 | 1.5 |
| UV ≥ 3 (h/day) | UV ≥ 6 (h/day) | |
|---|---|---|
| Jan | 6 | 2.5 |
| Feb | 6.5 | 4 |
| Mar | 7 | 4.5 |
| Apr | 7 | 4 |
| May | 8 | 5.5 |
| Jun | 8.5 | 6 |
| Jul | 8.5 | 6.5 |
| Aug | 7.5 | 4.5 |
| Sep | 7.5 | 5 |
| Oct | 6.5 | 4.5 |
| Nov | 6 | 2.5 |
| Dec | 5.5 | 1.5 |
Air quality in Cát Bà by month
Average fine-particle pollution (PM2.5) through the year — so you can see which months the air is worst, not just the yearly average.
Air quality in Cát Bà is worst in January — around 42 µg/m³ PM2.5 (poor), about 2.6× the cleanest month (July, 16 µg/m³).
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 42 | 42 | 41 | 40 | 26 | 19 | 16 | 18 | 21 | 27 | 29 | 39 |
| Level | Poor | Poor | Poor | Poor | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Poor |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 42 | Poor |
| Feb | 42 | Poor |
| Mar | 41 | Poor |
| Apr | 40 | Poor |
| May | 26 | Moderate |
| Jun | 19 | Moderate |
| Jul | 16 | Moderate |
| Aug | 18 | Moderate |
| Sep | 21 | Moderate |
| Oct | 27 | Moderate |
| Nov | 29 | Moderate |
| Dec | 39 | Poor |
Growing season
Cát Bà is frost-free year round — even the coldest nights rarely reach freezing, so there is no start or end to the growing season.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Frost-free chance (%) | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 |
| Frost nights | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Frost-free chance (%) | Frost nights | |
|---|---|---|
| Jan | 100 | 0 |
| Feb | 100 | 0 |
| Mar | 100 | 0 |
| Apr | 100 | 0 |
| May | 100 | 0 |
| Jun | 100 | 0 |
| Jul | 100 | 0 |
| Aug | 100 | 0 |
| Sep | 100 | 0 |
| Oct | 100 | 0 |
| Nov | 100 | 0 |
| Dec | 100 | 0 |
Growing degree days
Growing degree days tally heat above 10°C: each day adds however many degrees its average temperature runs over that threshold, and cold days add nothing. Cát Bà banks about 5,152 degree days a year, and the running total — which growers use to time plantings and predict maturity — climbs fastest around July.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Growing degree days (°C·days) | 228 | 225 | 317 | 409 | 527 | 571 | 593 | 578 | 535 | 497 | 387 | 286 |
| Growing degree days (°C·days) | |
|---|---|
| Jan | 228 |
| Feb | 225 |
| Mar | 317 |
| Apr | 409 |
| May | 527 |
| Jun | 571 |
| Jul | 593 |
| Aug | 578 |
| Sep | 535 |
| Oct | 497 |
| Nov | 387 |
| Dec | 286 |
Solar energy
Average daily shortwave solar energy reaching the ground, banded into brightness zones so the number means something at a glance.
Solar energy is how much sunlight actually reaches the ground each day, measured in kilowatt-hours per square metre (kWh/m²) — the combined effect of how long the sun is up, how high it climbs, and how much cloud gets in the way. It's the raw fuel a solar panel has to work with: for scale, 1 kWh/m² a day is dim and wintry, while 7+ is desert-bright.
Cát Bà receives about 4.3 kWh/m² a day of solar energy on average — bright — with a clear seasonal swing between 2.7 and 5.5 kWh/m².
The brighter stretch of the year lasts 6.9 months, from around Apr 1 to Oct 26. The brightest month is May, averaging about 5.4 kWh/m² (bright).
The dimmest month is January, down near 2.8 kWh/m² — roughly 48% less than the May peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solar energy (kWh/m²) | 2.7 | 3.1 | 3.8 | 5.0 | 5.4 | 5.3 | 5.2 | 4.8 | 4.6 | 4.5 | 3.6 | 3.0 |
| Level | Moderate | Moderate | Moderate | Bright | Bright | Bright | Bright | Bright | Bright | Bright | Moderate | Moderate |
| Solar energy (kWh/m²) | Level | |
|---|---|---|
| Jan | 2.7 | Moderate |
| Feb | 3.1 | Moderate |
| Mar | 3.8 | Moderate |
| Apr | 5.0 | Bright |
| May | 5.4 | Bright |
| Jun | 5.3 | Bright |
| Jul | 5.2 | Bright |
| Aug | 4.8 | Bright |
| Sep | 4.6 | Bright |
| Oct | 4.5 | Bright |
| Nov | 3.6 | Moderate |
| Dec | 3.0 | Moderate |
Where is Cát Bà?
Cát Bà sits at 20.7°N, 107.0°E, 24 m above sea level, in Vietnam. The nearest listed city is Ha Long, 25 km away.
Topography around Cát Bà
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Cát Bà.
Within 3 km, the terrain around Cát Bà has only modest variations in elevation — a maximum elevation change of 205 m around an average of 22 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 299 m; within 80 km, large variations in elevation — a maximum elevation change of 1,180 m.
The land around Cát Bà is covered by water (58%) and trees (36%) within 3 km, water (80%) within 16 km, and water (51%) and trees (29%) within 80 km.
Vietnam travel facts
- Travel advisory
- Level 1
- Exercise Normal Precautions
- Power plugs
- Type A / B / C / F
- 220 V · 50 Hz
- Prices
- ≈ 29% of US
- price level, 2025
- GDP per capita
- $5,066
- 2025
- Happiness
- 6.4 / 10
- World Happiness, 2025
- Safe drinking water
- 59%
- of population, 2024
- Homicide rate
- 1.5
- per 100k, 2011
- Road deaths
- 30.6
- per 100k/yr, 2019
- Income group
- Upper middle
- World Bank
- English
- Moderate
- EF EPI 500
- Religion
Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Cát Bà (20.7278°, 107.0482°, elevation 24 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. Tropical-cyclone seasons are the published climatological basin seasons (NOAA National Hurricane Center / regional warning centres). Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).