When you picture summer in Vientiane, get ready for long stretches of heat mixed with heavy tropical rains. Average daytime temperatures usually hover around 31°C to 34°C (88°F to 94°F), and frequent downpours really peak in July and August.
The air feels thick with humidity, often above 80%. That sticky weather definitely shapes how you plan your time outdoors.
You’ll notice summer brings both challenges and rewards. Rain shows up in short, intense bursts, leaving behind fresher air and greener views.
Cloud cover limits sunshine compared to the dry months, but you still get enough daylight to explore when the skies clear. It’s not all gloom, honestly.
From the rhythm of afternoon showers to the warm nights that rarely dip below 25°C (77°F), summer in Vientiane has its own atmosphere. Whether you’re planning cultural visits, riverfront walks, or day trips, knowing these patterns helps you enjoy the city without too many surprises.
Overview of Vientiane’s Summer Climate
Vientiane sits low along the Mekong River, where summer means steady heat, high humidity, and frequent rainfall. The city’s tropical setting shapes its weather, with long wet spells, cloudy skies, and warm nights that barely cool off.
Geographical Location and Elevation
Vientiane sits in central-western Laos, right along the Mekong and near Thailand’s border. The terrain is mostly flat, with only small changes in elevation.
At about 170 meters (560 feet) above sea level, Vientiane is low compared to much of Laos. This modest elevation keeps things consistently warm, since higher ground like the Annamite Mountains tends to be cooler.
The land around the city is a mix of cropland and urban sprawl. These surfaces soak up and hold heat, so nighttime temperatures don’t drop much. The flat land also means winds stay light, letting humid air linger.
Because of its spot and elevation, Vientiane doesn’t get sharp temperature swings. You’ll get steady warmth and heavy seasonal rainfall that really define the summer.
Tropical Climate Classification
Vientiane has a tropical wet and dry climate, also called a savanna climate under the Köppen system (Aw). This climate means a strong contrast between the dry winter and wet summer.
In summer, the monsoon takes over. Moist air from the southwest brings lots of showers and thunderstorms.
Rainfall totals can hit 250–330 mm per month, with August usually the wettest. Humidity stays very high, often close to 100% for much of the day.
The air feels heavy and it’s tough to cool off through evaporation. In contrast to drier places, you rarely get relief even after the sun goes down.
Because of its tropical climate, Vientiane stays warm all year. While winter gets a bit cooler and drier, summer is all about persistent heat, thick humidity, and cloudy skies.
Seasonal Weather Patterns
In summer, daily highs average around 89°F (32°C) and don’t often dip below 83°F or rise above 95°F. Nights stay warm, with lows near 77°F.
You won’t notice much difference between day and night compared to drier places. Cloud cover is almost constant, with skies overcast or mostly cloudy about 90% of the time.
Sunshine hours are limited, and the air feels damp most of the time. The wettest stretch hits in late August, with rainfall and storms at their peak.
Rain falls in short, intense bursts, usually in the afternoon or evening. Streets can flood quickly, but water drains away after storms.
Winds generally stay light, averaging 4–5 mph, and shift direction with the season. Early summer brings winds from the south, then mid-summer shifts to more westerly flow.
Calm conditions just add to the muggy feeling. Daylight hours slowly shorten through summer, but you still get about 12.5 to 13 hours of daylight each day.
With high humidity and long days, lush vegetation thrives, but the air just feels warmer than the thermometer says.
Typical Summer Temperatures
Summer in Vientiane brings steady warmth and high humidity. Expect hot days, warm nights, and not much relief—temperatures barely change all season.
Average Daytime and Nighttime Temperatures
Daytime temperatures usually stick around 88–89°F (31–32°C). It’s rare for them to drop below 83°F (28°C) or climb above 95°F (35°C).
Most afternoons feel hot, often with heavy clouds overhead. At night, the air stays warm.
Average lows hover around 77°F (25°C), with only minor changes week to week. Even after sunset, the humidity lingers, and muggy conditions are almost guaranteed.
Because day and night temperatures don’t vary much, you’ll want lightweight clothing and easy access to shade or air conditioning.
Monthly Temperature Variations
The hottest part of the year actually comes just before summer, but June through August still bring steady heat. In June, daily highs average close to 89°F (32°C) and lows near 77°F (25°C).
July feels about the same, keeping both days and nights warm. By late August, temperatures barely change, but rain chances go up.
On August 31, the average high hits 88°F (31°C), which is just a tiny drop from June. Month to month, the variation is minimal, so you can expect steady warmth whenever you visit in summer.
Rainfall and cloud cover, not temperature, are what really change how the weather feels.
Record Highs and Lows
Summer records in Vientiane don’t go wild, but they’re worth noting. Highs sometimes push above 95°F (35°C), although that’s not common.
The hottest day of the year, usually in mid-April, can reach 94°F (34°C), but by summer, the top temperatures ease a bit. On the cooler side, lows rarely fall below 74°F (23°C), even during heavy rain or cloudy nights.
High humidity and thick clouds prevent much cooling. Since records stay within a narrow range, you won’t face sudden temperature shocks.
The real challenge is the ongoing heat and muggy air that define Vientiane’s summer.
Rainfall and Humidity During Summer
Summer in Vientiane is the wet season—heavy rainfall, frequent storms, and high humidity are the norm. Early and late summer feel different, with rainfall peaking in August and humidity staying high all season.
Monthly Rainfall Totals
Rainfall jumps up fast from May as the monsoon arrives. May averages about 246 mm, and totals rise through June and July, peaking in August with around 399 mm.
September stays very wet, often close to August’s totals. In contrast, the dry winter months average less than 20 mm, showing just how extreme the seasonal shift is.
The summer months alone make up most of the city’s annual total of about 1,950 mm.
| Month | Avg. Rainfall (mm) |
|---|---|
| May | ~246 mm |
| June | ~280–300 mm |
| July | ~320–340 mm |
| August | ~399 mm |
| September | ~350–370 mm |
If you visit in summer, you’ll see heavy downpours almost every week.
Frequency of Rainy Days
Rain in Vientiane isn’t just heavy—it’s frequent. May brings rain on 15–18 days, and by August, that number climbs to about 24 rainy days. September is similar, with rain most days.
Rain usually falls in short, intense bursts rather than all day. Thunderstorms are common, especially late afternoon or evening.
This pattern leaves some dry hours, but you should always be ready for sudden showers. During the dry season, rain drops to just 1–3 days per month, so the summer difference is huge.
Relative Humidity Trends
Humidity in Vientiane during summer stays high. Average relative humidity sits in the 75–85% range, peaking in July and August.
The air often feels heavy and damp, especially right after rain. Mornings tend to be even more humid than afternoons, but honestly, it never really feels dry.
With temperatures often at 30–33°C, the humidity makes it feel even warmer. For comfort, expect sticky conditions and plan for cooling off indoors.
Travelers often rely on air conditioning or shaded outdoor spots to handle the humidity during summer.
Wind Conditions in Summer
During summer in Vientiane, the air mostly stays calm. Wind doesn’t have much impact on daily weather compared to rainfall and humidity.
Average Wind Speed
Winds in Vientiane during summer remain very light. The average speed is about 1 meter per second (3.6 km/h or 2.2 mph), which counts as light air on the Beaufort scale.
Most days, you won’t feel much movement. Smoke from a fire would rise almost straight up or drift just a bit.
Trees and plants hardly sway, and outdoor conditions feel still. Calm air makes the heat and humidity seem even more intense, since breezes hardly cool you down.
Some days bring short periods of slightly stronger breezes, but they rarely top 3 meters per second. Those brief gusts won’t disrupt your plans.
Since wind speeds stay low, summer in Vientiane isn’t considered windy. If you dislike strong winds, you’ll probably find things comfortable.
Prevailing Wind Direction
Wind direction in Vientiane during summer shifts with the monsoon. From late May through September, winds generally come from the southwest.
This brings moist air from the Indian Ocean and fuels the heavy rainfall of the wet season.
When the southwest winds pick up a bit, rain showers usually follow. These winds carry high humidity and cloud cover, which explains why skies are often overcast.
Local geography plays a part too. Because Vientiane sits on the Mekong River plain, winds move steadily across open areas but stay weak overall.
You won’t run into strong directional gusts, but the southwest influence remains consistent throughout the season.
Cloud Cover and Sunshine Hours
In Vientiane, summer brings lots of cloudiness, shorter stretches of direct sun, and noticeable changes in daylight as the months go by.
You’ll get a mix of heavy cloud cover and limited sunshine hours, especially during the peak of the rainy season.
Typical Cloudiness Levels
Cloud cover in Vientiane jumps sharply during the summer months. From May through September, skies often stay overcast or mostly cloudy most days.
June, July, and August bring the most cloud, with the sky covered more than half the time. Data points out that in June, sunshine only makes up about 31% of daylight hours, so nearly 70% of the day feels cloudy.
July and August look much the same, with clouds dominating the skies. By September, the cloud cover finally starts to let up, but it still hangs around for more than 50% of daylight hours.
The monsoon season causes this pattern, bringing heavy rain and thick clouds. If you visit during this stretch, expect long gray days and not much direct sunlight.
Average Daily Sunshine
Vientiane gets less daily sunshine during the wettest months. In June, the city only averages about 4 hours of sun per day—the lowest of the year.
July and August are just a bit brighter, with averages of 5 hours and 4 hours 48 minutes of sunshine each day. By September, sunshine climbs back up to nearly 6 hours daily as the rain starts to back off.
During the dry season, like in November and December, you might get over 8 hours of sunshine per day. With less sun in summer, not only do outdoor plans get tricky, but the air itself feels different.
High humidity and limited sun create a damp, heavy atmosphere. If you’re planning activities, mornings are usually the best time since breaks in the clouds happen more often then.
Daylight Duration Changes
Daylight in Vientiane shifts gradually through summer. May and June bring the longest days, with about 13 hours of daylight at the peak.
By July and August, the days shorten a bit to around 12 hours 40 minutes. September keeps trimming that number, averaging just over 12 hours of daylight.
The gap between the longest and shortest summer days is about an hour. Maybe that doesn’t sound huge, but it does affect how much usable light you get for travel or outdoor things.
Around midday in June and July, the sun sits high—altitude angle above 84°—so when the clouds break, the light can feel intense. Even short bursts of sun seem stronger than you’d expect, given all the clouds.
Additional Summer Weather Factors
When you plan for summer in Vientiane, you need to look at more than just temperature and rain. Humidity, dew point, air pressure, and UV exposure all play a part in your comfort and safety.
Reliable historical weather data can help you prepare for what the city throws at you.
Dew Point Patterns
The dew point in Vientiane during summer usually sits high, between 23°C and 25°C (73°F–77°F). This means the air feels very humid, making the heat feel heavier than the thermometer suggests.
When the dew point climbs above 24°C (75°F), outdoor activity can get uncomfortable, especially in the afternoon. Nights stay sticky too, since the dew point rarely drops enough to offer relief.
High dew points make afternoon thunderstorms more likely. The air’s moisture rises fast, forming clouds that drop heavy rain. That’s just how the monsoon works—showers can show up out of nowhere.
If humidity gets to you, plan for indoor breaks with air conditioning. Always carry extra water, since your body sweats more but cools down less efficiently when dew points are high.
Air Pressure and UV Index
Air pressure in Vientiane during summer mostly stays steady, with only small changes day to day. The city’s tropical location means pressure drops aren’t as dramatic as in cooler climates.
Still, if you notice a slight decline, storms might be on the way. The UV index is another thing to pay attention to. In summer, it often hits levels of 10 or higher, so unprotected skin can burn in less than 20 minutes.
Clouds don’t block UV rays as much as you’d hope, so don’t count on overcast skies to protect you. To lower your risks, put on broad-spectrum sunscreen, wear light protective clothing, and stay out of direct sun during midday.
Sunglasses with UV protection help too, especially since glare gets intense after rain. By keeping an eye on pressure and UV trends, you can plan outdoor time better and avoid getting caught off guard.
Accessing Historical Weather Data
If you want a clearer picture of Vientiane’s summer, try checking out historical weather data. Long-term records can show patterns in rainfall, dew point, temperature, and sunshine hours.
This info helps you compare averages with what you might actually experience on your trip.
For instance, past decades of data show that rainfall peaks in July and August, often topping 300 mm per month. Dew point and humidity stick around at high levels during these months, too.
Knowing this, you can prepare for wet conditions more easily.
You’ll find reliable info from meteorological services, airport weather stations, and climate archives. Many of these sources offer charts with daily averages, rainfall totals, and sunshine hours.
When you look at this data, go for multi-year averages instead of just a single year. That way, you’ll avoid getting thrown off by weird weather and get a more accurate sense of Vientiane’s summer climate.