Medan Weather Guide: Year-Round Tropical Climate Explained

The Equatorial Constant: Medan’s Primary Climate

Medan, the capital of North Sumatra, is characterized by a Tropical Rainforest Climate (Af). Positioned just 3 degrees north of the equator, the city experiences minimal seasonal temperature variation. Whether you visit in January or June, you will encounter a consistent daily range of 74°F to 90°F (23°C to 32°C). However, the true story of Medan’s weather lies not in its temperature, but in its profound relationship with moisture and the Strait of Malacca.

Daily Rhythms and the "Hot, Oppressive" Feel

The day typically starts with a brief period of clarity and relatively lower humidity around 6:00 AM. By mid-morning, the heat intensifies rapidly, pushing humidity levels toward 80-90%. This creates a "feels like" temperature that often exceeds 100°F (38°C), locally described as gerah—a heavy, stifling heat that feels like a weight on the skin.

Afternoon convection is a daily staple. As land temperatures peak between 2:00 PM and 4:00 PM, clouds gather quickly. It is common for a bright, sunny afternoon to transform into a torrential downpour within minutes, often accompanied by dramatic thunder. These rains provide a temporary, refreshing drop in temperature before the humidity rebounds as the ground dries under the evening sun.

Seasonal Trends: The Wet and the Wetter

While Medan is rainy year-round, locals categorize the year into two distinct phases defined by the monsoon winds:

• The Drier Phase (February to July): February is historically the driest month, receiving only about 3.5 inches of rain. During this window, the sun is most visible, and heatwaves can occasionally push temperatures toward 97°F (36°C). This is the period of highest UV exposure, requiring vigilance for those spending time outdoors.
• The Wet Phase (August to January): Rainfall ramps up significantly, peaking in October and November. October is the wettest month, often seeing over 10 inches of rain across 16+ rainy days. This season is defined by "monsoon surges" where rain can persist for several days, leading to the frequent overflowing of the Deli and Babura rivers.

Local Phenomena and Microclimates

• The Bukit Barisan Effect: The massive Barisan mountain range to the west acts as a barrier, causing orographic lift. While this often shields Medan from some western storms, it also traps moisture over the city, contributing to its legendary humidity.
• Sumatra Squalines (The "Sumatras"): These are localized, intense thunderstorm lines that develop over the Strait of Malacca at night and sweep into Medan in the early morning. They bring sudden, fierce winds and heavy rain even when the day's forecast appears clear.
• Whirlwinds (Puting Beliung): Occasionally, the city experiences small-scale tornadoes or whirlwinds during the transition between monsoon seasons, which can cause localized roof damage in high-density urban areas.

Historical Context and Modern Adaptation

Medan’s history is inextricably linked to its soil and rain, which fueled the colonial-era tobacco and rubber plantations. Today, the city is grappling with an increasing Urban Heat Island effect. The dense concrete of North Medan traps daytime heat, making the nights feel significantly warmer than the surrounding rural areas. To adapt, local life shifts to the evening; markets and social hubs thrive after 6:00 PM when the sun sets and a slightly cooler (though still humid) breeze settles over the city.

Traveler Awareness: Flooding and Visibility

Travelers should be aware that heavy rain in Medan often results in flash flooding. Because the city is built on a low-lying coastal plain, even two hours of intense rainfall can submerge major thoroughfares like Jalan Denai or regions near the riverbanks under 30–100 cm of water. During the peak wet season (Oct–Nov), local transportation often slows to a crawl as motorists navigate these waterlogged streets.