Surabaya, located just 7 degrees south of the equator on the northern coast of East Java, features a Tropical Monsoon (Am) climate transition into a Tropical Savanna (Aw) classification. The city is defined by a distinct two-season rhythm: the heavy Northwest Monsoon (Wet Season) and the breezy Southeast Monsoon (Dry Season).
The Daily Rhythm
In Surabaya, the sun rises and sets at nearly the same time year-round (roughly 5:30 AM to 5:45 PM).
- Mornings: Typically clear and extremely humid. As the sun rises, temperatures climb rapidly, reaching their peak by 1:00 PM.
- Afternoons: This is when the "thermal engine" of the city kicks in. In the wet season, clouds build up rapidly, leading to explosive thunderstorms by late afternoon. In the dry season, the Madura Strait provides a vital sea breeze that moderates the coastal heat.
- Evenings: The air remains thick. While the temperature drops into the mid-70s°F (24°C), the high dew points mean it rarely feels "cool" in the urban center.
Seasonal Trends
The Wet Season (November to April)
Powered by the Northwest Monsoon, this period is characterized by high atmospheric moisture.
- Peak Rainfall: January and February are the wettest months, often seeing over 300mm (12 inches) of rain. Flooding in low-lying areas of the city is a historical challenge locals have adapted to through extensive canal systems.
- The "Feel": The air is "heavy" and oppressive. Even when it isn't raining, cloud cover is persistent, and the humidity sits near 80-90%.
The Dry Season (May to September)
As the winds shift to the Southeast, dry air from the Australian continent moves over Java.
- Climate Behavior: This is the sunniest time of year. Rainfall is rare; August may see as few as 1 or 2 rainy days.
- The "Feel": While still hot (highs of 90°F / 32°C), the lower humidity makes the heat far more tolerable. July and August are the "coolest" months due to the stronger breeze, offering the most pleasant thermal comfort.
The "Transition" Heat (October)
October is technically the start of the transition toward the rainy season, but it is historically the hottest month of the year. With the sun passing directly overhead and the rains yet to arrive, the city experiences a "scorched" feel. Temperatures frequently exceed 95°F (35°C), and the ground retains heat long into the night.
Microclimates and Urban Geography
- Urban Heat Island: As Indonesia's second-largest city, Surabaya's dense concrete core is consistently 2-3°C warmer than the surrounding rural areas or the cooler slopes of nearby Mount Penanggungan.
- Coastal Influence: Areas near the Port of Tanjung Perak experience higher wind speeds and slightly lower daytime maximums due to the immediate proximity of the Madura Strait, whereas southern Surabaya (closer to Sidoarjo) can feel more stagnant and humid.
Local Adaptations and Phenomena
Locals refer to the period of relentless rain as Musim Hujan. Life in Surabaya is built to move around the rain; shopping malls and underground passages become social hubs during afternoon downpours.
- The Sea Breeze: Known locally for providing relief, the afternoon wind from the sea is a celebrated daily event that refreshes the city's air quality.
- Visibility: During the dry season, smoke from agricultural burning in the surrounding East Java countryside can sometimes create a characteristic haze, though the coastal winds usually clear this more quickly than in inland cities like Malang.