Guangzhou is the core city of South China. It is on the north of Zhu Jiang Delta (Pearl River Delta), where the Dong Jiang River (East River), Xi Jiang River (West River) and Bei Jiang River (North River) join together. On its South is the South China Sea. With its geographical advantages, Guangzhou has been a very important port in South China for hundreds of years. Today, it is the biggest and most important port for air, sea, and trains in China. The area of Guangzhou is about . The north part and middle part of Guangzhou are hills. The west part and south part are plains that have a lot of rivers and streams. Guangzhou is in the subtropics monsoon climate region. It has a lot of sunshine and rain. The average temperature is from 21.4 to 21.9 °C (about 71 °F) and the lowest temperature in winter is about . The rainy season lasts for almost six months and the typhoons in summer also bring lots of rain. The average humidity is about 77 percent.