Typhoon Dolphin has weakened to a tropical storm after making two landfalls in eastern China's Zhejiang province, but its moisture-rich circulation is continuing to move northwestward, threatening to unleash potentially extreme rainfall across parts of northern China, meteorologists said on Monday.

　　Dolphin, the 13th typhoon of the year, made two landfalls in Zhejiang on Sunday evening and weakened as it moved inland. But unlike many tropical cyclones that rapidly dissipate after landfall, its extensive cloud system and abundant moisture have allowed its remnants to persist and move northward and westward, said Zhang Fanghua, chief forecaster at the National Meteorological Center.

　　"The residual circulation could bring persistent and extreme rainfall to parts of eastern and northern China," Zhang said.

　　Dolphin's movement is forecast to significantly slow after Tuesday, and around Wednesday its remnants could stall near the border area of Hubei, Henan and Anhui provinces.

　　The residual vortex is expected to interact with an upper-level trough in the westerlies and a cold-air system, potentially triggering a new round of widespread and heavy rainfall, Zhang added.

　　The heavy rain will cover much of Shanghai as well as Zhejiang, Jiangsu, Anhui, Hubei, Henan and Shandong provinces through Tuesday.

　　As the rain belt moves northward on Tuesday and Wednesday, some locations in Henan, Hebei, and Shanxi could receive 400 to 600 millimeters of rain, with the possibility of exceptionally heavy downpours.

　　Meteorologists warned that the threat will also extend into the Beijing-Tianjin-Hebei region.