Typhoon Haikui was the third tropical cyclone in the span of a week to impact Mainland China during late July and early August 2012.

[citation needed] At 06:00 UTC on August 1, the Joint Typhoon Warning Center (JTWC) began to monitor an area of convection, associated with a gale-force non-tropical low embedded within the eastern end of a monsoon trough, located approximately 550 nmi (1,020 km; 630 mi) to the north of Guam.

At the time, the low had a poorly-defined low-level circulation center, with a large area of deep convection surrounding it, and was under an environment of good equatorial outflow and moderate wind shear.

[4] As the system was developing its center rapidly under increased wind shear, the JTWC issued a Tropical Cyclone Formation Alert (TCFA) late on the same day.

[5] Although it lacked deep convection near its center, the JTWC started issuing advisories on the depression at 21:00 UTC the next day, designating it as 12W.

[7] Moving westward under the southern periphery of a deep subtropical ridge to its north, Haikui continued organizing, with formative banding feeding to the northern side of its ragged center.

[12] By August 6, the system became partially exposed at its northern side, and had slowed its movement down due to the steering subtropical ridge weakening because of a mid-latitude trough developing over the Sea of Japan.

[14] Under an environment of 27–29 °C (81–84 °F) sea surface temperatures and weak wind shear, Haikui intensified to a Category 1-equivalent typhoon on the Saffir-Simpson scale at 15:00 UTC that same day.

[16] At 12:00 UTC that same day, the JMA upgraded the system to a typhoon;[17] however, the storm began to deteriorate, as its eye became elongated, with the convection being more shallow and loose.

[27] As a result, widespread heavy rains impacted regions still recovering from deadly floods triggered by Typhoon Saola less than a week earlier.

[28] During a 72‑hour span from 6–8 August, 1,007 mm (39.6 in) of rain fell in parts of Metro Manila, leading local media to compare the event to Typhoon Ketsana in 2009, which killed 464 in the city.

The head of the National Disaster Risk Reduction and Management Council (NDRRMC) compared the deluge to the Kevin Costner film Waterworld.

[34] In response to the flooding, the NDRRMC allocated approximately ₱13,000,000 worth of relief funds and deployed 202 personnel to assist in search and rescue missions.

Communications were affected badly, though distress calls and SMS from thousands of Metro Manila residents and their worried relatives flooded television and radio stations as most power and water connections were lost.

[45] Local residents feared the death toll could rise significantly as many people living in the area were undocumented migrant workers from other provinces.

[46] Heavy rains, in excess of 600 mm (24 in) in Anhui Province triggered severe flooding that destroyed 4,473 homes and affected 3 million people.

[53] In the wake of widespread flooding brought about by the typhoon, the National Commission for Disaster Reduction and the Ministry of Civil Affairs activated level four emergency plans in Anhui, Jiangxi, Shanghai, and Zhejiang Provinces.