Washi weakened slightly after passing Mindanao, but regained strength in the Sulu Sea, and made landfall again over Palawan on December 17.

On December 12, the Joint Typhoon Warning Center (JTWC) noted that a developing area of low pressure had persisted about 945 km (585 mi) south-southeast of Guam.

[5] Less than six hours later, both the JTWC and the Japan Meteorological Agency (JMA) classified the system as a tropical depression, with the former assigning the identifier 27W.

By December 14, convection redeveloped over the low and the JTWC subsequently assessed the system to have attained tropical storm status.

[8] Early on December 15, the system crossed west of 135°E and entered the Philippine Atmospheric, Geophysical and Astronomical Services Administration's (PAGASA) area of responsibility.

[12] On December 16, Washi reached its peak strength as a severe tropical storm and made its first landfall along the east coast of Mindanao.

After passing Mindanao, Washi weakened due to land interaction, but the storm quickly regained its strength, in the Sulu Sea.

Washi weakened to a tropical depression and dissipated on December 19, because of cool, dry air, in association with the Northeast Monsoon.

Across the Cagayan de Oro river basin, a localized heavy rain event occurred during Tropical Storm Washi's passage.

[3] Estimates from the Tropical Rainfall Measuring Mission jointly run by NASA and JAXA indicated that accumulations around the Cagayan de Oro river exceeded 400 mm (16 in).

[3] Starting in tributaries and later reaching the main Cagayan de Oro, Iponan, and Mandulog rivers, flash flooding manifested at a dramatic pace.

Located outside the main "typhoon belt," residents in the affected areas suffered from a false sense of security with tropical cyclone related disasters.

[1] Total casualties attributed to the event are uncertain, with the National Disaster Risk Reduction and Management Council's final report in February 2012 stating 1,268 fatalities, 181 people missing, and 6,071 injuries.

[27] President Benigno Aquino III visited Cagayan de Oro and Iligan on December 20, 2011, and declared a state of national calamity in the affected provinces.

[1] In the three years following Washi, ₱2.57 billion (US$58 million) was allocated to build 30,438 shelters, designed to withstand winds of 220 km/h (140 mph), in eight regions.

[32] The Danish government provided 300,000 DKK (US$53,000) in emergency funds for relief items such as food, water, sanitation materials, mattresses and blankets.

[32] The Japanese government provided 25 million yen (US$320,000) worth of relief goods, such as water tanks and generators, for victims of the storm.

On December 22, the United Nations Department of Humanitarian Affairs announced a plan to raise $26.8 million in aid for victims of Severe Tropical Storm Washi.