21°N 120°E and back to the beginning. Tropical cyclone bulletins are issued by PAGASA every three hours for all tropical cyclones within this area that are currently affecting the country, six hours when cyclones are anticipated to make landfall within the Philippines, or twelve hours when cyclones are not affecting land. As of March 23, 2022, PAGASA used to classify tropical cyclones into five categories: Tropical Depression – maximum 10-minute sustained winds of 39 to 61 km/h Tropical Storm – maximum 10-minute sustained winds of 62 to 88 km/h Severe Tropical Storm – maximum 10-minute sustained winds of 89 to 117 km/h Typhoon – maximum 10-minute sustained winds of 118 to 184 km/h Super Typhoon – maximum 10-minute sustained winds of more than 185 km/h. Tornadoes On August 27, 2007, PAGASA announced that it was putting up a tornado warning system, days after several more powerful and destructive tornadoes damaged houses in Central Luzon. On August 23, 2007, a second tornado destroyed 30 houses in 4 villages in San Miguel, Bulacan, the first tornado having damaged 27 houses in San Rafael, Bulacan on August 8, 2007. Doppler weather radar, weather stations and other equipment PAGASA installed its first Doppler weather radar station in Baler, Aurora and another in Baguio. The new weather radars can monitor the typhoon and its movements, amount of rainfall either moderate or heavy and real-time atmospheric forecasts using a visual radar monitor, an example was that of Typhoon Basyang in 2010. Data are used for warnings (such as rainfall) through Project NOAH since June 2012. PAGASA has installed at least sixteen Doppler weather radars in the country, currently operational stations are as follows: Luzon: Basco (in Batanes, currently under repair), Aparri (Cagayan), Baguio, Subic (Zambales), Baler, (Aurora), Tagaytay (Cavite), Busuanga and Quezon (both in Palawan), Daet (Camarines Norte), Virac (in Catanduanes, the country's most modern radar facility); Visayas: Mactan (Cebu), Iloilo, Alburquerque (Bohol), Guiuan (Eastern Samar); Mindanao: Zamboanga City, Tampakan (South Cotabato), Hinatuan (Surigao del Sur). Moreover, the weather bureau is now planning to construct at least three more Doppler weather radar stations in Agno (Pangasinan), Cataingan (Masbate) and in Laoang (Northern Samar). It aims to have twenty operational radar stations nationwide by the end of 2020. Before Nilo's leave, an automated rain gauge was also installed in a telecommunications cellsite in Montalban, Rizal (in cooperation with Smart Communications) to monitor excess rainfall as a warning