naming scheme for international use contains 140 names described above. The list is not restricted by year; the first name to be used in a typhoon season is the name after the last-named cyclone of the preceding season. The PAGASA naming scheme for Philippine use contains four lists, each containing twenty-five names arranged in alphabetical order. Every typhoon season begins with the first name in the assigned list, and the rolls of names are each reused every four years. An auxiliary list of ten names is used when the main list in a year had been exhausted. Not all Western Pacific cyclones are given names by both weather agencies, as JMA does not name tropical depressions, and PAGASA does not name cyclones outside the Philippine Area of Responsibility. In the case of both weather agencies, names are retired after a typhoon that carried it caused severe or costly damage and loss of life. Retirement is decided by the agencies' committees, although in PAGASA's case, names are routinely retired when the cyclone caused at least 300 deaths or ₱1 billion in damage in the Philippines. Retired names are replaced with another name for the next rotation, for JMA by the nation that submitted the retired name, and for PAGASA with a name sharing the same first letter as the retired name. Variability in activity On an annual time scale, activity reaches a minimum in May, before increasing steadily to June, and spiking from July to September, with August being the most active month for tropical cyclones in the Philippines. Activity reduces significantly in October. The most active season, since 1945, for tropical cyclone strikes on the island archipelago was 1993 when nineteen tropical cyclones moved through the country (though there were 36 storms that were named by PAGASA). There was only one tropical cyclone which moved through the Philippines in 1958. The most frequently impacted areas of the Philippines by tropical cyclones are northern Luzon and eastern Visayas. A ten-year average of satellite determined precipitation showed that at least 30 percent of the annual rainfall in the northern Philippines could be traced to tropical cyclones, while the southern islands receive less than 10 percent of their annual rainfall from tropical cyclones. Tropical cyclone warning signals The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) releases tropical cyclone warnings in the form of tropical cyclone warning signals. On March 23, 2022, PAGASA