<P> Tropical cyclones form in any month of the year across the northwest Pacific Ocean, and concentrate around June and November in the northern Indian Ocean . The area just northeast of the Philippines is the most active place on Earth for tropical cyclones to exist . Across the Philippines themselves, activity reaches a minimum in February, before increasing steadily through June, and spiking from July through October, with September being the most active month for tropical cyclones across the archipelago . Activity falls off significantly in November . The most active season, since 1945, for tropical cyclone strikes on the island archipelago was 1993 when nineteen tropical cyclones moved through the country . 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 . </P> <P> Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies . When the subtropical ridge position shifts due to El Nino, so will the preferred tropical cyclone tracks . Areas west of Japan and Korea tend to experience much fewer September--November tropical cyclone impacts during El Niño and neutral years . During El Niño years, the break in the subtropical ridge tends to lie near 130 ° E which would favor the Japanese archipelago . During La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific Ocean, which increases the landfall threat to China . </P>

The large annual precipitation in the wet equatorial climate is caused by which of the following