MANILA, Philippines--The rainy season has officially started this week, according to the weather bureau.

The wet season usually begins on the fourth week of May but with La Niña conditions persisting in the country, the start of the rainy season came a week early, said the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa).

The "slightly earlier" onset of rain has an "indirect relation" to climate change, triggering the frequency of El Niño and La Niña event, according to Pagasa Director Prisco Nilo.

"La Niña phenomenon [induces] the early onset of the rainy season," he told the Philippine Daily Inquirer Friday.

The weather bureau also attributed the early rainy season to the transit of typhoon "Butchoy" off the eastern coast of the archipelago last week, triggering the southwest wind flow or "habagat."

The two tropical storms "Cosme" and "Dindo," currently in the Philippine area of responsibility, also boosted the southwest monsoon, affecting wide sections of southern Luzon, including Metro Manila and western Visayas.

Weather will improve

"[Although] the rainy season started this week, the weather will gradually improve over northern and Central Luzon on Monday after Cosme [exits] the country," Pagasa weather branch chief Nathaniel Cruz said during a press briefing Friday.

At 10 a.m. Friday, Cosme was monitored 400 kilometers northwest of Calapan City, Oriental Mindoro, with maximum sustained winds of 65 kph near the center and gustiness of up to 80 kph.

It is expected to make landfall Saturday over the Ilocos area and cross northern Luzon in the evening while Dindo will move farther away from the Philippines toward Okinawa, Japan.

Tropical storm Dindo was spotted at 1,070 km northeast of Basco, Batanes, at 10 a.m. Friday with maximum winds of 75 kph with gustiness of up to 90 kph. Public storm signal No. 1 was hoisted over Bataan, Zambales, Pampanga, Tarlac, Pangasinan and Lubang Island. On Monday morning, Dindo is expected to be 130 km east of Aparri, Cagayan.

Peak in July/August

Cruz said the rainy season will peak in July and August, when more tropical cyclones enter the country, even if the La Niña phenomenon continues to weaken. There?s also a 60-percent possibility that conditions will be neutral from May to July.

This, however, will not reduce the normal amount of rainfall in the country during the rainy season, according to Nilo.

"Even if [La Niña] is in the receding stage, it will have a lingering effect that will generate above normal amount of rainfall," he said.