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Manila Bulletin devider Philippines devider National devider Tag-ulan na ba?: Key factors that signal the onset of rainy season in the Philippines

Tag-ulan na ba?: Key factors that signal the onset of rainy season in the Philippines

Published May 21, 2024 02:49 am
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Rain showers have become prevalent in some areas of the country in the past few days, indicating that the rainy season is about to begin. But when will the start of the rainy season be declared?

The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) declares the onset of the rainy season in the country based on several meteorological parameters and observations. 

PAGASA outlined the amended criteria for declaring the onset of the rainy season in 2019. 

Based on the following criteria, it closely monitors rainfall data from various stations across the country.

The onset of the rainy season is declared when a five-day period in May, June, or July accumulates a total rainfall of 25 millimeters or more, with at least 1 millimeter of rainfall recorded for three consecutive days.

For the declaration to be made, at least seven weather stations, or more than 50 percent of the total stations monitored must meet the aforementioned criteria. 

Specifically for Metro Manila, at least two weather stations within the region must satisfy the same criteria.

There are a total of 13 monitoring stations in areas under Climate Type 1. These are in Laoag City, Ilocos Norte; Vigan (Sinait), Ilocos Sur; Dagupan City, Pangasinan; Iba, Zambales; San Jose, Occidental Mindoro; Metro Manila (Science Garden, Quezon City; Port Area, Manila; Sangley Point, Cavite; NAIA, Pasay City); Ambulong, Batangas; Iloilo City, Iloilo; Muñoz, Nueva Ecija; Clark, Pampanga; Cubi Pt. Subic Bay; Coron, Palawan; and Cuyo, Palawan.

Climate Type 1 refers to areas characterized by having two pronounced seasons: dry from November to April and wet during the rest of the year. 

These areas typically experience a significant amount of rainfall, particularly during the rainy season, which usually occurs from May to October. 

In addition to monitoring rainfall, PAGASA also pays close attention to the wind pattern. 

Based on its criteria, prevailing winds should have westerly components over the western Philippines.

"The onset will be declared once the criteria are observed and satisfied. The onset will be the consecutive five days (pentad) wherein these criteria were met," PAGASA said.

The rainy season in the Philippines typically commences between the second half of May and the first half of June. 

In 2023, the onset of the rainy season was officially declared on June 2.

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