The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) on Sunday, May 26 said the passage of Tropical Storm “Aghon” may prompt the onset of the country’s rainy season by mid-week.
During a press briefing, PAGASA’s Deputy Administrator for Research and Development Marcelino Villafuerte II said as of Sunday, none of its monitoring stations had yet met the criteria for the onset of the rainy season.
However, further observations could lead to meeting the criteria and the eventual declaration of the onset of the rainy season “around May 28 or 29.”
“Due to the conditions we are monitoring, which require five days of significant rainfall, we anticipate that around May 28 to 29, the monitoring stations will likely meet the criteria for us to declare the onset of the rainy season,” Villafuerte explained in Filipino.
He said Aghon, which is expected to be in the northeastern section of the Philippine Sea by Tuesday, could potentially enhance the southwesterly surface wind flow, which is one of the criteria PAGASA uses to determine the onset of the rainy season in the country.
Based on PAGASA's revised criteria from 2019, 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.
This declaration requires that at least seven weather stations, or more than 50 percent of the total stations monitored, meet these criteria.
Specifically for Metro Manila, at least two weather stations within the region must meet the same criteria.
There are a total of 13 monitoring stations in areas classified as Climate Type 1, which have two pronounced seasons: dry from November to April and wet during the rest of the year.
These stations 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; 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.
Aghon’s rainfall
Based on the PAGASA’s 24-hour rainfall data from Tropical Storm Aghon, Weather Specialist Benison Estareja said the 10 highest observed rainfall amounts from 8 a.m. on May 25 to 8 a.m. on May 26 are as follows:
Mulanay, Quezon (229.4 millimeters); Tayabas City, Quezon (226.5 millimeters); Alabat, Quezon (152.2 millimeters); Infanta, Quezon (146.3 millimeters); Tanay, Rizal (98.4 millimeters); Casiguran, Aurora (77.5 millimeters); Science Garden, Quezon City (70.6 millimeters); Tanauan City, Batangas (70.1 millimeters); Romblon, Romblon (69.5 millimeters); and Calapan City, Oriental Mindoro (60.8 millimeters).
Mulanay and Tayabas City in Quezon province experienced torrential rainfall, while Alabat and Infanta, also in Quezon province, had intense rainfall.
The remaining six stations recorded heavy rainfall over the past 24 hours.
Aghon is the country’s first tropical cyclone for 2024.