A sidewalk vendor protects herself from the rain using a plastic cover at a footbridge in Pasay City on May 17, 2022. George Calvelo, ABS-CBN News/File

MANILA — The Philippines should expect normal onset and normal amount of rainfall this rainy season, weather bureau Pagasa said on Saturday. 

“Usually, ‘yung normal onset ng rainy season natin [ay] during the second half of May to first half of June. So anytime nagkaroon tayo ng mga sunud-sunod na pag-ulan at na-satisy ang criteria mula noong May 16 hanggang June 15, kapag nag-declare ang Pagasa, normal ang pasok ng ulan,” Climate Monitoring and Prediction Section chief Ana Liza Solis said in an interview with TeleRadyo Serbisyo.

(The rainy season usually starts between the second half of May and the first half of June. So anytime we record rains in successive days satisfying the criteria between May 16 and June 15 – that would be considered normal onset of the rainy season.) 

“Kung pa-iikliin ang onset date ay between the last week of May to the first week of June. Dun talaga mas karamihan na nagkakaroon ng normal onset ng rainy season – around May 27 hanggang June 5,” she added.

(If we shorten the period, most of the past rainy seasons began between May 27 and June 5.) 

Solis said that due to the presence of neutral conditions in the central Pacific or the absence of El Niño and La Niña, usual rainfall should be expected this wet season. 

“Nakikita natin since parang normal naman ‘yung onset ng southwest monsoon – ang normal nating southwest monsoon ay normal na maulan. [Pero] kahit normal ‘yung tag-ulan, makararanas pa rin tayo ng mga flash floods dahil may mga severe thunderstorms at possible ‘yung combined effects ng Habagat at itong mga papasok na bagyo. Ganyan ang normal nating Habagat – maulan at posible pa ring makapagpabaha.”

(We see that the start and the amount of rainfall during the rainy season will be normal. However, we may still experience flash flooding due to severe thunderstorms and the possible combined effects of the southwest monsoon or Habagat and tropical cyclones. The normal Habagat season is rainy and could still bring flooding.) 

In terms of tropical cyclones, fewer or average number of storms may enter or form inside the Philippine area of responsibility this year.

“‘Di pa tayo nagkakaroon ng bagyo kahit isa, so it's either below to near-normal ‘yung possible na bilang ng bagyo – pwedeng mga around 16 to 19 or 20.”

(We have not yet had a storm this year. We may have below to near-normal number – around 16 to 19 or 20.) 

NOT YET RAINY SEASON

To declare the start of the rainy season, Pagasa follows two criteria: the presence of rain and winds blowing from the west. 

“‘Yung five-day period na tinatawag na pentad dapat merong total rainfall na 25 millimeters at kailangan at least 1 mm rainfall for 3 consecutive days… Kung [more than] 50 percent ng mino-monitor na stations, first five days na ma-satisfy ‘yun, ‘yun ‘yung tinatawag nating onset ng tag-ulan. Kasama din dyan ‘yung hangin so kailangan may westerly component kahit hindi totally southwest ang wind flow natin.” 

(A five-day period called pentad should have an accumulated rainfall of 25 millimeters, with three consecutive days recording at least 1 mm rain. If more than 50 percent of the monitoring stations observe this, that’s when the rainy season onset is declared. We also include the wind component – it should be blowing from the west, not necessarily from the southwest.) 

The monitoring stations are located along the western section of the country, where Type I climate is experienced. 

“Ang minomonitor natin dyan ang Type I climate. Eto yung nasa western section ng ating bansa, particularly Luzon area at kasama rin ang parte ng Iloilo sa Western Visayas… ‘Pag sinabing climate type 1, ito ‘yung may distinct wet at distinct dry seasons. Ito ‘yung dominant na mga lugar na mas marami ang ulan at highly exposed sa southwest monsoon.” 

(Our monitoring stations are under Type I climate, located over the western section of Luzon and Panay. Areas under this climate type have distinct wet and dry seasons and are highly exposed to the southwest monsoon.)

Frequent thunderstorms? Warm and dry season not over yet: PAGASA

However, Solis clarified that based on their present monitoring, it's not yet the start of the rainy season.

“Hindi pa po, although mayroon na tayong mga pag-uulan lalo na sa dakong hapon at gabi, particularly sa Metro Manila at ibang bahagi ng Luzon area na mino-monitor natin. Pero kahit isang istasyon, wala pang nakaka-satisfy ng criteria para masabing tag-ulan na.” 

(It’s not yet rainy season although we have been experiencing afternoon and evening rains, particularly in Metro Manila and other parts of Luzon. Not a single monitoring station has satisfied the criteria to declare the beginning of the wet season.)

She further explained that the afternoon rain showers experienced in many parts of the country are localized and that a large-scale weather system is required to sustain the daily rainfall. 

“Kapag mga severe thunderstorm, due to localized effect ‘yan – ‘yung local na pag-init ng lugar. Kapag tag-ulan [naman], meron na talagang magdo-dominate [weather system] na magbibigay ng moisture o pag-uulan sa mga sunud-sunod na panahon kaya hinihintay rin natin ang pagdating ng southwest monsoon or Habagat. ‘Yun ‘yung nagsu-sustain ng moisture.” 

(Severe thunderstorms are caused by localized warming of areas. During rainy season, a dominant weather system that can supply the moisture for a prolonged period is needed. That is why we require the presence of Habagat that will sustain the moisture.)

AGRICULTURE AND HEALTH IMPLICATIONS

The climatologist said that the declaration of the start of the rainy season is very important to the agriculture sector. 

“‘Yung pagdeklara ng Pagasa ng onset ng rainy season, ito rin ‘yung hudyat dun sa mga rain-fed farmers o mga magsasakang umaasa sa tubig-ulan lang na meron nang enough moisture para dun sa pagsisimula ng kanilang pananim, lalo na kung palay ang kanilang tinatanim.” 

(The start of the rainy season also alerts rain-fed farmers that there is enough moisture for them to begin planting their crops, especially rice.) 

She added that aside from Habagat, tropical cyclones also bring significant rainfall required by farmers. 

“Fifty percent ng ating pag-ulan ay galing sa bagyo. Siya ‘yung nagpupuno o nagre-replenish ng mga dam para magamit sa multi-purpose activities, lalong-lalo na sa irrigation.” 

(Fifty percent of our rainfall comes from storms, which replenishes the water supply of our dams for multi-purpose activities, especially irrigation.) 

Apart from flooding and landslides, Pagasa said other hazards like lightning, hailstorms, and tornadoes may be more frequent during the rainy season. 

“Normal ‘yan na nangyayari pero ang posibleng epekto ng global warming as a result of climate change is ‘yung frequency ng pag-occur nito.” 

(These hazards are normal. The possible impact of climate change is the increased frequency of their occurrences.) 

Solis advised the public to only obtain weather information from Pagasa through its website and social media accounts to avoid getting fake news and false information. 

In the same Ligtas Dapat episode, the Department of Health also warned against the rise of different ailments more prevalent during the rainy season. 

They include water- and food-borne diseases, influenza-like illnesses, leptospirosis, and dengue, altogether called WILD diseases.

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