PAGASA: Southwest monsoon underway, but not yet rainy season

MANILA, Philippines – State weather bureau PAGASA announced on Wednesday, May 24, that the southwest monsoon or hanging habagat has begun in the country.

The southwest monsoon is characterized by warm and humid weather with rainfall, but PAGASA clarified that this is different from the onset of the rainy season.

“‘Pag sinabi po nating start of the southwest monsoon, not necessarily na ito ay onset na ng rainy season. Kumbaga, ito pa lang ‘yung panimula nung pag-uulan na ating mararanasan. Kapag full-blown southwest monsoon na, ibig sabihin ito na ‘yung onset of the rainy season,” explained PAGASA forecaster Robert Sawi in a press briefing on Wednesday.

(When we say start of the southwest monsoon, it does not necessarily mean the onset of the rainy season. It just means that this is the beginning of more frequent rainfall or the rainy season is approaching. When the southwest monsoon is already full-blown, that’s the time that we can declare the onset of the rainy season.)

In an advisory, PAGASA said its key indicators for declaring the start of the southwest monsoon was the “dominant southwesterly windflow” over the West Philippine Sea in the past several days, and the “eastward migration of the North Pacific high pressure area.”

The state weather bureau also noted that in most parts of Luzon and the Visayas, the weather has already been warm and humid, with occasional to frequent rainshowers and thunderstorms – more signs that the southwest monsoon is underway.

So when will the onset of the rainy season be declared?

The requirement is 5 days of rain generating a total amount of at least 25 millimeters (mm) of rainfall. These 5 days must also include 3 straight days of at least 1 mm of rainfall.

PAGASA Climate Monitoring and Prediction Section officer-in-charge Analiza Solis said in the press briefing that the rainy season would likely begin between May 28 and June 8, “plus or minus two days.”

So far, the Philippines has had 4 tropical cyclones this year – Auring, Bising, Crising, and Dante. The country is visited by an average of 20 typhoons a year. (READ: LIST: PAGASA’s names for tropical cyclones in 2017) – Rappler.com