MANILA, Philippines - An early onset of the rainy season will likely occur in the country if a tropical cyclone develops this month, Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) administrator Prisco Nilo said yesterday.
Despite experiencing rains the past several days in most parts of the country, Nilo stressed the summer season is not yet over.
“The development of a tropical cyclone may trigger the early onset of the rainy season associated with the southwest monsoon,” Nilo said in a phone interview.
He said a 25-millimeter rainfall requirement and a southwest monsoon that should be the prevailing wind system are just some of the criteria used in declaring the onset of the rainy season.
Nilo also said a total of 25 mm of rainfall must be recorded for five consecutive days in five weather stations in the western part of the country to say that the rainy season has indeed come.
Nilo said although the amount of rainfall recorded in the past several days has already exceeded the 25-mm requirement, the southwest monsoon is still not the prevailing wind system in the country.
Nilo said the two shallow low-pressure areas (SLPAs) monitored by Pagasa early this week have dissipated.
A low-pressure area is commonly associated with bad weather. A tropical cyclone, if at sea, can be formed in such condition.
Nilo said the intertropical convergence zone (ITCZ) is responsible for the rain showers in Metro Manila and other parts of the country.
The ITCZ is the main focal point for showers and thunderstorms in the tropics. The reason for this is that northeasterly trade winds to the north of the ITCZ meet southeasterly trade winds from the south.
The piling up of air near the surface due to the converging winds forces the warm, humid air over the tropical oceans to rise. As the air rises, it cools and water vapor condenses into clouds and rain.
In its 5 p.m. weather bulletin yesterday, Pagasa said the cold front would affect extreme Northern Luzon and Central Luzon in the next 24 hours.
The ITCZ, on the other hand, would prevail over Southern Luzon, the Visayas and Mindanao.
Nilo earlier said the country is experiencing an “abnormal” summer due to the presence of several rain-producing weather systems like the ITCZ, SLPAs and the cold front. He attributed this to climate change.