This means that the rainy season is on time, according to meteorologist Nonoy About of the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA).
About said this type of cloud, called the cumulo nimbus, is formed due to the extreme heating of the land surface during the summer months and the subsequent accumulation of water vapor in the atmosphere.
"The abrupt massive vertical or upward wind motion creates a temporary vacuum over the land mass. This vacuum is filled by the wind from the ocean. As condensation occurs over the land mass, cumulo nimbus clouds are developed," he told The STAR.
Thunderstorms have started occurring too, usually in late afternoon and early evening.
"This is the thunderstorm genesis or the beginning of the thunderstorm period and the prevailing conditions suggest that the onset of the rainy season is on time, climatologically speaking, during the last part of May," the PAGASA meteorologist said.
The weatherman also pointed to the shifting of the wind flow as an indication that the rainy season will be on time this year. The shift, he said, is indicated in the 24-hour public weather forecast issued daily by PAGASA’s Weather Forecasting Section.
The southwest wind flow, he added, is now prevailing in India as influenced by the movement of the wind from the Indian Ocean.