MANILA –  The weather bureau officially declared on Friday the onset of La Niña, which is likely to persist until the first quarter of 2022.

"Recent oceanic and atmospheric conditions indicate La Niña has developed in the tropical Pacific,” said Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) Deputy Administrator Esperanza Cayanan in a virtual presser.

Four to six tropical cyclones are expected to enter or develop in the Philippine Area of Responsibility, Cayanan added.

Most of these are landfalling tropical cyclones, and are forecast to enhance the northeast monsoon and trigger floods, flash floods, and rain-induced landslides over susceptible areas, particularly in the eastern section of the country which normally receives greater amount of rainfall at this time of the year.

La Niña is usually associated with above normal rainfall conditions over most parts of the country.

Cayanan said adverse impacts are likely over the vulnerable areas.

Meanwhile, weather specialist Ana Clauren said the southwest monsoon or "habagat" has weakened, prompting PAGASA to declare that the "habagat season" is officially over.

"So (the country) is now in the transition period towards what we call the northeast monsoon or 'amihan' season. Gradual cooling is expected in the coming days and weeks," she said.

Despite the onset of La Niña, Clauren said no tropical cyclone is forecast to affect the country in the next two to three days.

She, however, noted that PAGASA is monitoring the situation and urges local government units to prepare for possible impacts of La Niña. (PNA)