The Bicol region is among the areas that face the most risk for the La Niña phenomenon which experts increasingly forecast as possibly developing later this year.
"If La Nina develops then as predicted, its big impact will be felt during 2017's first quarter in eastern parts of the country," said Climate Monitoring and Prediction Section OIC Anthony Lucero from State-run Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA).
He noted first quarter of the year is also when the rainy season generally peaks in the country's eastern portion so communities there must prepare accordingly.
"La Nina aggravates the rainy season," he continued.
Apart from Bicol, also at risk are Isabela, Quezon, Leyte and Samar provinces, and the Caraga region.
Such areas border the Pacific Ocean where La Nina and thedrought-driving El Nino phenomenon develop.
According to experts, La Nina and El Nino are the corresponding cool and warm phases of a recurring natural climate pattern called El Nino-Southern Oscillation (ENSO) across tropical Pacific.
An ENSO-neutral state is one in which conditions are near long-term average, they said.
They said above-normal rainfall is a mark of La Nina while shortage of precipitation is a manifestation of El Nino.
Landslides and flooding are among consequences of above-normal rainfall during La Nina, they noted.
This week, PAGASA said the prevailing strong El Nino continues weakening and will likely be ENSO-neutral already by mid-2016.
"The possibility of a developing La Nina is favored during the second half of 2016," PAGASA also said.
Such forecast prompted government to reactivate its La Nina watch.
Data indicate La Nina and El Nino generally occur alternately.
The last La Nina episode occurred from August-September-October 2011 to February-March-April 2012, data also show.
Citing as basis latest available climate models and historical data, Lucero estimated an 80 percent chance for La Nina's development during the second semester of 2016.
"Historical records show three out of four La Nina episodes occurred after strong El Nino events," he said.
Earlier, PAGASA wasn't as upbeat about La Nina's development this year as Lucero noted two internationally renowned institutions' previous climate models instead forecast continuation of El Nino through 2016's second semester.
Fresh data indicate La Nina may develop possibly around the June-July-August 2016 period, however, he noted.
"We might see La Nina's manifestations starting October this year," he warned.
PAGASA forecast above-normal rainfall in most parts of the country that month. (With report from Catherine Teves/PNA)