Dr. Flaviana Hilario, chief of the Climatology and Agrometeorology Branch of the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa), said the possibility of a La Niña occurrence in the country remains at 50 to 60 percent.
However, she urged the Department of Agriculture, Department of Environment and Natural Resources, the National Disaster Coordinating Council, the Office of Civil Defense and local government units to make the necessary preparations for La Niña.
La Niña is a weather phenomenon characterized by excessive rainfall and abnormal cooling of the eastern and central equatorial Pacific.
Pagasa earlier said the further cooling of subsurface water in the central to eastern equatorial Pacific shows initial evidence of an emerging La Niña that may be experienced in the country in the next few months.
"This may be the first sign of an emerging La Niña, but it will take a few months more before a clear trend becomes evident," Pagasa said in its weather outlook for May.
Current global observations and forecasts predict the potential development of La Niña during the next three months, it said, adding that the prevalence of a neutral condition is most likely until the end of this month.
Meanwhile, Pagasa said the weather systems that could affect the country this month are the ridge of a high pressure area, easterly wave, intertropical convergence zone, southwest monsoon (hanging habagat), and the potential development of one tropical cyclone.
The shifting of the winds from the "easterlies" to the "southwesterlies" during the second half of May, according to Pagasa, signals the start of the rainy season under the so-called Type 1 climate, in the western section of the country.
Near normal rainfall is expected in most parts of the country, except in Guimaras, Iloilo and Negros, which are expected to receive above normal rainfall.
Below normal rainfall is expected in Ilocos Sur, La Union, Cagayan, Nueva Vizcaya, northern Bicol, and parts of Eastern Visayas.
Pagasa said warmer than normal temperatures are likely to be felt in most parts of the country.
The predicted ranges of temperature this month are 16 to 26 degrees Celsius in mountainous areas in Luzon; 24 to 37 degrees Celsius in the rest of Luzon; 25 to 34 degrees Celsius in the Visayas; 20 to 32 degrees Celsius in mountainous areas in Mindanao; and 28 to 35 degrees Celsius in the rest of Mindanao.
Pagasa chief Nathaniel Cruz earlier said that if the La Niña phenomenon would fully develop in the coming months, it would not yet affect the rainfall pattern in the country this rainy season.
"Let us say that if La Niña develops this June or July, its impact on the country’s rainfall pattern will be felt in September or October and not this rainy season," he said.