PAGASA: Rainy season coming

The La Niña weather phenomenon, which brings about and intensifies the effects of heavy rains and tropical storms, is weakening even as the rainy season is set to begin by the second half of this month, weather experts said yesterday.

Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) officer-in-charge Prisco Nilo said the latest data and international forecast indicate that the temperature at the surface of the Pacific Ocean is returning to normal, bringing back the normal atmospheric conditions in the Philippines.

This translates into the weakening of La Niña, which is attributed to the abnormal cooling of the sea surface.

Nilo, however, said rains will still come as a normal weather condition this month.

"Current sea-surface temperatures observations in the central equatorial Pacific are close to their average, or normal values. Neutral conditions are expected in the second half of the year. Rainfall in most parts of the country will likely be near normal during the May to July 2006 period," he said.

Dr. Flaviana Hilario, chief of Pagasa’s climatology and agrometeorology branch, said the weakening of La Niña has led to a significant decrease in the intensity of rainfall across most parts of the country in April.

She emphasized, however, that while the sea-surface temperatures in the central equatorial Pacific is nearing the normal or neutral levels it would still be early to declare if the La Niña is already over.

Hilario said the impact of La Niña’s weakening has a lag time of one to two months before Pagasa could finally declare that the weather phenomenon has ended.

"For the month of April 2006, rainfall observed in most parts of Luzon and Visayas, including Western Mindanao were below to way below average," she said.

Hilario added that the onset of the rainy season is expected to occur by third or fourth week of May, associated with tropical cyclone activities, strong monsoon winds, and scattered thunderstorms.

She said that in the Philippine Climate Outlook covering May to July this year, six to eight tropical cyclones are expected to enter the Philippine area of responsibility during this period.

Hilario said up to two tropical cyclones are expected to arrive this month, two tropical cyclones in June, and as many as four tropical cyclones will enter the Philippines in July.

"(But) we predict that the rainfall for the coming three months will be near normal with the weakening of the La Niña," she said.

Hilario also said that during this three-month period, rainfall amounts of more than 1,200 millimeters are expected over mountainous areas of Luzon; 901 to 1,200 mm. over Ilocos Sur, Pangasinan, Zambales, and Nueva Vizcaya; 601 to 900 mm. over western, central, and southern Luzon, Bukidnon, Zamboanga del Sur, Maguindanao, Davao Oriental, and some areas of western Visayas; while the rest of the country will receive rainfall from 301 to 600 mm.

Nilo pointed out that the onset of the rainy season will likely affect the western part of the country, including Metro Manila.

PAGASA said in the central and eastern equatorial Pacific have ranged between -0.5 to -1.0 degree Celsius below normal since late last year, noting that the cooler than average sea-surface temperatures and the persistently higher than average value of the Southern Oscillation Index are consistent with those of a developing La Niña event. Above-average cloud developments were also observed over Indonesia, Northern Australia and the Philippines since that time.

According to PAGASA, these conditions over the Pacific have influenced the local climate of the country, as most parts of the Philippines experienced wetter than average rainfall conditions from December 2005 up to March this year.

However, international weather forecasting units regarded the latest La Niña event as "very peculiar." Weather experts said the latest La Niña event developing so late in the year is "very unusual" as it usually becomes most mature during winter.

They also said that the current La Niña phenomenon is different from past events because its impact and implications are "very uncertain."