MANILA, Philippines - The weather bureau said Friday that Northern Luzon provinces may suffer from sweltering heat of up to 40 degrees Celsius from May to June.

Nathaniel Cruz, operations and services chief of the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA), said Metro Manila and several areas in central and southern Luzon will start feeling hotter weather from 34-degree to 37-degree Celsius starting April up to June.

"Most likely, by middle of May up to June [or] before the start of the rainy season, the temperature in Northern Luzon, particularly Cagayan Valley, will reach as high as 40-degrees Celsius," Cruz told ANC's News@8.

Cruz, meanwhile, said that despite the dry spell being experienced in several Luzon and Visayas provinces for the past weeks, summer or the dry season, has not yet officially set in.

He said, however, that the northeast monsoon has started to decrease in intensity, and summer may eventually come by next week.

"We will issue an advisory on the official start of the dry season, or what people call the summer season, next week," Cruz said.

Meanwhile, Cruz said the dominant weather system at present is the ridge of high pressure area prevailing across Luzon and Visayas.

He said people in affected provinces should "expect warmer days ahead' and cloudless skies during the weekend because of the effects of the high-pressure area.

The effects of the El Niño phenomenon have taken its toll on crops and animals in various provinces of Luzon and the Visayas.

There have been reports of mass deaths of fish and chickens in La Union and Pangasinan provinces because of the ongoing dry spell.

Water reserves spread across the two Philippine islands have been drying up, weakening irrigation water supply.

Rotating brownouts are now being implemented in several provinces in Mindanao while people in Metro Manila are bracing for an expected water supply shortage by June.

The Department of Health (DoH) has also started reporting an increase in the number of cases of measles around the country.

The health department said measles is one of the diseases that usually crop up during the summer season.