This year's first heat wave advisory has been issued for the central part of the country including Seoul and neighboring provinces as daytime highs soared to over 30 degrees Celsius in most of the region for a second day on Monday.

The heat will persist until Tuesday but subside to some extent on Wednesday, when the central region comes under the influence of the monsoon front, according to the Korea Meteorological Administration.

The advisory, which was introduced for the first time in 2008, is issued when daytime highs over 33 degrees Celsius are expected to persist for two days or longer.

Children lie down at an outdoor swimming pool in Yangjae, Seoul on Sunday. /Newsis

This year's first advisory came about two months earlier than last year (Aug. 20), about 50 days earlier than in 2009, and about 20 days earlier than in 2008. Experts said sizzling heat will grip the country more often and more vehemently.

The heat wave comes because a monsoon front that built up over Jeju on June 8 was unable to move north due to an anticyclone that developed over the central part.

"Under the continental anticyclone, hot sun rays hit the earth's surface in the central region of the country day after day, and their cumulative effect caused the heat wave," a KMA official said.

Once it moves north, the monsoon front will hit the central region on Wednesday afternoon and then travel slowly south across the entire nation from Thursday, the KMA forecast.

KMA spokesman Kim Seung-bae said torrential rains will fall in some regions between Wednesday and Friday.