EXPLAINER: What is a monsoon break?

Following the continuous Southwest Monsoon rains that lasted for most of August, the Philippines is now experiencing a monsoon break, according to state weather bureau Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA).

But what is a monsoon break?

PAGASA Administrator Nathaniel T. Servando told GMA News Online that there were lesser rain during a monsoon break.

“Monsoon break is a temporary decrease in daily rainfall during the duration of the monsoon. There is also a weakening of the low-level southwesterly winds,” Servando said in a mix of English and Filipino.

Servando said that on average, it happens twice every Southwest Monsoon season, and could last four to five days.

Researchers Lyndon Mark P. Olaguera from the Ateneo de Manila University, John A. Manalo from PAGASA and the Tokyo Metropolitan University, and Jun Matsumoto from the Tokyo Metropolitan University and the Japan Agency for Marine Earth Science and Technology examined the monsoon breaks in the Philippines from 1979 to 2020 in a study called "Climatological characteristics of the monsoon breaks during the southwest monsoon season of the Philippines."

The study, published in the International Journal of Climatology in 2023, defined a monsoon break as a decrease in rainfall for at least three consecutive days.

“A monsoon break is usually characterized by a temporary decrease in rainfall or suppression of convective activities and weakening of the prevailing low-level wind,” the researchers wrote.

Most of the monsoon breaks occurred during the suppressed phases of the Boreal Summer Intraseasonal Oscillation (BSISO). The BSISO is a major climate pattern that influences weather phenomena such as the development of tropical cyclones, as well as southwest monsoons.

Types of monsoon breaks

They defined three types of monsoon breaks. A short break lasts three to four days, a medium break lasts five to nine days, while a long break lasts around 10 days.

The scientists identified 208 monsoon breaks from 1979 to 2020 with 131 described as short breaks while 71 were medium. There were only six long monsoon breaks, according to the study.

“Long-lasting monsoon break events often lead to dry spell conditions or drought and have adverse effects on hydrological resources, agriculture and the economy of the country. Therefore, understanding the mechanisms inducing these monsoon break events is necessary to mitigate their impacts,” the study read.

The researchers found that the longest monsoon break was 15 days; it was recorded from July 28 to August 10, 1980.

Long breaks are rare, the study said. The six long monsoon breaks were recorded in 1980, 1981, 1983, 1997 and two times in 2019.

The year 1993 had the highest number of breaks in a single year at 11 incidents, and was only followed by 2020 with 9 cases. The years 1982, 2012 and 2014 had the lowest number of monsoon breaks with only two short breaks each.

The study found that most of the monsoon break events mostly occurred from June to mid-July, with fewer instances in August. — BAP, GMA News