PAGASA sees increasing likelihood that La Niña will reemerge by 4Q 2021

Published August 25, 2021, 6:15 PM

by Ellalyn De Vera-Ruiz


There is now around 65 percent chance that the La Niña weather phenomenon will reemerge during the October-December 2021 period, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) said during its climate outlook forum on Wednesday, Aug. 25.

A La Niña Watch is currently in effect as conditions are favorable for the development of La Niña conditions within the next six months.

PAGASA’s Climate Monitoring and Prediction Section chief Ana Liza Solis said “La Niña is more likely to start in October-November-December season” with around 65 percent probability.

However, based on recent monitoring, Solis said that the cooling of the sea surface temperature may not persist long enough to constitute a full-blown La Niña event.

It can only be considered a full-blown La Niña event if it has satisfied a minimum of five consecutive three overlapping months with Oceanic Niño Index (ONI) values of -0.5°C or lower, she explained.

“‘Yung nakikita natin dalawang ONI season lang (We only see two ONI seasons), October-November-December and November-December-January, kaya sinasabi natin na (that’s why we are saying that) it is not [going] to persist long enough to constitute a La Niña event,” Solis said.

“Based on the definition of Climate Prediction Center and NOAA [National Oceanic and Atmospheric Administration], kapag nagkaroon ng at least dalawang consecutive ONI na merong cooling at nasa La Niña threshold tinatawag na nila itong (if there have been and at least two consecutive ONIs that have sustained cooling and are within the La Niña thresholds they consider it) La Niña conditions but not necessarily a full-blown La Niña,” she added.

Solis still advised the public to continue to monitor the possible development of La Niña.

“If there is a La Niña, it increases the likelihood of above-normal rainfall conditions na posible mag-cause ng flooding and heavy rainfall events, landslides sa highly vulnerable areas kaya (that could cause flooding and heavy rainfall events and landslides in highly vulnerable areas so) we need to monitor and watch out for further development,” she said.

“Kasi itong nakikita natin ay based on recent condition of what is happening in the tropical Pacific. So napaka-dynamic ng ating ocean-atmosphere interaction so we need to keep on monitoring (Because what we see is based on recent conditions of what is happening in the tropical Pacific. Our ocean-atmosphere interaction is very dynamic so we need to keep on monitoring),” she added.

If La Niña develops later this year, it will be a back-to-back event as the 2020-2021 La Niña only ended in June 2021.

Solis said a back-to-back La Niña episode is not unusual, noting that the last six episodes occurred back-to-back.

These were in 2007-2008 and 2008-2009; 2010-2011 and 2011-2012; and 2016-2017 and 2017-2018.