Why PAGASA did not raise cyclone warnings for Gorio right away

Why did PAGASA take so long to raise cyclone warnings for TS Gorio?

PAGASA meteorologists have been monitoring Gorio ever since it was an unnamed low pressure area on Monday, July 27. But it was only late Thursday afternoon that PAGASA raised a cyclone warning over Batanes, despite heavy rains in Metro Manila and across Luzon through the day.

It came as a surprise to many that a cyclone passing through the Philippine Area of Responsibility (PAR) would raise no warnings despite the heavy downpour.

Misvisualizing the PAR

To begin with, at least part of the confusion can be traced to a lack of a visual understanding of what's going on: it has long been a common misunderstanding that when a cyclone enters the PAR, it's already "in the country".

However, the PAR actually covers an area so vast that you could fit the Philippines several times into it: Project NOAH estimates the PAR's size at roughly 4.6 million sq km, over 15 times the size of the Philippines' 300,000 sq km land area. The PAR is so far-reaching that it even encompasses Palau in the east and most of the country of Taiwan to the north.

Also, not all cyclones in the PAR make it to land: according to one study, only half of the roughly 20 cyclones that enter or are born in the PAR make landfall. 

Moreover, as its name implies, the PAR is the internationally agreed-upon area within which PAGASA takes the lead in monitoring weather disturbances. It helps give the Philippines a heads-up for approaching cyclones. 

Misunderstanding of cyclone warnings

Gorio's path through the PAR is far from the Luzon mainland, which continues to be unaffected by the storm's winds. It was only late Thursday, when adjusted forecasts showed that Gorio's winds would directly affect the Batanes islands, that PAGASA hoisted its first cyclone warning.

Contrary to popular belief, tropical cyclone warnings have nothing to do with rainfall: PAGASA's current warning system describes the strength of a cyclone's winds in places in its path—and, as of Thursday afternoon, this includes only the Batanes islands.

This misunderstanding is a problem that PAGASA is seeking to rectify with an upcoming revised warning system that emphasizes the effects of a cyclone's winds more than just its wind speeds.

Enhanced Habagat monsoon

Also, the rains that drenched Luzon on Thursday are actually from the Habagat southwest monsoon. Gorio's movement is said to be "enhancing" the monsoon, pulling in more rainclouds than the Habagat would normally bring in on its own.

This phenomenon often happens during the Habagat monsoon season as cyclones east of the country pull at the monsoon. Among the most notorious of these in recent memory are the Habagat floods of 2012: in August of that year, typhoons Saola (known locally as "Gener") and Haikui successively enhanced the Habagat monsoon, leading to torrential rains and severe floods in Metro Manila despite neither cyclone directly affected in the country.

Improving public knowledge

In a press briefing Thursday noon, PAGASA administrator Vicente Malano encouraged the public to keep posted on PAGASA's constantly-updated stream of thunderstorm warnings and to learn more about hazard maps available from the agency.

"Dapat nakatutok ka sa thunderstorm warning sa lugar niyo. (At) kung may hazard map ka, kung saan bumuhos ang ulan titignan mo kung ano ang epekto ng ulan sa inyong lugar," he said.

Such information can help the public make informed decisions for themselves, in complement with the more general warnings issued by PAGASA and local governments. — GMA News