Photo/Illutration Red-and-white flags are designed to warn people on a beach and in the sea of the risk of a tsunami. (Asahi Shimbun file photo)

Beachgoers are being told to flee immediately to higher ground or coastal evacuation towers if they see a red-and-white plaid flag hoisted.

The warning from the Japan Meteorological Agency carries heightened urgency after it issued its first-ever advisory Aug. 8 on a potential megaquake along the Nankai Trough in the Pacific Ocean.

The JMA issues a tsunami warning or advisory about three minutes after an earthquake strikes.

Beaches along the Pacific coast are expected to be packed during the midsummer Bon holidays this week.

Authorities figure the only way to grab the attention of bathers is to hoist a special flag to denote an emergency.

Lifesavers and others will wave the flag on beaches or display it in a nearby building when a tsunami warning or advisory is issued.

According to the JMA, a tsunami exceeding 10 meters in height can be expected along the Pacific coast from the Kanto region to the southwestern main island of Kyushu if a major earthquake strikes along the Nankai Trough.

The JMA’s Aug. 8 advisory covers 707 municipalities in Tokyo and 28 prefectures, many along the Pacific coast.

It was issued after a magnitude-7.0 temblor hit the southern part of Kyushu with its epicenter in the Hyuganada Sea, which lies in the westernmost part of the estimated hypocentral region of an anticipated megaquake along the Nankai Trough.

Authorities also are urging bathers to confirm evacuation sites and routes in advance.

For example, a tsunami evacuation map is displayed at the administration office of the Southern Beach Chigasaki swimming beach in Chigasaki, Kanagawa Prefecture.

The map is also posted on the city government website.

Some beaches have banned swimming since the advisory was issued.

“A tsunami will hit three minutes after an earthquake at the earliest. It is necessary to reconfirm where and by what route to evacuate,” Naoshi Hirata, who serves as chairman of the JMA’s Nankai Trough Earthquake Assessment Committee, told an Aug. 8 news conference.

“In my opinion, as long as that is done properly, there is no particular problem with people going bathing in the sea.”

(This article was written by Kyota Tanaka and Hiroshi Nakano.)

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