自然現象

太平洋津波警報センターが発する津波予報

ハワイ州オアフ島にある太平洋津波警報センター(PTWC: Pacific Tsunami Warning Center)の発令情報(PTWC Tsunami Messages)には以下のようなタイプがあります。  
ハワイで起きた地震の場合：マグニチュードがマグニチュードが6.9から7.5だと、緊急ローカル津波警報(Urgent Local Tsunami Warning)が発令されます。マグニチュードが7.6以上だと、ハワイ州全体に緊急ローカル津波警報(Statewide Urgent Local Tsunami Warning)が発令されます。
ハワイより遠く離れたところで起きた地震の場合：マグニチュード7.9以上で、予測される津波の到達時間が3時間内であれば津波警報(Tsunami Warning)、マグニチュード7.9以上で、予測される津波の到達時間が3時間から6時間であれば津波注意報(Tsunami Watch)、マグニチュード7.9以上で、予測される津波の到達時間が6時間より長い場合はTsunami Advisoryが発令されます。 
>>> 過去90日間の発令情報はNOAA NWC PTWCのウェブサイトにあるTsunami Messagesで確認できます。  
>>> PTWCの責任地域はNOAA NWC PTWCのウェブサイトにあるAreas of Responsibilityを示すマップを見るとよくわかります。
>>> 津波警報が発令された場合、ハワイ島で非難すべき地区はCivil Defense Tsunami Evacuation Zones for Hawaii Countyにあるマップをクリックするとわかります。 
津波の危険レベル：

• Tsunami Warning （津波警報）
  The highest level of tsunami alert. Warnings are issued due to the imminent threat of a tsunami from a large undersea earthquake or following confirmation that a potentially destructive tsunami is underway. They may initially be based only on seismic information as a means of providing the earliest possible alert. Warnings advise that appropriate actions be taken in response to the tsunami threat. Such actions could include the evacuation of low-lying coastal areas and the movement of boats and ships out of harbors to deep water. Warnings are updated at least hourly or as conditions warrant to continue, expand, restrict, or end the warning.

• Tsunami Watch （津波注意報）
  The second highest level of tsunami alert. Watches are issued by the TWCs based on seismic information without confirmation that a destructive tsunami is underway. It is issued as a means of providing an advance alert to areas that could be impacted by destructive tsunami waves. Watches are updated at least hourly to continue them, expand their coverage, upgrade them to a Warning, or end the alert. A Watch for a particular area may be included in the text of the message that disseminates a Warning for another area.

• Tsunami Advisory
  The third highest level of tsunami alert. Advisories are issued to coastal populations within areas not currently in either warning or watch status when a tsunami warning has been issued for another region of the same ocean. An Advisory indicates that an area is either outside the current warning and watch regions or that the tsunami poses no danger to that area. The Center(s) issuing the Advisory will continue to monitor the event, issuing updates at least hourly. As conditions warrant, the Advisory will either be continued, upgraded to a watch or warning, or ended.

• Tsunami Information Bulletin/Statement
  A text product issued to inform that an earthquake has occurred and to advise regarding its potential to generate a tsunami. In most cases, a Tsunami Information Bulletin indicates there is no threat of a destructive tsunami, and are used to prevent unnecessary evacuations as the earthquake may have been felt in coastal areas. A Tsunami Information Bulletin may, in appropriate situations, caution about the possibility of a destructive local tsunami. A supplemental Tsunami Information Bulletin may be issued if important additional information is received such as a sea level reading showing a tsunami signal. A Tsunami Information Bulletin may also be upgraded to a watch or warning if appropriate.