What is a ‘Tsunami Watch’ and what should I do?


Tsunami Brochure

A Tsunami Watch is an alert issued to areas outside the warned area. The area included in the watch is based on the magnitude of the earthquake. For earthquakes over magnitude 7.0, the watch area is 1-hour tsunami travel time outside the warning zone. For all earthquakes over magnitude 7.5, the watch area is 3 hours tsunami travel time outside the warning zone. The watch will either be upgraded to a warning in subsequent bulletins or will be cancelled depending on the severity of the tsunami.

What to Do When a Tsunami Watch Is Issued

You should:

  • Use a NOAA Weather Radio or stay tuned to a Coast Guard emergency frequency station, or a local radio or television station for updated emergency information.
  • Follow instructions issued by local authorities. Remember, authorities will issue a watch only if they believe there could be a threat from tsunami. The next level would be a Tsunami Warning.

FOR CURRENT INFORMATION Listen to local radio, television broadcasts, internet media

Local sources for information in Hawai’i include:

NOAA Weather Radio Broadcasts on following frequencies:
162.400 MHZ (Kauai, Maui)
162.450 MHz (Hawaii Kai)
162.500 MHz (North Kohala)
162.550 MHZ (Oahu, South Point)

NOAA Weather Radio Broadcasts recording phone numbers:
Hawaii State Forecast: (808) 973-5286
Kauai: (808) 245-6001
Oahu: (808) 973-4380
Maui: (808) 944-5025
Hawaii Island: (808) 935-8555

Tsunami Information Links
Pacific Tsunami Warning Center
West Coast and Alaska Tsunami Info
International Tsunami Information Center
Big Island Tsunami Evacuation Maps (mirror site for maps)
Pacific Disaster Center
Recent and Historical Tsunami Events
Tsunami Evacuation Centers for Hawaii Island

Civil Defense/Emergency Management Agency Links
Hawaii Emergency Management Agency (formerly State Civil Defense)
Hawaii County Civil Defense
Maui County Emergency Management Agency
City and County of Honolulu Department of Emergency Management
County of Kauai Emergency Management Agency

USGS: How large does an earthquake have to be to cause a tsunami?

Magnitudes below 6.5
Earthquakes of this magnitude are very unlikely to trigger a tsunami.

Magnitudes between 6.5 and 7.5
Earthquakes of this size do not usually produce destructive tsunamis. However, small sea level changes may be observed in the vicinity of the epicenter. Tsunamis capable of producing damage or casualties are rare in this magnitude range but have occurred due to secondary effects such as landslides or submarine slumps.

Magnitudes between 7.6 and 7.8
Earthquakes of this size may produce destructive tsunamis especially near the epicenter; at greater distances small sea level changes may be observed. Tsunamis capable of producing damage at great distances are rare in the magnitude range.

Magnitude 7.9 and greater
Destructive local tsunamis are possible near the epicenter, and significant sea level changes and damage may occur in a broader region.

Note that with a magnitude 9.0 earthquake, the probability of an aftershock with a magnitude exceeding 7.5 is not negligible. To date, the largest aftershock recorded has been magnitude 7.1 that did not produce a damaging tsunami.

Tsunami Awareness

A Decade of Great Earthquakes