UPDATE:
The tsunami watch was downgraded to a tsunami advisory at 10:23 a.m. local time (5:23 a.m. Korea). It will be in effect until 7 p.m.

ORIGINAL POST:
I wake up this morning and they're telling us that Hawaii is under a tsunami watch thanks to an undersea earthquake near Samoa that measure 7.9 on the Richter scale. It is not known for sure if a tsunami was generated. A more serious tsunami warning was issued for New Zealand.

The earthquake occurred at 7:48 a.m. on Tuesday, Hawaii time, which would be 2:48 a.m. on Wednesday, Korea time. The watch was declared seventeen minutes later, at 8:05 a.m. If a tsunami were to reach the Hawaiian Islands, about 4200 kilometers (2600 miles) away, they're saying the earliest expected arrival time would be 1:11 p.m. local time (8:11 a.m. Korea time).

The earthquake struck at a depth of 20.5 miles. For those wishing to Google it, the earthquake 110 miles east-northeast of Hihifo, Tonga; 125 miles south-southwest of Apia, Samoa; 435 miles north-northeast of Nukualofa, Tonga; and 1670 miles north-northeast of Auckland, New Zealand.

New Zealand, home to at least some of my readers, is one of several areas under a more serious tsunami warning: American Samoa, Samoa, Niue, Wallis-Futuna, Tokelau, Cook Islands, Tonga, Tuvalu, Kiribati, Kermadec Islands, Howland-Baker, Jarvis Island, New Zealand, French Polynesia, and Palmyra Atoll.

Hawaii is listed as under a tsunami watch along with Vanuatu, Nauru, Marshall Islands, Solomon Islands, Johnston Atoll, New Caledonia, Kosrae, Papua New Guinea, Pohnpeo, Wake Island, Pitcairn Island, and Midway.

My understanding was that the difference between a watch and a warning (for hurricanes, tornadoes, tsunamis) was that a watch was a possibility based on current conditions but a warning indicated a significantly more stepped-up likelihood of the event occurring in the near future. [Edit: It appears I wasn't far off.]

Honolulu is along the south side of Oahu, more vulnerable to events in that direction than, say, the North Shore.

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