Summary:

At 527 am HST, a 7.9 magnitude earthquake occurred south of Tonga. This prompted the Pacific Tsunami Warning Center to issue a Tsunami Watch for Hawaii. As additional data from buoys and tide gauges in the South Pacific arrived at the Pacific Tsunami Center over the next couple of hours, the indication was that no large, potentially damaging tsunami had been created. Thus at 739 am HST, the Tsunami Watch for Hawaii was cancelled.

Although the risk for a damaging tsunami no longer existed, a small tsunami had been generated by the quake. The tsunami reached Hawaii around noon HST and was recorded by a number of tide gauges across the state maintained by NOAA's National Ocean Service.

Based upon the gauge readings, the tsunami that reached Hawaii was generally one-half to one foot (6 to 12 inches), although local effects in Kahului Harbor resulted in a slight enhancement with the tsunami about 1 1/2 ft high. The only report received at this office was of unusual tidal surge behavior observed at Hanalei Bay, Kauai shortly after 100 pm HST.

The links below provide graphical and text depictions of sea level height measurements. Take note of the red line which represent actual measured sea level height and the green line which is the departure of the observed from the predicted height (blue line). The tsunami arrival can be seen by the sudden swings up and down in both the red and green lines. What will also be apparent is that a tsunami is not made up of one single wave, but rather a long lasting series. In fact, at some locations the swings in sea height continued into the next day. This may be a result of local seiches occurring within the harbors. Tsunamis are not like familiar surf-able breaking waves, but rather a surge, like a very fast changing tide. Even small tsunamis can result in fast changing currents close to shore.

Go here for more information on tsunamis and tsunami safety.

* Please note that these preliminary raw data have not been quality controlled by NOAA/NOS and should be used with caution.

Questions/Comments - please email Andy Nash, Director of Operations.