Yesterday, around 0400 UTC 15 January (8 PM PST 14 January), there was a massive, explosive eruption near Tonga, in the southern tropical Pacific, about 5642 miles from Seattle (see map).
The volcano was clearly evident in satellite imagery from the massive ash cloud (see below, about 1-h after the eruption)
The explosive eruption created shock waves in the atmosphere (pressure waves) that rapidly propagated away. These waves are evident in some infrared (water vapor channel) imagery as concentric rings (shown below).
The oceanic eruption also pushed away a massive amount of water, which created a tsunami on nearby islands (such as Tonga) and deep water waves that moved away at the speed of a jet plane, reaching the West Coast this morning. This is why some local tsunami warnings went out this AM.
The Pressure Wave Reaches the Northwest
Local barometers indicated a well-defined pressure wave passing over our region around 4:30 AM this morning. Here in Seattle, the University of Washington barometer showed the feature, with an amplitude of roughly 2 hPa (2 mb). The arrow indicates the feature. Very impressive.
So it took about eight hours and 30 minutes to go about 5643 miles–thus a speed around 664 miles per hour. This corresponds to the speed of sound in the upper atmosphere around 30,000 ft. Makes sense.
The water wave moves slower, around 400 mph (and occasionally approaching 500 mph)….so a later arrival was expected. Thus, at Neah Bay, at the entrance to the Strait of Juan de Fuca, the water wave arrived around 9 AM (17:00 UTC as shown on the chart), as indicated by the waviness in the water level after that time. The amplitude of the variation is around 2 feet.
If you really want to be impressed, check out the same figure at Monterey, California. Just wow. The amplitude was up to 3-4 feet.