Thursday, August 18, 2011
Strong Sound Breeze and Tragedy
Last night's 11 PM news and today's Seattle Times related a story about the tragic death of a young man near Seward Park who had been using a Yamaha personal water craft. The ST article is found here. In this article there was a brief mention of a sudden increase in wind and choppiness of Lake Washington.
Was there a meteorological origin to this terrible incident? If so, could it have been predicted?
I think I caught a piece of whatever happened while bicycling home around 6:30 PM from the UW-- not far from NOAA Sand Point I was impressed by the strength of the head wind out of the north. It was really strong. Now on warm sunny days a northerly wind often develops north of Seattle and is called the Sound Breeze. But this time it came up fast and hard.
Probably the best observation for the boating incident was from the wind sensors at the central part of the Evergreen Floating Bridge. As shown in the map below the bridge was upwind of the accident site (X for the incident location and O for the wind sensor). The winds were from the north so the Evergreen Point wind sensor was in the perfect location.
Here is the wind speed record on the Evergreen Bridge. Wow. Around 6 PM there was a very sudden ramp up of wind speed to over 20 mph from roughly 3-5 mph. That wind, plus a good water fetch north of Seward Park meant rapid growth of waves.
The high resolution computer models had a good idea that strong winds would push into the Strait of Juan of Fuca and down into Puget Sound. Here is a forecast for 8 PM of surface winds from the UW's ultra high resolution model prediction (1.3 km grid spacing!):
But why were the winds so strong and why did they come up so suddenly on Wednesday? I suspect the answer was the passage of an upper level disturbance that afternoon which really revved up the pressure differences between the coast and inland yesterday. Here is an upper level map showing you the heights of the 500hPa pressure surface at 5 PM--can you see the trough over us? I think that is the culprit.
My hope is that in a few years we can combine our observations and improved models with modern communications (e.g., smartphones and the like) to allow us to provide highly useful and timely warnings of such events. We won't stop all such tragedies, but hopefully many injuries and deaths can be avoided.
Posted by Cliff Mass at 9:55 PM