Graphic courtesy of Tammy Pelletier, WA State Dept of Ecology Wave height is dependent on a) wind speed b) fetch length and c) duration of time the wind blows consistently over the fetch. ![]() Wave Formation: Waves are formed by wind blowing along the water's surface. As we head toward the warmer months of the year, when southeast Alaska waters become more populated, let's review basic ocean wave characteristics so that mariners can interpret marine weather forecasts as NWS forecasters intended. WFO Juneau's marine weather forecasts include information about prevailing wind speed and direction and significant wave height. This diverse audience is comprised of weekend recreational boaters, commercial fishers, and large passenger ships. Mariners on southeast Alaska waters comprise a large percentage of our audience and seek out weather information daily. More than half of our forecast area is over water. NOAA's National Weather Service Forecast Office (WFO) in Juneau is responsible for informing citizens about weather conditions over a 150,000 square mile area that includes the east half of the Gulf of Alaska and the entire Alaska Panhandle. NOAA's National Weather Service Forecast Office (WFO) in Juneau is responsible for informing citizens about weather conditions over a 150,000 square mile area that includes the east half of the Gulf of Alaska and the entire Alaska Panhandle But the term 'significant wave height' has a specific definition, and anyone using marine weather information should have a clear understanding of what it means.įigure 1. In my opinion, that solitary wave that hit the side of the 4th deck of the Matanuska was certainly a significant one. ![]() Until that wave, our seats were at least 15 feet above the tops of the foaming wave crests. Not long before this power-washing wave hit, people were outside our window gripping the rail and squinting with awe into the wind that required a forward lean and wide stance to maneuver through. As the water poured off the deck and back into the Sound, my wife and I exchanged silent glances. We were watching a movie in a theater room on the 4th deck when, out of the blue, the port side windows were slammed by a drenching wave. While crossing Queen Charlotte Sound off British Columbia in gale force winds on a Saturday afternoon, the ship rolled through seas I estimated to be 15- or 20-feet high on average. When my family and I moved to Juneau a number of years ago, we sailed on the 408-foot Alaska State Ferry 'Matanuska' from Bellingham, WA. Of course, the size of wave that someone considers to be 'significant' is very subjective and dependent on the size of the vessel on which that person's encounter took place. The topic also regularly causes a mix of wonder and panic online.When Do Ocean Waves Become 'Significant'? A Closer Look at Wave Forecasts Tom Ainsworth, NOAA/National Weather Service Forecast Office, Juneau, AKĪnyone who has spent time on a vessel, large or small, can probably recall an encounter with significant waves. The place where they seem to be most prevalent is off the coast of La Rochelle in France, namely the Isle of Ré - the spectacle often attracting a great number of tourists each year. This is likely due to vessels taking on water from waves coming at them from two different directions at once and the fact that the resulting swells can reach up to 10 feet high. It's also a phenomenon which is far more common than you might think and has even been attributed to a number of boating accidents and shipwrecks over the years. Deadliest tsunami in history when hero elephant saved Brit girl’s life on Boxing Day. ![]()
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