Extended Abstract (1.4M)P4.3
Forecast Challenges and Lessons from the 2008 Saint Patrick's Day Super Swell
Mark Willis, NOAA/NWS, Newport, NC; and K. Korte and J. Elardo
Accurate and timely ocean wave forecasts are vital to coastal safety and economics. The Outer Banks of North Carolina are especially prone to wave action due to its large directional exposure to North Atlantic storm activity, low elevation, topography largely consisting of dynamic sand dunes, and narrow continental shelf which limits wave dissipation. The National Weather Service (NWS) forecast office in Morehead City, NC (WFO MHX) is responsible for issuing wave forecasts for the near-shore waters off the Outer Banks out to 20 nautical miles (37 km). WFO MHX likely receives more inquiries from mariners regarding the wind and wave forecast off the Outer Banks than any other forecast information, which reinforces the importance of wave forecasting to the NWS mission of protecting life and property.
A complex frontal system moved through the Southeastern states during 15-16 March 2008, which produced a severe weather outbreak leading to 51 tornado reports, 163 severe hail reports, and 83 reports of wind damage. As the parent surface low pressure system moved offshore during 16-17 March 2008, it intensified into a hurricane force cyclone in the Northwest Atlantic. The large marine storm ultimately sent a significant long period swell to the East Coast and Caribbean, leading to breaking waves in excess of 15 feet (4.6 m) along the Outer Banks, strong rip currents, and ocean over-wash, which temporarily closed portions of Highway 12 on Pea Island. Numerical Weather Prediction models did a poor job of representing the surface wind field associated with this storm when compared to surrounding buoy observations and winds observed from the SeaWinds Scatterometer aboard the QuikSCAT satellite, especially in the north semicircle, which was the effective fetch pointed at the Outer Banks. The failure of the atmospheric models led to a collapse of the wave model guidance available to NWS forecasters. The NOAA Wavewatch 3 model (WW3) wave heights were underdone by over 100% during the peak of the swell event as compared to Diamond Shoals buoy 41025 on 18 March 2008. WW3 was also several seconds too low with its peak wave period initializations and forecasts. A detailed case study of the meteorology and oceanography associated with this event will be discussed, in addition to an analysis of satellite derived wave tools that helped forecasters improve on the available computer model guidance. Finally, a review of the situational awareness challenges associated with this post-catastrophic severe weather event will also be presented.
Poster Session 4, POSTERS: Small-Scale Studies
Wednesday, 14 January 2009, 2:30 PM-4:00 PM, Hall 5
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