Eddy Observations
The patch of ocean off the Kona coast where the SeaSondes are mapping currents provides for some very interesting ocean dynamics. To the North is the nearly 2000 m deep ʻAlenuihāhā Channel separating Maui and Hawaii. With strong tradewinds blowing from the East, there is a funneling effect on the wind through this channel that can also drive strong currents. As the wind and wind-driven currents flow past the northern tip of Hawaii to the leeward side, high vorticity features can develop. West of the Kona coast the bathymetry drops quickly to nearly 5000 m. In this area, a larger-scale anti-cyclonic gyre has been reported that can drive strong southerly currents as we sometimes see on the Western edge of our current maps.
Not only do winds get funneled around the Northern tip of Hawaii, but tradewinds blowing between the five volcanos on the island can also produce a funneling effect forming strong surface current jets emanating from the coast. Throughout the Kona SeaSonde deployment, high vorticity surface current features, both cyclonic and anti-cyclonic, can be seen and often persist over days. These features have typically been 15 - 60 km in diameter. The surface current dynamics appear to be more complex than ROMS model predictions, although ROMS wind forecasts often show similar features indicating that wind probably provides the primary forcing in this season.
The interaction of these currents creates zones of convergence and divergence that are important to the local fishery dynamics. Additional mid-range systems to North and South coupled with Long Range systems could give a more complete picture of this dynamic and unique coastal ocean system.
