The Skill of an Urban Ocean Forecast System

Abstract

The New York Harbor Observing and Prediction System (NYHOPS) has been quasioperational since late 2003. The system provides hindcasts/nowcasts/forecasts of water properties in an urban ocean environment. The environment includes the waters of the New York /New Jersey Harbor Estuary, from the coast eastward to the continental shelf break of the New York Bight and all of Long Island Sound in one contiguous fashion. Each day NYHOPS produces a 24-hour hindcast/nowcast and a 48-hour forecast of the physical state of water level, currents, temperature, and salinity. The model hindcast/nowcast/forecast skill assessment has been quantified for the entire year 2004 in terms of mean error (ME), standard deviation of the error (SD), RMS error and correlation coefficient. For the hindcast/nowcast, at most of the locations, errors in computed water levels are less than 8.5% of the local tidal range and correlations between the data and model exceed 0.94. The mean RMS errors and correlations degrade to 10 % and 0.91 for the 1 st day forecast and to 14 % and 0.83 for the 2 nd day forecast. The performance of the model for salinity and temperature are very encouraging. The vertical salinity stratification and its temporal variations in the different regions in the model domain are accurately reproduced in the model. For the hindcast/nowcast, the correlation coefficients range at various stations from 0.64 to 0.79 for salinity, and are typically greater everywhere than 0.96 for temperature. The 1 st day and 2 nd day forecasts of salinity and temperature have almost the same skill as the hindcast. The experience gained over more than one year of quasi-operational status has led to a NYHOPS system that is capable of describing the entire spectrum of time scales of the computed quantities. NYHOPS data and model products are all available in real-time at www.stevens.edu/maritimeforecast). Future extensions of NYHOPS include the assimilation of temperature, salinity and CODAR derived surface current measurements.