The National Weather Service has developed an automated technique for forecasting extratropical storm surges along the northeast coast of the U.S. The storm surge is the rise of water level above the normal tide and is caused mainly by the strong winds associated with extratropical storms over nearshore areas.
Empirical forecast equations have been derived for 10 locations from Portland, Me., to Norfolk, Va. The equations were derived using data from 68 storms that occurred from 1956 through 1969. Input data to these forecast equations are sea-level pressure values as forecast by the numerical weather model of the National Meteorological Center. A sample forecast equation is shown.
The forecast method was put into operation in Oct., 1971, on an experimental basis. Forecasts are transmitted via teletypewriter and consist of values projected out to 48 hours at 6-hour intervals. These projections are used by Weather Service forecasters as guidance in preparing actual storm surge forecasts. A sample teletype message is shown.
Forecasts of the devastating storm surge of Feb. 19, 1972, are discussed. Forecast charts of sea-level pressure are compared to sea-level pressure analyses, and storm surge forecasts are compared to observed storm surges. Experience so far has emphasized the extreme importance, of the input sea-level pressure forecasts. Indications are that the system is useful and will be expanded to include other locations.
The coastal storm of March, 1962, affected the entire Atlantic Coast of the U.S. and produced record-breaking high tides at some locations. This storm was the most devastating storm on record, as it caused damage estimated at over $200 million. Figs. 1 and 2 show some of the damage at Virginia Beach, Va., and Rehoboth Beach, Del.
It is, of course, extremely important to forecast the flooding associated with such storms. The critical time to forecast such conditions is also the time when forecasters are burdened with the usual bad weather conditions associated with coastal storms, such as extensive areas of rain or snow. The main purpose of automating the method is to produce better storm surge forecasts by providing guidance forecasts to Weather Service forecast offices.
Storm surge is defined as the meteorological effect on sea level and is computed as the algebraic difference between the observed tide and the normal astronomical tide. Fig. 3 illustrates this definition with a 2 day length of tide record. Here the observed tide is showy by the upper solid curve, the normal (or predicted) astronomical tide by the dashed line, and the storm surge by the lower curve.
