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ABSTRACT A simple and useful technique for prediction of sea breezes, based on readily available wind vector and air temperature predictions from synoptic models in conjunction with observed coastal sea surface temperatures, is presented for evaluation by coastal forecasters. A statistical prediction scheme using the sea-breeze index has been devised and was found to possess significant nowcasting skill, when used with observed synoptic wind vectors and temperatures and with observed coastal sea surface temperatures. The ready availability of data for these variables and the simplicity of the scheme give it the potential of being useful to many coastal forecast offices, once tuned to the area in which it is applied. The technique can be used on simple workstations or even by manual calculation and thus provides a simple method for local tuning of general-area forecasts to coastal areas. For the 1998 sea-breeze season tested, the algorithm, which was built on June data and tested by nowcasting on data from July through October, had a skill score of 31.3% over climatology.
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1. Introduction
Recognizing the immense impact coastal weather phenomena, including the sea breeze, often have on issues of health, welfare, and economics in coastal South Carolina, the forecast office and the College of Charleston cooperated to support studies of the sea breeze, starting in 1997. On 27 April 1999, the National Weather Service (NWS) Forecast Office in Charleston, South Carolina, assumed forecast and warning responsibility for 20 counties along coastal South Carolina and southeastern Georgia. One impact of this was the opportunity to incorporate in more detail the effects of sea breezes on local weather, necessitating the tuning of synoptic forecasts for this mesoscale effect.
Generally, the sea breeze develops when the mean boundary layer temperature difference between the two air masses overlying coastal waters and coastal land is sufficient to create a density (and therefore pressure) gradient. This gradient in turn creates a thermally directed circulation that favors low-level flow of relatively cool air onshore at the coast in the daytime. If the synoptic gradient flow opposes it, that is, if the overland winds are offshore, interaction with this onshore gradient flow will form a sea-breeze front. The balance of forces determines whether the coastal...