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  • Author or Editor: Leonard J. Pietrafesa x
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Joseph J. Cione, Sethu Raman, and Leonard J. Pietrafesa

Abstract

Midlatitude cyclones develop off the Carolinas during winters and move north producing gale-force winds, ice, and heavy snow. It is believed that boundary-layer and air-sea interaction processes are very important during the development stages of these East Coast storms. The marine boundary layer (MBL) off the mid- Atlantic coastline is highly baroclinic due to the proximity of the Gulf Stream just offshore.

Typical horizontal distances between the Wilmington coastline and the western edge of the Gulf Stream vary between 90 and 250 km annually, and this distance can deviate by over 30 km within a single week. While similar weekly Gulf Stream position standard deviations also exist at Cape Hatteras, the average annual distance to the Gulf Stream frontal zone is much smaller off Cape Hatteras, normally ranging between 30 and 100 km.

This research investigates the low-level baroclinic conditions present prior to observed storm events. The examination of nine years of data on the Gulf Stream position and East Coast winter storms seems to indicate that the degree of low-level baroclinicity and modification existing prior to a cyclonic event may significantly affect the rate of cyclonic deepening off the mid-Atlantic coastline. Statistical analyses linking the observed surface-pressure decrease with both the Gulf Stream frontal location and the prestorm coastal baroclinic conditions are presented. These results quantitatively indicate that Gulf Stream-induced wintertime baroclinicity may significantly affect the regional intensification of East Coast winter cyclones.

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Lian Xie, Shaowu Bao, Leonard J. Pietrafesa, Kristen Foley, and Montserrat Fuentes

Abstract

A real-time hurricane wind forecast model is developed by 1) incorporating an asymmetric effect into the Holland hurricane wind model; 2) using the National Oceanic and Atmospheric Administration (NOAA)/National Hurricane Center’s (NHC) hurricane forecast guidance for prognostic modeling; and 3) assimilating the National Data Buoy Center (NDBC) real-time buoy data into the model’s initial wind field. The method is validated using all 2003 and 2004 Atlantic and Gulf of Mexico hurricanes. The results show that 6- and 12-h forecast winds using the asymmetric hurricane wind model are statistically more accurate than using a symmetric wind model. Detailed case studies were conducted for four historical hurricanes, namely, Floyd (1999), Gordon (2000), Lily (2002), and Isabel (2003). Although the asymmetric model performed generally better than the symmetric model, the improvement in hurricane wind forecasts produced by the asymmetric model varied significantly for different storms. In some cases, optimizing the symmetric model using observations available at initial time and forecast mean radius of maximum wind can produce comparable wind accuracy measured in terms of rms error of wind speed. However, in order to describe the asymmetric structure of hurricane winds, an asymmetric model is needed.

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