Investigation of Convective Downburst Hazards to Marine Transportation.pdfVIP

Investigation of Convective Downburst Hazards to Marine Transportation Mason, Derek Thomas Jefferson High School for Science and Technology Alexandria, VA Abstract Convective downbursts are known to produce potentially hazardous weather conditions. Currently, severity indices are used to estimate the strength of a potential downburst, but this information does not readily translate to the variables affected by downburst events. The effects of downbursts are often associated with aviation because of rapid changes in wind direction and speed, but can also be observed in marine conditions. Three recently observed downburst events have been selected as case studies to evaluate the effects of the downbursts on the marine environment. The information gathered on these events includes wind speed, gusts and direction at the surface, air temperature and pressure, water level, and Wet Microburst Severity Index (WMSI) values. The events selected occurred at Tolchester Beach, MD, on September 28, 2006 at 23:06 GMT, North Jetty, near Galveston, TX, on October 13, 2006 at 2:48 GMT, and again at North Jetty on October 27, 2006 at 5:30 GMT. Correlation between the WMSI values, the maximum wind gust, and the change in water level is suggested. Introduction A downburst is a powerful downdraft produced by a convective storm that causes damaging winds for five to thirty minutes. (Fujita, 1985) Once identified, downbursts can be divided into two categories, microburst and macroburst. Winds from a microburst are horizontally limited (less than four kilometers), meaning that a smaller area is affected but also that higher wind speeds may result. Winds from a macroburst spread farther than four kilometers but are more limited in wind speed. (Fujita, 1985) Downbursts are also divided into categories based on their execution such as traveling or stationary, wet or dry, or radial or twisting. Wet microbursts are distinguished from dry ones by the prese