GPS data new tool in reading tropical storms

The first tropical storm of the Atlantic hurricane season formed this past weak. “Alex,” which eventually became a hurricane, tracked across the Yucatan peninsula, and then northwestward into southern Texas, bringing the usual deluge of heavy rains and strong winds.

This was the first June hurricane since 1995. With the disastrous oil spill in the Gulf, scientists are paying extra special attention to tropical storms as they form across the area. While forecasting and tracking the location of tropical storms is important, being able to predict the intensity of storms is important, too.

One of the new pieces of data meteorologists are using to help predict the intensity of tropical storms, is GPS (global positioning system) signals. GPS signals, transmitted by satellite and received on the ground, are slowed down and bent by water vapor in the earth’s atmosphere. The effect used to be considered a problem, as it related to GPS systems, but now scientists have learned to “read” this effect to measure the area’s water vapor content. Moisture rich air can make a hurricane more intense, while dry air can weaken it. In the past, it was difficult to collect such water vapor measurements over the ocean. This hurricane season, Frisbee-sized satellite antennas have been placed atop stationary platforms in the Gulf of Mexico, and scientists will incorporate this new GPS water vapor data into forecast computer models, which should result in improvements in storm forecasts.

When it comes to computer models, the more data that can be fed into it, the better the forecast product. The Weather In-Situ Deployment Optimization Method, or WISDOM project, will launch up to 200 weather balloons from the East Coast as well as several international sites several days before a hurricane threatening the United States makes landfall. These balloons will acquire much needed additional wind and pressure data over the open ocean, which when fed into computer models will help forecasters improve the 3- to 6-day hurricane track forecast.

Some people have wondered if the oil slick in the Gulf is going to have any impact on hurricane formation, or on a hurricane itself if it passes through the oil. In general, the answer is no. Firstly, the span of a typical hurricane (200 to 300 miles) is far wider than the current size of the spill. According the National Oceanic and Atmospheric Administration, the oil slick would not have any appreciable affect on either the intensity or track of a fully developed tropical storm or hurricane. As far as the oil slick hindering evaporation of water over the ocean (thus decreasing the “fuel” needed for hurricane formation), that is unlikely as well. Except for immediately near the source of the leak, the oil slick is very patchy. Because of that, the oil would have a negligible effect on evaporation.