Making Hurricane Predictions

Name: _________________________________ Date: _____________

Is it possible to predict hurricanes? Consider these facts. In hurricane season, a storm's windspeed must be at least 39 miles per hour for it to earn a name. Before the 2005 hurricane season began on June 1, meteorologists predicted the number of named storms would be about double the seasonal average of ten. Hurricane Katrina, which blasted the Gulf Coast late in August 2005, was already the 11th. Soon after Katrina hit, meteorologists predicted many more strong Atlantic storms would follow and were quickly proven right. By the time the 2005 season ended, a record twenty-eight named storms had roared out of the Atlantic. Fifteen of these became hurricanes, also a new record.

It's not possible to predict where and when any individual hurricane will form, nor the exact path it will take once it does form. But their recent track record proves that scientists are getting better at predicting the number and intensity of storms in a given season. How do they do it? In this activity, you'll explore some of the data scientists use to shape their seasonal predictions.

To begin, look at this graph relating year-by-year hurricane frequency in the Atlantic to sea surface temperature. The red line shows how mean sea surface temperature (SST) has compared to normal since 1951. Positive numbers are warmer than normal and negative numbers are cooler. The blue line, called the ACE (Accumulated Cyclone Energy) Index, shows total year-by-year hurricane activity. Positive numbers represent years with high (above-normal) activity and negative numbers show low activity.
1. How did Atlantic hurricane activity relate to sea surface temperature between 1951 and 1970?
2. What happens to both graphs between 1971 and 1994?
3. What happens to both graphs between 1995 and 1999?
4. Based on your answers above, form a hypothesis that relates sea surface temperature and hurricane activity.
Next, you'll see actual Atlantic sea surface temperature data from late in the summer of 2005 when Katrina hit. Read the caption.
1. What does the black box in the center show?
2. Name the continents on either side of the black box.
3. Look at the color scale. Is ocean water in the black box above or below normal temperature?
4. Give the range (in degrees Fahrenheit) for how much above or below normal the water is.
Another factor in hurricane formation is sea level air pressure. Look closely at the graphic of pressure in the Atlantic in the summer of 2005 and read the caption.
1. What colors represent lower than normal air pressure?
2. Was sea-level pressure above or below normal in the hurricane development region (black box)?
3. Form a hypothesis relating sea-level pressure and hurricane formation.
Scientists also look at something called vertical wind shear data. This is a sudden change in vertical wind speed or direction. When there's a large amount of wind shear over the ocean, it's tough for hurricanes to form. Look at the graphic and read the text.
1. What does the red color represent?
2. What were vertical wind shear conditions like in the hurricane region in the summer of 2005?
3. What is the result of this pattern?
Aside from wind shear, prevailing winds also play a big part in hurricane formation, as this graphic shows.
1. Where do upper-level Easterlies (green arrow) originate from?
2. During the period from August to October 2005, what effect were these winds expected to have (light blue arrows) on hurricane formation in the Atlantic?
3. List four conditions shown on this map that favor hurricane formation.