Hurricane Season: Predicting Storm Threats for 2011

Q&A with UAlbany Professor and Chair of Atmospheric and Environmental Sciences Chris Thorncroft

Tropical Storm Arlene became the first major storm to make landfall during the 2011 hurricane season.

ALBANY, N.Y. (July 15, 2011) -- On June 30, Tropical Storm Arlene made landfall in Mexico, becoming the first named storm of the 2011 'Hurricane Season.'  Each year, the Climate Prediction Center of the National Weather Service provides an outlook of the upcoming Atlantic Hurricane season. The prospect for 'named storms' takes on added significance from June 1 through Nov. 30, officially hurricane season in the Atlantic Ocean.

UAlbany Professor and Chair of Atmospheric and Environmental Sciences Chris Thorncroft discusses the process by which weather experts predict the upcoming season, the power of hurricanes, and the potential impact on the United States' eastern seaboard and gulf coast.

Q. How do meteorologists predict the expected number of storms in advance of the season?

A: Among the key factors that impact the number of Atlantic hurricanes in a season are the sea surface temperatures (SSTs) in the main development region where most hurricanes form. When the SSTs are warmer than normal there tends to be more hurricanes and when SSTs are colder than normal there tends to be less.

Atmospheric Sciences Chair Chris Thorncroft

The reason that meteorologists are able to predict the number of hurricanes a season ahead is because  SSTs change very slowly; so slowly that a warm or cold anomaly observed in June can persist for months or years. Thus, if we know, for example, that the Atlantic was warmer than normal in June it would likely be warmer than normal for much of the hurricane season and so we would expect an active hurricane season.

Variability of SSTs in the tropical Pacific can also impact hurricane activity in the Atlantic. Warmer than normal SSTs in the central and east pacific (El Niño) is often associated with more rising air that forms part of an west-to-east overturning circulation that impacts the Atlantic region where hurricanes tend to form. The enhanced winds blowing from west to east are detrimental to hurricane development. Colder than normal SSTs in the central and eastern Pacific (La Niña) have the opposite effect.

Q. Why is June considered the start of hurricane season?

A: June is a month when the environmental conditions become more favorable for the development of hurricanes. This includes the presence of warm sea surface temperatures that provide energy for their growth as well as strong weather systems coming off the coast of West Africa that trigger them. It's not a firm date; hurricanes can form earlier if the environmental conditions for that year are particularly favorable.

Q. What is the expectation for this season?

A: NOAA's climate prediction center is making the following predictions for this year's hurricane season:

• 12 to 18 named storms (winds of 39 mph or higher), of which:
• 6 to 10 could become hurricanes (winds of 74 mph or higher), including:
• 3 to 6 major hurricanes (category 3, 4 or 5; winds of 111 mph or higher).

Two key inputs to this forecast are the anomalously warm SSTs in the Atlantic and a weak -- but persisting -- La Niña.

Q. How did the naming convention for hurricanes begin, and what are the criteria for a storm to be "named?"

A: The naming of tropical cyclones began in the Australian region at the beginning of the 20th century. Forecasters started naming tropical cyclones after politicians so that they could ridicule politicians in public by saying things like "Smith is causing havoc in the pacific", "Smith is wandering aimlessly..."

The names for the 2011 season are: Arlene, Bret, Cindy, Don, Emily, Franklin, Gert, Harvey, Irene, Jose, Katia, Lee, Maria, Nate, Ophelia, Philippe, Rina, Sean, Tammy, Vince, and Whitney.

Q. What has been the busiest hurricane season on record?

A: The busiest hurricane season on record was 2005 with 28 named storms; that included 15 hurricanes and 7 major hurricanes.

Q. What characteristics of Hurricane Katrina led it to cause so much devastation?

A: Often most of the damage associated with land-falling hurricanes is associated with the storm surge. High winds on the right of track tend to pile-up the water on that side which can lead to flooding on landfall. In the case of Katrina, the flooding was exacerbated by the failing levies.

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