Forecasters are predicting yet another very active hurricane season for 2007, but this year meteorologists expect to be able to more accurately predict the path, structure, and intensity of storms. The device that will make this happen is a new hurricane-forecasting model developed by scientists at the National Oceanic and Atmospheric Administration (NOAA) Environmental Modeling Center. It will utilize advanced physics and data collected from environmental-observation equipment to outperform current models and provide scientists with real-time three-dimensional analysis of storm conditions.
The model is able to see the inner core of the hurricane, where the eye wall is located, better and in higher resolution than all other models, says T. N. Krishnamurti, a professor of meteorology at Florida State University. The eye wall is the region around the hurricane eye where the strongest winds and heaviest rains are located, thus the place of the highest storm intensity. “It is a very comprehensive model that is a significant development for hurricane forecasting,” says Krishnamurti.
Currently, experts at the National Hurricane Center and the National Weather Service rely mostly on the Geophysical Fluid Dynamics Laboratory (GFDL) model. The model, which has been in use since 1995, forecasts the path and intensity of storms. Until now, it was the only global model that provided specific intensity forecasts of hurricanes. And while it is a very good model, it’s limited by the amount of data it’s based on. “It has a very crude representation of storms,” says Naomi Surgi, the project leader for the new model and a scientist in the Environment Modeling Center. “GFDL is unable to use observations from satellites and aircraft in its analysis of the storm.”
Isaac Ginis, a professor of oceanography at the University of Rhode Island (URI) who helped develop the GFDL model, agrees that the old model “has too many limitations” and, while it’s able to forecast the path of a storm well, it is not as skillful at forecasting the intensity or power of a storm. Ginis is now a principal investigator for the new model, called the Hurricane Weather Research and Forecast (HWRF) model, which is able to gather a more varied and better set of observations and assimilate that data to produce a more accurate forecast.
This new model will use data collected from satellites, marine data buoys, and hurricane hunter aircraft, which fly directly into a hurricane’s inner core and the surrounding atmosphere. The aircraft will be equipped with Doppler radars, which provide three-dimensional descriptions of the storm, most importantly observing the direction of hurricane winds. The aircraft will also be dropping ocean probes to better determine the location of the loop current, a warm ocean current in the Gulf of Mexico made up of little hot spots, known as warm core eddies, that give hurricanes moving over them a “real punch,” says Surgi.
The hurricane model will then assimilate the data–wind conditions, temperature, pressure, humidity, and other oceanic and atmospheric factors in and around the storm–and analyze it using mathematics and physics to create a model, explains Surgi. To understand hurricane problems in the tropics, it is imperative to understand the physics of the air-sea interface. “In the last several years, we have learned a lot about the transfer of energy between the upper part of the ocean and the lowest layers of the atmosphere,” she says. “And the energy fluxes across that boundary are tremendously important in terms of being able to forecast a hurricane’s structure.”
View images of the GFDL and HWRF models.
Improving the intensity forecast of a storm and being able to precisely analyze a hurricane’s structure were scientists’ main goals in developing the new model. It can now forecast these aspects from 24 hours out up to five days out with extreme accuracy, says Ginis. The new model was put to the test by running three full hurricane seasons–2004, 2005, and 2006–for storms in both the Atlantic and east Pacific basin, totaling close to 1,800 tests runs. For example, the model was able to reproduce the life cycle of Hurricane Katrina very well, accurately forecasting that it would become a category 5 hurricane over the Gulf of Mexico–something the old model was unable to predict.
Over the next several years, scientists at NOAA will continue to improve upon these initial advancements with further use of ocean observations. They plan to couple the HWRF with a wave model, which will allow scientists to better forecast storm surge, inland flooding, and rainfall. NOAA has, in addition to partnering with URI in 2006, started collaborating with researchers at the University of Southern Alabama to work on coupling the HWRF with a wave model and enhancing its forecasting features.
“This model is enormously important for emergency response and emergency managers, and also the public,” says Ginis, “because we not only want to know where the storm is going to make landfall, but also how powerful it is going to be.”