Archive of Spotlight Feature Articles

Improving Hurricane Intensity Prediction with High Resolution Computer Models

Written by Erica Rule and Dr. Sundara Gopalakrishnan of AOML

Photo Credit: NOAA
Image of Katrina eyewall, 2005.

To save lives and protect property when a ferocious hurricane threatens our shores, researchers at NOAA know that it’s not enough to correctly track these massive storms. They also want to better forecast the intensity of storms when they make landfall.

The Atlantic hurricane season runs from June 1 through November 30, with the peak of hurricane activity falling between the months of August, September and October. NOAA is the federal agency charged with the responsibility of preparing the best possible forecasts and warnings to help coastal communities be forewarned of any impending impact. That means not only predicting the future track of the hurricane, but also the intensity or maximum sustained wind speed of the storm when it makes landfall. NOAA has made great strides in improving its ability to forecast the track a storm will take. Predicting the intensity of a hurricane has proven to be a much greater challenge and thus is the current focus of hurricane research at several NOAA research laboratories.

HWRFX 3 km run of Hurricane Rita in 2005

Forecasting intensity change in hurricanes is a complex and challenging problem. The environmental factors that are known to influence intensity change may vary in scales ranging between several hundreds of miles (e.g. environmental shear and upper ocean structure) to a few miles (e.g. hurricane scale interactions and ocean waves) and, perhaps sometimes, even down to a few hundred yards (e.g. individual clouds).

The Hurricane Forecast Improvement Project (HFIP) is a unified NOAA approach to guide and accelerate improvements in hurricane track and intensity forecasts, with an emphasis on rapid intensity change. The goals of HFIP are:

Improve Forecast Accuracy of track by 50% in 10 years
Improve Forecast Accuracy of intensity by 50% in 10 years
Improve Forecast Accuracy of storm surge impact locations and severity
Extend forecast reliability out to 7 days

HWRFX model run at 8 km resolution for Hurricane Ike in 2008

An integral component of the HFIP will be the development of improved high-resolution regional models that can simulate the atmosphere, ocean, and land surface processes down to a one kilometer resolution. The Experimental Hurricane Weather Research and Forecasting System (HWRFX) is a version of the NCEP’s HWRF system specifically adopted and developed jointly at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) and Earth System Research Laboratory (ESRL) to study the intensity change problem at the highest model grid resolution of about 1 kilometer. During the 2008 hurricane season the baseline evolutionary version of the HWRFX system was tested at about 9 kilometer resolution at AOML with a home grown UNIX cluster, named after AOML’s esteemed former hurricane modeler, Vic Ooyama.

As a part of NOAA’s continuous effort to improve forecasts of intensity changes, HWRFX was further improved and the model resolution was enhanced to 3 kilometers after the 2008 season. The new version was then evaluated on the High Performance Computing System facility at ESRL for 69 elusive cases from the 2005 and 2007 hurricane seasons which posed special challenges to the hurricane specialist at the NHC. Initial findings from these model runs indicate significant improvement in terms of both track and intensity predictions.

Photo Credit: NOAA
Sea-state in hurricane Isabel in 2003

Nevertheless, the intensity change forecasting problem is not a model resolution problem alone. Better representation of physical processes such as convection, eye-wall mixing and air-sea interactions in numerical models, improved hurricane-scale data assimilation techniques, and above all, better verification of available observations with model predictions may all lead to improved intensity forecasting. All these issues are being investigated in current evolution of the HWRFX. By the end of the 2009 season AOML hopes to be running this model in near real time at 1 kilometer resolution.

August 11, 2009

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