he busiest part of the Atlantic hurricane season will get underway in just a few weeks, and it is supposed to be an active one, with the possibility of three to five Category 3 or greater hurricanes.

There was a bit of good news accompanying the outlook, which updated May's forecast (E&ENews PM, May 23) and was released yesterday by the National Weather Service's Climate Prediction Center.

Due to a lack of a La Niña and cooling in the Atlantic, the number of major hurricanes was scaled back some.

"Fortunately, we've reduced the upper end, the number of major hurricanes," said Gerry Bell, the lead seasonal hurricane forecaster at the Climate Prediction Center. Bell stressed, however, that there is still a strong chance of an above-normal hurricane season.

"The key issue for today and for hurricane preparedness is that people understand an above normal season is still on track," Bell said. "We are now entering the peak of the Atlantic hurricane season."

There is a 70 percent chance for 13 to 19 named storms, with top winds of 39 mph or higher. Six to nine of these are likely to be hurricanes, and three to five are likely to be major.

There are a number of signals that point to the chance for an above-average hurricane season, said Philip Klotzbach, a scientist who creates hurricane forecasts for the Tropical Meteorology Project at Colorado State University.

First, there is no El Niño. When there is an El Niño, it affects high-level winds in the Atlantic and reduces the chance that hurricanes can form. A La Niña, on the other hand, increases the chance that hurricanes will form. Neither phenomenon is in place this year, however.

Warmer Atlantic waters aid storms
"So then the other big thing that people always look at is what the conditions are in the Atlantic," Klotzbach said.

If water temperatures in the Atlantic are higher than normal, as they are now, hurricanes, which feed off warm ocean water, are more likely to form.

Klotzbach noted that the Atlantic Ocean is in the positive part of a 25- to 40-year-long cycle that influences hurricanes.

In 1995, this cycle, known as the Atlantic Multidecadal Oscillation, switched to a phase that generally leads to higher Atlantic Ocean temperatures. Because of this, hurricanes are more likely.

This year, in part as a response to the devastation caused by Superstorm Sandy, which was not classified as a hurricane when it landed, the National Weather Service has adopted some changes to its tropical storm warning system.

Some in the weather and emergency management community had criticized the service for confusing the public by failing to issue hurricane warnings as Sandy moved ashore, because it was no longer technically a hurricane.

A change adopted in April allows forecasters to keep issuing advisories and keep a hurricane or tropical storm watch or warning in effect for a system that poses significant threat to life and property, even if it no longer technically fits the definition.

Working on prompter warnings
The National Weather Service is also working to improve its hurricane forecasts for storms once they have formed.

The Hurricane Forecast Improvement Project (HFIP), which began in 2009, is an effort to improve the service's ability to forecast hurricane tracks and intensity further in advance.

To date, the team has been able to make measurable improvements in predicting the track of a hurricane. Predicting its intensity has been more difficult, said Robert Gall, the development manager at HFIP.

But last year, the team was able to improve the resolution on its hurricane model, which helped improve the intensity predictions.

This year, it has several more new tools that are proving useful. The scientists changed the way they initialize, or start up, their model, called the Hurricane Weather Research and Forecasting model.

They've also gotten better at plugging real-time data into the model from the aircraft that fly into the hurricane to collect information on conditions inside the storm.

"We haven't been good at using that [real-time] data in our models, and this year that will be used regularly whenever the data is available," Gall said.

The Weather Service is also using the additional supercomputing power it put in place in late July, which processes data twice as fast, to improve its forecasts. At the end of the season, it will evaluate its forecasts to see whether those tools led to improvements, Gall said.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500