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Predicting storm paths now more accurate
by Bill Clough
Jul 22, 2013 | 348 views | 0 0 comments | 0 0 recommendations | email to a friend | print
National Weather Service Corpus Christi meteorologist Robert Hart explains some of the changes occurring this year in the National Hurricane Center forecasts. Forecasted paths are becoming more accurate but officials remind that dangerous winds extended far beyond the point of a hurricane’s impact.
National Weather Service Corpus Christi meteorologist Robert Hart explains some of the changes occurring this year in the National Hurricane Center forecasts. Forecasted paths are becoming more accurate but officials remind that dangerous winds extended far beyond the point of a hurricane’s impact.
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Warning Coordinating Meteorologist John Metz, at the Corpus Christi National Weather Service office, outlines how the Weather Service has expanded its use of social media to communicate with the public in the time of emergency.
Warning Coordinating Meteorologist John Metz, at the Corpus Christi National Weather Service office, outlines how the Weather Service has expanded its use of social media to communicate with the public in the time of emergency.
slideshow
CORPUS CHRISTI – A number of improvements in hurricane forecasting for the current season were outlined last Thursday, July 18, at the National Weather Service office here.

Among them:

• More advanced forecasting of storm development

• Increased accuracy of storm path prediction

• Heightened radar capability to track tropical systems and the tornadoes they produce

• Revision of the Saffir-Simpson scale for measuring hurricanes.

The National Hurricane Center (NHC) in Miami is confident enough in its results of four years of experimenting to issue forecasts on the potential of a system developing into a tropical storm five days in advance. The first forecasts should start appearing sometime in August, although the NHS still will label them as an experimental product, according to meteorologist Robert Hart of the Corpus Christi office.

In addition, on the NHC website (www.nhc. noaa.gov), graphics showing tropical storm system intensity predictions soon will show predicted paths of the storms as well. The NHC will label the new graph as a prototype.

Each season, the NHC accuracy of predicting what path a storm will take has increased. Starting this year, the NHC is narrowing its “cone of uncertainty” of a storm’s predicted path.

The width of the cone indicates that the NHC is forecasting there is a 67 percent chance that the eye of the storm will fall within that cone.

The increased accuracy still has its dangers.

“A cone tells you where the NHC is predicting the center of a storm will be in 12, 24, 36, 48, 72, 96 and 120 hours,” Corpus Christi meteorologist Jason Runyan says.

What it doesn’t tell is how far out the tropical storm/hurricane-force winds will extend, when they will begin, the height of the storm surge, how far the surge will extend, when flooding from the storm surge should begin, expected rainfall, the extent of flooding rain, when the rain will begin or end, where tornadoes are expected or when a tornado threat may begin.

NHC forecasters warn that people who rely on the cone of uncertainty to decide what action they should take during an approaching storm do so at their peril.

Still, the experimental accuracy of predicting a storm’s path up to seven days in advance now is as accurate as NHC five-day forecasts a decade ago.

In addition, intensive research is underway to increase the accuracy of what path tropical disturbances will take before they develop into tropical storms. Usually, forecasters find their predictions for which track a disturbance will take are 10 to 20 percent less accurate than the predictions for tropical storms.

Accuracy in predicting the future intensity of a storm, however, remains minimal.

Thanks to a technological upgrade, all 160 Doppler weather radar stations across the United States now can more easily detect and track tornadoes that often occur during a hurricane.

The upgrade to dual polarization means that as the radar antenna makes its 360-degree sweep, it transmits a horizontal pulse and then a vertical pulse.

By comparing the two radar returns, computers not only can differentiate among hail, snow and rain but also can measure the intensity and size of raindrops.

The Corpus Christi radar was upgraded this spring.

“The old system could detect the size of a return,” forecaster Todd Beal explains. “The dual-pol system can give us the size, variety and type of return, its intensity, whether it is rain or hail and can pick up insects, bats or birds.”

And more.

On average, hurricane-produced tornadoes occur when a storm is moving north to northwest, 30 percent occur before landfall, 70 percent occur over land, 90 percent form in the right-front quadrant, most happen in daylight and they are devilishly difficult to find on radar.

Until the upgrade.

What excites forecasters is that the dual polarity radars can clearly detect debris thrown into the air by a tornado funnel produced by a hurricane.

Ironically, the lowest and highest number of tornadoes or waterspouts associated with a hurricane occurred in 2004: Hurricane Ivan produced 131; Hurricane Gaston generated 21.

A victim of NHC advances is the traditional Saffir-Simpson hurricane scale that divides tropical systems into categories 1 through 5.

Of the four killer aspects of a hurricane — storm surge, tornadoes, flooding rain and damaging winds — the scale only measures wind speeds.

Starting this hurricane season, the scale has been renamed to the “Saffir-Simpson Hurricane Wind scale.”

It is used too indicate the maximum sustained winds of a hurricane which provides a measure of how much damage it may do.

But the limitations of the traditional scale are numerous.

“For instance,” Runyan explains, “it doesn’t indicate how far inland that hurricane-force winds will occur, showing that in 1961, Hurricane Carla generated 75 mph winds nearly to Austin.

Nor does the scale give any information about the predicted storm surge — the rise in sea level that accompanies landfall — caused by a number of factors that include the angle at which the storm hits land, the steepness of the Continental Shelf, the speed of the winds around the eye and the action of the waves.

Another factor, that turns out to affect the surge, but by only 5 percent, is the atmospheric pressure inside the eye.

Runyan listed some recent examples illustrating the Saffir-Simpson scale’s inability to predict storm surge: Hurricane Charley, category 4, produced a surge of seven feet. But Hurricane Katrina, a Category 3 storm, produced a storm surge of 27 feet.

Another danger of the scale is psychological. A misconception is that until a hurricane strengthens to category 3, it isn’t dangerous.

Nothing in the retinue of hurricane forecasting is farther from the truth.

Although it will not see the light of day this year, the NHC say it will offer a storm surge forecast within the next two years. It hopes to produce storm surge warnings by 2014 and improved inundation graphics a year later.

Motivation is high: of the fatalities from Hurricane Sandy’s hitting the Northeast last year, 33 percent were from high winds; 66 percent were from flooding.

Robert Bridge, Bee County’s emergency management coordinator, points out that Beeville is safe from storm surge threat. But what is a threat is public apathy. It’s easy to think about Beeville as being an inland community.

But the Gulf in only 57 miles away. If encountering a large storm, such as Hurricane Sandy — which was 940 miles across — or a small storm such as Hurricane Katrina — 415 miles across — those 57 miles are insignificant.

Bill Clough is a reporter at the Bee-Picayune and can be reached at 358-2550, ext. 122, or at beepic@mySouTex.com.
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