SR SSD 2001-29

Technical Attachment

They Nailed Every Move

Curtis Morgan
The Miami Herald

Officially, hurricanes remain unpredictable, but you wouldn't know it by Hurricane Michelle. For a week, forecasters at the National Hurricane Center nailed every wobble of the dangerous storm whirling close enough to evacuate the Keys and spawn plywood lines from Homestead to Hollywood. They said it would cut northeast across Cuba. It did. They said it would give South Florida only get a blustery brush. It did. "This is as accurate as I've ever seen a forecast," Chuck Lanza, emergency management director for Miami-Dade County, said Monday as Michelle's dreary fringe dissolved by day's end - just as predicted. "This is the ultimate. Do I expect them to do the same every time? No. "


For the National Hurricane Center and the National Weather Service, the tracking of Michelle proved a triumph of skill, science and, particularly, a new generation of computer modeling systems powerful enough to churn 1.2 trillion calculations per second and chart weather on a global scale. Echoing Lanza, forecasters emphasized their profession remains an inexact science. But it improves with each season -- 1.1 percent more accurate annually since 1970. Michelle proved as close as forecasters get to a bull's-eye, and they took the shot under intense pressure with a Category 4 storm approaching Florida's most populated region. "This is one we'd like to bottle," said Ed Rappaport, deputy director at the hurricane center, on Florida International University's main campus.


During the past decade, the center's average error for a storm forecast 72 hours ahead is about 225 nautical miles. Initial analysis shows the deviation on Michelle was only 120 miles, nearly 50 percent more accurate than average. The precision is particularly stunning when compared with 30 years ago, when 450-mile errors were the norm. Back then, of course, meteorologists were armed with what now, technologically speaking, is akin to sticking a finger in the wind -limited satellite images and scattered wind and temperature readings, often from ships. Today, the hurricane center has data-gathering and -crunching tools undreamed of in the 1960s and '70s. There are a bevy of satellites, some devoted just to weather watching. There is a wider, more accurate range of sea buoys, ships and land stations monitoring weather.

U.S. Air Force Reserve and National Oceanographic and Atmospheric Administration "hurricane hunter" prop planes are supplemented by a swift NOAA G-IV jet. They drop devices with esoteric names like the dropwindsonde, a high-tech weather lab in a tube, directly into storms. And, most critical, all that information now runs through ever-faster computers that spit out projected paths called "models." Years ago, forecasters largely relied on statistical history, the movement of past storms.


Now, under what Rappaport called "an evolution and maybe a revolution" of computer analysis, the most accurate projections are from "dynamic" models capable of making sense of floods of data from around the world -- from high-level wind currents to deep-sea water temperatures. Forecasters have used them with increasing success for nearly a decade, but during this season, one model that is run on a National Weather Service super-computer in Bowie, MD, has emerged as a star. "This is really the first year the model has performed so fabulously,"said Naomi Surgi, advanced projects leader for hurricanes for the National Weather Service's environmental modeling center in Maryland.

Called the "Aviation Run" or AVN, it was right on Michelle's track from Day One, and unlike a handful of other usually reliable models, never wavered. One model, early on, had the storm bending west into the Yucatan peninsula. Another repeatedly plotted a path into the tip of South Florida. "What was important was not only the accuracy but the consistency," Rappaport said. The AVN program, Surgi said, divides the world into 80-kilometer grids, measuring or estimating constantly changing weather conditions in each grid at 42 levels from the surface on up: air and water temperature, wind speeds, moisture levels, cloud composition, on and on.


The programs are constantly tweaked and tested. This year, for instance, the weather service made several changes: better use of moisture data detected by microwave sensors on satellites and improved analysis of deep cloud formations around eyewalls and the heat that generates, among others. "We're thrilled about the improvements," said hurricane specialist Richard Pasch. It's a process that takes years, Surgi said. "Science takes time to mature. This is the first year we're really able to see the payoffs."

Rappaport and hurricane center Director Max Mayfield called the job on Michelle a team effort, citing everyone from the center's six forecasters to hurricane hunter crews who were repeatedly bounced and battered to pull critical meteorological data out of Michelle's eye. But Lanza and other emergency management officials credited Mayfield's leadership for making their job easier. The county makes its calls on opening shelters and starting evacuations based on time lines from its own computer models.

"The difference this time around is that Max really showed a lot of leadership," said Roman Gastesi, Miami-Dade's water resources manager, who was monitoring flooding concerns. Emergency managers talked to the center every three to four hours and got a consistent message. "They were very open about their different scenarios but they kept sticking to the model that was taking it east," Gastesi said. "In a nutshell, they nailed it."

Published Tuesday, November 6, 2001 -- The Miami Herald
© 2001 The Miami Herald and wire service sources