Vision inside the eye of the storm gets sharper
Robert Isaacks, a 26-year resident of High Island, Texas, calls himself a weather veteran. Certainly he knows the hurricane drill: board up the windows, and secure whatever possible.
These are preparations he did not have time to make last September, when Hurricane Humberto made a late-night landfall, just east of this tiny town on the Gulf of Mexico. “We weren’t prepared for it to be a hurricane,” said Isaacks. “This one caught us, so to speak, with our pants down.”
In fact, Humberto turned out to be one the most rapidly intensifying storms on record, strengthening from a tropical depression to a Category 1 hurricane within 19 hours of landfall, surprising even forecasters.
This hurricane season, which begins June 1, coastal residents like Isaacks may be better forewarned of such an event.
For the first time, the National Hurricane Center will use a new way to remotely track changes in a storm’s strength from up to about 120 miles from the coast. Called VORTRAC (Vortex Objective Radar Tracking and Circulation), the method is just one in a set of recent developments that may improve hurricane intensity measurements and forecasts in coming years.
As anyone glued to the Weather Channel knows, it’s common for the strength of a developing storm to fluctuate. Such changes are also notoriously difficult to measure, let alone predict. That’s because a hurricane’s strength, measured by either wind speed or the pressure in the eye, is the sum of a huge array of complex small-scale churnings. Satellites, so useful for tracking the paths of storms, are not as good at capturing these inner dynamics.
Instead, such data often comes from airplanes, piloted by “hurricane hunters” who fly through storms and parachute down sets of instruments. “The best case is they fly through every hour or two, sometimes it’s three hours or maybe more,” said Paul Harasti, a scientist at the Naval Research Laboratory, who developed VORTRAC with two other scientists from the National Center for Atmospheric Research. And as the hurricane gets very close to land, it often becomes too dangerous to fly these reconnaissance missions.
By contrast, VORTRAC, which operates using data from about 20 existing land-based radars along the Atlantic and Gulf coasts, calculates wind speed and central pressure estimates every six minutes. “It fills in the gaps,” said Colin McAdie, a meteorologist at the National Hurricane Center. This information, he said, will help them to quickly spot trends in changing storms. “If you are in a landfall situation, you want to know that as soon as possible.”
The technique was approved after it successfully simulated results similar to the actual data from Hurricane Humberto and Hurricane Charley, a Category 4 storm that smacked into southwestern Florida in 2004, after its top winds increased dramatically within six hours of land. Since VORTRAC can analyze only storms already nearby, its information won’t often change evacuation orders, which are issued usually at least a day in advance.
Emergency planners, however, would welcome any improvements. “If we could get intensity forecasts as good as the hurricane center is right now at forecasting tracks, that would be extremely valuable,” said Jerry Mallet, an emergency coordinator for Charlotte County, where Charley hit.
For Charley, many “played the skinny black line,” and chose not to evacuate, said Mallet. Warning of changes in the strength a storm could save the lives or property for those who remain.
“Even in the hours before landfall, we do not want people to be caught unawares,” said McAdie.
Further offshore, from August to October this year, the National Oceanographic and Atmospheric Administration is hoping to do better than a few hours. They are beginning to use unmanned aircraft systems, which are remote-controlled planes, to monitor tropical storms as they develop. In a test last year, one of these “drones” flew through the eye wall of a hurricane, for the first time.
“The biggest thing is the ability for these aircrafts to fly where it’s mostly unsafe for a manned one, especially close to the sea surface,” said Eric Uhlhorn, who works in the hurricane research division of NOAA’s Atlantic Oceanographic and Meteorological Laboratory. The planes can also stay continuously inside the core of the storm much longer than a manned flight.
These missions, said Uhlhorn, will not only improve monitoring of individual storms, but will eventually help scientists improve the statistical computer models used to forecast the behavior of hurricanes. NOAA has invested $3 million this year to expand the use of drones for several applications, including hurricane monitoring and Arctic sea ice surveying.
Though the U.S. intensely monitors developing storms near its shores, other countries can’t always afford this, says Nicholas Makris, an ocean engineer at the Massachusetts Institute of Technology. He is researching the use of underwater microphones to calculate a hurricane’s wind speeds based on the sound it generates in the churning ocean waters. The results of one successful use of the method were accepted for publication in Geophysical Research Letters this March. Makris hopes to catch a few storms in the Pacific Ocean this summer, where he’s set up a pilot test in cooperation with the Mexican Navy.
Monitoring hurricane intensity is vital in places like the Bay of Bengal, said Makris, where Bangladesh and India are frequently ravaged by storms. “This is a cheap and easy way to do that,” he said.
Today, scientists debate whether hurricanes are getting stronger on average, owing to the rise in global temperatures. In this context, getting a better handle on the intensity of approaching storms will become increasingly important.
However it’s done, Isaacks, whose roof was damaged by Humberto, would be grateful to avoid another surprise. “Down here on the beach, everyone keeps a close eye on storms,” he said. “The earlier warning we can get to people in our town, the better.”