Raging monster grew from depression

By Andrew Revkin
August 30, 2005

As ripples of vapour-filled turbulence began to organise into a storm over the steamy waters of the south-eastern Bahamas early last week, Tropical Depression 12 was born, giving few hints it was an embryonic monster that would grow into Hurricane Katrina.

Last Tuesday forecasters at the National Hurricane Centre in Miami noted that, given the lack of storm-shredding wind shear and the presence of ample heat in the Atlantic, "at least steady intensification appears to be in order".

From that time on, the storm continued to favour the worst outcomes projected by meteorologists and a half-dozen supercomputer simulations.

By Wednesday evening, the hurricane centre gave the first hint that what had already become a tropical storm "could intensify a little more than anticipated" and might become a small hurricane before striking southern Florida.

Still, when it hit Florida about 24 hours later, killing nine people and knocking out the electricity for a million more, its power seemed to catch many by surprise.

The storm kept "nudging" the upper limits of the predictions, said Bill Read, a meteorologist tracking the storm for the hurricane centre. In an unusual manner, the storm kept its swirling shape and retained its strength as it quickly rumbled across the state.

In the Gulf of Mexico, all projections had been that the storm would intensify as it drew energy from the warm waters there. Chance events favoured growth.

It churned directly over the "loop current", a great, deep whorl of hot sea water that pulses in between Mexico's Yucatan Peninsula and Cuba each year, then stays south of Louisiana into late summer.

Often, even in the gulf, storms weaken as they suck up cool water that lies stratified beneath the warm surface. However, in the loop, even the depths are hot. This "is like adding high-octane fuel to the fire", the centre said on Friday.

Forecasters then watched in wonder as a series of conditions, many poorly understood, caused the storm to do what no one wanted: intensify, expand and maintain a terrifying trajectory.

The energy, the near-record low pressure in the storm's core, and its huge dimensions added up to an inevitable disaster, Mr Read said. "That's why they're basically forecasting Armageddon when it goes inland," he said as New Orleans braced itself last night.

Disaster modelling suggests the consequences of a category four storm could be dire: New Orleans' pumps disabled by flooding, six metres of water in the streets and tens of thousands dead. Experts have warned that the city could be left paralysed for months by water, debris, demolished buildings, and a hazardous soup spiked with sewage, petrochemicals, alligators and fire ants.

New Orleans' vulnerability stems from several factors. The newly deposited soil the city was built on has been settling for 300 years, and drainage for development has made it sink faster. It is still sinking by a centimetre a year, and the sea is rising. Ships passing along the levee on the Mississippi River float metres higher than streets in the French Quarter.

And a century of flood control projects upstream have cut off the flow of sediment downriver, allowing the gulf to erode the Mississippi delta.

"That natural buffer of marshes and barrier islands has diminished by 40 to 50 per cent since the middle of the 20th century," said Shea Penland, a University of New Orleans geologist. "Anyone who lives down there will tell you that [what were once considered] small storms have become big storms in the last several decades."

The New York Times, The Baltimore Sun
