Shreveport, Louisiana

Storm, model, cone, voluntary, mandatory, contraflow: the language of hurricanes takes innocuous-looking everyday words and endows them overnight with new and sinister significance. Next day, they're on everyone's lips.

Everyone here is an amateur hurricane expert, though they don't call them hurricanes: they're storms. Everyone has the National Hurricane Center bookmarked on their computer. Everyone knows that a model is one of up to twenty lines on a map showing a storm's possible track, calculated by supercomputers crunching trillions of numbers every second.

The lines form an inverted cone spreading out from a storm's current location and showing the area which it could hit: in the case of Gustav, anywhere from southwest Texas to the Florida panhandle.

When things start to look especially grim, the authorities will declare first a voluntary evacuation - we strongly suggest you get out now - and then a mandatory one, meaning if you don't get out now, you're on your own, and if we catch you in the street, we may arrest you.

They'll also introduce a contraflow system on major highways out of cities like New Orleans so that all lanes flow inland towards safety. Hurricanes are dependent on warm water for their energy, so much of their force is spent after they hit land.

It's not just words that acquire special meanings: so do the numbers from 1 to 5.

If the storm is a category 1 or 2 on the Saffir-Simpson scale, with winds of up to 110 mph, people will consider battening down the hatches and sitting it out. If it's a 3, 4 or 5 and you have any sense, you'll evacuate.

If you return home a few days later after a false alarm - the storm hit some other poor unfortunate further down the coast, or it was only a 1 instead of the forecast 5 - no one will laugh at you. Better safe than sorry.

Katrina was a 5, but slowed to a 3 by the time she made landfall - it was the storm surge and poorly engineered levees that made her the most destructive hurricane in US history. Gustav is already a 4, and still has a thousand miles of open water from which to suck up fuel.

Pam and I left on Friday in the car which we'd conveniently and coincidentally bought only a week earlier; otherwise we'd have had to wait for one of the 700 buses that ferry people out of the city to shelters inland. As I write this on Saturday morning, the lines at the main bus terminal are already more than a mile long.

It was a beautifully, sunny, hot day, which made it hard to summon a sense of urgency. We emptied the fridge (if Gustav hits, the city will almost certainly be without power), closed the shutters and put away objects like flowerpots and dustbins that could cause damage if they blew around. But we made the hopefully realistic assumption that there wouldn't be any serious flooding: our house is in the 20% of the city that didn't flood during Katrina.

Outside was a flurry of activity as the neighbours loaded their cars with food, water, pet carriers and elderly relatives. The traffic on the interstate was stop-go, stop-go for the first hour and a half - it's also Labor Day weekend - but at least it wasn't gridlock. Pam once took thirteen hours just to travel the seventy miles to the nearest big city, Baton Rouge, during an evacuation.

After that, the 340-mile drive to Shreveport was relatively painless, and we're now staying with Pam's cousin Bill and his family. It's very strange not knowing whether we'll be returning home some time later next week (Gustav is expected to show up early on Tuesday morning) or remaining for much longer. I hope we don't outstay our welcome.

In an ironic coincidence, Friday was also the third anniversary of Katrina, and as a result we received an unexpected visit just before we left.

My sister Jacqui lives in Florida, and was the only British journalist in New Orleans on that fateful day in August 2005. She spent weeks here covering the aftermath and subsequent anniversaries, and has a deep affection for the city.

Recently, on a whim, she called the state coroner and asked whether there were still any unclaimed and unidentified bodies left over.

"Funny you should ask," he said. "It's three years now, and there are still eighty left. Three of them were babies. I was thinking I'd hold a jazz funeral to lay them all to rest." So Jacqui came to cover this moving story for several UK papers: here's one of her pieces.