Science can make predictions, but government has to act on them or they aren’t any use.

On Wednesday evening, Harvey was still just a tropical depression with winds of 35 miles per hour. The National Hurricane Center forecast that it would intensify to 40 miles per hour by Thursday morning, and reach its peak intensity two days later at 75 miles per hour – just barely crossing the threshold to be called a hurricane – just before landfall.

By 10 AM Central on Thursday, the picture had radically changed. The storm’s winds had already jumped up to 65 miles per hour, and the rapid intensification was forecast to continue, with Harvey reaching 115 miles per hour – category 3 on the Saffir-Simpson scale – before landfall. With these more intense winds came a prediction of 6-10 feet of storm surge for parts of the Texas coast, and an increase in forecast rainfall, with potential for up to two feet in some locations. Suddenly Harvey looked likely to produce a major disaster.

The machinery of government, media, and private sector began to engage, with emergency preparations and warnings ramping up to amplify the State of Disaster already issued Wednesday for 30 counties by Texas’ Governor.

Harvey was still just a tropical storm at this moment. All the emergency actions were predicated on forecasts of future changes in Harvey’s intensity. Intensity prediction is normally considered the weak point in the science of hurricane forecasting, and rapid intensification just before landfall, in particular, has often been called a “forecaster’s nightmare”. But the forecasters predicted it with confidence, and no one, as far as I know, questioned that prediction. The conditions were right, with sea surface temperatures in the Gulf very warm and vertical wind shear (the difference in the steering winds at different heights that can disrupt a hurricane’s circulation) very low. With landfall still somewhere between 36 and 48 hours away – not nearly as much lead time as would be ideal, but enough for many life- and property-saving actions – the NHC’s experts were able to sound the alarm effectively.

The forecasts quickly proved right. Harvey is closing in on the coast near Corpus Christi, and NHC a few hours ago declared it a category 3 Major Hurricane, with sustained winds now up to 125 miles per hour. A storm with winds of this magnitude has not made landfall in the US in over 11 years, but that “drought” will almost certainly end tomorrow.

These forecasts are a scientific success story, but their value depends on the actions of the state, local and federal governments.

Corpus Christi, a city of 325,000 people, is directly in Harvey’s sights. Much of the city – and all of its oil refineries – lie close to the water on a bay that can funnel and amplify the surge, now forecast to be between 6-12 feet (it’s already more than 4 feet as I write). The flooding will come with winds well in excess of hurricane force, and will likely be exacerbated and prolonged by heavy rains that could continue for days.

Yet on Thursday, the Mayor of Corpus Christi decided not to issue a mandatory evacuation order, but instead just to “encourage” evacuation of residents in the lowest-lying areas. I can’t understand this decision.

In a press conference this morning, the Mayor stood by it. When a reporter asked how many people might be left in the areas most at risk, the Mayor replied that he didn’t know, as there’s no way at this moment to take a survey. That’s probably true, but it would have been better if he could have said “we’re doing everything possible to get every one of those people out of harm’s way”. He couldn’t say that, because he hadn’t.

The motivation for avoiding a mandatory order appears to have been a fear of risking first responders’ lives by sending them in to enforce it. But there was no need to send them in. In the United States, a mandatory evacuation order is almost never truly mandatory in that sense. The Mayor could have simply said it was mandatory, and warned everyone in Harvey’s path that if they stayed in defiance of it, no one would be able to come and help them.

How many more people would have evacuated if the order had been mandatory? It’s impossible to know. Some won’t leave no matter what. But it’s hard to imagine that it wouldn’t have made a difference to some people if they’d heard their Mayor tell them they have to leave now, rather than just that it seems like a good idea.

By now, it is probably too late for anyone to get out who hasn’t already. I hope not many are left, and for those who are, I hope Harvey’s impacts turn out less catastrophic than predicted. Corpus Christi may get some luck yet – as I write, the latest forecasts have the center coming in very close to the city, which could put the strongest winds and surge just to the east. Several of the closest counties on that side have issued mandatory evacuation orders; some have not.