Hurricane Gustav's 110-mile-an-hour winds, punishing sheets of rain and funnel clouds would test the psyche of any city, but the fact that this hurricane is assaulting New Orleans means it carries the potential for deep and long-lasting psychological trauma to residents there.

The mental health impact of Hurricane Katrina in 2005 was enormous. The Substance Abuse and Mental Health Administration estimated that 500,000 people required counseling. According to one study, 31.2 percent of those who lived through it came to suffer a disorder of anxiety or mood or both. More than 16 percent fell victim to post-traumatic stress disorder (PTSD), a condition that can include not only distressing and intrusive memories and dreams, but also a sense that one is actually reliving the catastrophe. This puts Katrina in the same league as life events like serving in combat or being the victim of a rape. Studies of those who have lived through those traumas have revealed a rate of PTSD between 10 and 30 percent.

It's particularly important, as well, that PTSD commonly causes changes in body physiology-including blood pressure and heart rate-when victims are exposed to stresses resembling the initial trauma. Body and mind are both affected.

The evacuation of New Orleans and the arrival of Gustav, with levees being tested again, means that millions of Americans are being traumatized-having to wonder and worry about their own safety, the well-being of their loved ones and what the storm will do to their property and finances. But it also means that a substantial percentage of them are being re-traumatized, compounding the psychological risks.

For an untold number of residents of New Orleans in 2005, Katrina wasn't, of course, the only painful chapter in their life stories. That hurricane itself carried the potential to reawaken unresolved feelings of vulnerability and loss from years, even decades, before. Now, we have Gustav.

This layering of traumas, one storm after another, makes leadership in today's crisis critical. It is inevitable that those who have fled New Orleans-including children and adolescents old enough to have survived both disasters-will look for signs that there is strong leadership in place, a plan for them and resources they can use as they return to their brave and battered city. Those resources will necessarily include mental health counselors, social workers, psychologists and psychiatrists. Residents of New Orleans should call upon their skills early on, with the certain knowledge that doing so for oneself or one's loved ones is a sign of strength, not weakness, and a critical step on the road back home.

Dr. Keith Ablow is a psychiatrist and member of the Fox News Medical A-Team.