Seven feet of seawater swamps Key Biscayne and 45 miles of coastline from Miami Beach to Deerfield Beach. Saltwater surges through some houses in Hollywood, Coconut Grove and elsewhere. Waist-deep freshwater blankets vast regions of suburban Broward and Miami-Dade counties.

Ferocious winds crush tens of thousands of roofs and gut numerous office buildings. Residents who defy orders to evacuate skyscrapers in Miami Beach, on Hollywood's beach and along Miami's downtown corridors could be blown out of their apartments. Power outages persist for months rather than weeks.

According to simulations conducted for The Miami Herald by scientists at the National Hurricane Center and interviews with a wide range of experts, those are not merely theoretical worst-case scenarios.

"Don't ever ask the question, `What else could happen?'" said Marcia Paul Leone, a mortgage banker who was surveying the new damage to her Katrina-flooded home.

She would go no farther than the front porch of her house Thursday morning. Windows were blown out, and the building appeared to be leaning.

"I've been in the mortgage business for 20 years. I know when something's unsafe," she said.

Electricity was knocked out at Louis Armstrong International Airport, rounding passenger flights and leaving travelers to wait in a dimly lit terminal powered by generators. The storm also ripped off part of a concourse roof, slammed one jetway into another, and flipped motorized runway luggage carts.

A hurricane's winds are mostly horizontal, not vertical. So the vertical churning that leads to lightning doesn't normally happen.

Lightning has been seen in hurricanes before. During a field campaign in 1998 called CAMEX-3, scientists detected lightning in the eye of hurricane Georges as it plowed over the Caribbean island of Hispaniola. The lightning probably was due to air forced upward—called "orographic forcing"—when the hurricane hit the mountains.

"Hurricanes are most likely to produce lightning when they're making landfall," says Blakeslee. But there were no mountains beneath the "electric hurricanes" of 2005—only flat water.

It's tempting to think that, because Emily, Rita and Katrina were all exceptionally powerful, their sheer violence somehow explains their lightning. But Blakeslee says that this explanation is too simple. "Other storms have been equally intense and did not produce much lightning," he says. "There must be something else at work."

Katrina's sustained winds reached 175 mph and its minimum central pressure dropped as low as 902 millibars the fourth lowest on record for an Atlantic hurricane, NOAA's National Climatic Data Center reported.

The storm weakened slightly before it reached landfall and had less powerful winds than Hurricane Camille, which devastated coastal Mississippi in August, 1969.

But the size of Katrina, with hurricane force winds extending 120 miles from its center, was much larger and the destruction more widespread than Camille.

The central pressure in a hurricane is a good indicator of the strength of the winds of the storm. The strongest observed hurricane in the Atlantic basin was Gilbert in 1988 with a pressure of 888 millibars in the northwest Caribbean. Normal average sea level air pressure is 1,016 millibars.

...Devastating damage expected...

.Hurricane Katrina...a most powerful hurricane with unprecedented strength...rivaling the intensity of Hurricane Camille of 1969.

Most of the area will be uninhabitable for weeks...perhaps longer. At least one half of well constructed homes will have roof and wall failure. All gabled roofs will fail...leaving those homes severely damaged or destroyed.

The majority of industrial buildings will become non functional. partial to complete wall and roof failure is expected. All wood framed low rising apartment buildings will be destroyed. Concrete block low rise apartments will sustain major damage...including some wall and roof failure.

High rise office and apartment buildings will sway dangerously...a few to the point of total collapse. All windows will blow out.

Airborne debris will be widespread...and may include heavy items such as household appliances and even light vehicles. Sport utility vehicles and light trucks will be moved. The blown debris will create additional destruction. Persons...pets...and livestock exposed to the winds will face certain death if struck.

Power outages will last for weeks...as most power poles will be down and transformers destroyed. Water shortages will make human suffering incredible by modern standards.

The vast majority of native trees will be snapped or uprooted. Only the heartiest will remain standing...but be totally defoliated. Few crops will remain. Livestock left exposed to the winds will be killed.

An inland hurricane wind warning is issued when sustained winds near hurricane force...or frequent gusts at or above hurricane force...are certain within the next 12 to 24 hours.

Once tropical storm and hurricane force winds onset...do not venture outside!

Maximum sustained winds at flight level during the 7am Hurricane Hunter mission into Katrina were 153 knots, which translates to 160 mph at the surface, making Katrina a minimal Category 5 hurricane. The winds are likely to increase to "catch up" to the rapidly falling pressure, and could approach the all-time record of 190 mph set in Camille and Allen. Winds of this level will create maximum storm surge heights over 25 feet, and this storm surge will affect an area at least double the area wiped clean by Camille, which was roughly half the size of Katrina. Katrina has continued to expand in size, and is now a huge hurricane like Ivan. Damage will be very widespread and extreme if Katrina can maintain Category 5 strength at landfall.

The storm caused widespread damage at Fort Lauderdale-Hollywood International Airport. High winds "shredded" the pedestrian canopy between Terminals 2 and 3, said Roger Desjarlais, the county administrator.

The winds knocked over a small private plane, overturned an 18-wheeler truck, knocked down power lines on the west side of the airport and flattened fences along the south side. -- David Fleshler at the Broward Emergency Operations Center