Isaias is now a Category 2. Why that number undersells the danger

Hurricane Isaias strengthened to a Category 2 storm with maximum sustained winds near 100 mph Thursday afternoon, according to the National Hurricane Center's 4 p.m. CDT advisory. Forecasters expect it to keep strengthening through early Friday and make landfall on the northern Gulf Coast late Friday or early Saturday.

But the storm's category tells only part of the story. The scale used to rank hurricanes measures wind, and nothing else.

## Where Isaias stands

As of 4 p.m. CDT Thursday, Isaias was about 215 miles north of Progreso, Mexico, moving northeast at about 12 mph, the hurricane center said. Its minimum central pressure was 975 millibars. Hurricane-force winds extended up to 15 miles from the center, and tropical-storm-force winds up to 125 miles.

A hurricane warning covers the coast from Ocean Springs, Mississippi, to the Bay/Gulf County line in Florida. A storm surge warning stretches from the mouth of the Mississippi River to Florida's Suwannee River.

## What the category does and doesn't measure

Hurricanes are ranked on the Saffir-Simpson Hurricane Wind Scale. A Category 2 storm has sustained winds of 96 to 110 mph. Category 3, the threshold for a "major" hurricane, starts at 111 mph.

The hurricane center states plainly that the scale "does not take into account other potentially deadly hazards such as storm surge, rainfall flooding, and tornadoes."

That matters because a storm's label can make it sound less dangerous than it is.

## The threats beyond wind

**Storm surge.** If peak surge arrives at high tide, the hurricane center forecasts 5 to 7 feet of storm surge from Ocean Springs to Indian Pass, Florida, including Mobile Bay. Forecasts call for 4 to 6 feet from Indian Pass to Florida's Steinhatchee River, and 3 to 5 feet from the mouth of the Mississippi to Ocean Springs.

**Rain and flooding.** The center forecasts 4 to 8 inches of rain across southern Alabama, the Florida Panhandle and Big Bend, and southwest Georgia from Friday through the weekend, with local totals up to 15 inches. It says flash and urban flooding is likely and river flooding is expected, some of it potentially significant.

**Tornadoes.** An isolated tornado risk begins Friday night along coastal Alabama, the Florida Panhandle and far southwest Georgia, and continues Saturday farther inland.

## How officials are responding

According to CBS News, mandatory evacuations took effect Thursday in parts of Florida's Okaloosa and Walton counties, and coastal areas of southeastern Alabama are under voluntary evacuations. Florida has declared a state of emergency for more than two dozen counties, and Alabama for 40 counties, CBS reported. ABC News reported that waves near and east of where the storm comes ashore are expected to be large and dangerous.

## What it means for you

If you live, go to school or are traveling near the northern Gulf Coast, the storm's category is not the only number to watch. Surge and rain forecasts for your area matter just as much. Follow your county's emergency management orders, even if the storm is "only" a Category 1 or 2.

The hurricane center expects heavy rain and flooding well inland, including southwest Georgia, through the weekend.

## What happens next

The hurricane center will issue an intermediate advisory at 7 p.m. CDT and a full advisory at 10 p.m. CDT Thursday. Hurricane conditions are expected in the warning area Friday night into early Saturday, with tropical-storm conditions arriving earlier on Friday.