'Rapidly Intensifying' Hurricane Irma Now A Category 3 Storm

TAMPA, FL — As Tropical Depression Harvey fizzles out, Hurricane Irma is drawing the spotlight. The National Hurricane Center upgraded Irma to a Category 3 storm early Thursday evening, saying she would likely remain a powerful storm for the next few days at least. The center's forecasters described the storm as "rapidly intensifying" in announcing the upgrade.

As of the center’s 5 p.m. Aug. 31 update, Irma was located about 720 miles west of the Cabo Verde Islands. She was packing maximum sustained winds of 115 mph while moving west-northwest at 12 mph. Irma started out Thursday as a tropical storm, but was upgraded to a Category 2 hurricane by the center's 11 a.m. update.

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Center forecasters said Irma might experience "fluctuations in strength, both up and down," but will likely remain "a powerful hurricane for several days."

In her current position over open water, Irma poses no immediate threat to land. On her projected path, she may become a concern for Puerto Rico and the Dominican Republic by sometime early next week. It remains too early to tell what, if any, impact Hurricane Irma might have on the mainland United States.

Meanwhile, Harvey, the storm that slammed into Texas’ Gulf Coast on Friday as a Category 4 hurricane, was showing signs of fizzling out after crossing into Louisiana on Thursday. The National Hurricane Center announced at 11 a.m. it had issued its last advisory on Harvey.

Harvey has been blamed for at least 37 deaths since Friday. Some parts of Houston received more than 50 inches of rain, forcing thousands to evacuate.

• See also: Harvey Isn't Done Punishing Texas Yet

Harvey and Irma both formed during the peak of the 2017 hurricane season. Forecasters call the period between mid-August and mid-October the “season within the season.” This eight-week period “is often the most active and dangerous time for tropical cyclone activity,” according to NOAA.

Watch: Top 5 Most Devastating Hurricanes To Hit The U.S.

"As we reach the midpoint of the hurricane season and with Hurricane Irma intensifying over the eastern tropical Atlantic, this is a good time for all of us to make some 'halftime adjustments,'" Dr. Rick Knabb from The Weather Channel said in a Thursday statement. "Find out your evacuation zone and plan your evacuation route today, go shopping now to restock supplies, and do everything you can to strengthen your home."

While Irma's eventual path remains unclear, Knabb said, "We cannot rule out eventual impacts in the continental U.S. This is the reality of what we contend with during the peak of the season, one that has been forecast to be very active and with more than three months to go."

The peak period is historically responsible for major spikes in tropical weather activity, NOAA said. In fact, it accounts for roughly 78 percent of all tropical storm days on record. It is also the period when 87 percent of the category 1 and 2 hurricane days on record occurred. In addition, this period is responsible for “a whopping 96 percent of the major (category 3, 4 and 5) hurricane days.”

The conditions gradually become less ripe for development in mid-October when increased wind shear tends to reappear and water and air temperatures cool.

The Atlantic hurricane season runs from June 1 to Nov. 30 each year. Average seasons produce about 12 named storms, of which six become hurricanes. Three of the hurricanes are generally deemed major.

Residents readying for the ongoing season can get tips and advice on the federal government’s Ready.gov website.

Graphics courtesy of the National Hurricane Center