Hurricane Milton: What’s a Category 5 storm and why is it so dangerous?

Florida’s west coast braces for high-speed winds and torrential rainfall weeks after devastation caused by Hurricane Helene.

Preparations and evacuations are under way on Florida’s west coast, where Category 5 Hurricane Milton with sustained wind speeds of 258km/h (160mph) is expected to make landfall over the next 24 hours.

However, Milton, which comes two weeks after Hurricane Helene, might weaken in intensity as it approaches landfall, forecast for Wednesday night or early Thursday.

The National Hurricane Center has said Milton presents an “extremely life-threatening situation” and is expected to bring damaging winds and torrential rainfall that will extend inland and outside the forecast cone.

Florida is still reeling from the devastation caused by Hurricane Helene on September 26. The Category 4 hurricane with a wind speed of about 225km/h (140mph) had caused damage in other southeastern states as well.

How are hurricanes categorised?

The National Hurricane Center has used the Saffir-Simpson Hurricane Wind Scale since 1973 when the scale was introduced to the general public.

It was developed by civil engineer Herbert Saffir and meteorologist Robert Simpson.

The scale rates hurricanes from Category 1 to Category 5, depending on their maximum sustained wind speed. This provides an estimate of potential property damage.

Category 1: 119-153km/h (74-95mph). These hurricanes are deemed very dangerous and are expected to cause some damage to power lines and poles.

Category 2: 154-177km/h (96-110mph). Such wind speeds are expected to cause extensive damage, causing some shallow-rooted trees to break off and block roads. A near-total power cut is expected from several days to weeks.

Category 3: 178-208km/h (111-129mph). Devastating damage is expected from this category. Trees can snap and uproot, and electricity and water supplies can be disrupted from several days to weeks after the hurricane passes.

Category 4: 209-251km/h (130-156mph). The National Weather Service (NWS) warns of catastrophic damage from Category 4 and 5 hurricanes. A Category 4 hurricane could lead to trees and power poles falling, as well as power outages for weeks or months.

Category 5: 252km/h and higher (157mph and higher). Roofs and walls of houses are likely to be damaged or collapse. A lasting power outage is expected.

After Category 5 Hurricane Wilma hit Florida, Cuba and the Yucatan Peninsula in 2005, the Saffir-Simpson scale was criticised. Experts, including Massachusetts Institute of Technology climatologist Kerry Emanuel, who was quoted by LiveScience at the time, argued the scale considers only wind speed and does not account for the rainfall and rain-related damage a hurricane can cause.

Destroyed houses in the aftermath of Hurricane Wilma, North Bay Village, Florida, October 24, 2005 [AP Photo]

Other hurricane scales, such as the Integrated Kinetic Energy (IKE) and Accumulated Cyclone Energy (ACE), provide broader assessments by factoring in storm size, duration and overall energy, rather than just wind speed like the Saffir-Simpson scale.

How to prepare for a hurricane

The NWS website lists a series of measures when a hurricane approaches. These include:

• Prepare a hurricane emergency kit with items including water, food, flashlights, first aid kits, a whistle to call for help, a dust mask to filter contaminated air, materials for shelter such as plastic sheets and duct tape, local maps, and phones with chargers or backup batteries.
• Strengthen your home and minimise damage by keeping trees around your house trimmed, shield your windows properly from dust, move loose outdoor furniture and items indoors, and secure all doors.
• Fill bathtubs and sinks with water in case the water supply is disrupted. Make sure your vehicle’s fuel tank is full.
• Know your zone and evacuation plan, and make sure not to travel too far, just away from the evacuation area. Additionally, communicate evacuation plans with someone outside the storm zone and have a plan for where your pets will go.
• Stay updated about the hurricane through media, radio, and social media.
• Review your insurance policies to ensure your house and personal property are adequately covered.
• Keep your pets indoors and adequately facilitated.