Miami could get hit by the ‘dirty side’ of Irma. Here’s what that means

There’s no pleasant side of a hurricane, but there is a “dirty side.” Others refer to it more simply as “the bad side” or “the side you don’t want to be on.”

And Miami is at risk for being on that side for Hurricane Irma.

The dirty side is generally known as the right side of the storm when looking at it from above, but it’s more accurate to say it’s on the right side of whatever direction the storm is moving, according to the National Oceanic and Atmospheric Administration. So if the storm is moving west, as Irma currently is, the north side is the dirty side. If it’s moving north, as the National Hurricane Center predicts Irma will turn once it’s under Florida, the east side is the dirty side.

The right side of the storm is worse due to the direction of hurricane winds, according to NOAA. Hurricane winds rotate counterclockwise, so the strength of the storm on the dirty side is the hurricane’s wind speed plus its forward velocity. The absolute worst spot in a hurricane is on the dirty side closest to the eye of the storm, according to NOAA.

“A hurricane with a 90 mph winds while stationary would have winds up to 100 mph on the right side and only 80 mph on the left side if it began moving (any direction) at 10 mph,” the NOAA website says by example.

Don’t think 20 miles per hour will make that much of a difference in wind force? Watch the video below.

But here’s the – somewhat – good news: Irma has become such a “well-developed, symmetrical storm” that the dirty side might not really matter in this case, according to Robert Garcia, lead meteorologist at the National Weather Service.

“The difference between the dirty side and the ‘clean side’ in this case, is probably just the difference between regular and diet soda,” Garcia said. “Even if we get fortunate with Irma, folks should definitely be preparing for the worst and hoping for the best.”

Garcia said Miami has a 70 percent chance of experiencing tropical storm-force winds and a 33-40 percent chance of hurricane-force winds. Those chances are likely to increase as the storm moves closer, he said.

Irma’s maximum sustained winds, according to the National Hurricane Center’s latest update at 11 a.m. Wednesday, clocked in at 185 miles per hour. Hurricane-level winds extend 50 miles from the eye of the storm.

The storm already hit Barbuda, with sustained winds of 118 miles per hour and a maximum recorded gust of 155 miles per hour “before the instrument failed earlier this morning,” according to the National Hurricane Center.

The latest projected path of Irma by hurricane specialists has it falling just to the east of Miami by early Sunday, which would keep Miami outside of its dirty side, and then continuing along the east coast of Florida. But the projected cone of Irma could have the storm hitting anywhere in Florida, and predictions about hurricane paths more than 72 hours in advance vary highly.

The Bahamas and Turks and Caicos Islands are at more immediate risk of being on the dirty side of Hurricane Irma.

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