Miami and other cities along the east coast of Florida are in a particularly precarious spot as the latest forecasts for Hurricane Irma from the National Hurricane Center show the projected storm path shifting to the west.
If Irma stays on course the storm will make landfall as a Category 4 storm late Saturday near the southern tip of the Florida peninsula heading northwest, placing Miami northeast of the hurricane's eye — within the zone that typically has the strongest winds.
Sometimes referred to as the "dirty side," the Hurricane Research Division of the National Oceanic and Atmospheric Administration defines this "right side" of the storm with respect to the direction the storm is headed.
"In general, the strongest winds in a hurricane are found on the right side of the storm because the motion of the hurricane also contributes to its swirling winds," HRD explains. "A hurricane with a 90 mph [145 km/hr] winds while stationary would have winds up to 100 mph [160 km/hr] on the right side and only 80 mph [130 km/hr] on the left side if it began moving (any direction) at 10 mph [16 km/hr]." Near the eye of the storm is usually where the conditions are the worst.
Like all cyclones that exist in the Northern Hemisphere of the Earth, Irma is spinning counter-clockwise (they spine clockwise in the Southern Hemisphere). What this means is that as the storm heads northwest, the winds on the northeast side of the storm are typically moving in the same direction, creating a cumulative effect (see an example here). If Irma retains its 155 mph sustained winds and continues to move as a whole at 12 mph, that means the dirty side could experience winds of 167 mph.
According to the Saffir-Simpson Hurricane Wind Scale, which the NHC uses, a Category 5 storm has sustained winds of 157 mph or higher.
However this effect isn't guaranteed, according to National Weather Service Miami-South Florida meteorologist Andrew Hagen, who when asked about the dirty side said this is more of a theory than a sure thing, should other factors come into play.
"You could have strong thunderstorms on left side for hours," which Hagen offered as an example to the Washington Examiner, which he said means the winds on the left side of the storm could end up stronger than the winds on the right side.
Hagen also cautioned that there is too much uncertainty to say for sure where exactly the eye of Irma will make landfall. "It's too early to rule out east coast landing," he said.
#Irma is clearing out it's bigger eye as it nears the Florida Straights. Plenty of summer thunderstorms over Florida ahead of the monster pic.twitter.com/e8fmP6os4E— Jonathan (@JonathanBelles) September 8, 2017
The forecast will depend on how soon Irma turns north after it hits Cuba, which is south of Florida.
How quickly Irma turns to the north after lashing Cuba, the Turks and Caicos and Bahamas will determine whether the center of the storm makes landfall in Southern Florida or skirts right along the east coast of Florida.
"The timing of this turn is critical for where Irma will track during Sunday," said AccuWeather hurricane expert Dan Kottlowski. The weather forecasting company said that a slower turn north would result in more severe weather, including possible isolated tornado spin-ups, all across the Florida peninsula, while a quicker turn would mean the worst of the storm would remain offshore on the east side.
Though variations of wind speed are possible, the entirety of southern Florida Friday afternoon remain under a "life-threatening" "extreme" wind threat and the coasts on both the east and west sides face an "extreme" storm surge threat, according to NWS Miami-South Florida.
7am Fri 9/8: Hurricane #Irma expected to hit South Florida Saturday through Monday. Preparations should be complete by tonight! #FLwx pic.twitter.com/S9C146UamW— NWS Miami (@NWSMiami) September 8, 2017
A mass exodus of people are streaming out of Southern Florida, tying up roadways, as mandatory evacuations have been ordered across the state, including in Miami.
Florida Gov. Rick Scott said on Friday that all Floridians should be ready to evacuate as the state braces for Hurricane Irma, even if they are not in an evacuation zone. "We can expect additional evacuations as this storm continues to come up through the state," Scott said during a news conference. "I cannot stress this enough, do not ignore any evacuation orders. All Floridians should be prepared to evacuate."
Miami-Dade, Broward and Palm Beach counties on the east coast have about 6 million residents in total.