JACKSONVILLE, Fla. – Hurricane Ian slammed Southwest Florida with storm surge and extreme winds, but Central Florida dealt with another major impact — historic flooding.
Ian churned inland during the early morning hours of Thursday, Sep. 29, creating significant issues across much of the central portions of the state.
While the worst of the wind stayed southwest of Orlando in DeSoto and Highlands counties, the flooding rains covered much of the Orlando metro area.
The ‘odd’ rainfall pattern
Hurricanes are divided into four quadrants. Each quadrant brings its own risk to areas during landfall and when the storm is inland.
The worst rain with most hurricanes is in the right-front and right-rear quadrants. This is sometimes the “active” side of a hurricane.
With Ian, the core of the system pushed south of Orlando. This meant the heavy rainfall would primarily be over the Treasure Coast and South Florida, on the right side of the storm.
But that did not happen.
Ian began to ingest dry air near landfall over Southwest Florida. This dry air was significant and immediately began to dry out the southern end of the storm.
The heavy rain bands were rotated northward by the storm, pushing the flooding rains north of the center.
And the results were devastating to the urbanized Orlando region.
The rains came
There were warning signs days in advance that a significant flooding event could occur with Ian.
One run of the American forecast model, also known as the GFS, had an incredible 25- to 35-inch rain band from the Tampa area through the far western suburbs of Orlando.
This was an indication that significant rains were very possible on the north end of the storm.
The first outer rain band from Ian arrived late on Tuesday, Sep. 27.
It would go on to rain almost all day Wednesday, Sep. 28, and Thursday, Sep. 29.
The rains would finally diminish and exit into the Atlantic in the early morning hours of Friday, Sep. 30.
When it was over, the Orlando International Airport had received 13.20 inches of rain, while the Sanford International Airport received a stunning 16.10 inches of rain.
A ‘500-year flood’
Heavy rainfall and flooding are always a concern with tropical systems, but it is especially worrisome in urbanized areas.
Drainage systems can only take in so much water per hour, and those systems can sometimes back up during heavy rains.
Lakes and ponds can easily spill out of their banks, flooding the surrounding neighborhoods.
The first Flash Flood Warning for the Orlando area was issued in the overnight hours of Thursday, Sep. 29.
This was the first signal that significant flooding was becoming likely.
And the flooding continued to worsen.
Just before 5 a.m. on Thursday, Sep. 29, a very rare Flash Flood Emergency was issued for portions of Seminole County. Flash Flood Emergencies are only issued by the National Weather Service for life-threatening flash flooding.
Three more Flash Flood Emergencies were issued that morning. Many neighborhoods were experiencing floodwaters at levels never seen before, and water rescues were increasing.
Portions of Orlando had experienced a “500-year flood.”
This does not mean similar flooding happened 500 years ago. This is a probability the government uses to assess flooding risk.
A 500-year flood means an area has a 0.2% chance of experiencing flooding of that magnitude in a region. The 0.2% chance is multiplied through the years, meaning there is a high chance a flood of that magnitude would occur once every 500 years.
Many neighborhoods had experienced flooding that only had a 0.2% chance of happening or a 1-in-500 chance.
A regional event
It wasn’t just metro Orlando dealing with significant flooding with Ian.
Before arriving in Orlando, the heavy rain bands dumped well over 10 inches of rain across portions of Hardee, DeSoto and Polk counties.
This left major highways like U.S. 17 completely underwater and cut off some communities completely.
Volusia County also experienced significant issues.
A Flash Flood Emergency was also issued for southern Volusia, and even portions of Daytona International Speedway were underwater.
The recovery for Central Florida will take months, as some homes will have to be rebuilt and reconstructed, businesses relocated and government officials considering potential new flood mitigation measures.
We will continue to discuss Ian and its impacts in the coming days.