About half of those are due to storm surge: Storm surge is the rise in sea level during a big storm. It is measured as the height of the water above what the normal predicted astronomical tide height would be.
Since New Orleans and Lake Pontchartrain are currently west of Sally's estimated landfall, storm surge here will be lower than other areas east such as, Dauphin Island and Gulf Shores, Alabama, which can expect a 4 to 7 feet surge, or Pensacola and Destin, Florida, which could see a 3 to 5 feet surge.
Inland flooding is a danger that can occur far from where the eye of the hurricane and heavy winds make landfall.
"An average September sees around 4-5 inches of rainfall along the Gulf Coast in MS/AL/Florida panhandle — Sally will drop this amount in a couple of hours and likely produce several months' worth across some areas before the storm leaves the region," explains CNN meteorologist Brandon Miller.
Models have shifted to the east in the past 24 hours, and that means the heaviest rain has also shifted farther east, putting a place like Dauphin Island, Alabama, with a forecast of up to 20 inches of rain (isolated amounts up to 2 feet).
"Ironically, this the exact spot Hurricane Danny (1997) dropped a state record 37" on the island," says Pedram Javaheri, CNN meteorologist.
1:30 p.m. ET, September 15, 2020
Sally is the 7th hurricane this season. An average season only sees six.
From CNN's Brandon Miller
Sally is the seventh hurricane of the season, an average season only sees six – and we just now reaching the peak of the season, with two and a half months to go.
Sally will be the fourth hurricane to strike the US. That's the first time that has happened since the infamous year of 2005 (Katrina and Rita year). The other three this year were Hanna, Isaias and Laura.
In addition, an eighth hurricane could be forming in the Atlantic soon.
1:23 p.m. ET, September 15, 2020
Sally could bring several months' worth of rain to the Gulf Coast in less than 2 days
From CNN's Brandon Miller
Hurricane Sally, which is already impacting the Gulf Coast, will continue to batter the shore with worsening conditions through the day and night as the storm creeps towards land.
The storm is is currently moving at 2 mph — slower than an average human walking pace of 3-4 mph.
That slow movement will allow for several months’ worth of rainfall over the Gulf Coast in only one or two days
An average September sees four to five inches of rainfall along the Mississippi-Alabama-Florida panhandle. In parts of the area, Sally will drop this in a couple of hours.
Before the storm exits the region, three to four months’ worth of rain could accumulate in some spots.
The National Hurricane Center is saying “historic flooding is possible from Sally with extreme life-threatening flash flooding likely."