Moderate northwesterly shear prevented significant intensification for the first two days, but convection continued to grow towards the center and Sally slowly intensified.

However, an increase in wind shear and upwelling of colder waters halted the intensification and Sally weakened slightly on September 15 before turning slowly northeastward.

Numerous watches and warnings were issued in anticipation of the imminent approach of Sally, and several coastline counties and parishes on the Gulf Coast were evacuated.

In South Florida, heavy rain led to localized flash flooding while the rest of peninsula saw continuous shower and thunderstorm activity due to the asymmetric structure of Sally.

[4] Sally was the costliest of several destructive 2020 hurricanes whose names were not retired by the World Meteorological Organization following the season, along with Hanna, Isaias, Delta, and Zeta.

[9] Contrary to the NHC's forecasts,[1]: 13  the system developed into a tropical depression, the nineteenth of the season, by 18:00 UTC that day while situated between Andros Island and Bimini in the Bahamas, or about 115 mi (185 km/h) east-southeast of Miami, Florida.

[13] As Sally rounded the southern edge of the ridge and turned west-northwest, modest wind shear inhibited significant intensification over the next day.

[15] A temporary reprieve in wind shear enabled Sally's core to become more vertically aligned and convective bursts occurred throughout the day into September 14.

[19] The northern outer bands of the hurricane began impacting the Florida Panhandle early on September 14, primarily along the coast of Apalachee Bay.

[20] Rainfall continued to spread west into Alabama and slightly inland and its persistence led to soil saturation of 85 percent well-before the storm's core arrived.

[1] By the start of September 15, steering currents collapsed and Sally largely stalled south of the Florida Panhandle and Mobile Bay with a slight drift west.

[23][24] Although wind shear did not abate, upper-level divergence increased significantly and enabled the hurricane to unexpectedly intensify as it approached the Alabama coastline.

"Significant and life threatening flash flooding" began late on September 15 as rainfall intensified to rates up 3 in (76 mm) per hour along the coast, primarily between Gulf Shores, Alabama, and Destin, Florida.

[1]: 18  The hurricane ultimately made landfall at peak strength in Gulf Shores at 09:45 UTC with maximum sustained winds of 110 mph (175 km/h) and a minimum pressure of 965 mbar (hPa; 28.49 inHg).

Briefly crossing the border into the Florida Panhandle, the hurricane weakened to a tropical storm by 18:00 UTC as it moved back over southeastern Alabama.

[1]: 4 [35] The system transitioned into post-tropical cyclone soon after as it merged with a frontal boundary over Georgia six hours later, and a defined warm front became established to the east-northeast.

[1]: 4  A convergence zone developed across northern North Carolina into southeastern Virginia as warm, moist air from the remnant system interacted with an unseasonably strong cold front, creating an axis of heavy rain across the region.

[57] Mississippi governor Tate Reeves urged residents to prepare for Sally, which he said could produce up to 20 inches (510 mm) of rain in the southern part of the state.

Some shelters were opened, although officials urged people who were evacuating to stay with friends, relatives, or in hotels, if possible, because of the threat of coronavirus superspreading.

[58] Additionally, Dauphin Island mayor Jeff Collier strongly encouraged all people to evacuate the west end after water started to encroach on the main roadway.

[59] A state of emergency was declared by governor Kay Ivey on September 14, 2020, as public schools and university classes were either canceled or moved online in anticipation of the storm.

[61] Warm and humid southerly flow associated with the circulation of Sally brought scattered showers and thunderstorms to western and central areas of Cuba on September 12–13.

Additionally, the storm's slow movement caused coastal areas between Mobile, Alabama, and Pensacola, Florida, to be in the northern eyewall for hours.

Over 500,000 customers in Louisiana, Alabama, Florida, and Georgia lost power and parts of I-10, including the Escambia Bay Bridge, were shut down.

[86] In Pensacola, a 27-year-old boater went missing when he left his home in a 12-foot jon, in an attempt to find his mother's pontoon boat that became untethered in the strong currents and whipping winds brought on by the hurricane; one week after his disappearance, his body was found washed ashore near the Blue Angel Recreation Park.

[91] Continuous onshore flow from Sally caused storm surge flooding to occur on Dauphin Island beginning early on September 14.

[59] Two unoccupied riverboat casinos in Bayou La Batre near Mobile broke loose due to the constant wave action with one of them hitting a dock.

[44][85][82] Several sewage overflows were reported across Mobile County following heavy rain from Hurricane Sally, causing contamination to Dog River and Rabbit Creek.

[99] The winds from the outer bands of Sally caused the south side of Lake Pontchartrain in Louisiana to overflow its banks, flooding Lakeshore Drive.

[82] The agricultural industry of Alabama, which was already under stress due to COVID-related impacts, suffered another devastating blow with many farmers' fields completely flooded, crops torn apart, and structures destroyed.