(Reuters) – A tropical storm that quickly formed off the coast of South Carolina on Wednesday threatened to unleash heavy rainfall that could produce life-threatening flash flooding after making landfall near Charleston, the National Hurricane Center said.

With maximum sustained winds of 45 miles per hour (72 km/h), Tropical Storm Bertha was expected to hit South Carolina in the next few hours, then move inland toward North Carolina and southwest Virginia as it weakens to a tropical depression.

“The good news is that it is just 30 miles offshore and is going to move inland during the next few hours so this is not going to get any stronger,” said Dennis Feltgen, a communications officer and meteorologist at the NHC in Miami, Florida.

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The NHC issued a tropical storm warning for the areas along the South Carolina coast from Edisto Beach to South Santee River, and warned that Bertha could bring two to four inches of rain in much of the affected areas, potentially triggering dangerous flash flooding.

Feltgen said experts had been tracking the system for a couple of days and that it is not uncommon for storms to form close to the coastline and develop quickly.

U.S. forecasters expect an above-normal 13 to 19 named storms during the 2020 Atlantic hurricane season, the National Oceanic and Atmospheric Administration’s Climate Prediction Center said earlier this month.

NOAA forecasters estimate three to six major hurricanes packing winds of at least 111 mph may form. The last two years have seen an above-average number of named storms, with 18 last year and 15 in 2018.