POPLARVILLE — Hurricane Isaac might be classified as a Category 1 storm based on its winds, but if they had a classification system based on rainfall, it would be a Category 5.

Isaac’s torrential rains, which will probably prove historic, lashed Pearl River County all night Tuesday, all day and night Wednesday and it was supposed to continue all day Thursday.

Some isolated portions of the county were estimated to be receiving up to 20 inches, which officials said was unprecedented.

“It will definitely cause significant flooding,” said Emergency Management Director Danny Manley.

The torrential rains have to go somewhere — it’s called runoff — and its down the tributaries of Pearl River southeast of Picayune.

Officials on Thursday were fighting the effects of rains that have fallen continuously beginning Tuesday night as Isaac moved ashore near Houma, La. Pearl River County was in the most potent portion of the storm, the northeast quadrant.

Winds did some damage, but officials expect flooding to do more as the runoff from Isaac’s torrential rains flow down the Wolf and Pearl rivers and down East and West Hobolochitto creeks and all the little creeks that flow into them.

Already in East Picayune, along Loftin Street, flood waters were approaching homes from a tributary stream to East Hobolochitto Creek that was backing up into a residential district.

Standing on his driveway watching the waters rise, Donald McDougle, who was flooded out during Katrina, and numerous times before, said, “I have seen this many times with hurricanes, and it is the same old thing. I have tried to get help but no one will help me; they say I make too much money. But when you have been hit as many times as I have, you wonder about it; my family has suffered.”

Manley said that since midnight Tuesday, emergency responders have rescued five people from areas that are flooding. He said 36 county roads had been closed, or partially closed, to traffic regulated because of flooding.

Authorities at 6 a.m. on Thursday closed the southbound lanes of Interstate 59 at Poplarville, at Mile Marker 32, as the Wolf River rose and flooded those lanes, and was threatening the northbound lanes.

Wolf River begins in northeast Pearl River County and drains all the way to the Gulf Coast near Pass Christian and Bay St. Louis.

Manley said MDOT was thinking of closing the northbound lanes, also, but that depended on whether or not Wolf River overflowed those lanes, too.

A tow truck driver, Gregory Alan Parker, 62, was killed in Picayune when a tree fell on the cab of his truck, officials reported.

No other deaths attributed to Isaac were reported by noon Thursday.

Officials were worried about East and West Hobolochitto creek flooding as the crest from Isaac’s torrential rains moved down stream of the two creeks which drain central and western Pearl River County from north of Poplarville on down to Picayune.

In Picayune at the Hermitage, they meet and form Hobolochitto Creek, which drains into East Pearl River southwest of Picayune.

There are numerous homes along the creeks and some will be subject to flooding as the creeks are expected to crest on Friday morning and reach historic levels.

Already at 11 a.m. on Thursday West Hobolochitto Creek at McNeill was at 20 feet, which is five feet above flood stage, and East Hobolochitto Creek was at 18.5, 3.5 feet above flood stage. Both are expected to go higher by Friday morning’s crest.

On the Pearl River at Bogalusa, La., the river was at 18 ft., right at the flood stage of 18 feet, and it was expected to go to at least 20 feet by sometime Friday. Pearl River is not expected to crest until Monday.

Historic flooding is expected to take place there, too.

Early Thursday morning, Pearl River County District Four Supervisor and board president J. Patrick Lee said he has never seen “rain of this magnitude here.”

“Isaac might have been a category 1 storm, but as to rain, I have never seen as much rain persist as long as it has. We are worried about flooding most of all. I have never in my lifetime seen Wolf River overflow I-59. That is unprecedented,” said Lee.

If matters weren’t bad enough, Mississippi officials said the dam at Percy Quin State Park showed signs of weakness and could give way. That would send the reservoir’s waters tumbling down the Tagipahoa River. However, that river flows into Lake Pontchartrain and that situation, if it happens, was not supposed to threaten Pearl River County.

Slidell, La., officials in a 10 a.m. press conference said South Slidell was flooding because bayous, backed up by rising lake levels and heavy rains, were flooding neighborhoods.