UPDATE 8:35PM 7-20:
Myrtle fire still at 7,500 acres. Now 15 percent contained.
Thunderstorms are moving over the fire this evening - no word yet if beneficial precipitation fell on the blaze.
Hot Springs now has a evacuation shelter set up at the Mueller Center.
The Myrtle fire near Pringle more than tripled in size Thursday night.
And although winds died down Friday morning, increased activity in the afternoon has some worried it could triple again.
At 7,500 acres as of Friday afternoon, the fire was still just 5 percent contained.
"The way the fire's moving at extreme rates of spread, that's all we can get right now," said Matt Spring, incident commander for the fire.
He said the unpredictable behavior is forcing hundreds from their homes. At last check, 242 residences had been evacuated.
"Every time we were trying to fight that at the head or any flanks and in an anchor point, the wind would switch and do bad things to us," Spring said.
Even with multiple helicopters and planes dropping water and retardant, it's hard to say where the fire will go next.
"We sheltered a couple of folks last night," said Dan Kuecker with the Black Hills Red Cross. "We expect more tonight as there have been more evacuations and people become aware that we're actually here."
They've actually been there for a while. Kuecker said the Red Cross staged a practice shelter drill in May to prepare.
"At that time," he said, "we placed the trailer in Custer full time because we anticipated that something like this might possibly."
"Now here we are," he added.
The trailer has enough cots and supplies for a hundred people, with "additional trailers up in Rapid City on standby if we have to go beyond that," Kuecker said.
With an estimated 300 firefighters there on Friday, spiking up to around 500 Saturday when a national Type 1 team will take over management, Kuecker hopes they won't need that many beds.
But Spring said they'll need a little help to curb the flames.
"I need rain," he said. "As much as I can get."
The Red Cross shelter also has a check-in option for those who don't want to stay at Custer Middle School.
That option lets family members around the country see that their relatives are out of danger's way.