Savage heading to Lotho Minor to find Maul caused Dooku, Anakin, Ahsoka, Yoda and IIRC some others to feel something "sinister" coming, i.e Maul. Yoda meditating further realised what it meant and who was coming.
“I can sense him, Grievous. That creature Savage Opress is growing stronger and stronger as each day passes.”
“You consider him a threat?”
“He is a threat to all of us, even the Jedi. With the Nightsister’s eradicated, there is no one left to control him. Something is rising. Something… sinister.”
―Count Dooku and General Grievous (The Clone Wars: Season 4 Episode 21: Brothers)“I sense a disturbance… something sinister.”
“All the way out here?”
“Yes.”
“Do you know what or who it is?”
“No… but whatever it is… it feels familiar.”
―Anakin Skywalker and Ahsoka Tano (The Clone Wars: Season 4 Episode 21: Brothers)
“Feel the disturbance in the Force, do you?”
“Yes Master.”
“Fear you are in danger, I do. From the dead, an old enemy has awakened, seeking vengeance.”
“An old enemy?”
“Killed your master many moons ago, he did.”
“How can this be? I killed him myself.”
“It is so, I feared.”
“Darth Maul… alive?”
―Yoda and Obi-Wan Kenobi (The Clone Wars: Season 4 Episode 21: Brothers)
Master Yoda had been the first to feel the disturbance in the Force. Through meditation he had discovered its source―Obi-Wan’s ancient enemy had somehow returned from the dead.
―Darth Maul Shadow Conspiracy