Tropical Storm Idalia strengthened as it neared Cuba and the abnormally hot waters of the Gulf of Mexico on Monday, with forecasters predicting it could become a major hurricane before roaring ashore in Florida this week. Florida Governor Ron DeSantis warned the storm could have “major impact” along the Gulf coast, telling a news conference that evacuations would take place and residents should “prepare accordingly” for Idalia. US President Joe Biden spoke with DeSantis earlier Monday and approved an emergency declaration for the state, promising it would have his “full support,” a White House spokesman said. Idalia was set to reach hurricane status as it nears Cuba on Monday, where a hurricane warning was already in place for western Pinar del Rio province, the US National Hurricane Center said. It will then move out over the Gulf, which scientists say is experiencing a “marine heat wave” — feeding Idalia as it barrels towards Florida. The storm “will be moving over waters near 31C (88 degrees Fahrenheit),” the NHC said in an update. Heat is one factor that fuels hurricanes and “rapid intensification is becoming increasingly likely before landfall … Idalia should keep strengthening up to landfall along the Gulf coast of Florida” as a major hurricane on Wednesday, it warned. Major hurricanes are usually a Category 3 and up on the five-level Saffir-Simpson scale — storms that the NHC says can cause “devastating” and “catastrophic” damage. The US Federal Emergency Management Agency (FEMA) is already preparing for the storm’s impact, including deploying some of its staff, according to the White House.