The National Weather Service issued a dire warning on Sunday about Tropical Storm Harvey. “This event is unprecedented & all impacts are unknown & beyond anything experienced. Follow orders from officials to ensure safety,” the NWS wrote on Twitter. The storm made landfall in Texas as a category 4 hurricane, and has dumped at least 20 inches of rain in the Houston area over the last 24 hours. At least five people are known to have been killed, while thousands have been rescued from rising flood waters.