The rapid intensification that turned this week's Typhoon Rai into the strongest storm to hit the Philippines this year surpassed all predictions, forecasters said, leaving nearly 400 people dead and almost a million displaced.

While it's unclear exactly how global warming is affecting the intensification of such storms, the U.N.'s climate change agency has found it is "likely that the frequency of rapid intensification events have increased over the past four decades" as temperatures rise.

Before Rai underwent a process of rapid intensification, forecasters at first warned of a storm that could bring "considerable damage," with winds of up to 165 kph (102 mph).