The United States likely will not see the full force of a powerful El Nino until early next year and the weather phenomenon has not shown any sign of slowing down, NASA announced Tuesday.

El Nino occurs when part of the Pacific Ocean is warmer than usual, setting off a far-reaching ripple effect that brings atypical and often extreme weather throughout the world. A variety of weather experts, including those with the United Nations, have said this year’s pattern is shaping up to be one of the three strongest in the past 65 years, but NASA said that the latest satellite images suggest the United States probably has yet to see the worst of the weather.

The images show “a striking resemblance to one from December 1997,” captured during the strongest El Nino on record, according to NASA. While the National Weather Service previously said that the pattern “matured,” NASA said Tuesday that the latest images indicate El Nino “shows no signs of waning,” and the fact that some elements of the Pacific Ocean are different now than they were 18 years ago could mean the weather pattern might actually intensify.

“Although the sea surface height signal in 1997 was more intense and peaked in November of that year, in 2015, the area of high sea levels is larger,” Josh Willis, a project scientist at NASA’s Jet Propulsion Laboratory, told NASA’s website. “This could mean we have not yet seen the peak of this El Niño.”

The announcement comes in the wake of deadly flooding throughout the central United States that has sent multiple river gauges to historic levels and forced mandatory evacuations. This El Nino has already been blamed for historic flooding in coastal India, widespread wildfires in Indonesia and several crop-damaging droughts and floods across the globe, according to NASA.

NASA says it’s still not clear when El Nino will make its full presence felt in the United States, or the effects it could have. Generally, the National Weather Service has said the southeast is likely to see more precipitation and colder temperatures, while the northwest is expected to see hotter temperatures and less precipitation. However, that’s not an all-encompassing forecast, and NASA noted past El Ninos have been known to produce extreme storms such as a massive ice storm that slammed the northeast United States and parts of Canada in January 1998.

The National Weather Service has said El Nino is likely to linger into early summer.