It won't matter at this point if Iota gets to Category 5 or even weakens a little before it comes ashore, because disastrous effects are nearly inevitable, said Dan Kottlowski, a meteorologist at commercial forecaster AccuWeather.
Iota is expected to continue moving west and northwestward over the next few days until it makes landfall sometime late on Monday or early Tuesday morning in Central America.
Iota rapidly gained strength after becoming the 13th hurricane of the Atlantic season Sunday, threatening to bring more risky winds and rains to Nicaragua and Honduras - countries recently clobbered by Category 4 Hurricane Eta.
Nicaragua's government said authorities had begun evacuating some people near the country's border with Honduras, an area that forecasts said likely would be in Iota's path.
Iota had increased in intensity from a tropical storm to a hurricane at Category 1 strength, with 90 miles per hour winds, by Sunday morning, before intensifying again to a Category 2 hurricane by Sunday night.
The hurricane center said Iota could strengthen and possibly become a Category 5 hurricane before landfall.
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In Nicaragua, authorities were preparing for "floods, rain, high tides, wind and landslides on saturated soil", said Guillermo Gonzalez, head of the country's disaster response agency Sinapred.
Catastrophic wind damage is expected where Iota's eyewall moves onshore within the Hurricane Warning area in Nicaragua tonight with tropical storm conditions expected by this afternoon.
The 2020 Atlantic hurricane season has seen the most named storms on record, with 30 named storms and 13 hurricanes.
In the Nicaraguan coastal city of Bilwi, residents were desperately trying to secure roofs of flimsy wooden homes with the same zinc sheets ripped off by Eta.
That could lead to "significant, life-threatening flash flooding and river flooding, along with mudslides", the NHC said.
Iota was forecast to drop 200-400 millimetres of rain in northern Nicaragua, Honduras, Guatemala and southern Belize, with as much as 750 millimetres in isolated spots.
Initial estimates show "some 80,000 families are going to be at risk", he said, with evacuations underway in communities along the border with Honduras.
Warmer seas caused by climate change are making hurricanes stronger for longer after landfall, scientists say. Costa Rica and Panama: 4 to 8 inches, with isolated maximum totals of 12 inches. Remnants of Theta, the 29th, dissipated Sunday in the eastern Atlantic Ocean.
There have been no other Novembers on record with two major hurricanes.