Several observers are already estimating that Hurricane Harvey and the flooding in caused the Houston area has likely created the most expensive natural disaster in U.S. history, even though an accurate accounting is still likely years away.

On Thursday, AccuWeather founder Joel Myers said the cost of Harvey would exceed the combined costs of Hurricane Katrina and Superstorm Sandy, which had been the top two most expensive natural disasters to hit the United States.

"This is the costliest and worst natural disaster in American history," Myers said Thursday. "AccuWeather has raised its estimate of the impact to the nation's gross national product... to $190 billion or a full one percent, which exceeds totals of economic impact of Katrina and Sandy combined."

On the same day major fuel pipelines were expected to shut down, Myers added that the storm will create a real hit on the U.S. economy.

"Business leaders and the Federal Reserve, major banks, insurance companies, etc. should begin to factor in the negative impact this catastrophe will have on business, corporate earnings and employment," Myers said. "The disaster is just beginning in certain areas. Parts of Houston, the United States' fourth largest city will be uninhabitable for weeks and possibly months due to water damage, mold, disease-ridden water and all that will follow this 1,000-year flood."

Hurricane Katrina, which devastated New Orleans in 2005, forced the federal government to shell out $120 billion to aid the recovery effort, and Sandy prompted $50 billion in federal relief.

Even on Wednesday, Texas' Republican Gov. Greg Abbott was predicting the cost of recovering from Harvey would likely exceed the costs of Katrina.

"When you look at comparisons - the population, the size, the square-mile area impacted both by the hurricane swath and the flooding -- it's far larger than Katrina, far larger than Sandy," Abbott said, according to the Houston Chronicle.

In the first few days of the storm, lawmakers who were on the scene were predicting huge costs associated with the cleanup.

Rep. Al Green, D-Texas, predicted costs would exceed $100 billion. Rep. Sheila Jackson Lee, D-Texas, reportedly predicted $150 billion in costs, and then followed that up by predicting $200 billion.

President Trump on Tuesday was already predicting Harvey would be the most expensive disaster in U.S. history.

"Probably there's never been anything so expensive in our country's history," he said. "There's never been anything so historic in terms of damage and in terms of ferocity as what we've witnessed with Harvey."

The National Oceanic and Atmospheric Administration puts the total cost of Katrina relief at $160 billion in inflation-adjusted dollars. Superstorm Sandy cost about $70 billion in current dollars.