Story highlights As of Tuesday morning, FEMA'S Disaster Relief Fund had just $1.01 billion left

The Senate is expected to vote on a bill Thursday

(CNN) As Hurricane Irma barrels toward Florida, the Federal Emergency Management Agency is on the brink of running out of cash for disaster relief and could be in the red by the end of the week.

The lack of money could force the agency to essentially start operating on IOUs if Congress doesn't act in time.

As of Tuesday morning, FEMA'S Disaster Relief Fund had just $1.01 billion left. Of that, $541 million was "immediately available" for response and recovery efforts related to Hurricane Harvey, according to a spokeswoman.

An official with Office of Management and Budget told CNN Thursday that the latest estimate shows that FEMA has enough to get through Saturday. When asked how much money remains in the FEMA disaster relief fund as of Thursday the official said, "it's hard to say at this point as this not like traditional spending."

The House passed an emergency relief bill Wednesday that would provide $7.85 billion in emergency funds -- the vast majority of which to FEMA, with some going to the Small Business Administration.

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