Could 19 October be a catastrophic day for the US economy?

The USD 28.4 trillion debt limit was renewed on 1 August.
By extraordinary measures, Treasury Secretary Janet Yellen has been able to take steps that allow the government to borrow additional funds without breaching the debt ceiling.
Yellen warned lawmakers that if Congress fails to raise or suspend the debt ceiling, the federal government will exhaust those extraordinary measures by October 18.
What could happen on October 19? Yellen’s response has indicated there could be a bit of flexibility, but not much.
“We’re simply in an impossible situation in which it will be impossible for Treasury on that day, or a few days thereafter…We’ll have very limited resources”, Yellen said.
The nonpartisan Congressional Budget Office issued a report that suggests there may be additional time beyond October 18 for lawmakers to avoid a catastrophic default.
If the debt limit remains unchanged, Treasury’s ability to borrow using extraordinary measures will be exhausted and it will most likely run out of cash near the end of October or the beginning of November.