The August 2020 Deficit was $198 billion

The federal budget deficit in August 2020 was $198 billion, CBO estimates, $3 billion less than the deficit in August of last year. The cumulative federal budget deficit for the first 11 months of fiscal year 2020 was $3.0 trillion [actually $3.002 tn], CBO estimates, $1.9 trillion more than the deficit recorded for the same period last year. CBO projects that the 2020 deficit will total $3.3 trillion.

https://www.cbo.gov/system/files/2020-09/56552-MBR.pdf

So, the September deficit is expected to be about $300 billion.

Where did the money go?

The Small Business Administration’s outlays were $575 billion (mostly for the Paycheck Protection Program), compared with $467 million during the same period last year. Outlays for unemployment compensation were $410 billion more than in the same five months in 2019. Payments of refundable tax credits—including recovery rebates that began in April under the CARES Act—totaled $274 billion more than in the same months in 2019. Outlays totaling $149 billion were made from the Coronavirus Relief Fund, which provides aid to state, local, tribal, and territorial governments. Outlays for the Public Health and Social Services Emergency Fund (included in the “Other” category below) were $105 billion, compared with $1 billion during the same five month period last year. Medicare outlays were $95 billion more than in the same five months last year (after removing the effect of a timing shift in 2019 that increased outlays in that year), largely because of the expansion of two programs. Outlays for the Department of Education (included in “Other”) from April through August this year were $50 billion higher than in the same period last year.  Spending for Medicaid was $34 billion higher than in the same period last year.

Some of these outlays are one time events (SBA).  Some of them will continue next year but at a lower rate (unemployment compensation).  But some of these will continue ratcheting up (Medicare, Medicaid) and are the real problems.  The government loves to spend money, and it will be very hard for them to stop doing it after developing the taste for blood, err spending other people's money.

I believe the monthly deficit will average $200 billion, even after recovery from the current crisis.  The CBO projects that deficits will be much lower than that ($1,810 bn in 2021, $1,336 bn in 2022, $1,1234 bn in 2023) but of course they have to be optimistic.  I seriously doubt that the 2021 deficit will be under $2.4 trillion.

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The Treasury Department's Monthly Treasury Statement for August 2020 show slightly different numbers.  They say the deficit in August was $200 billion, and the fiscal year to date deficit was $3,007 billion. 

There was a surplus in September 2019 of $82 billion ($374 bn revenue less $291 bn outlays), so it is possible, although unlikely, that September 2020 could have a surplus as well.