The centre of Florence is expected to hit North Carolina's southern coast on Friday, then drift southwest before moving inland on Saturday.
The weather office has also issued a marine warning for strong winds and high seas on Saturday.
On Thursday, the mercury level is likely to rise to 48C in Al Khor and 46C in Doha.
Strong winds are expected in some places in the early hours of Monday. Windy conditions and high seas are also likely in offshore areas.