The phrase "a sharp warning" is correct and usable in written English.
It can be used when you want to convey a strong or serious caution about a potential danger or issue.
Example: "The report issued a sharp warning about the impending storm, urging residents to take necessary precautions."
Alternatives: "a stern warning" or "a strong warning".
In welcoming them, he issued a sharp warning.
In March of last year, just before Kabul Bank's problems surfaced, Karzai got a sharp warning.
North Korea sent a sharp warning in comments before the vote.
Presumably for that reason, Mr. Bush's chief spokeswoman, Karen P. Hughes, issued a sharp warning after Ms. Harris spoke.
But last month, the China Banking Regulatory Commission issued a sharp warning, ordering investment trust companies to stop selling such products in cooperation with banks.
The revolts in North Africa appear to have made Mr. Mugabe's inner circle nervous — and the arrests were a sharp warning to those emboldened by them, they said.
Col. Marcel Aviv, the Israeli commander of the Bethlehem area, issued a sharper warning.
C1 Business Digest C1 OBITUARIES B9 EDITORIAL A14-15 EditoriAlsharperarper warning on warming; the Subway Series ride; unfinished business in Ivory Coast; unfair car loans.
Her words took on a sharper warning as timed passed with this roommate.
"Whether this is a conscious statement to sound a real sharp warning, there's no question that the frustration among the American military establishment is palpable regarding coalition operations in Afghanistan," he said.
And last month, China's highest judge came out with an unusually sharp warning against Western legal influence: "We should resolutely resist erroneous influence from the West: 'constitutional democracy,'separationof of powers' and 'independence of the judiciary.' We must make clear our stand and dare to show the sword".
