In a special manner; specially.
The phrase 'be especially careful' is correct and usable in written English, and it can be used any time you want to emphasize caution in a given situation. For example, "Be especially careful when walking on icy sidewalks in the wintertime.".
"Now we have to be especially careful".
And women need to be especially careful with their approach.
Where issues of the back are concerned, Day must be especially careful.
Be especially careful not to take any laptops, video games, iPhones, BlackBerrys, briefcases or co-workers.
As we crossed the border into Iran, he told us to be especially careful.
And be especially careful with financial companies.
Drivers should be especially careful on the road this weekend.
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union