"Grimly note" is a phrase that refers to a serious and perhaps negative observation or statement. Some synonyms for this phrase include "solemnly observe," "stoically acknowledge," or "grimly remark." Another option may be to use a stronger verb in place of "note," such as "declare," "announce," or "pronounce." Alternatively, you could try rephrasing the sentence or thought to convey the same meaning in a different way. For instance, instead of saying "I grimly noted that the situation was getting worse," one could say "The situation was becoming increasingly dire, and I could not help but feel a sense of apprehension.