When it comes to expressing "in strength," there are numerous synonyms to consider. "Forcefully" is one viable option as it implies a high level of power or intensity. "Firmly" is another possibility, indicating a strong and unwavering position or belief. "Robustly" is another option, conveying a sense of health and vitality. "Stoutly" is yet another alternative, emphasizing strength and endurance. There are numerous other synonyms to consider, including "potently," "resolutely," and "steadfastly." Ultimately, the best synonym to use for "in strength" will depend on the context and tone of the sentence, but hopefully, this list will serve as a useful starting point.