How to Say "is astonished" in Spanish
The Spanish word for “is astonished” is “extraña” — B1 level.

Examples
A nadie le extraña que haya renunciado después de eso.
Nobody finds it strange that he resigned after that.
Me extraña que no esté lloviendo hoy.
I find it surprising/strange that it's not raining today. (Literally: 'It surprises me that...').
Surprise = Subjunctive
When you use 'extraña' to mean finding something surprising (e.g., 'Me extraña que...'), the verb in the second part of the sentence must be in the special 'wish/doubt' form (subjunctive). Notice how 'no esté lloviendo' uses 'esté' instead of 'está'.
Forgetting the Object Pronoun
Mistake: “Saying 'Extraña que no llueva' (It finds strange that it doesn't rain), forgetting to specify *who* is surprised.”
Correction: You must include the person who is surprised: 'Me extraña que no llueva' (It surprises *me* that it doesn't rain).
Related Translations
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