Translation:However, it is not warm today.
I find that Japanese people often say あったかい (attakai) instead of あたたかい (atatakai), it really is a tongue twister kind of word.
Warm, 温かい, is a positive connotation. Hot, 暑い, is negative. Warm is like a warm jacket in winter, hot is like touching a hot pan or a smeltering summer day.
"However, today is not warm." was incorrect. Why? Isn't 'today' the subject of the sentence.?