Yeast tend to get stressed when fermentations happen on the high side of their range, and stressed yeast produce fusels (higher order alcohols) that contribute a "hot," harsh flavor to the resulting mead that can take some time to age out. The good news is that fusels will eventually break down into simpler compounds, and that harshness will eventually age away. But that can take months (to years) to happen. Stressed yeast are also more likely to produce various phenolic compounds as a byproduct of fermentation, and those phenolics can take even longer to mellow out. So, it is best to keep your fermentation temps on the low side of your yeast's recommended range. BTW - Most yeast strains have temperature range data available, so you can choose a strain better adapted to fermentation under warm conditions if you can't otherwise cool your must. Medsen Fey, living in Florida, has lots of experience with which yeast strains work best in higher temperature climates.