I have not fertilized or sprayed recently btw.

could be the lethal yellowing disease. If the center frond pull out easily and has an awful smell that may be the issue (hope not) I had a palm that had this problem and lost it.

Hi
If winter I'd say it got burned but since the heat of summer i'm guessing a virus . . Might look it up on the internet to see what they recommend . There are treatments but IME not very effective. Good luck gary

If your zone is 9b, then your coconut might be the northern point of all coconuts. I know of coconuts in Merritt Island but they have a special micro clime. It may have been cold damage that was not bad enough to kill it but to severely damage it and finally die. Just speculation. Virus is a real possibility. When planting it is important to get virus resistant trees. I'd ask my county agent. Good luck.

That looks like it is a nutrient deficiency. It maybe cold related. Give it a good feeding of palm fertilizer and water it in good. Young coconut palms are very sensitive to cold/cool weather. If it gets below around 50 degrees the roots shut down. So often later in spring/summer a leaf or 2 comes out distorted as it did not recieve adequate nutirents when the leaf was developing. It should grow out of it.

Definitely isn't cold damage, it put out new fronds this year already that were fine looking. I read online that boron deficiency could do this, especially during heavy rains. I applied a handful of borax and a handful of essential minor elements. Hopefully the new frond is better...

Cold damage can happen to the developing leaf if the roots shut down. Often the existing fronds will show no damage but newly opened leaves will. It is usually a manganese deficiency caused by the cold.