Bleaching has struck 90 percent of the coral reefs around Phuket, he added, and already between 10 percent and 40 percent could not be saved even if sea temperatures dropped quickly now.
Greater than usual exposure to hot sun in warmer than normal water has placed the entire Andaman region's reefs at risks this year. Other reefs around Thailand and the Great Barrier Reef off Australia have also been affected.
Khun Niphon went diving off Phuket on Tuesday and placed reef temperatures at 30.5 degrees. Prolonged exposure at 31 degrees or above is what has put the colorful reefs at risk.
Last week's thunderstorms and clouds over Phuket and the Anbdaman Sea have helped, but perhaps not enough.
''Half a degree is better however we still need the temperature to move to 29 degrees quickly or there could be residual damage and death,'' he said.
Loss of reefs around Phuket ''would not take many years'' to replace because they were fast-growing varieties, he said. But he said more hot seasons could worsen the situation quickly. ''We just can't tell from season to season because so many factors now come into play,'' he said.
More sophisticated measurement techniques involving taking the temperatures of reefs regularly would help diagnosis but not treatment, he said.