"I promise to take the very best care of the kids", he said in a note given to divers on Friday. "I also sincerely apologise to the kids' parents".
But if heavy rains start again, divers will try to remove the boys right away.
The coach also wrote to his relatives waiting on the outside, "To my aunt and grandmother, I am doing well, please don't be too anxious about me".
"The environment inside the cave is challenging".
The twelve boys and their coach got caught by flood waters while visiting the Tham Luang cave in the north of the country in late June, launching an worldwide rescue effort.
A senior army commander, Maj. Gen. Chalongchai Chaiyakham said.
In the meantime, oxygen levels have fallen inside the cave complex.
The boys, members of a football team between the ages of 11 and 16, have been trapped with their coach in Tham Luang cave in northern Chiang Rai Province since late June. Monsoon flooding cut off their escape and prevented rescuers from finding them for nearly 10 days.
The Thai boys trapped deep inside a partially flooded cave will be evacuated alongside experienced scuba divers in what is being called a "buddy dive". He also offered suggestions on how to improve the rescue effort. Getting to safety requires a roughly five-hour dive through murky waters and suffocatingly narrow passageways - hard for even experienced divers - to a point closer to the mouth of the cave where the group could be brought out on stretchers. Queue said he had visited the cave four times this year, always with their coach. The boys are weak but for the most part physically healthy.
Narongsak said the drills would have to pierce 600 metres (1,970 feet) of fragile limestone rock to reach the boys and rescuers were discussing drilling angles.
Park officials and police find handprints and footprints believed to belong to the boys and think they likely retreated into the winding tunnels as they became hemmed in by rising floodwaters. "The war ends when we win all three battles - the battles to search, rescue and send them home". But Queue said he'd never been during this time of year, Thailand's rainy season. "If there's too much risk we will wait but we can not wait until the rain".
Although he had left the navy, Saman, a triathlete, felt a calling to join the rescue effort. "It's going to be muddy water". Some asked for fried chicken, while others simply told their parents that they loved them. "What will really be the hardest thing for the kids is just staying calm".
The "Wild Boar" football team have been trapped inside the Tham Luang cave complex for two weeks.
But the rain had begun to fall.
After several days of searching, rescuers found all 13 people alive but face a challenge to extract them from the situation . The only way to reach them was by navigating dark and tight passageways filled with muddy water and strong currents. Reportedly, none of the boys can swim. Ropes have been installed to help guide the boys through the darkness.
The fatality raises fears that a rescue mission could be fraught and even deadly for the boys, who have been trapped for almost two weeks. The path out is considered especially complicated because of twists and turns in narrow flooded passages.
If more rain begins to fall, Warild said, "then the whole scene's going to change". Words of love, reassurance and encouragement are interspersed with talk of food the boys are craving - and birthday parties. "Now, we chose the best option, and we rehearsed it", Maj.