Diving Similans October illegal or no?

Yes, the park is closed officially.

This means that any operators offering trips there before 1 November have to pay a fine to the national park officers. This fine is the same amount as the otherwise payable national park fees.

Yes, the parks are officially closed until Nov 1. And yes, it is illegal. Some boats go out a day or two early and pay the park entry and visitor fees on Nov 1 when the rangers are officially on duty. There are operators beginning trips earlier, and they make "special" arrangements which they may claim are officially sanctioned but are more likely under-the-table deals. I do not recommend going out when the parks are officially closed given that any rescue would be delayed (and bad weather is a distinct possibility), particularly since the park offices are likely not fully staffed.

Here are some official Thailand government documents that you can refer to for verification that travel in the parks before Nov 1 is illegal:
http://www.dnp.go.th/Rules/seatrade_en.pdf (See paragraph 3.4.1 on page 4, which specifically discusses the legality of visits during park closures.)
http://web3.dnp.go.th/parkreserve/close_np.asp?lg=2 (see the entries under Mu Koh Similan and Mu Koh Surin in the South region for official closure dates.)

"any rescue would be delayed (and bad weather is a distinct possibility), particularly since the park offices are likely not fully staffed."

Since the park offices are not involved in rescues whatsoever, any rescue would be organised the same as always. No delays.

In fact, that's incorrect, stevenl. The park authorities together with the navy and some dive charter boats were all involved in getting stranded tourists back to the mainland during the severe weather period last March.

Yes, that is the exception I knew you would start about. First time that has happened in history.

Nevertheless, if I were on a boat when it happened, I would be glad that the park was officially open, as it was in March, so that transfers could be facilitated.

I continue to recommend that my customers wait until the parks are officially open to visitors. Of course I could make more money by selling trips whenever they are offered, but I subscribe strictly to highly ethical business practices, which require me to give the best advice possible. The best advice is to obey the law.

Having worked for the chamber and organized dozens of evacuations - the park does help, and in fact is the primary point of contact for most emergencies. They have two speedboats operating inside the park - when the park is open and operating. In addition, they need to be involved in any evacuation that involves helicopters (rare, but it happens). These services are not available before the park officially opens.

I am sorry to say Steven - but when coordinating these evacuations I have personally sat on these speedboats supplied by the National park on at least 5 times. The boats are smaller, faster and designated for these purposes. They do not operate at night for safety reasons, and if an emergency happens at night, we would use the services of private operators. These policies may not still be in place, but this was the procedure the four years I coordinated evacuations.

Something very important to consider:
It is illegal to enter the park during these closure times - as noted above. As the parks are closed and it any activity inside the park is illegal - insurance companies do not cover such activities (read your policy). Yes - many insurance companies do not do thorough investigations and will pay out in case of accidents. However, there has been cases of insurance companies not paying claims.

Any operator, agents and potential client who respects the laws of Thailand (and elsewhere) needs to be applauded.

Thank you to everyone who responded. Very interesting discussion. I had figured as much being Thailand and all (and I love Thailand). Safe diving!

I assume the Surin Islands have no date limitations should we arrive a few days prior to Nov.1? How good is the snorkeling in the Similans vs, the Surin's in general in early November?
Thanks.