If that date of 28 August is your enter before date, you will need to purchase a reentry permit. Unless you plan to make other trips out of the country a single reentry permit will take care of your return after your departure.
Or one could apply for a non imm o-a multi entry visa which would give the user a year, and with a border run just prior to the visa enter before date, the user could get a second year before needing to deal with extension of stay applications.
Krishn Menaria the non imm o-a multi entry visa is obtained via a Thai Embassy or official Thai Consulate in one’s home country for those 50 years and older. It is a one year visa with no need for border runs. However, each time the holder leaves Thailand prior to the enter before date stamped on the visa, when the holder re-enters Thailand he/she will be given an additional year from that date. So if the holder times thing correctly he/she could essentially get almost two years before needing to apply for extensions of stay at their local Thai immigration office. There are requirements to getting the visa - income/savings that can remain in one’s home country, a police check and a medical form that must be completed. For specific requirements I suggest you view the website of the embassy/consulate where you would be obtaining this visa - there are slightly different requirements depending on the specific embassy/consulate. I like it in that it provides some breathing room for those moving to Thailand before applying for extensions of stay etc. It is just another possible option.
If you intend to move to Thailand and are still in your home country you may want to consider obtaining a non imm o-a multi entry visa. That visa will allow you to keep your money in your home country bank for a year - two years if you make a border run just prior to the enter before date on the visa. And you will only need to deal with immigration for the 90 day reports for the two year period.
