The normal procedure is for each water park to be closed for nine weeks for general rehab, including such things as disassembling and rebuilding all of the pumps. Generally one will close either the last Sunday in October or the first Sunday in November. The first will reopen generally the first Sunday in January and the second will be closed starting that same date. It will then be either the second or third Sunday in March that both are open.
Last year was an unusual situation. There had been major cracks developing on the floor of the wave pool at TL. It was necessary to completely tear out the bottom of the lagoon and replace it. So much concrete had to be used that they had to allow 26 days for the concrete to cure.
And, in the interest of saving money, Typhoon will always close first. This is because BB is themed to winter holidays; if BB was closed during November and December Disney would have to decorate TL for the holidays.