(UPDATE) The amount of water released from the notch tanks (2) is 40 tonnes so far, according to Jiji. Cesium-137 in the water was 21Bq/L, within the provisional standard at Fukushima I NPP of 25Bq/L.
From Japan Meteorological Agency's English Site:
It looks like Fukushima will be in the north-west quadrant of the area with 50 knots or more wind.
As for TEPCO's preparation, the company finally has a standard (after more than two and a half years) for the release of rainwater inside the dam (or low barrier) that surrounds the water storage tanks (both contaminated and treated). The standard has been approved by Nuclear Regulation Authority. According to Jiji Tsushin (10/16/2013):
If the density of cesium-137 is less than 25Bq/L, [the rainwater inside the dam] will be released.
TEPCO Nuclear has just tweeted:
Due to rainfall as the typhoon approaches, as of 5:40AM this morning we started discharging the water from the notch tanks [short, square tanks] in the East-C and West-C areas, as the water meets the standard for discharge. We plan to pump water from the dams surrounding the tanks into this notch tanks. http://www.tepco.co.jp/cc/press/2013/1231442_5117.html
The link in TEPCO's tweet has more details of this standard:
No additional gamma nuclides
They are 1/3 to 1/4 of legal limits for the discharge from a functioning nuclear power plant.